Conference contributions

Conference contributions

Some of the conference contributions are published in proceedings and are labelled with the icon . You can read most article abstracts if you click on [Abstract].

Year	Title
2012 (05)	Ringelstein, M. ; Berthe, A. ; Schneider, T. ; Kertzscher, U. ; Affeld, K.: Flow regulation in multi branched models of blood vessels. In: 46. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Jena, Germany 2012. Biomedizinische Technik, 2012 accepted. [BibTeX]
BibTeX @inproceedings{Ringelstein2012, author = {M. Ringelstein and A. Berthe and T. Schneider and U. Kertzscher and K. Affeld}, title = {Flow regulation in multi branched models of blood vessels}, booktitle = {46. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Jena, Germany}, journal = {Biomedizinische Technik}, year = {2012 accepted} }
2012 (04)	Weber, S. ; Strommenger, D. ; Kertzscher, U. ; Affeld, K.: Continuous blood pressure measurement with ultrasound. In: 46. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Jena, Germany 2012. Biomedizinische Technik, 2012 accepted [BibTeX]
BibTeX @inproceedings{Weber2012, author = {S. Weber and D. Strommenger and U. Kertzscher and K. Affeld}, title = {Continuous blood pressure measurement with ultrasound}, booktitle = {46. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Jena, Germany}, journal = {Biomedizinische Technik}, year = {2012 accepted} }
2012 (03)	Weber, S. ; Strommenger, D. ; Scharfschwerdt, P. ; Kertzscher, U. ; Affeld, K.: New method for continuous blood pressure measurement. In: 39th European Society for Artificial Organs Congress, Rostock, Germany 2012. International Journal of Artificial Organs, 2012 accepted. [BibTeX]
BibTeX @inproceedings{Weber2012a, author = {S. Weber and D. Strommenger and P. Scharfschwerdt and U. Kertzscher and K. Affeld}, title = {New method for continuous blood pressure measurement}, booktitle = {39th European Society for Artificial Organs Congress, Rostock, Germany}, journal = {International Journal of Artificial Organs}, year = {2012 accepted} }
2012 (02)	Weber, S. ; Strommenger, D. ; Kertzscher, U. ; Affeld, K.: Kontinuierliche Blutdruckmessung mit Ultraschall. In: 26. Treffpunkt Medizintechnik, Berlin, Germany 2012. [BibTeX]
BibTeX @inproceedings{Weber2012b, author = {S. Weber and D. Strommenger and U. Kertzscher and K. Affeld}, title = {Kontinuierliche Blutdruckmessung mit Ultraschall}, booktitle = {26. Treffpunkt Medizintechnik, Berlin, Germany}, year = {2012} }
2012 (01)	Weber, S. ; Kertzscher, U. ; Affeld, K.: Bewegungsartefakte bei der nichtinvasiven Blutdruckmessung. In: Workshop "Innovative Verarbeitung bioelektrischer und biomagnetischer Signale" 2012. [BibTeX]
BibTeX @inproceedings{Weber2012c, author = {S. Weber and U. Kertzscher and K. Affeld}, title = {Bewegungsartefakte bei der nichtinvasiven Blutdruckmessung}, booktitle = {Workshop "Innovative Verarbeitung bioelektrischer und biomagnetischer Signale"}, year = {2012} }
2011 (20)	Berthe, A. ; Gärtlein, S. ; Goubergrits, L. ; Lederer, C. ; Kertzscher, U. ; Spence, P. ; Giridharan, G. ; Koenig, S.: Hemodynamics of a valveless counterpulsation heart assist device: Particle Image Velocimetry and wall-Particle Image Velocimetry. In: 38th European Society for Artificial Organs Congress, Porto, Portugal, October 9–12, 2011. International Journal of Artificial Organs Volume 34 , 2011(8) [Abstract] [BibTeX]
Abstract Objectives: The long-term application of counterpulsating devices (CPD) is limited by blood stagnation induced thrombus formation. A new CPD with 32ml stroke volume was designed to prevent this cause of thrombus formation. Utilizing two measurement techniques, the blood washout behavior and wall shear stresses in the new design are obtained. A set of operating mode conditions, based on the time of membrane movement, were tested. Methods: The time resolved flow in the disk-shaped lumen of the valveless CPD was investigated with Particle Image Velocimetry (PIV) and with wall-Particle Image Velocimetry (wall-PIV). The PIV study is focused on the central plane of the blood pump, where maximal velocities are anticipated. The wall-PIV investigations consider potential areas of blood stagnation on the housing of the blood pump. Results and Discussion: Flow investigations found that a tangentially designed CPD inlet port forms during a filling phase a strong, generally two-dimensional (2D) moving vortex fully filling the blood chamber. No regions of persistent blood stagnation or recirculation bubbles were observed. Shear stresses were moderate inside the blood chamber. The velocities in the lumen decay exponentially. Temporal vortex behavior was analyzed by its circulation frequencies. By comparison of wall shear rates and circulation frequencies the stagnation risk caused by different operation conditions was investigated. Conclusions: The time resolved flow in the CPD lumen shows good washing characteristics with no stable areas of blood stagnation. By setting a threshold for the shear rate a maximal hold time can be identified.
BibTeX @inproceedings{Berthe2011, author = {A. Berthe and S. Gärtlein and L. Goubergrits and Ch. Lederer and U. Kertzscher and P.A. Spence and G.A. Giridharan and S.C. Koenig}, title = {Hemodynamics of a valveless counterpulsation heart assist device: Particle Image Velocimetry and wall-Particle Image Velocimetry}, booktitle = {38th European Society for Artificial Organs Congress, Porto, Portugal, October 9--12, 2011}, journal = {International Journal of Artificial Organs}, year = {2011}, volume = {34}, number = {8} }
2011 (19)	Spuler, A. ; Berthe, A. ; Schaller, J. ; Hege, H.-C. ; Goubergrits, L.: Visualization of near-wall flow by wall particle image velocimetry in experimental cerebral aneurysms. In: 14th European Congress of Neurosurgery, Rome, Italy, October 9–14, 2011. , 2011 [Abstract] [BibTeX]
Abstract Objective: Wall shear stress (WSS) and its derivations are the fluiddynamic parameters describing the impact of blood flow on the vessel wall. Thus WSS is the force driving vessel remodelling. As in other vessels, near-wall flow defines WSS in cerebral aneurysms. Classic dye wash-out methods used for flow evaluation in aneurysmal models are not adequate to visualize the near-wall flow. We compared computationally simulated near-wall flow with measured and visualized near-wall flow in experimental aneurysm models. Methods: Taking routine angiography data (CT angiography or 3D rotational angiography) and using standard tools of image segmentation, we generated 3D isosurface data sets of aneurysms and their associated arteries. Up-scaled transparent silicon models were fabricated from these data sets. Flow experiments with these models were performed using a test fluid containing a molecular dye and nearly monodisperse particles with diameters of between 71 and 75 µm. We performed particle image velocimetry (PIV) in these flow experiments and analyzed the resulting images pixel by pixel to obtain near-wall particle pathlines. Results: We were able to visualize the pathlines of particles up to a distance of 140 mm from the vessel wall. Manipulations mimicking therapeutic interventions like hunterian ligation changed the near-wall pathlines matching the corresponding computational simulations of flow changes. Conclusion: Wall-PIV allows experimental validation of computer simulated flow changes in cerebral aneurysms and permits the experimental analysis of near-wall flow after endovascular interventions e.g. coiling which elude realistic computational simulation so far.
BibTeX @inproceedings{Spuler2011, author = {A. Spuler and A. Berthe and J. Schaller and H.-C. Hege and L. Goubergrits}, title = {Visualization of near-wall flow by wall particle image velocimetry in experimental cerebral aneurysms}, booktitle = {14th European Congress of Neurosurgery, Rome, Italy, October 9--14, 2011}, year = {2011} }
2011 (18)	Goubergrits, L. ; Berthe, A. ; Lederer, C. ; Spence, P. ; Giridharan, G. ; Koenig, S.: Hemodynamics of a valveless counterpulsation heart assist device: laser Doppler velocimetry and computational fluid dynamics. In: 38th European Society for Artificial Organs Congress, Porto, Portugal, October 9–12, 2011. International Journal of Artificial Organs Volume 34 , 2011(8) [Abstract] [BibTeX]
Abstract Objectives: Single port valveless pneumatic counterpulsations heart assist devices have had, normally, a high incidence of thrombus formation due to blood stagnation regions in the blood chamber. This prevents a success of these device types in a long-term application. Blood chamber flow of a novel 32 ml stroke volume blood chamber design was investigated. Methods: To investigate blood washout behavior of the new design of a valveless counterpulsation device (CPD) with disk-shaped blood chamber (30 mm radius and 25 mm maximal thickness), laser Doppler velocimetry (LDV) and Computational Fluid Dynamics (CFD) were applied. Simplified static CFD model using flow solver FLUENT (ANSYS Inc., USA) was used to visualize 3D flow structure at the end-filling phase. The time resolved flow investigation of the CPD chamber and the inlet port was done by two-component LDV device (Dantec Dynamics, Denmark). Results and Discussion: Flow investigations found that tangentially designed CPD inlet port of a 10 mm diameter forms during a filling phase a strong, in general two-dimensional (2D) moving vortex fully filling the blood chamber. Such vortex is considered to be indicative for a good washing. No regions of persistent blood stagnation or recirculation bubbles were observed. Laminar shear stresses estimated by CFD were well below the known hemolysis threshold of 400 Pa inside the blood chamber. The short curved graft generated the helical flow pattern forming a minor secondary flow (helicity) of the 2D vortex. This secondary flow is considered to be favorable for the washing of the region between the membrane and the chamber housing. Conclusions: The CPD blood chamber flow has good washing characteristics without stable areas of blood stagnation during the entire pump cycle thus promising a low risk of thrombus formations.
BibTeX @inproceedings{Goubergrits2011a, author = {L. Goubergrits and A. Berthe and Ch. Lederer and P.A. Spence and G.A. Giridharan and S.C. Koenig}, title = {Hemodynamics of a valveless counterpulsation heart assist device: laser Doppler velocimetry and computational fluid dynamics}, booktitle = {38th European Society for Artificial Organs Congress, Porto, Portugal, October 9--12, 2011}, journal = {International Journal of Artificial Organs}, year = {2011}, volume = {34}, number = {8} }
2011 (17)	Kertzscher, U. ; Schulz, S. ; Scharfschwerdt, P. ; Goubergrits, L. ; Affeld, K.: Permanent central venous catheter with a lock balloon. In: 38th European Society for Artificial Organs Congress, Porto, Portugal, October 9–12, 2011. International Journal of Artificial Organs Volume 34 , 2011(8) [Abstract] [BibTeX]
Abstract Objectives: Permanent vascular access is essential for hemodialysis, parenteral nutrition and drug administration. Mostly a central venous catheter (CVC) is used. However, this use poses a problem: infection. The cause is the intraluminal space, which acts as a bioreactor during the time when the CVC is idle. To prevent this, a bactericidal liquid, called a lock solution, is injected into the intraluminal space. For fluid mechanical reasons, it is not possible to completely fill the intraluminal space without injecting the lock solution into the bloodstream. The proposed lock balloon fills the intraluminal space and makes a lock solution redundant. Methods: A standard single lumen central venous catheter of 1.4mm inner and 2.1mm outer diameter was chosen to be equipped with a lock balloon. The latter was fabricated from a 25-micrometer polyurethane membrane. The membrane was inserted into the catheter and glued in. A bi-stable actuator was designed and attached to the lock balloon. The lock balloon is filled with 0.3-milliliter air. Results: During infusion the lock balloon is collapsed and the lumen is free for the passage of the infused liquid. However, the cross section is reduced and the resistance is doubled. After infusion the lock balloon can be inflated again and then it completely fills the intraluminal catheter space. The bi-stable actuator permits to activate and deactivate the lock balloon like a switch. Conclusions: The concept appears valid and further investigations will deal with miniaturization of the lock balloon and animal experiments. The animal experiments are designed to model the routine of CVC use. Conventional CVCs will be compared to lock balloon CVCs. Blood cultures after catheter use will be used as a control.
BibTeX @inproceedings{Kertzscher2011, author = {U. Kertzscher and S. Schulz and P. Scharfschwerdt and L. Goubergrits and K. Affeld}, title = {Permanent central venous catheter with a lock balloon}, booktitle = {38th European Society for Artificial Organs Congress, Porto, Portugal, October 9--12, 2011}, journal = {International Journal of Artificial Organs}, year = {2011}, volume = {34}, number = {8} }
2011 (16)	Schirrmann, K. ; Kertzscher, U. ; Affeld, K.: Passive flow regulation in capillary networks. In: 38th European Society for Artificial Organs Congress, Porto, Portugal, October 9–12, 2011. International Journal of Artificial Organs Volume 34 , 2011(8) [Abstract] [BibTeX]
Abstract Objectives: Capillary blood flow is a two-phase flow: blood cells and plasma are moving through a network. Which forces shape this flow? How are the cells distributed? What are the regulation mechanisms? This is investigated experimentally with an enlarged model, which is made to simulate the deformability of the red blood cells and the resulting effects on flow resistance. This experimental model was developed because in experiments with real blood the network is too minute and detailed numerical simulation is too complex. Methods: We use a blood model that consists of water droplets of about 1mm diameter (red blood cells) and sunflower oil (plasma). Two syringe pumps pump the components into a bifurcation, where the droplets are formed. The model is applied to flow through bifurcations and through a network. The network model is made of transparent silicone rubber. It consists of capillary segments, whose diameters and lengths are statistically similar to the pulmonary capillary network of rats, but enlarged to an average diameter of 1.2mm. Results: The experiments in the capillary network model show a droplet distribution which is variable, especially in segments with lower droplet fraction. A segment holds only a small number of droplets. Hence, a segmental flow resistance changes considerably when a droplet enters it or leaves it. Consequently, the flow distribution changes, which acts back on the number of droplets entering the segment - an unsteady flow is induced. Conclusions: Effects seen in both systems – in vivo and in the model – must be essentially influenced by the properties they have in common. This means, the variable hematocrit seen in pulmonary networks is at least in part a passive mechanism, induced by the flow resistance change due to the red blood cells and the droplets, respectively.
BibTeX @inproceedings{Schirrmann2011, author = {K. Schirrmann and U. Kertzscher and K. Affeld}, title = {Passive flow regulation in capillary networks}, booktitle = {38th European Society for Artificial Organs Congress, Porto, Portugal, October 9--12, 2011}, journal = {International Journal of Artificial Organs}, year = {2011}, volume = {34}, number = {8} }
2011 (15)	Schaller, J. ; Kragh, T. ; Kertzscher, U. ; Reininger, A. ; Spannagl, M. ; Affeld, K.: Time-resolved characterization of platelet deposition in a stagnation point flow chamber. In: 38th European Society for Artificial Organs Congress, Porto, Portugal, October 9–12, 2011. International Journal of Artificial Organs Volume 34 , 2011(8) [Abstract] [BibTeX]
Abstract Objectives: Thrombus formation still poses a problem in the development of devices in the cardiovascular system. The process is determined by the components of Virchow’s triad, which describes the interaction of blood, flow and surface. The objective of this work is the development of a method to quantify Virchow’s triad. For this endeavor the stagnation point flow is chosen. Methods: For the experiments a stagnation point flow chamber was designed and manufactured. The blood flows through a bore perpendicular onto a flat plate. In a radial distance the blood is collected in an annular channel. This creates a stagnation point flow with axial symmetry but with radially varying shear rates. The flat plate is a microscopic cover slip made out of native glass. It permits a fluorescent video microscopy with an inverted microscope. The blood was drawn from voluntary healthy donors into standard syringes containing sodium citrate. To dye the platelets with calcein red-orange AM, platelet rich plasma is temporarily separated. With a flow rate of 18mL/h the blood enters a microfluidic device to mix with adenosine diphosphate (ADP) (2mL/h, 20 µM) to stimulate the platelets. The activated platelets deposit on the cover slip influenced by shear rate. Results: In the onset of the experiment the platelets deposit evenly, but shortly after this a preference of certain regions are observed. The region around the stagnation point attracts more platelets, while the stagnation point itself remains nearly platelet free. In addition a development of insular pattern of platelet deposition is observed. These insular depositions develop in flow direction with elliptic shapes in the beginning. Conclusions: With this method temporal resolved platelet formation can be observed using also alternative surfaces modifications. From the results thrombus formation can be modeled considering Virchow’s triads.
BibTeX @inproceedings{Schaller2011, author = {J. Schaller and T. Kragh and U. Kertzscher and A. Reininger and M. Spannagl and K. Affeld}, title = {Time-resolved characterization of platelet deposition in a stagnation point flow chamber}, booktitle = {38th European Society for Artificial Organs Congress, Porto, Portugal, October 9--12, 2011}, journal = {International Journal of Artificial Organs}, year = {2011}, volume = {34}, number = {8} }
2011 (14)	Gabel, G. ; Kikhney, J. ; Reiter, K. ; Affeld, K. ; Große-Siestrup, C. ; Kertzscher, U.: A catheter model for the evaluation of anti-biofilm agents in rats. In: 38th European Society for Artificial Organs Congress, Porto, Portugal, October 9–12, 2011. International Journal of Artificial Organs Volume 34 , 2011(8) [Abstract] [BibTeX]
Abstract Objectives: The colonization of indwelling catheters by bacteria and the formation of biofilms is a frequent problem in today’s clinical setting. These infections, mostly caused by coagulase-negative staphylococci, are among the most common nosocomial infections and may even cause the sepsis syndrome. The biofilms are often highly resistant to conventional antibiotics. In this study we evaluate the effect of the antibiotic, e.g. Daptomycin whose therapeutic mechanism is supposed to also affect bacterial biofilms. Methods: A previously published rat model was modified using a peripheral venous catheter for human use that was adapted for the application in rats. For this study the Teflon tip of the catheter was replaced by a polyurethane tube, to soften and to prolong the line. The system was sterilized using formalin gas and inserted in the right Vena jugularis externa. The proximal tip of the catheter was subcutaneously tunneled and passed outwards between the scapulae. To secure the position of the catheter the adjacent plastic wings were sued onto the adjacent tissue. Then the lumen was inoculated with S. epidermidis and allowed to indwell within the catheter for 7 days. Afterwards antibiotics were infused in different rats according to their standard instructions for human use. Saline was used as negative control. The rats were sacrificed and the catheters explanted. After embedding in methacrylate and sectioning, fluorescence-in-situ-hybridisation technique (FISH) was used for the quantification of microorganisms and bacterial activity. Results: The system was well suited for the respective experiments and was well tolerated by the animals. Biofilms were successfully grown in the catheters and could be visualized and quantified using the FISH technique. Conclusions: This catheter model allows the in-situ-analysis of different antibiofilm strategies like antibiotics and the evaluation concerning their biocompatibility and effectiveness in rats. Acknowledgements: The study is funded by Novartis Pharma AG.
BibTeX @inproceedings{Gabel2011, author = {G. Gabel and J. Kikhney and K. Reiter and K. Affeld and Ch. Große-Siestrup and U. Kertzscher}, title = {A catheter model for the evaluation of anti-biofilm agents in rats}, booktitle = {38th European Society for Artificial Organs Congress, Porto, Portugal, October 9--12, 2011}, journal = {International Journal of Artificial Organs}, year = {2011}, volume = {34}, number = {8} }
2011 (13)	Großhauser, J. ; Affeld, K. ; Reiter, K. ; Große-Siestrup, C. ; Kertzscher, U.: Development of a CAPD catheter with infection proof exitsite. In: 38th European Society for Artificial Organs Congress, Porto, Portugal, October 9–12, 2011. International Journal of Artificial Organs Volume 34 , 2011(8) [Abstract] [BibTeX]
Abstract Objectives: In Western countries peritoneal dialysis (PD) only plays a minor role compared to hemodialysis. This is partly due to the high risk of exit-site infections, the leading complications with peritoneal dialysis. The infection is caused by a biofilm, originating at the exit-site. Drug-eluting catheters or catheters containing silver particles have not yet solved the problem. Objective of the project is to develop an infection resistant catheter, which uses a mechanical method to permanently prevent the infection. Methods: The presented catheter is equipped with a protective sleeve, which surrounds the catheter in the skin penetrating area. Subcutaneously the sleeve is folded and the inner end is hermetically sealed to the catheter. It is made of medical grade polyurethane (PUR) and its surface is coated with polyethylene terephthalate (PET) fibers to enable the ingrowth of connective tissue. After the implantation, the protective sleeve is slowly pulled outwards by means of a small traction device at a rate of few millimetres per week. Thus, it can grow out of the skin but still moves fast enough to prevent the down growth of the biofilm. Results: In a key experiment 6 of the devices were implanted in goats. The catheters remained infection-free over a period of 420 days, while control devices became infected. For the ongoing experiments the catheter setup was improved. So far, 8 catheters have been implanted in 4 goats and show no signs of pocket generation. The experiment is designed to last one year. Conclusions: The newly developed catheters show good promise for the prevention of infections of the exit-sites of PD-catheters. The principle could also be used for other skin penetrating implants such as power lines of heart assist devices.
BibTeX @inproceedings{Grosshauser2011, author = {J. Großhauser and K. Affeld and K. Reiter and C. Große-Siestrup and U. Kertzscher}, title = {Development of a CAPD catheter with infection proof exitsite}, booktitle = {38th European Society for Artificial Organs Congress, Porto, Portugal, October 9--12, 2011}, journal = {International Journal of Artificial Organs}, year = {2011}, volume = {34}, number = {8} }
2011 (12)	Weber, S. ; Kertzscher, U. ; Affeld, K.: Blood pressure simulator for noninvasive blood pressure measurement methods. In: 45. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik – Biomedizinische Technik, Freiburg, Germany, September 27–30, 2011. Biomedizinische Technik Volume 56 , 2011(Suppl. 1) [BibTeX]
BibTeX @inproceedings{Weber2011b, author = {S. Weber and U. Kertzscher and K. Affeld}, title = {Blood pressure simulator for noninvasive blood pressure measurement methods}, booktitle = {45. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik -- Biomedizinische Technik, Freiburg, Germany, September 27--30, 2011}, journal = {Biomedizinische Technik}, year = {2011}, volume = {56}, number = {Suppl. 1} }
2011 (11)	Großhauser, J. ; Affeld, K. ; Reiter, K. ; Große-Siestrup, C. ; Kertzscher, U.: Development of a CAPD Catheter with Infection Proof Exit-Site. In: 45. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik – Biomedizinische Technik, Freiburg, Germany, September 27–30, 2011. Biomedizinische Technik Volume 56 , 2011(Suppl. 1) [Abstract] [BibTeX]
Abstract Introduction In western countries peritoneal dialysis (PD) only plays a minor role compared to hemodialysis. This is part-ly due to the high risk of exit-site infections, the leading complications with peritoneal dialysis. The infection is caused by a biofilm, originating at the exit-site. Drug-eluting catheters or catheters contain-ing silver particles have not solved the problem. Objective is to develop an infection resistant catheter, which uses a mechanical method to permanently prevent the infection. Methods The presented catheter is equipped with a protective sleeve, which surrounds the catheter in the skin pene-trating area. Subcutaneously the sleeve is folded and the inner end is sealed to the catheter. It is made of polyurethane (PUR) and its surface is coated with polyethylene terephthalate (PET) fibers to enable the in-growth of connective tissue. After the implantation the protective sleeve is slowly pulled outwards by means of a traction device at a rate of few millimetres per week. Thus it can grow out of the skin but still moves fast enough to prevent the down growth of the biofilm. Results In a key experiment 6 of the devices were implanted in goats. The catheters remained infection free over a period of 420 days, while control devices became infected. For the ongoing experiments the catheter setup was improved. So far 8 catheters have been implanted in goats and show no signs of infection or pocket generation. The experiment is designed to last one year. Conclusion The newly developed catheters show good promise for the prevention of infections of the exit-sites of PD-catheters. The principle could also be used for other skin penetrating implants such as power lines of heart assist devices.
BibTeX @inproceedings{Grosshauser2011a, author = {J. Großhauser and K. Affeld and K. Reiter and Ch. Große-Siestrup and U. Kertzscher}, title = {Development of a CAPD Catheter with Infection Proof Exit-Site}, booktitle = {45. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik -- Biomedizinische Technik, Freiburg, Germany, September 27--30, 2011}, journal = {Biomedizinische Technik}, year = {2011}, volume = {56}, number = {Suppl. 1} }
2011 (10)	Kertzscher, U.: Scherbelastung des Blutes: Modelle und Methoden. In: 45. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik – Biomedizinische Technik, Freiburg, Germany, September 27–30, 2011. Biomedizinische Technik Volume 56 , 2011(Suppl. 1) [BibTeX]
BibTeX @inproceedings{Kertzscher2011a, author = {Ulrich Kertzscher}, title = {Scherbelastung des Blutes: Modelle und Methoden}, booktitle = {45. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik -- Biomedizinische Technik, Freiburg, Germany, September 27--30, 2011}, journal = {Biomedizinische Technik}, year = {2011}, volume = {56}, number = {Suppl. 1} }
2011 (09)	Schirrmann, K. ; Kertzscher, U. ; Affeld, K.: Blood model for capillary blood flow. In: 45. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik – Biomedizinische Technik, Freiburg, Germany, September 27–30, 2011. Biomedizinische Technik Volume 56 , 2011(Suppl. 1) [Abstract] [BibTeX]
Abstract Introduction Capillary blood flow is a two phase flow: blood cells and plasma are moving through a network. What forces shape this flow? How are the cells distributed? This is investigated experimentally with an enlarged model. The model is made to simulate the deformability of the red blood cells and the resulting effects on flow resistance. The deformability is modeled with water droplet – representing blood cells – in oil as plasma. This experimental model was developed because in experiments with real blood the network is too minute and detailed numerical simulation is too complex. Methods Water droplets of about 1 mm diameter model the red blood cells and sunflower oil the plasma. Two syringe pumps pump the components into a bifurcation, where they continually mix and form the blood model. We study the equivalents of both the Fåhraeus effect – hematocrit reduction – and the Fåhraeus-Lindquist effect – the effective viscosity variation: Droplet distance and the pressure drop are measured in a straight tube (d=1.2 mm) for various water flow fractions (representing the hematocrit) and droplet diameters. Flow distributions are studied at symmetric and asymmetric bifurcations. Results The experiments show a good agreement of the model behavior and the Fåhraeus/Fåhraeus-Lindquist effect for capillaries between 4 and 10 µm. The equivalent hematocrit reduction is slightly smaller than in blood. The droplet flow distribution patterns at asymmetric bifurcations are similar to those seen in vivo, including plasma separation effects. Symmetric bifurcations show a symmetric droplet flow distribution, which cannot be seen in vivo, where bifurcations are not perfectly symmetric. Conclusion The water-droplet-oil model mimics relevant properties of capillary blood, especially those of flow resistance and flow distribution at bifurcations. Thus, it lends itself to investigate the flow distribution in capillary networks.
BibTeX @inproceedings{Schirrmann2011a, author = {Kerstin Schirrmann and Ulrich Kertzscher and Klaus Affeld}, title = {Blood model for capillary blood flow}, booktitle = {45. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik -- Biomedizinische Technik, Freiburg, Germany, September 27--30, 2011}, journal = {Biomedizinische Technik}, year = {2011}, volume = {56}, number = {Suppl. 1} }
2011 (08)	Schneider, T. ; Goubergrits, L. ; Paschereit, C. ; Kertzscher, U. ; Affeld, K.: Messung der Scherung in stationären Strömungen mittels Spannungsoptik-Tomographie. In: 19. GALA-Fachtagung Lasermethoden in der Strömungsmesstechnik, Ilmenau, Germany, September 6–8, 2011. Deutsche Gesellschaft für Laseranemometrie, GALA, 2011 [Abstract] [BibTeX]
Abstract Die Spannungsoptik-Tomographie ist ein neuartiges optisches Messverfahren zur quantitativen Messung von Scherungen in Strömungen. Dieses nutzt die Doppelbrechung bestimmter Fluide unter dem Einfluss der Scherung. Eine Quantifizierung der Scherung mit diesem Ansatz ist bisher nur bei zweidimensionalen Strömungen bekannt. Durch die Zumischung einer Emulsion ist es gelungen die Intensität von Streulicht deutlich zu erhöhen und damit aus Signalen einzelner Schichten eine Tomographie der Scherungen zu realisieren. Als doppelbrechende Flüssigkeit wird eine wässrige Lösung von Baumwollgelb eingesetzt, dem ein emulgiertes Mineralöl zur Verstärkung des Streulichts zugefügt wird. Die tomographische Erfassung des Untersuchungsvolumens erfolgt mit parallelen Laserlichtschnitten und der Messung der Streulichtintensität per Kamera. Mit einem neuen Rekonstruktionsalgorithmus wird aus den gewonnenen Bilddaten ein dreidimensionales Scherfeld ermittelt. Mit einer weiteren Kalibration des Fluids kann auch das Schubspannungsfeld ermittelt werden. Die erste Anwendung dieser Methode wurde für die laminare, stationäre Rohrströmung mit Rechteck-querschnitt vorgenommen. Es konnte eine gute Übereinstimmung zwischen theoretischen und experimentellen Feldern festgestellt werden.
BibTeX @inproceedings{Schneider2011, author = {Schneider, T. and Goubergrits, L. and Paschereit, C.O. and Kertzscher, U. and Affeld, K.}, title = {Messung der Scherung in stationären Strömungen mittels Spannungsoptik-Tomographie}, booktitle = {19. GALA-Fachtagung Lasermethoden in der Strömungsmesstechnik, Ilmenau, Germany, September 6--8, 2011}, publisher = {Deutsche Gesellschaft für Laseranemometrie, GALA}, year = {2011} }
2011 (07)	Berthe, A. ; Gärtlein, S. ; Goubergrits, L. ; Lederer, C. ; Kertzscher, U.: Instationäre wandnahe Schubspannungsmessungen in einer Blutpumpe durch LDA und Wand-PIV. In: 19. GALA-Fachtagung Lasermethoden in der Strömungsmesstechnik, Ilmenau, Germany, September 6–8, 2011. Deutsche Gesellschaft für Laseranemometrie, GALA, 2011 [Abstract] [BibTeX]
Abstract Die instationäre Strömung einer Blutpumpe wurde flächig durch wandnahe Particle Image Velocimetry (Wand-PIV) untersucht. Bildsequenzen wurden mit 1000 Hz aufgezeichnet (Redlake MotionProY4, Redlake Inc., USA). Auf Grundlage der vermessenen Strömungsfelder wurden die Wandschub-spannungen flächig und zeitaufgelöst berechnet. Weiterhin wurde die Strömung mit einer zwei-Komponenten Laser Doppler Velocimetry Anlage (Dantec Dynamics, Dänemark) untersucht. Entlang der horizontalen Mittelachse erfolgten Messungen mit seitlichen Abständen von 2 mm und Tiefenabständen von 0,5 mm. An vier Messpunkten wurde für die Berechnung von Wandschubspannungen die Tiefenauflösung auf 0,1 mm erhöht. Die Messzeit an jedem Messpunkt betrug 15 s, was etwa 15 Herzzyklen entspricht. Auf Grundlage dieser Daten wurde für den gesamten Herzzyklus alle 50 ms mittlere Wandschubspannungen berechnet. Die Wandschubspannungen von Wand-PIV-Messungen und LDV-Messungen zeigt eine gute Übereinstimmung. Hiermit ist erstmals eine zeitaufgelöste flächige Wandschub-spannungsmessung an der gewölbten Oberfläche einer Blutpumpe mittels Wand-PIV durchgeführt und validiert.
BibTeX @inproceedings{Berthe2011a, author = {A. Berthe and S. Gärtlein and L. Goubergrits and Ch. Lederer and U. Kertzscher}, title = {Instationäre wandnahe Schubspannungsmessungen in einer Blutpumpe durch LDA und Wand-PIV}, booktitle = {19. GALA-Fachtagung Lasermethoden in der Strömungsmesstechnik, Ilmenau, Germany, September 6--8, 2011}, publisher = {Deutsche Gesellschaft für Laseranemometrie, GALA}, year = {2011} }
2011 (06)	Weber, S. ; Kertzscher, U. ; Affeld, K.: Belastungsarme Blutdruckmessung mit Ultraschall. In: Lange Nacht der Wissenschaften, Berlin, Germany, May 28, 2011. , 2011 [BibTeX]
BibTeX @inproceedings{Weber2011a, author = {S. Weber and U. Kertzscher and K. Affeld}, title = {Belastungsarme Blutdruckmessung mit Ultraschall}, booktitle = {Lange Nacht der Wissenschaften, Berlin, Germany, May 28, 2011}, year = {2011} }
2011 (05)	Schirrmann, K. ; Kertzscher, U. ; Affeld, K.: Blutströmung in Lungenkapillaren. In: Lange Nacht der Wissenschaften, Berlin, Germany, May 28, 2011. , 2011 [BibTeX]
BibTeX @inproceedings{Schirrmann2011c, author = {K. Schirrmann and U. Kertzscher and K. Affeld}, title = {Blutströmung in Lungenkapillaren}, booktitle = {Lange Nacht der Wissenschaften, Berlin, Germany, May 28, 2011}, year = {2011} }
2011 (04)	Weber, S. ; Kertzscher, U. ; Affeld, K.: Neuartige Methode für die belastungsarme nichtinvasive Langzeitmessung des Blutdrucks. In: 25. Treffpunkt Medizintechnik „Nicht-invasive Diagnostik“, Berlin, Germany, May 26, 2011. , 2011 [BibTeX]
BibTeX @inproceedings{Weber2011, author = {S. Weber and U. Kertzscher and K. Affeld}, title = {Neuartige Methode für die belastungsarme nichtinvasive Langzeitmessung des Blutdrucks}, booktitle = {25. Treffpunkt Medizintechnik „Nicht-invasive Diagnostik“, Berlin, Germany, May 26, 2011}, year = {2011} }
2011 (03)	Goubergrits, L. ; Wiegmann, N. ; Schaller, J. ; Berthé, A. ; Kertzscher, U. ; Petz, C. ; Hege, H.-C. ; Hoch, H. ; Spuler, A.: In vitro therapy planning after a failed coiling of the basilar artery aneurysm. In: 6th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, Netherlands, April 14–15, 2011. , 2011 [Abstract] [BibTeX]
Abstract Introduction Hemodynamics plays a significant role in formation and growth of cerebral aneurysms and influences the effectiveness of therapy. We present the case of an aneurysm at a fenestrated basilar artery. Control angiography (6 months later the coiling procedure) revealed partial refilling of the aneurysm (see fig. 1, left). In this situation, incomplete Hunterian ligation i.e. clipping of one of the two vertebral arteries would be a surgical option. The flow changes due to such a procedure were investigated experimentally. Methods Three-dimensional Rotational Angiography was performed after the failed coiling procedure. Geometry of the aneurysm rest and the corresponding arteries was reconstructed (see fig. 1, right) from data with an isotropic voxel size of 0.222 mm3 using software ZIB-Amira (Berlin, Germany). From these data a two-fold enlarged transparent silicone model was fabricated. Flow changes due to clipping of the left or the right vertebral artery under pulsatile flow conditions for two different (low and high) flow rates were studied by means of particle image velocimetry (PIV). Results Vector fields revealed remarkable differences between the simulated flow patterns in the original setting and after partial hunterian ligation (fig. 2). Clipping of the left or right vertebral artery causes either an increase or a decrease of the flow in the aneurysm baring segment of the parent vessel. Flow increase, however, may be accompanied by an unwanted increase of flow irregularities, which may promote thrombus formations. Conclusions Hunterian ligation may change the flow near the aneurysmal neck thus preventing further aneurysmal growth. The selection of the site for clipping is, however, challenging and requires further studies.
BibTeX @inproceedings{Goubergrits2011b, author = {Leonid Goubergrits and Nils Wiegmann and Jens Schaller and Andre Berthé and Ulrich Kertzscher and Christoph Petz and Hans-Christian Hege and Heiner Hoch and Andreas Spuler}, title = {In vitro therapy planning after a failed coiling of the basilar artery aneurysm}, booktitle = {6th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, Netherlands, April 14--15, 2011}, year = {2011} }
2011 (02)	Schaller, J. ; Kragh, T. ; Spannagl, M. ; Reininger, A. ; Kertzscher, U. ; Affeld, K.: Experimental Setup for Quantifying of the Virchow Triad. In: 6th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, Netherlands, April 14–15, 2011. , 2011 [Abstract] [BibTeX]
Abstract Introduction Thrombus formation still poses a problem in the development of devices in the cardiovascular system. The process is determined by the components of Virchow´s triad, which describes the interaction of blood, flow and surface. The objective of this work is the development of a method to quantify Virchow´s triad and especially quantify influence of the surface material. For this endeavour the stagnation point flow is chosen. Methods For the experiments a stagnation point flow chamber was designed and manufactured. The blood flows through a bore perpendicular onto a flat plate. This is the test surface. In a radial distance the blood is collected in an annular channel. This creates a stagnation point flow with axial symmetry but with radially varying shear rates. The flat plate is a microscopic cover slip and permits a fluorescent video microscopy with an inverted microscope. The cover slip is coated with the test material. The blood was drawn from voluntary healthy donors into standard syringes containing sodium citrate. To dye the platelets with calcein red-orange AM, platelet rich plasma is temporarily separated. With a flow rate of 18 ml/h the blood enters a microfluidic device to mix with adenosine diphosphate (ADP) (2ml/h, 20 µM) to stimulate the platelets. The activated platelets deposit on the cover slip influenced by shear rate and surface. This process is recorded and analysed. Three different surfaces were tested: native glass, von-Willebrand-Factor coating, triethoxysilyl modified hyperbranched polyglycerol coating. Results The three test surfaces show clear differences in the deposition. The triethoxysilyl modified hyperbranched polyglycerol surface shows no platelet deposition. The other both shows a ring of deposited platelets around the stagnation point after addition with ADP (see figure left). Without stimulation no signficiant deposition appears. (see figure right). Conclusions With this method all three components of the triad can be modified and their impact on the deposition of platetlets can be assessed. Further work will be to differentiate the influence of each of the triad´s three components.
BibTeX @inproceedings{Schaller2011a, author = {Jens Schaller and Thorsten Kragh and Michael Spannagl and Armin Reininger and Ulrich Kertzscher and Klaus Affeld}, title = {Experimental Setup for Quantifying of the Virchow Triad}, booktitle = {6th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, Netherlands, April 14--15, 2011}, year = {2011} }
2011 (01)	Schirrmann, K. ; Kertzscher, U. ; Affeld, K.: Shear Stress in Capillaries and its Effect on the Flow in the Pulmonary Capillary Network. In: 6th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, Netherlands, April 14–15, 2011. , 2011 [Abstract] [BibTeX]
Abstract Introduction Precapillary sphincters control the flow in systemic capillary networks but do not exist in the lung. There, different regulation mechanisms ensure appropriate flow distributions; one is addressed here. In capillaries, blood flow is dominated by its non-Newtonian nature, since red blood cells (RBCs) and vessel diameter are of the same order. The wall shear stress is locally increased in the presence of the deformed RBCs. This results in a hematocrit dependency of the flow resistance, which affects the flow distribution in capillary networks [1]. Also, at bifurcations the number of RBCs in the daughter branches is non-linearly determined by the flow ratio [1]. The hypothesis is that the hematocrit dependent resistance together with the flow dependent hematocrit behind a bifurcation can cause flow variations as seen in isolated perfused canine lungs [2] and act as a passive regulation mechanisms in the pulmonary capillary network. For the investigation of this hypothesis, we present a water droplet oil system as an enlarged blood model that mimics the two phase nature of blood in capillaries and related hemorheological properties. Methods Dyed water droplets with a diameter of circa 1 mm model the RBCs, sunflower oil the plasma. The model is continuously produced with syringe pumps. For validation, the relative effective viscosity of the blood model is calculated from pressure drop measurements along a 1.2 mm tube. In addition, the ratio of tube water fraction ft (equivalent to the hematocrit) and discharge water fraction fd is calculated from droplet distance and preset water flow rate. Phase separation effects are studied in Y-bifurcations with preset flow rates. The capillary network model is similar to the pulmonary capillary network and has an averaged diameter of 1.2 mm. The analysis of the flow distribution is based on particle tracking methods. Results The relative effective viscosity of the blood model is water fraction dependent. It decreases with increaseing ratio of droplet to tube diameter (rel=2.1 to 1.3), as does the water fraction ratio (ft/fd=1.1 to 0.8). The results are in accordance with the hematocrit reduction (Fåhraeus effect) and with the effective viscosity reduction (Fåhraeus-Lindquist effect) seen for blood in glass capillaries between 3 and 10 µm [3]. The phase separation effects seen at bifurcations are similar to those in blood [1]: For example, a 10% overall flow rate in a branch results in zero droplet flow. The experiments in the capillary network model show a droplet distribution which is variable, especially in segments with lower water fraction. Here, the number of droplets and the length to diameter ratio are small. Under these conditions, the segmental flow resistance can change significantly with single droplets entering or leaving a segment. Then the flow distribution changes, which results in a change of droplet flow, which induces a resistance change again; in other words, an unsteady flow is induced. Conclusions The model mimics the two phase nature of blood in capillaries and both the RBCs and the droplets deform. Thus, effects seen in both systems and its consequences on shear stress must be essentially influenced by these properties. Additionally, since the important rheological effects are included in the model, it can be used to study network flow distributions experimentally. The results of these experiments are in line with the hypothesis of a flow regulation mechanism that is, in the end, shear stress induced. References [1] Schmid-Schönbein GW, Skalak R, Usami S, Chien S, Cell Distribution in Capillary Networks, Microvascular Research, 19:18-44, 1980. [2] Baumgartner WA, Peterson AJ, Presson RG, Tanabe N, Jaryszak EM, Wagner WW, Blood flow switching among pulmonary capillaries is decreased during high hematocrit. J Appl Physiol 97: 522:526, 2004. [3] Pries AR, Secomb TW, Microvascular blood viscosity in vivo and the endothelial surface layer, Am J Physiol Heart Circ Physiol, 289:H2657-H2664, 2005.
BibTeX @inproceedings{Schirrmann2011b, author = {Kerstin Schirrmann and Ulrich Kertzscher and Klaus Affeld}, title = {Shear Stress in Capillaries and its Effect on the Flow in the Pulmonary Capillary Network}, booktitle = {6th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, Netherlands, April 14--15, 2011}, year = {2011} }
2010 (11)	Weber, S. ; Kertzscher, U. ; Affeld, K.: Blutdruckmessung mit Hilfe von Ultraschall-Doppler Signalen. In: 44. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik – Biomedizinische Technik, Rostock, Germany, October 5–8 2010. Biomedizinische Technik, Volume 55, 2010(Suppl. 1) [Abstract] [BibTeX]
Abstract Der Blutdruck ist einer der wichtigsten Einflussgrößen von Erkrankungen des Herz-Kreislauf-Systems. Diese Erkrankungen stellen die Haupttodesursache in Deutschland dar. Ein wichtiges Verfahren für die Diagnose ist dabei die 24h Messung. Das bisherige Verfahren, die automatisierte Armmanschettenmessung nach Riva-Rocci, ist für den Patienten unangenehm, stark artefaktbelastet und erfordert eine Unterbrechung jeder motorischen Tätigkeit während der Messung. Es wird deshalb versucht ein Messsystem zu entwickeln, das diese Nachteile vermeidet. Es ist durch folgende Eigenschaften charakterisiert: anstelle aller Armgefäße wird nur eine oberflächliche Arterie okkludiert. Hierzu wird ein kleines Kissen eingesetzt, das über der Arterie durch eine leicht lösbare Klebung fixiert wird. Da nur ein kleiner Gewebebereich über der Arterie mit dem Druck beaufschlagt wird, ist die Messung belastungsarm. Der Blutfluss in der Arterie wird mit dem Ultraschall-Doppler-Verfahren gemessen. Diese Blutflusskurve wird mit dem aufgebrachten Druck korreliert. Daraus kann der systolische Blutdruck ermittelt werden. In einem weiteren Entwicklungsschritt soll auch der diastolische Blutdruck aus dem Verlauf der Blutflusskurve ermittelt werden.
BibTeX @inproceedings{Weber2010a, author = {S. Weber and U. Kertzscher and K. Affeld}, title = {Blutdruckmessung mit Hilfe von Ultraschall-Doppler Signalen}, booktitle = {44. Jahrestagung Deutsche Gesellschaft für Biomedizinische Technik -- Biomedizinische Technik, Rostock, Germany, October 5--8}, journal = {Biomedizinische Technik}, year = {2010}, volume = {55}, number = {Suppl. 1} }
2010 (10)	Schneider, T. ; Goubergrits, L. ; Kertzscher, U. ; Paschereit, C.: Polarimetric planar difference tomography for 3D shear stress field measurements: Calibration of birefringent fluids. In: Euromech Fluid Mechanics Conference - 8, Bad Reichenhall, September 13–16 2010. [Abstract] [BibTeX]
Abstract Direct measurement and visualization of a three-dimensional (3D) shear stress field of a fluid flow is of great interest for biofluid mechanics because of the strong correlation between shear stress and processes of blood coagulation or thrombus formation. Polarimetric Planar Difference Tomography (pPDT) is a new 3D measurement approach to quantify shear stress fields. This technique utilizes the Maxwell effect: shear stress induces a net orientation of anisotropic molecules contained in a liquid and thus optical anisotropy of the fluid. A polarized light beam changes its state of polarization when propagating through this sheared liquid because of the optical anisotropy in the form of birefringence (refractive index change Δn). When leaving the fluid, the light beam's direction of polarization carries the integrated information about the shear stress field along its path. Since pPDT is an optical method based on birefringent liquids, one has to characterize the applied fluid: rheological properties, light absorption (dichroism), and especially the stress-optical relation (Δn vs. τ) have to be determined. For this procedure a setup with a plate-plate shear cell with the possibility to send light obliquely through the sample has been designed. Until the 1980s Milling Yellow solution was a standard liquid in rheo-optical studies but was unavailable for almost 25 years. First quantitative stress-optical measurements with Milling Yellow in our plate-plate shear cell are reported. The sample was a 16 days old 1.45% w/w solution of Milling Yellow (Pylam Products, Tempe, US-AZ) in distilled water at 22.8°C.
BibTeX @inproceedings{Schneider2010, author = {T. Schneider and L. Goubergrits and U. Kertzscher and C.O. Paschereit}, title = {Polarimetric planar difference tomography for 3D shear stress field measurements: Calibration of birefringent fluids}, booktitle = {Euromech Fluid Mechanics Conference - 8, Bad Reichenhall, September 13--16}, year = {2010} }
2010 (09)	Weber, S. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: Permanent central venous catheter with a lock balloon. In: 37th European Society for Artificial Organs Congress, Skopje, Macedonia, September 8–11 2010. [Abstract] [BibTeX]
Abstract Objectives: Permanent vascular access is essential for hemodialysis, parenteral nutrition and drug administration. Mostly a central venous catheter (CVC) is used. However, this use poses a problem: infection. The cause is the intraluminal space, which acts as a bioreactor during the time when the CVC is idle. To prevent this, a bactericidal liquid, called a lock solution, is injected into the intraluminal space. For fluidmechanical reasons, it is not possible to completely fill the intraluminal space without injecting the lock solution into the bloodstream. The proposed lock balloon fills the intraluminal space and makes a lock solution redundant. Methods: Simulation of lock solution inflow: The inflow of a lock solution into a double lumen catheter was investigated using computational fluid dynamics (CFD). Conceptional work: The lock balloon was realized by replacing the axial filling with a radial filling and by using a membrane interface instead of a fluid. Results: The CFD simulation showed the protrusion of a central core of the lock solution during infusion. The wall remained free of the lock solution. The filling of the lumen was achieved with the lock balloon, an elongated, enclosed balloon remaining permanently inside the CVC. During infusion the lock balloon is collapsed and the lumen is free for the passage of the infused liquid. After infusion the lock balloon is inflated again and completely fills the intraluminal catheter space. A bi-stable piston secures the simple collapse and filling action of the lock balloon. This was realized for a 10 French single lumen catheter. The lock balloon was fabricated of polyurethane with a thickness of 0.1 mm. Filling and emptying was done with a fluid. The collapsed lock balloon only slightly reduced the infusion flow. Conclusions: The concept appears valid and further investigations will deal with miniaturization of the lock balloon and animal experiments. The animal experiments are designed to model the routine of CVC use. Conventional CVCs will be compared to lock balloon CVCs. Blood cultures after catheter use will be used as a control.
BibTeX @inproceedings{Weber2010, author = {S. Weber and L. Goubergrits and U. Kertzscher and K. Affeld}, title = {Permanent central venous catheter with a lock balloon}, booktitle = {37th European Society for Artificial Organs Congress, Skopje, Macedonia, September 8--11}, year = {2010} }
2010 (08)	Berthe, A. ; Goubergrits, L. ; Lederer, C. ; Spence, P. ; Giridharan, G. ; Kertzscher, U.: Study of a valveless counterpulsation heart assist device with two measurement methods. In: 37th European Society for Artificial Organs Congress, Skopje, Macedonia, September 8–11 2010. [Abstract] [BibTeX]
Abstract Objectives: The flow field investigation of blood pumps allows a first estimation of the risk regions of thrombus formation. The pump under consideration is a novel long-term implantable counterpulsation device (CPD). The CPD is a single port, valveless 32 mL stroke volume blood chamber attached to the subclavian artery. It can be implanted subcutaneously, similar to a pacemaker. Materials and Methods: The time resolved flow investigation of the CPD was done by Particle Image Velocimetry (PIV) to obtain the flow field in the central plane and Wall-PIV to obtain the near wall flow. Both methods were realized on a setup, consisting of a Windkessel and the CPD. Especially a 1in2 operation mode (one pump action every two heart beats), which is more prone for thrombus formation due to waiting period between fillings and emptying phases, was investigated. The pressure head was set to 90 mmHg. As a test fluid a mixture of water and glycerin, simulating the blood viscosity was used. PIV images were recorded with a high speed camera. To investigate the flow along the curved walls of the CPD, we used the Wall-PIV technique developed in our laboratory and allowing the assessment of velocity in the near wall layer of about 200 µm. Results: During ejection phase the fluid flows towards the port of the CPD uniformly, resulting in a good washout. During filling phase a steadily rotating vortex, extending over the complete blood pump, with a permanently moving center, is observed. This large vortex was sustained for over 1.2 seconds of the hold time after the completion of CPD filling providing adequate washing even in a 1in2 operation mode. Conclusions: The investigated CPD has a good washout of the whole pump volume. Regions of stagnation are inhibited by a persistent steady rotating vortex. A low risk of thrombus formation in the blood chamber is expected.
BibTeX @inproceedings{Berthe2010a, author = {A. Berthe and L. Goubergrits and Ch. Lederer and P.A. Spence and G.A. Giridharan and U. Kertzscher}, title = {Study of a valveless counterpulsation heart assist device with two measurement methods}, booktitle = {37th European Society for Artificial Organs Congress, Skopje, Macedonia, September 8--11}, year = {2010} }
2010 (07)	Affeld, K. ; Loewenhoff, K. ; Pöthke, J. ; Watanabe, N. ; Kertzscher, U.: Shear rate and platelet deposition in whole blood. In: 37th European Society for Artificial Organs Congress, Skopje, Macedonia, September 8–11 2010. [Abstract] [BibTeX]
Abstract Objectives: Objective of the research is to quantify the shear rate, which is likely to favor the deposition of platelets in whole blood. This is important, because cardiovascular implants, such as assist devices, frequently cause thromboembolic complications. These still severely limit their clinical application. One reason for these complications is the activation of platelets by high mechanical shear stress followed by a flow of low shear stress in the vicinity of a foreign material. Methods: Whole blood is sheared in a gap between two parallel glass plates with a diameter of 35 mm and a distance of 50 µm. The lower plate remains stationary, while the upper plate is rotated. This shearing device is attached to an inverted microscope (Fluovert FU, Leica) and the deposition of the platelets is recorded and analyzed. The platelets are stained with Mepacrine and are illuminated by ultraviolet light with 355--425 nm wavelength and respond with an emission of green light with 496 nm wavelength. Results: When the deposited platelets per time unit are plotted as a function of shear rate, a peak is observed at a shear rate around 100 1/s. Conclusions: This is interpreted as the interaction of two modes of transport of thrombo-active substances in blood: diffusive and convective. When both modes combine in a specific relation, an optimal transport is achieved, which favors the generation of a thrombus.
BibTeX @inproceedings{Affeld2010, author = {K. Affeld and K. Loewenhoff and J. Pöthke and N. Watanabe and U. Kertzscher}, title = {Shear rate and platelet deposition in whole blood}, booktitle = {37th European Society for Artificial Organs Congress, Skopje, Macedonia, September 8--11}, year = {2010} }
2010 (06)	Großhauser, J. ; Affeld, K. ; Kertzscher, U. ; Reiter, K. ; Abdin-Bey, N. ; Große-Siestrup, C.: Development of a CAPD catheter with protective sleeve to avoid infection. In: 37th European Society for Artificial Organs Congress, Skopje, Macedonia, September 8–11 2010. [BibTeX]
BibTeX @inproceedings{Grosshauser2010, author = {J. Großhauser and K. Affeld and U. Kertzscher and K. Reiter and N. Abdin-Bey and Ch. Große-Siestrup}, title = {Development of a CAPD catheter with protective sleeve to avoid infection}, booktitle = {37th European Society for Artificial Organs Congress, Skopje, Macedonia, September 8--11}, year = {2010} }
2010 (05)	Schneider, T. ; Jansen, S.: Validation of CFD with PIV and other methods. In: yESAO-young Researchers' Initiative, Skopje, Macedonia, September 8 2010. [BibTeX]
BibTeX @inproceedings{Schneider2010a, author = {Schneider, Torsten and Jansen, Sebastian}, title = {Validation of CFD with PIV and other methods}, booktitle = {yESAO-young Researchers' Initiative, Skopje, Macedonia, September 8}, year = {2010} }
2010 (04)	Pöthke, J. ; Goubergrits, L. ; Petz, C. ; Kertzscher, U. ; Hege, H.-C. ; Spuler, A. ; Affeld, K.: New tool to visualize near wall flow in cerebral aneurysms. In: 4th International Symposium on Modelling of Physiological Flows, Centro Congressi Chia Laguna Resort, Sardinia, Italy, June 2–5, 2010. [Abstract] [BibTeX]
Abstract Problem: The assessment of rupture risk of cerebral aneurysms is a still unresolved problem. The data in the international literature show an influence of the shape of the aneurysm, which determines both the tensile stresses of the wall and also the flow. Regarding the latter, the flow close to the wall is regarded as the major influence. This near wall flow causes the wall shear stress – WSS –, which is well investigated - in its distribution at the wall, its strength and course over time. However, no conclusive hypothesis has yet evolved. Methods: The wall shear stress was simulated with the flow solver Fluent (Ansys Inc., USA). Rigid walls were assumed and a now-Newtonian model was used. The anatomical basis was assessed with the rotational angiography of five unruptured and four ruptured aneurysms. From these data the grid for the computation was derived. The boundary condition for inflow and outflow were taken from the literature and Murray´s law. The resulting instationary field of wall shear stress was exported and analyzed by ZIBAmira program (Zuse Institute Berlin, Germany). This new tool permits to visualize the instationary near wall flow in animated form. Results: The new tool permits to visualize the highly complex flow inside an aneurysm. It extracts points of zero wall shear stress from the dynamic field of the near wall. Points and near wall flow fields were visualized. Usually 5 to 8 of these points are detected on the dome each aneurysm. Some of these points are stationary, other move around over the whole cycle. Discussion: A discrimination of the ruptured aneurysms has not yet been achieved. More cases are needed for statistical evaluation of flow field features differences between the ruptured and unruptured group of cerebral aneurysms.
BibTeX @inproceedings{Poethke2010, author = {J. Pöthke and L. Goubergrits and Ch. Petz and U. Kertzscher and H.-Ch. Hege and A. Spuler and K. Affeld}, title = {New tool to visualize near wall flow in cerebral aneurysms}, booktitle = {4th International Symposium on Modelling of Physiological Flows, Centro Congressi Chia Laguna Resort, Sardinia, Italy, June 2--5, 2010}, year = {2010} }
2010 (03)	Goubergrits, L.: Impact of side branches in wall shear stress profiling of coronary arteries of different groups of patients. In: 4th International Symposium on Modelling of Physiological Flows, Centro Congressi Chia Laguna Resort, Sardinia, Italy, June 2–5, 2010. [BibTeX]
BibTeX @inproceedings{Goubergrits2010, author = {Leonid Goubergrits}, title = {Impact of side branches in wall shear stress profiling of coronary arteries of different groups of patients}, booktitle = {4th International Symposium on Modelling of Physiological Flows, Centro Congressi Chia Laguna Resort, Sardinia, Italy, June 2--5, 2010}, year = {2010} }
2010 (02)	Pöthke, J. ; Schäfer, M. ; Petz, C. ; Hege, H.-C. ; Kertzscher, U. ; Affeld, K. ; Spuler, A. ; Goubergrits, L.: Hemodynamics of three cerebral aneurysms with daughter aneurysms. In: 5th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, Netherlands, April 15–16, 2010. [Abstract] [BibTeX]
Abstract Introduction The mechanisms of development, growth and rupture of cerebral aneurysms are still incompletely understood. However, blood flow is believed to have a major impact. Some aneurysms develop smaller aneurysms, so-called daughter aneurysms - see figure. In this study the influence of these daughter aneurysms was investigated. The blood flow with and without these daughter aneurysms was simulated and compared. The study is intended to find hemodynamic parameters responsible for mechanisms of aneurysm development and growth. Methods Three-dimensional data of three cerebral aneurysms – one ruptured and two unruptured - were acquired. Two of the aneurysms have two daughter aneurysms each. The surfaces of the aneurysms and vessel branches were reconstructed with software amira® (Zuse Institute Berlin). Aneurysms without daughter aneurysms were reconstructed with the tool ReMESH (IMATI, Genova, Italy). Unsteady flow simulations were performed with the flow solver Fluent (Ansys Inc.) The blood was assumed non-Newtonian. The instationary inlet flow rates were taken from literature. The outlet flow distribution was calculated with Murray's Law. Distributions of time averaged wall shear stress (WSS), oscillatory shear index (OSI) and time averaged temporal WSS gradients were calculated and compared. Furthermore, wall bounded critical points (WSS=0) were calculated and visualized using time averaged WSS vector field. Results All daughter aneurysms are located on the aneurysm halves with an impingement zone, which is characterized by the highest WSS at the aneurysmal wall. The hemodynamics of each original aneurysm is affected by a strong vortex. The ends of vortex cores are located in three of five daughter aneurysms. Other both daughter aneurysms are located in the impingement zone. The major features of flow fields are not affected by the presence of the daughter aneurysms. The distributions show minimal changes of magnitudes and distributions of the investigated parameters excluding the areas in the direct vicinity of daughter aneurysms. The near wall flow analysis of the aneurysm models without DA’s found critical points near the sites where the three DA’s existed (see figure). Conclusions The results suppose a correlation between daughter aneurysms and the vortex core and the impingement zone. The limitation of this study is the assumption of the aneurysm geometry without daughter aneurysms and small number of investigated cases. Therefore, more cases are needed to demonstrate preliminary findings of the study.
BibTeX @inproceedings{Poethke2010a, author = {Jens Pöthke and Merlin Schäfer and Christoph Petz and Hans-Christian Hege and Ulrich Kertzscher and Klaus Affeld and Andreas Spuler and Leonid Goubergrits}, title = {Hemodynamics of three cerebral aneurysms with daughter aneurysms}, booktitle = {5th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, Netherlands, April 15--16, 2010}, year = {2010} }
2010 (01)	Schaller, J. ; Kragh, T. ; Kertzscher, U. ; Reininger, A. ; Affeld, K.: Interaction of blood, flow and material on platelet deposition in a stagnation point flow model. In: Joint ESAO-ASAIO Winter School: Bioartificial Organs & Cell Therapy, Semmering, Austria, January 21–23, 2010. [Abstract] [BibTeX]
Abstract Objectives Thrombus formation severely limits the use of blood contacting artificial devices like cardiac valves, blood pumps and catheters. This thrombus formation is influenced by Virchow´s trias - conditions of blood, flow and surface. Objective of this project is to develop a model of thrombus development based on experiments with the stagnation point flow. Design and Methods The stagnation point flow model is based on the microscopic observation of a stagnation point flow of blood. This flow is modeled with computational fluid dynamics (CFD) methods to properly select the dimensions of the flow chamber. Flow rate and dimensions are such selected, that in the image field shear rates of stagnation point flow vary from zero at the stagnation point itself to 200 s-1 in radial direction. The flow rate is 20 ml/h. The final flow model is designed and fabricated. The surface of the glass plate is varied to investigate the role of the blood contact material. This stagnation point flow model is placed on an inverse microscope. The microscopic images are recorded with a CCD camera with a 16 frames per second and 960 x 720 pixels. Fresh human blood is drawn from voluntary donors into 3.8% sodium citrate solution. The platelets are separated, labeled with calcein red-orange AM and rejoined with the remaining red blood cells. This blood is pumped into the flow chamber with a flow rate of 20 ml/h. Platelets are activated by continuously injecting a flow of adenosine diphosphate into the tubing leading to the stagnation point flow model. Results Native glass plates and native glass covered with von Willebrand factor have been tested. The platelet deposition shows a radially differentiated rate. However, in some experiments a non-uniform platelet deposition in angular position was observed. Closer analysis showed, that blood and adenosine diphosphate was unevenly mixed in the tube. This is a low Reynolds number effect. Consequently, a laminar microfluidic mixer was designed and used in further experiments. Conclusion The combination of the long known principle of the stagnation point flow with modern methods of fluid mechanics (CFD) permits to quantify Virchow´s trias.
BibTeX @inproceedings{Schaller2010, author = {Jens Schaller and Thorsten Kragh and Ulrich Kertzscher and Armin Reininger and Klaus Affeld}, title = {Interaction of blood, flow and material on platelet deposition in a stagnation point flow model}, booktitle = {Joint ESAO-ASAIO Winter School: Bioartificial Organs & Cell Therapy, Semmering, Austria, January 21--23, 2010}, year = {2010} }
2009 (14)	Großhauser, J. ; Affeld, K. ; Kertzscher, U. ; Gabel, G. ; Timmel, T. ; Große-Siestrup, C.: Entwicklung eines CAPD-Katheters mit einer Infektionsschutzmanschette. In: Jahrestagung Deutsche Gesellschaft für Biomaterialien (DGBM), Tübingen, Deutschland, Oktober 8–10. , 2009 [BibTeX]
BibTeX @inproceedings{Grosshauser2009, author = {J. Großhauser and K. Affeld and U. Kertzscher and G. Gabel and T. Timmel and Ch. Große-Siestrup}, title = {Entwicklung eines CAPD-Katheters mit einer Infektionsschutzmanschette}, booktitle = {Jahrestagung Deutsche Gesellschaft für Biomaterialien (DGBM), Tübingen, Deutschland, Oktober 8--10}, year = {2009} }
2009 (13)	Berthe, A. ; Weber, S. ; Kondermann, D. ; Goubergrits, L. ; Kertzscher, U.: Untersuchung der wandnahen Strömung von Hirnaneurysmen: Vergleich zwischen Wand-PIV und CFD. In: 17. Fachtagung Lasermethoden in der Strömungsmesstechnik (GALA), Erlangen, Deutschland, September 8–10. , 2009 [Abstract] [BibTeX]
Abstract Die Betrachtung der wandnahen Strömung ist von großer Bedeutung für die Untersuchung und Beurteilung krankhafter Gefäßerweiterungen (Aneurysmen). Jährlich erleiden etwa 10 von 100.000 Menschen eine akute Blutung infolge der spontanen Ruptur eines Hirnaneurysma. Die Blutströmung spielt bei Entstehung, Wachstum und Ruptur von Aneurysmen eine wichtige Rolle. Langfristig wird durch Untersuchung der Strömung in anatomisch realistischen Gefäßgeometrien versucht, Zusammenhänge zwischen Strömung und Rupturrisiko herzuleiten. Ziel der hier vorgestellten Arbeit war der qualitative Vergleich zwischen numerischen Strömungsberechnungen und wandnahen Strömungsuntersuchungen mittels Wand-PIV.
BibTeX @inproceedings{Berthe2009b, author = {A. Berthe and S. Weber and D. Kondermann and L. Goubergrits and U. Kertzscher}, title = {Untersuchung der wandnahen Strömung von Hirnaneurysmen: Vergleich zwischen Wand-PIV und CFD}, booktitle = {17. Fachtagung Lasermethoden in der Strömungsmesstechnik (GALA), Erlangen, Deutschland, September 8--10}, year = {2009} }
2009 (12)	Kertzscher, U. ; Schneider, T. ; Goubergrits, L. ; Spuler, A. ; Affeld, K.: Head Motion Therapy after Subarachnoid Hemorrhage: Preliminary Results of an in Vitro Study in a Basal Cistern Model. In: World Congress on Medical Physics and Biomedical Engineering, September 7–12, Munich, Germany. IFMBE Proceedings Volume 25/IV Springer, 2009, pp. 2103–2106. [Abstract] [BibTeX] Article (PDF-file; 0.44 MB) Poster (PDF-file; 1.90 MB)
Abstract Subarachnoid hemorrhage (SAH) is a serious threat for patients with ruptured cerebral aneurysms or head injury. Especially a cerebral arterial vasospasm after SAH is a complication with a high morbidity and mortality rate. An external supported washout of the blood clot from the basal cistern may reduce this rate considerably. This washout process can be supported by shaking the patient. The effect of different shaking strategies (low and high shaking frequencies, low and high shaking amplitude) was investigated by dye washout method in a model of a basal cistern. In this paper the experimental setup and the washout results for two shaking experiments are presented.
BibTeX @inproceedings{Kertzscher2009, author = {U. Kertzscher and T. Schneider and L. Goubergrits and A. Spuler and K. Affeld}, title = {Head Motion Therapy after Subarachnoid Hemorrhage: Preliminary Results of an in Vitro Study in a Basal Cistern Model}, booktitle = {World Congress on Medical Physics and Biomedical Engineering, September 7--12, Munich, Germany}, journal = {IFMBE Proceedings}, publisher = {Springer}, year = {2009}, volume = {25/IV}, pages = {2103--2106} }
2009 (11)	Poethke, J. ; Spuler, A. ; Petz, C. ; Hege, H.-C. ; Goubergrits, L. ; Affeld, K. ; Kertzscher, U.: Cerebral Aneurysm Hemodynamics and a Length of Parent Vessel. In: World Congress on Medical Physics and Biomedical Engineering, September 7–12, Munich, Germany. IFMBE Proceedings Volume 25/IV Springer, 2009, pp. 1608–1611. [Abstract] [BibTeX]
Abstract Patient specific analysis of cerebral aneurysm hemodynamics is based on methods of computational fluid dynamics (CFD) and non-invasive medical imaging. The flow results are influenced by the reconstructed geometry, especially by the length of the reconstructed parent vessel. To investigate the influence of the length of the parent vessel, rotational angiography data (3DRA) of three cerebral aneurysms were used. The aneurysms were segmented and three models of each aneurysm with different vessel lengths were generated. For these nine models, flow simulations were performed using the CFD program FLUENT. The objective was the analysis of the wall shear stress (WSS) distributions at the aneurysm dome. The results show that the reconstructed parent vessel should be as long as possible - the minimum length should be at least 6 times the diameter of the inlet vessel.
BibTeX @inproceedings{Poethke2009, author = {J. Poethke and A. Spuler and Ch. Petz and H.-Ch. Hege and L. Goubergrits and K. Affeld and U. Kertzscher}, title = {Cerebral Aneurysm Hemodynamics and a Length of Parent Vessel}, booktitle = {World Congress on Medical Physics and Biomedical Engineering, September 7--12, Munich, Germany}, journal = {IFMBE Proceedings}, publisher = {Springer}, year = {2009}, volume = {25/IV}, pages = {1608--1611} }
2009 (10)	Timmel, T. ; Bauer, A. ; Kertzscher, U. ; Affeld, K. ; Hengstler, J.: Quantification of the Time Course of Proliferation and Scattering Activity of Cells in Time Lapse Videos. In: World Congress on Medical Physics and Biomedical Engineering, September 7–12, Munich, Germany. IFMBE Proceedings Volume 25/X Springer, 2009, pp. 161–162. [Abstract] [BibTeX]
Abstract Introduction: Cell cultures frequently are observed using time lapse microscopic recording. Without the use of fluorescence markers the automatic quantification of morphological changes often fails. We established a semi automated technique allowing the quantification of the following parameters: number of cells and nuclei, cell death and division events and the extent of cell scattering. Errors caused by changing illumination conditions and scattering of frame positions have to be corrected. Methods: Time lapse videos of rat hepatocytes cultured for 5d were used. The scattering of frame positions was corrected. The counting of objects and events of interest starts with the manual marking of all objects in the first image. In subsequent images only changes are captured. Analysis of the markers is done automatically. The scattering activity is quantified using a cross-correlation based algorithm comparing every image with its successor. Errors are filtered by an appropriate curve smoothing method. Results: Several cell culture videos were processed and analyzed. The time course of the relative population of nuclei of vital and dead cells was displayed graphically as a step function and relevant events were shown as impulses. The scattering activities based on the correlation coefficient were calculated and - due to a lack of methods for validation - compared to the subjective judgment of the scattering by experienced experimenters. Discussion and Conclusions: The semi automated method allows the quantification of cell death and cell division events in time lapse videos of cell cultures. Hence the assessment of the approximate time of events is possible. The new method to quantify the cell's scattering activity proved to be robust enough against errors and sensitive to the scattering. The results compare very well to the subjective judgment of the observed scattering. The combination of both methods allows new insights into the development of a cell culture.
BibTeX @inproceedings{Timmel2009a, author = {T. Timmel and A. Bauer and U. Kertzscher and K. Affeld and J. Hengstler}, title = {Quantification of the Time Course of Proliferation and Scattering Activity of Cells in Time Lapse Videos}, booktitle = {World Congress on Medical Physics and Biomedical Engineering, September 7--12, Munich, Germany}, journal = {IFMBE Proceedings}, publisher = {Springer}, year = {2009}, volume = {25/X}, pages = {161--162} }
2009 (09)	Timmel, T. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: Defined Mass Transport in Monolayer Cell Cultures of Hepatocytes. In: World Congress on Medical Physics and Biomedical Engineering, September 7–12, Munich, Germany. IFMBE Proceedings Volume 25/IV Springer, 2009, pp. 2032–2034. [Abstract] [BibTeX]
Abstract Introduction: Monolayer culture systems are a frequently used form of cell culture for hepatocytes. In such a culture mass transport of gases and nutrients is driven only by diffusion. However, Fick's Law reveals that only for very low oxygen consumption rates sufficient oxygen reaches the cells. At higher rates the state of the hepatocytes is not defined and hypoxia may occur. Methods: Flow chambers were developed where the diffusive mass transport is superimposed by convection. For 3 different rates of oxygen consumption the flow was simulated numerically. Results: The flow simulation shows an even flow distribution above the cells. The values of the partial pressure of oxygen (pO2) at the cells are even for high oxygen consumption at least 8fold the critical pO2. The wall shear stresses are 2-3 magnitudes lower than the physiological values. Discussion & Conclusion: Unlike the limited diffusive mass transport of conventional monolayer cultures, a sufficient oxygen distribution above the cells in the flow chamber was shown. Though the hepatocytes are exposed to a flow, the wall shear stresses are far below physiological values of the sinusoidal capillaries. Loading the cells with a specific shear is also possible if desired. Hence the flow chamber permits control of physicochemical parameters in the cell culture.
BibTeX @inproceedings{Timmel2009b, author = {T. Timmel and L. Goubergrits and U. Kertzscher and K. Affeld}, title = {Defined Mass Transport in Monolayer Cell Cultures of Hepatocytes}, booktitle = {World Congress on Medical Physics and Biomedical Engineering, September 7--12, Munich, Germany}, journal = {IFMBE Proceedings}, publisher = {Springer}, year = {2009}, volume = {25/IV}, pages = {2032--2034} }
2009 (08)	Weber, S. ; Bonfantini, M. ; Schirrmann, K. ; Kertzscher, U. ; Affeld, K.: Modeling blood flow in pulmonary capillary networks. In: World Congress on Medical Physics and Biomedical Engineering, September 7–12, Munich, Germany. IFMBE Proceedings Volume 25/IV Springer, 2009, pp. 992–994. [Abstract] [BibTeX]
Abstract Understanding the mechanisms of perfusion in pulmonary capillary networks is essential for understanding gas exchange between air and blood. A two-phase-fluid model was developed to investigate mechanisms of blood perfusion and distribution of erythrocytes in the capillary of the lung. Rheological investigation of the model fluid was performed showing non-Newtonian behavior of the model. The flow around red blood cell models was examined in a Y-bifurcation using particle image velocimetry.
BibTeX @inproceedings{Weber2009, author = {S. Weber and M. Bonfantini and K. Schirrmann and U. Kertzscher and K. Affeld}, title = {Modeling blood flow in pulmonary capillary networks}, booktitle = {World Congress on Medical Physics and Biomedical Engineering, September 7--12, Munich, Germany}, journal = {IFMBE Proceedings}, publisher = {Springer}, year = {2009}, volume = {25/IV}, pages = {992--994} }
2009 (07)	Affeld, K. ; Kertzscher, U. ; Gabel, G. ; Grosshauser, J. ; Timmel, T. ; Große-Siestrup, C.: Development of a CAPD catheter with infection proof exit site. In: 36th European Society for Artificial Organs Congress, Compiègne, France, September 2–5. , 2009 [BibTeX]
BibTeX @inproceedings{Affeld2009, author = {K. Affeld and U. Kertzscher and G. Gabel and J. Grosshauser and T. Timmel and Ch. Große-Siestrup}, title = {Development of a CAPD catheter with infection proof exit site}, booktitle = {36th European Society for Artificial Organs Congress, Compiègne, France, September 2--5}, year = {2009} }
2009 (06)	Affeld, K. ; Watanabe, N.: Microscopy of platelets under shear. In: 36th European Society for Artificial Organs Congress, Compiègne, France, September 2–5. , 2009 [BibTeX]
BibTeX @inproceedings{Affeld2009a, author = {K. Affeld and N. Watanabe}, title = {Microscopy of platelets under shear}, booktitle = {36th European Society for Artificial Organs Congress, Compiègne, France, September 2--5}, year = {2009} }
2009 (05)	Berthe, A. ; Lederer, C. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: Investigations of a counterpulsation heart assist device by PIV and wall-PIV. In: 36th European Society for Artificial Organs Congress, Compiègne, France, September 2–5. , 2009 [Abstract] [BibTeX]
Abstract Objectives: The investigation of blood pumps for regions of blood stagnation allows a first estimation of the risk of thrombus formation. The pump under consideration is a novel long-term implantable counterpulsation device (CPD). The CPD is a single port, valveless 32 ml stroke volume blood chamber. Attached to the subclavian artery, it can be implanted subcutaneously on the right anterior chest, similar to a pacemaker. Materials and Methods: The investigation of the flow inside the CPD was done by Particle Image Velocimetry (PIV) to obtain the flow field in the central plane and Wall-PIV to obtain the near wall flow. Both methods were realized on a simplified mock circulation, consisting of a Windkessel and the blood pump. Filling time was 600 ms plus a hold time of 850 ms. The emptying time was set to 250 ms. This corresponds to a 1in2 operation mode, which is more prone for thrombus formation. The pressure head was set to 90 mmHg. As a test fluid we used a mixture of water and glycerin, simulating a blood viscosity of 3.5 mm2/s. Images were recorded with a MotionPro X3 (Redlake Inc., USA) camera with 2000 frames per second (fps). The central plane measurement setup allows an insight into the general flow pattern of the pump. For illumination we used a Quantum CW-laser at 0.65 W. To investigate the flow along the curved walls of the CPD, we used the Wall-PIV technique developed in our laboratory. Two LED light sources and a molecular dye at 0.3 g/l (Patent Blue V) allow the near wall region illumination with restricted light depth penetration. Results: During ejection phase the fluid flows towards the port of the CPD uniformly, resulting in a good washout. A steadily rotating vortex, extending over the complete blood pump, with a permanently moving center, is observed during filling phase and hold time. Conclusions: The investigated 1in2 mode has a good washout of the whole pump volume. Regions of stagnation are inhibited by a persistent steady rotating vortex. Due to this pump flow we expect a low risk of thrombus formation.
BibTeX @inproceedings{Berthe2009a, author = {A. Berthe and Ch. Lederer and L. Goubergrits and U. Kertzscher and K. Affeld}, title = {Investigations of a counterpulsation heart assist device by PIV and wall-PIV}, booktitle = {36th European Society for Artificial Organs Congress, Compiègne, France, September 2--5}, year = {2009} }
2009 (04)	Goubergrits, L. ; Osman, J. ; Affeld, K. ; Kertzscher, U.: First experience with an FDA critical path initiative: CFD and hemolysis. In: 36th European Society for Artificial Organs Congress, Compiègne, France, September 2–5. , 2009 [BibTeX]
BibTeX @inproceedings{Goubergrits2009b, author = {L. Goubergrits and J. Osman and K. Affeld and U. Kertzscher}, title = {First experience with an FDA critical path initiative: CFD and hemolysis}, booktitle = {36th European Society for Artificial Organs Congress, Compiègne, France, September 2--5}, year = {2009} }
2009 (03)	Weber, S. ; Bonfantini, M. ; Kertzscher, U. ; Affeld, K.: Flow of a blood model in a Y-bifurcation. In: 36th European Society for Artificial Organs Congress, Compiègne, France, September 2–5. , 2009 [BibTeX]
BibTeX @inproceedings{Weber2009a, author = {S. Weber and M. Bonfantini and U. Kertzscher and K. Affeld}, title = {Flow of a blood model in a Y-bifurcation}, booktitle = {36th European Society for Artificial Organs Congress, Compiègne, France, September 2--5}, year = {2009} }
2009 (02)	Goubergrits, L. ; Poethke, J. ; Kertzscher, U. ; Petz, C. ; Hege, H.-C. ; Hoch, H. ; Spuler, A.: Hemodynamics of Cerebral Aneurysms: Project in Berlin. In: 4th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, The Netherlands, April 16–17. , 2009 [BibTeX]
BibTeX @inproceedings{Goubergrits2009a, author = {L. Goubergrits and J. Poethke and U. Kertzscher and Ch. Petz and H.-Ch. Hege and H. Hoch and A. Spuler}, title = {Hemodynamics of Cerebral Aneurysms: Project in Berlin}, booktitle = {4th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, The Netherlands, April 16--17}, year = {2009} }
2009 (01)	Poethke, J. ; Petz, C. ; Affeld, K. ; Kertzscher, U. ; Hege, H.-C. ; Spuler, A. ; Goubergrits, L.: Cerebral Aneurysm – Geometric Variations and the Near Wall Flow Field Features. In: 4th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, The Netherlands, April 16–17. , 2009 [BibTeX]
BibTeX @inproceedings{Poethke2009a, author = {J. Poethke and Ch. Petz and K. Affeld and U. Kertzscher and H.-Ch. Hege and A. Spuler and L. Goubergrits}, title = {Cerebral Aneurysm -- Geometric Variations and the Near Wall Flow Field Features}, booktitle = {4th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, The Netherlands, April 16--17}, year = {2009} }
2008 (15)	Poethke, J. ; Goubergrits, L. ; Kertzscher, U. ; Spuler, A. ; Petz, C. ; Hege, H.-C.: Impact of imaging modality for analysis of a cerebral aneurysm: comparison between CT, MRI and 3DRA. In: 4th European Conference of the International Federation for Medical and Biological Engineering, Antwerpen, Belgien, November 23–27. IFMBE Proceedings Volume 22 Springer, 2008 Berlin Heidelberg., pp. 1889–1893. [Abstract] [BibTeX] [DOI ]
Abstract Cerebral aneurysms are potentially life threatening. Computational fluid dynamics with non-invasive imaging methods can determine biofluidmechanical parameters of aneurysms. This study investigate the impact of the imaging techniques ? magnetic resonance imaging (MRI), computed tomography (CT) and rotational angiography (3DRA) ? to geometry reconstruction and calculated wall shear stress (WSS) distributions in a model of a basilaris artery. The comparison of the reconstructed geometries shows that the MRI and the 3DRA based reconstructions with mean 0.097 mm and 0.1 mm Hausdorff surface distance to the original geometry are better than the CT based reconstruction with mean 0.242 mm by similar resolutions of about 0.13 mm³ voxel sizes. Comparison of calculated mean WSS shows partially good correlation for the whole aneurysm bifurcation surface (4.02 Pa in the original geometry, 3.06 Pa in the CT, 3.62 Pa in the MRI and 4.17 Pa in the 3DRA based models).
BibTeX @inproceedings{Poethke2008a, author = {J. Poethke and L. Goubergrits and U. Kertzscher and A. Spuler and Ch. Petz and H.-Ch. Hege}, title = {Impact of imaging modality for analysis of a cerebral aneurysm: comparison between CT, MRI and 3DRA}, booktitle = {4th European Conference of the International Federation for Medical and Biological Engineering, Antwerpen, Belgien, November 23--27}, journal = {IFMBE Proceedings}, publisher = {Springer}, year = {2008}, volume = {22}, pages = {1889--1893}, note = {ISBN: 978-3-540-89207-6}, doi = {http://dx.doi.org/10.1007/978-3-540-89208-3_450} }
2008 (14)	Berthe, A. ; Kondermann, D. ; Goubergrits, L. ; Kertzscher, U.: Visualisierung einer wandnahen Blutpumpenströmung mittels Wand-PIV. In: Tagungsband der 16. Fachtagung Lasermethoden in der Strömungsmesstechnik, Karlsruhe, Deutschland, September 9–11. , 2008 [Abstract] [BibTeX]
Abstract Druckgetriebene Blutpumpen weisen gewölbte Oberflächen und Membranen mit periodischen Verformungen bis zu zwei Hertz auf. Die flächendeckende Vermessung der Strömung an diesen Oberflächen ist zur Untersuchung und Minimierung der Blutaktivierung und -schädigung von höchster Bedeutung. Diese Aufgabe soll Mittels Wand-PIV Technik gelöst werden. Bei der Wand-PIV Technik werden reflektierende Partikel (Tracer), die der Strömung folgen, dem Fluid beigefügt und das Modell wird frontal mit diffusem Licht beleuchtet. Durch Zumischung von Farbstoff zum Modellfluid kann die Eindringtiefe des Lichts und damit die Tiefe des wandnahen Untersuchungsgebietes begrenzt werden. Die vorgestellten Ergebnisse resultieren aus der ersten Anwendung von Wand-PIV an einer realen pneumatisch angetriebenen 10 ml Blutpumpe mit periodischer Strömung. Die Experimente wurden in einem Testkreislauf mit einem Vorlaufdruck von 15 mmHg und einem Nachlaufdruck von 75 mmHg durchgeführt. Als Tracer wurden gesiebte Conduct-o-fil AGSL 150-30 TDR (Potters Industries Inc., Carlstadt, USA) verwendet. Das Testfluid aus 37,5 Vol-% Glyzerin und 62,5 Vol-% destilliertem Wasser reproduzierte bei 24 °C die dynamische Viskosität von Blut mit 0,0035 Pa s und wies eine Dichte von 1,1038 g/cm³ auf. Zur Absorption wurden 0,3 g/l an Molekulare Farbe Patentblau V (E 131, Schumann und Sohn, Deutschland) zugefügt. Beleuchtet wurde mittels je 52 Leuchtdioden vom Typ Luxeon III (3 W, Philips Lumileds Lighting, USA) mit Wellenlängen von ? = 627 nm und ? = 617 nm. Durch einen erweiterten Optischen Fluss Algorithmus wurden alle drei Geschwindigkeitskomponenten der wandnahen Strömung ermittelt. Auf Grundlage der Vektorfelder erfolgt eine Visualisierung der Flussfelder mit Hilfe der Software AMIRA® als linear integral convolution (LIC). Die Messungen zeigen zu Beginn der Diastole und am Ende der Systole eine gute Auswaschung der Pumpe. Die Auswaschung wird durch einen Wirbel verursacht, welcher die gesamte Pumpe ausfüllt, sowie durch eine Umkehr des Flusses Richtung Zulauf während des Beginns der Systole. Die Ergebnisse haben gezeigt, dass die Wand-PIV Methode sehr gut geeignet ist für die wandnahe, flächige Untersuchung von Blutpumpen.
BibTeX @inproceedings{Berthe2008a, author = {A. Berthe and D. Kondermann and L. Goubergrits and U. Kertzscher}, title = {Visualisierung einer wandnahen Blutpumpenströmung mittels Wand-PIV}, booktitle = {Tagungsband der 16. Fachtagung Lasermethoden in der Strömungsmesstechnik, Karlsruhe, Deutschland, September 9--11}, year = {2008}, note = {ISBN: 978-3-9805613-4-1} }
2008 (13)	Schneider, T. ; Goubergrits, L. ; Kertzscher, U. ; Paschereit, C.: Entwicklung eines bildgebenden optischen Verfahrens zur Ermittlung des 3D-Schubspannungsfeldes mittels doppelbrechender Flüssigkeit. In: Tagungsband der 16. Fachtagung Lasermethoden in der Strömungsmesstechnik, Karlsruhe, Deutschland, September 9–11. , 2008 [Abstract] [BibTeX]
Abstract Dieser Beitrag stellt die Entwicklung eines neuen optischen Messverfahrens zur direkten Ermittlung von dreidimensionalen Schubspannungsfeldern dar. Das Verfahren basiert auf dem Effekt der Doppelbrechung in strömenden Fluiden in Verbindung mit zugefügten Partikeln. Mit einem linear polarisierten, monochromatischen Lichtschnitt wird das Untersuchungsvolumen gescannt. Das in der Lichtschnittebene von den Partikeln reflektierte Licht passiert einen Polarisationsfilter und wird mit einem CCD-Sensor aufgenommen. Die Lichtintensität im Bild ist dann ein Maß für den Effekt der Doppelbrechung und damit der Schubspannung auf dem Weg des Lichts durch das Fluid. Das Untersuchungsvolumen wird durch eine Serie paralleler Lichtschnitte mit zwei synchronen Kameras tomographisch erfasst. Durch die Kombination mehrerer Bilder kann das Schubspannungsfeld dreidimensional aufgelöst werden. In diesem Beitrag werden das Messprinzip und Messaufbau erläutert, eine Empfindlichkeitsanalyse der Polariskop-Anordnung durchgeführt sowie eine Untersuchung zur Partikelauswahl vorgestellt. An einem statischen Modellexperiment, in welchem drehbare PVC-Scheiben die durchleuchteten Fluidschichten nachbilden, wurde eine Machbarkeitsuntersuchung des Verfahrens durchgeführt.
BibTeX @inproceedings{Schneider2008a, author = {T. Schneider and L. Goubergrits and U. Kertzscher and C.O. Paschereit}, title = {Entwicklung eines bildgebenden optischen Verfahrens zur Ermittlung des 3D-Schubspannungsfeldes mittels doppelbrechender Flüssigkeit}, booktitle = {Tagungsband der 16. Fachtagung Lasermethoden in der Strömungsmesstechnik, Karlsruhe, Deutschland, September 9--11}, year = {2008}, note = {ISBN: 978-3-9805613-4-1} }
2008 (12)	Kertzscher, U.: Method to investigate the flow in the vicinity of the wall in bloodpumps. In: 35th European Society for Artificial Organs Congress, Geneva, Switzerland, September 3–6. , 2008 [BibTeX]
BibTeX @inproceedings{Kertzscher2008a, author = {U. Kertzscher}, title = {Method to investigate the flow in the vicinity of the wall in bloodpumps}, booktitle = {35th European Society for Artificial Organs Congress, Geneva, Switzerland, September 3--6}, year = {2008} }
2008 (12)	Weber, S. ; Berthe, A. ; Kondermann, D. ; Pöthke, J. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: A cerebral aneurysm flow visualization using a new technique. In: 35th European Society for Artificial Organs Congress, Geneva, Switzerland, September 3–6. , 2008 [Abstract] [BibTeX]
Abstract Objectives: Investigation of the near wall flow of aneurysm models is important for the understanding and estimation of the aneurysm rupture risk and as an optimization of the therapeutic options that includes coiling and clipping. Methods: The proposed Wall-PIV (particle image velocimetry) technique is a modification of the conventional PIV that allows the flow investigation in the near wall region even for curved or vaulted walls. The Wall-PIV uses diffuse monochromatic light, which is directed towards the surface of the object. The light passes through the transparent surface into the test fluid containing a molecular dye which absorbs the light. This restricts the penetration of the light to a specific depth that may be adjusted. The light reflecting particles added into the fluid allow a near wall flow visualization that is acquired by a digital camera. Particles that are further away from the surface will appear darker than particles closer to the surface. This allows a determination of the third component of the particle position by applying Beer Lambert's law. The presented results are the first application of the Wall-PIV technique on two anatomically realistic enlarged silicone models of a basilaris artery aneurysm. The experiments were conducted under steady flow conditions. The flow fields were estimated using an adapted optical flow algorithm. Results: Visualization of the flow fields were realized as vector fields and linear integral convolution images using software AMIRA®. The results of flow visualization revealed a very complex flow patterns in the near wall flow region of the aneurysms including stagnation, saddle and repelling points. Conclusion: The Wall-PIV technique was successfully applied to the complex geometry of the aneurysm models. The experiments have shown that the new method is a suitable instrument to investigate the flow in models of natural vessels and of artificial organs.
BibTeX @inproceedings{Weber2008, author = {S. Weber and A. Berthe and D. Kondermann and J. Pöthke and L. Goubergrits and U. Kertzscher and K. Affeld}, title = {A cerebral aneurysm flow visualization using a new technique}, booktitle = {35th European Society for Artificial Organs Congress, Geneva, Switzerland, September 3--6}, year = {2008} }
2008 (11)	Berthe, A. ; Kondermann, D. ; Christensen, C. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: A blood pump flow visualization using a Wall-PIV technique. In: 35th European Society for Artificial Organs Congress, Geneva, Switzerland, September 3–6. , 2008 [Abstract] [BibTeX]
Abstract Objectives: Investigation of the near wall flow of blood pumps is important for the understanding and possible reduction of adverse reactions such as thrombus formation. Methods: The proposed Wall-PIV technique is a modification of the conventional PIV that allows a flow study at near wall region for curved or vaulted walls. The Wall-PIV uses diffuse monochromatic light directed towards the surface of the investigated object. The light passes through the transparent surface into the test fluid containing a molecular dye which absorbs the light. This restricts the penetration of the light to a specific depth that may be adjusted. The light reflecting particles added into the fluid allow a near wall flow visualization that is acquired by a digital camera. Particles that are further away from the surface will appear as a darker grey than particles closer that allows a determination of the third component of the particle position by applying Beer Lambert's law. The presented results are the first application of the Wall-PIV technique on a real pneumatically driven 10 cc blood pump with cyclic flow conditions. The experiments were conducted in a mock circulation set-up with a pre-load pressure of 15 mmHg and an after-load pressure of 75 mmHg. The flow fields were estimated using an adapted optical flow algorithm. Results: Visualization of the flow fields were realized as vector fields and linear integral convolution images using software AMIRA®. The results of flow visualization during the end of diastole and the beginning of the systole show a good washout caused by a vortex filling the whole blood pump and a redirection of the flow towards the inlet port during the start of the systole. Conclusion: The Wall-PIV technique was successfully applied to the blood pump. The method has shown that it possesses high potential for the measurement of near wall flows. The application of this method in pumps allows the optimization and improvement of the blood pump's long term functionality.
BibTeX @inproceedings{Berthe2008b, author = {A. Berthe and D. Kondermann and C. Christensen and L. Goubergrits and U. Kertzscher and K. Affeld}, title = {A blood pump flow visualization using a Wall-PIV technique}, booktitle = {35th European Society for Artificial Organs Congress, Geneva, Switzerland, September 3--6}, year = {2008} }
2008 (10)	Affeld, K.: Plate-plate shearing device to shear and simultaneously observe platelets. In: 35th European Society for Artificial Organs Congress, Geneva, Switzerland, September 3–6. , 2008 [BibTeX]
BibTeX @inproceedings{Affeld2008, author = {K. Affeld}, title = {Plate-plate shearing device to shear and simultaneously observe platelets}, booktitle = {35th European Society for Artificial Organs Congress, Geneva, Switzerland, September 3--6}, year = {2008} }
2008 (09)	Schneider, T. ; Goubergrits, L. ; Kertzscher, U. ; Paschereit, C.: Development of a New 3D Shear Stress Measurement Technique Using the Birefringence. In: Proceedings of 14th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, July 7–10. , 2008 [Abstract] [BibTeX] Article (PDF-file; 1.40 MB)
Abstract A new measurement technique allowing a direct assessment of a three-dimensional shear stress field is proposed. The method is based on liquids exhibiting the optical effect of streaming birefringence that is visualized using the apparatus called polariscope. Spherical reflecting particles are added into the birefringent fluid and illuminated with a polarized, monochromatic light sheet. Three kinds of the light sources were tested: CW-Laser diode, low-pressure sodium lamps and light emitting diodes. In order to resolve a 3D shear stress field, a test volume is scanned by a set of parallel light sheets. Each sheet is acquired by two identical synchronized cameras from opposite directions that results in two different images. The light intensity in each image is a measure of the optical effect of streaming birefringence on the way of the light from reflecting particles to the sensor chip of each camera. By a combination of two images for one light sheet and one final image with a light transmission through the test volume an optical effect of the birefringence on the way between light sheet and camera may be separated and a 3D resolution of the effect in a test volume may be solved. The method is a tomography, but without a use of multi-projectional line-of-sight measurements. This paper describes the first steps of the development of this new measurement technique. The study included a choice, development, calibration and analysis of the experimental setup: light source, particles, polariscope, camera and birefringent fluid. Furthermore, the method viability was tested in experiments using a simple 2D-setup of polyvinyl chloride (PVC) plates. Rotated PVC-plates simulate different fluid layers with different shear stress values. Experimental results indicate that the rotation of the PVC-plates can be recovered from camera measured gray values with a deviation of approximately 0.8°. These preliminary tests show that the proposed measurement technique may be successfully realized.
BibTeX @inproceedings{Schneider2008b, author = {T. Schneider and L. Goubergrits and U. Kertzscher and C.O. Paschereit}, title = {Development of a New 3D Shear Stress Measurement Technique Using the Birefringence}, booktitle = {Proceedings of 14th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, July 7--10}, year = {2008}, url = {http://ltces.dem.ist.utl.pt/lxlaser/lxlaser2008/papers/02.3_1.pdf} }
2008 (08)	Berthe, A. ; Weber, S. ; Kondermann, D. ; Goubergrits, L. ; Kertzscher, U.: Application of the Wall-PIV technique on cerebral aneurysm models. In: Proceedings of the 13th Int Symp on Flow Visualization, Nice, France, July 1–4. , 2008 [Abstract] [BibTeX]
Abstract Cerebral aneurysms (pathalogic enlargements of vessels) are potentially life threatening. The main risk inherent to cerebral aneurysms is rupture. Computational fluid dynamics (CFD) with non-invasive imaging (CT, MRT) provide a means for analysis of the in-vivo main biofluidmechanical parameter ? the wall shear stress (WSS). This parameter together with other biomechanical parameters (pressure, wall surface curvature) may enable patient-specific analysis of rupture risk and may thus facilitate treatment. However, the assessment of WSS using CFD in reconstructed aneurysms is challenging and should be validated by experimental methods. Up to now there is no measurement technique to easily access WSS on vaulted walls, as they exist in aneurysms and many other fields of biofluidmechanics. This presentation describes the first measurement of WSS in a reconstructed aneurysm with Wall-PIV, a measurement technique for flow fields and WSS adjacent to vaulted walls. A basilar artery bifurcation aneurysm underwent a CT angiography for surgical planning. Raw CT data were used for 3D-reconstruction of the aneurysm with an inlet diameter of the parent vessel of 3.8 mm. Reconstruction was done using the data analysis program amira® (Mercury Computer Systems, Chelmsford, USA). Using the reconstruction data a threefold upscale aneurysm model was fabricated using rapid prototyping technique with a resolution of 0.1 mm in order to produce a rubber mold. The mold was filled with hot wax resulting in a cast, which was used to fabricate a nearly rigid transparent silicone (ELASTOSIL RT 601) model for experiments. The applied measurement technique Wall-PIV illuminates the vaulted near wall region of the transparent model with light emitting diodes (LEDs). These LEDs (Luxeon III 3 Watt, 617 nm, type Lambertain 140°, Philips Lumileds, San Jose, USA) were mounted in front of the aneurysm model. The light was limited to the near wall region by a molicular dye (patentblue V, Schumann & Sohn GmbH, Karlsruhe, Germany), added to the fluid. It absorbed the incoming and outgoing light according to Beer-Lambert's law. Thereby different distances of particles (Potters Industries Inc, Carlstadt, USA) normal to the wall result in different gray values for particle images on a CCD device (259 fps, Fastcam-Super 10K, Photron, Tokyo, Japan) mounted beside the LEDs. 3D-3C-information is obtained.
BibTeX @inproceedings{Berthe2008, author = {A. Berthe and S. Weber and D. Kondermann and L. Goubergrits and U. Kertzscher}, title = {Application of the Wall-PIV technique on cerebral aneurysm models}, booktitle = {Proceedings of the 13th Int Symp on Flow Visualization, Nice, France, July 1--4}, year = {2008} }
2008 (07)	Kondermann, D. ; Kondermann, C. ; Berthe, A. ; Kertzscher, U. ; Garbe, C.: Motion estimation based on a temporal model of fluid flows. In: Proceedings of the 13th Int Symp on Flow Visualization, Nice, France, July 1–4. , 2008 [Abstract] [BibTeX]
Abstract In optical flow estimation of experimental fluids, regularisation has become a major area of research employing prior knowledge on resulting flow fields. Up to now, the main focus has been spatial regularisation by means of analytic terms. Here, we propose a new method for estimating optical flow fields of particle image sequences using parametric models of mainly temporal instead of spatial models, which are acquired by unsupervised learning techniques. In many applications, typical and likely flow fields are known a priori. Thus, learning models from physical simulations (e.g. CFD) of situations similar to real data sets is possible. This is more accurate than heuristically creating data sets or simply assuming generic prior knowledge. As a result, our trained model is able to implicitly impose a physics-based regularisation on the flow estimation process. This also renders our method highly adaptable with respect to application-specific requirements. Finally, the new method is purely local and hence can be implemented using parallel local optimization techniques with little memory usage. To evaluate the performance of our method, several image sequences were generated based on CFD simulations of a real blood pump with highly turbulent fluid motion. We carefully assessed three properties of the algorithm in experiments: performance in the presence of 1) large displacements, 2) simple and complex occlusions and 3) different Gaussian noise scales. All results are compared to the well-known state of the art ?combined local-global? method of Bruhn et al. (2005). Results show that our method yields superior results in real and synthetic particle image sequences containing large displacements and difficult occlusions. In the case of small displacements (one pixel and less) almost perfect results can be obtained as was validated on ground truth test sequences. Both, our method and the combined local-global approach proved to be equally robust against Gaussian noise. Finally, we applied our algorithm to real-world particle image sequences showing promising results for the estimation of near-wall fluid flows.
BibTeX @inproceedings{Kondermann2008, author = {D. Kondermann and C. Kondermann and A. Berthe and U. Kertzscher and Ch. Garbe}, title = {Motion estimation based on a temporal model of fluid flows}, booktitle = {Proceedings of the 13th Int Symp on Flow Visualization, Nice, France, July 1--4}, year = {2008} }
2008 (06)	Goubergrits, L. ; Wellnhofer, E. ; Kertzscher, U.: Impact and choice of a non-Newtonian blood model for wall shear stress profiling of coronary arteries. In: Proceedings of 14th Nordic-Baltic Conference on Biomedical Engineering and Medical Physics, Riga, June 16–20. Springer, 2008, pp. 111–114. [Abstract] [BibTeX]
Abstract The modelling of the in-vivo physiological situation is complex and time-consuming. Methodological simplifications are desirable. The aim of this study was to investigate the impact of non-Newtonian blood modelling and to determine the best suitable blood model. This study simulates numerically steady blood flow in an anatomically realistic model of the left coronary artery main bifurcation. The geometry was reconstructed from a post-mortem vessel cast. Three non-Newtonian (Casson, Walburn-Schneck and Generalized Power Law) as well as the Newtonian blood models were compared. First we tested the ability of the models to fit different experimental data performed with different hematocrit and total protein minus albumin (TPMA) concentration values under different temperatures. It was found that wall shear stress (WSS) is influenced by the used model. However, only the Walburn-Schneck model revealed significantly varied WSS distribution (mean difference of about 30 % measured point by point) and magnitude (17 % higher mean WSS) if compared with Newtonian model. The adapted Generalized Power Law (GPL) model allows the best fitting to the known experimental data with a Pearson's coefficient of R = 0.9998. This is especially valid for fitting the flattening of the viscosity curve to very low shear rate values under pulsatile flow conditions. An adapted GPL model which includes the dependence of hematocrit, temperature and TPMA concentration is proposed. The impact of the non-Newtonian blood model in WSS profiling of coronary artery flow may be neglected for clinical studies with normal or obstructive (narrowed) coronary arteries. However, for dilated (enlarged) coronary arteries, the non-Newtonian blood model is significant and should be included in the numerical model of the coronary flow.
BibTeX @inproceedings{Goubergrits2008c, author = {L Goubergrits and E Wellnhofer and U Kertzscher}, title = {Impact and choice of a non-Newtonian blood model for wall shear stress profiling of coronary arteries}, booktitle = {Proceedings of 14th Nordic-Baltic Conference on Biomedical Engineering and Medical Physics, Riga, June 16--20}, publisher = {Springer}, year = {2008}, pages = {111--114} }
2008 (05)	Kertzscher, U. ; Weber, S. ; Goubergrits, L. ; Berthe, A. ; Affeld, K.: Comparison of the near wall flow in a cerebral aneurysm model visualized with the line integral convolution method for numerical simulation and with a novel wall particle image velocimetry method. In: 3rd international symposium on 'Biomechanics in Vascular Biology and Cardiovascular Disease' Rotterdam, April 24–25. , 2008 [Abstract] [BibTeX]
Abstract The development of cerebral aneurysms is life threatening. The risk of aneurysms is linked with the blood flow. Especially the knowledge of the flow close to the aneurysmal wall is important to understand the growing and eventually rupturing of an aneurysm. This work compares two methods to assess the near wall flow in an anatomically realistic model of the basilaris artery aneurysm: the numerical flow simulation using CFD program FLUENT combined with a line integral convolution method (LIC) for a visualization of the wall shear stress (WSS) vector field and the experimental wall particle image velocimetry (WallPIV). The LIC technique is a numerical method to visualize vector fields in flows. It averages an image of white noise in the size of the original dataset and in the directions of the flow field vectors which results in a visualisation of the field lines. We applied LIC to the WSS vector field in order to visualize a near wall flow. The WSS vector field was calculated using CFD program FLUENT. WallPIV extends the well known PIV principle: It allows the assessment of all three velocity components in a defined thin flat volume (layer) close to the wall. The light penetration depth was set to 150 µm. The special advantage of this method is that it can be applied not only at flat or curved walls but even at vaulted walls. Both methods were applied in a threefold enlarged silicon transparent model of a cerebral aneurysm of the basilaris artery. The model was reconstructed based on the standard computed tomography procedure. The results show the feasibility of the novel WallPIV method to assess the near wall flow in a complex geometry with a vaulted wall.
BibTeX @inproceedings{Kertzscher2008, author = {U. Kertzscher and S. Weber and L. Goubergrits and A. Berthe and K. Affeld}, title = {Comparison of the near wall flow in a cerebral aneurysm model visualized with the line integral convolution method for numerical simulation and with a novel wall particle image velocimetry method}, booktitle = {3rd international symposium on 'Biomechanics in Vascular Biology and Cardiovascular Disease' Rotterdam, April 24--25}, year = {2008} }
2008 (04)	Poethke, J. ; Kertzscher, U. ; Goubergrits, L. ; Affeld, K. ; Hege, H.-C. ; Spuler, A.: Numerical analysis of wall shear stress distributions in a realistic cerebral aneurysm with different non-newtonian blood models. In: 3rd international symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, April 24–25. , 2008 [Abstract] [BibTeX]
Abstract The rupture risk of cerebral aneurysms depends on the aneurysm wall stress. The wall thickness and the wall properties are influenced by the wall shear stress (WSS) and wall stress. Computational fluid dynamics (CFD) combined with non-invasive imaging methods for geometry assessment can determine intra-aneurysmal flow parameters. In CFD simulation the blood viscosity model got an impact on the WSS. Therefore three non-Newtonian models and the Newtonian approach are used to study their influence on the WSS distributions in anatomically realistic cerebral aneurysm of the basilaris artery. A 68-year-old female with an unruptured basilar tip aneurysm underwent a computed tomography angiography for surgical planning. The image stack consisted of slices of 2 mm thickness with 1 mm distance in a 512×512 pixel matrix or 0.4 mm × 0.4 mm × 1 mm voxel size. Raw data were used for 3D-reconstruction of the aneurysm. Three non Newtonian models ? Casson, Walburn-Schneck and generalized Power Law (GPL) ? were fitted on literature data of blood rheology under pulsatile flow conditions. The best fitting was achieved by the GPL model with a Pearson?s correlation coefficient of R=0.998. The Walburn-Schneck and Casson models achieved values of R=0.975 and R=0.899. A reference WSS distribution was determined with the Newtonian viscosity model (3.5 mPas). Three WSS ranges were defined for comparative analysis (low: 0 to 0.4 Pa; mid: 0.4 to 1.5 Pa; high: >1.5 Pa) and the corresponding area percentage of the aneurysm dome were determined. The fitted GPL model shows the best agreement to the experimental data. This difference between the models seems to have an impact to the distribution of wall shear stress in cerebral aneurysms.
BibTeX @inproceedings{Poethke2008, author = {J. Poethke and U. Kertzscher and L. Goubergrits and K. Affeld and H.-Ch. Hege and A. Spuler}, title = {Numerical analysis of wall shear stress distributions in a realistic cerebral aneurysm with different non-newtonian blood models}, booktitle = {3rd international symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, April 24--25}, year = {2008} }
2008 (03)	Watanabe, N. ; Affeld, K. ; Poethke, J. ; Goubergrits, L. ; Schaefer, M. ; Kertzscher, U.: Device to subject platelets to shear stress and simultaneously observe their aggregation and deposition. In: 3rd international symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, April 24–25. , 2008 [Abstract] [BibTeX]
Abstract Many cardiovascular implants such as valves or assist devices cause thrombo-embolic complications, which may severely limit their clinical application. The cause of this is the activation of platelets by high mechanical shear stress followed by a flow of low shear stress in the vicinity of a foreign material. The low shear stress permits the diffusion of thrombo-active substances and causes further activation of platelets and their deposition at the wall. Many methods have been developed to shear platelets and than assess their behavior. Usually, the platelets are sheared in one device and than transferred into another device or vessel to quantify their deposition. There is no method known, which avoids this transfer. Objective of this project is to model the process of platelet activation and deposition in one single device ? ?shear, see and assess? ? which subjects the platelets to shear stress, permits to observe their subsequent deposition with microscopic methods and permits to assess the deposition quantitatively. A plate-plate shearing device was designed and built with the following specifications: diameter of the plates: 35 mm, distance of the plates: 50 µm, thickness of the plates: 170 µm, material: glass. The lower plate remains stationary, while two motors activate the upper plate. One motor provides an oscillation of up to 25 Hz with maximal amplitude of 150 degrees. This translates to an oscillating shear stress of 165 Pa at the largest radius, which is 10 mm. Since both plates are plane, the shear stress falls to zero at the center. After the oscillating shear load follows a period of constant low shear stress. This is set to a shear load of 2 Pa, lasting for 2 minutes. This is generated by another motor, which rotates with a motor speed of 1.6 rpm. This shearing device is mounted on top of an inverted microscope (Axiovert XX, Carl Zeiss AG, Oberkochen, Germany) and observed and photographed through 40× objective. Platelet rich plasma was prepared from freshly drawn blood from a human male volunteer. It was drawn into two 20mL-syringes containing 2 ml Acid-citrate-dextrose solution for the anti-coagulation. From these samples, the platelet rich plasma was prepared through the centrifugation using the centrifuge separator (Verifuge 3.0R, Heraeus sepatech) at 800 g and duration of 20 minutes. Then, proteins were separated from the platelets through the column Chromatography using SEPHAROSE CL-2B 300, Sigma-Aldrich, and then the platelets-rich-Hepes-buffered solution was added. After that, platelets were labeled by the Fluorescent Dyes, (fura-2, AM). In the microscope, the labeled platelets were illuminated with ultraviolet light of 470 nm wavelength and responded with an emission of 512 nm wavelength, which was detected with a long-pass filter. Initial experiments were performed with a frequency of 21 Hz and amplitude of 250 and duration of 30 seconds. This translates to a sinusoidal shear stress of 115 Pa. After the shearing operation platelets were deposited as expected and formed thick clumps. No evaluation of yet been performed, as a proof of principle was the objective of the first trials. The experiments showed the feasibility of the new concept ? to shear platelets and to see the effect immediately after the action in the shearing device itself. However, the experiments showed also improvements have to be made in regard of the handling of the device, the whole sequence of adjusting, focusing, inserting the sample, shearing and observing has unnecessary dead times and needs an optimization. Further, the glass surface will have to be replaced by a less thrombogenic material to imitate a cardiovascular implant well, which can be achieved by the use of one of the many surfaces which are applied in artificial organs.
BibTeX @inproceedings{Watanabe2008, author = {N. Watanabe and K. Affeld and J. Poethke and L. Goubergrits and M. Schaefer and U. Kertzscher}, title = {Device to subject platelets to shear stress and simultaneously observe their aggregation and deposition}, booktitle = {3rd international symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, April 24--25}, year = {2008} }
2008 (02)	Goubergrits, L. ; Pöthke, J. ; Hege, H.-C. ; Spuler, A. ; Kertzscher, U.: 3D Bildgebung von zerebralen Aneurysmen: Vergleich zwischen CT und MRT. In: Proceedings des Workshops Bildverarbeitung für die Medizin 2008 Berlin, Germany, April 6–8. Springer Verlag, 2008, pp. 153–157. [Abstract] [BibTeX]
Abstract Patientenspezifische Strömungs- und die Geometrieanalyse von Blutgefäßen und Aneurysmen basiert auf der Rekonstruktion von 3D-Geometrien aus Daten, die mit modernen Methoden der Bildgebung (CT, MRT, Angiographie) gewonnen werden. Die unterschiedlichen Charakteristika der Bildgebungsverfahren und die damit verbundenen Unsicherheiten führen zu Variationen der rekonstruierten Geometrien, die sich auf die numerische Berechnung von wichtigen Strömungsparametern, wie z. B. die Wandschubspannung, auswirken können. Basierend auf CT- und MRT-Aufnahmen eines anatomisch realistischen Referenzmodells eines zerebralen Aneurysmas der Arteria Basilaris vergleichen wir die rekonstruierten Geometrien und die hierin simulierten Blutströmungen. Die Segmentierung und Rekonstruktion des Aneurysmas erfolgte mit Hilfe des Programms AMIRA. Die numerischen Strömungsberechnungen wurden mit dem Strömungslöser FLUENT durchgeführt.
BibTeX @inproceedings{Goubergrits2008b, author = {L Goubergrits and J Pöthke and H-Ch Hege and A Spuler and U Kertzscher}, title = {3D Bildgebung von zerebralen Aneurysmen: Vergleich zwischen CT und MRT}, booktitle = {Proceedings des Workshops Bildverarbeitung für die Medizin 2008 Berlin, Germany, April 6--8}, publisher = {Springer Verlag}, year = {2008}, pages = {153--157}, note = {ISBN: 978-3-540-78639-9} }
2008 (01)	Petz, C. ; Prohaska, S. ; Goubergrits, L. ; Kertzscher, U. ; Hege, H.-C.: Near-wall flow visualization in flattened surface neighborhoods. In: Proceedings of the 2008 Simulation and Visualization Conference Magdeburg, Germany, February 28–29. SCS Publishing House, 2008, pp. 93–105. [Abstract] [BibTeX]
Abstract We present a method that flattens a curved surface and its neighborhood to create effective, uncluttered visualizations by applying standard flow visualization techniques in the deformed space. Level sets of the distance from the curved surface are mapped to parallel planes. Data fields are mapped accordingly. Our method eases the visual inspection and analysis of a curved surface's vicinity by providing a flat space that supports the creation of standardized views. This is particularly useful for visualizing flow fields in the boundary layer.
BibTeX @inproceedings{Petz2008, author = {Ch. Petz and S. Prohaska and L. Goubergrits and U. Kertzscher and H.-Ch. Hege}, title = {Near-wall flow visualization in flattened surface neighborhoods}, booktitle = {Proceedings of the 2008 Simulation and Visualization Conference Magdeburg, Germany, February 28--29}, publisher = {SCS Publishing House}, year = {2008}, pages = {93--105} }
2007 (09)	Kertzscher, U. ; Schirrmann, K. ; Kübler, W.M. ; Affeld, K.: Ein mechanisches Modell der Lungenalveolen. In: 41. DGBMT-Jahrestagung BMT 2007, Aachen, Germany, September 26–29. Biomed Tech (Berl) Volume 52 Suppl , 2007 [Abstract] [BibTeX]
Abstract Druck und Volumen der Lunge werden durch das Zusammenwirken von Oberflächenspannung und elastischer Spannung des Gewebes bestimmt. Das ist ein komplexer Vorgang, der nicht völlig verstanden ist. So wird diskutiert, ob bei der Volumenzunahme der Lunge einzelne Alveolen plötzlich geöffnet (rekrutiert) werden oder ob alle nur elastisch gedehnt werden. Das Verständnis dieser Vorgänge ist wesentlich für die Beurteilung der Spannungen und Dehnungen in der Lunge während der künstlichen Beatmung, bei der immer wieder Lungenschäden auftreten. Als Beitrag zu dieser Diskussion wird ein mechanisches Modell vorgestellt. Bei diesem Modell werden die Alveolen durch Luftblasen in einem Rohr simuliert, das mit Flüssigkeit gefüllt ist, und die elastische Dehnung wird durch den hydrostatischen Druck abgebildet. Wesentliche Eigenschaften der Druck-Volumenkurve einer natürlichen Lunge können so im Modell nachgeahmt werden. Als Flüssigkeit wird Methylalkohol verwendet.
BibTeX @inproceedings{Kertzscher2007b, author = {Ulrich Kertzscher and Kerstin Schirrmann and Wolfgang M. Kübler and Klaus Affeld}, title = {Ein mechanisches Modell der Lungenalveolen}, booktitle = {41. DGBMT-Jahrestagung BMT 2007, Aachen, Germany, September 26--29}, journal = {Biomed Tech (Berl)}, year = {2007}, volume = {52 Suppl} }
2007 (08)	Schirrmann, K. ; Kertzscher, U. ; Goubergrits, L. ; Kübler, W.M. ; Affeld, K.: Ein Zweiphasenmodell zur Blutströmung in Kapillaren. In: 41. DGBMT-Jahrestagung BMT 2007, Aachen, Germany, September 26–29. Biomed Tech (Berl) Volume 52 Suppl , 2007 [Abstract] [BibTeX] Article (PDF-file; 0.11 MB)
Abstract Die Blutströmung in Kapillaren, insbesondere in Kapillarnetzen, ist noch nicht vollständig verstanden. Sie ist für numerische Untersuchungen zu komplex und für experimentelle Untersuchungen fehlte bisher ein geeignetes Modell. Ein solches vergrößertes physikalisches Modell für die Blutströmung in Kapillaren wurde entwickelt und soll hier vorgestellt werden. Das Modell besteht aus Wassertropfen von ca. 2,4 mm Durchmesser, die sich in Öl bewegen. Die Wassertropfen modellieren die Erythrozyten, das Öl das Plasma und die Grenzflächen-spannung zwischen den beiden Medien die Membran. Es wird gezeigt, dass bestimmte Eigenschaften des Modells zu denen von Blut in Kapillaren ähnlich sind. Dafür werden Untersuchungen zum Hämatokrit, zum Druckabfall und zum Verhalten an Verzweigungen herangezogen. Das Blutmodell ist zur Modellierung der Verteilung der Blutströmung in Kapillarnetzen geeignet.
BibTeX @inproceedings{Schirrmann2007, author = {Kerstin Schirrmann and Ulrich Kertzscher and Leonid Goubergrits and Wolfgang M. Kübler and Klaus Affeld}, title = {Ein Zweiphasenmodell zur Blutströmung in Kapillaren}, booktitle = {41. DGBMT-Jahrestagung BMT 2007, Aachen, Germany, September 26--29}, journal = {Biomed Tech (Berl)}, year = {2007}, volume = {52 Suppl} }
2007 (07)	Timmel, T. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: Definierte Überströmung von Monolayer-Zellkulturen. In: 41. DGBMT-Jahrestagung BMT 2007, Aachen, Germany, September 26–29. Biomed Tech (Berl) Volume 52 Suppl , 2007 [Abstract] [BibTeX] Article (PDF-file; 0.10 MB)
Abstract Monolayer-Zellkulturen bestehen typischerweise aus einer Zellschicht am Boden einer Zellkulturflasche oder Well-Platte unter einer Schicht eines Nährmediums von mehreren Millimetern Dicken. Sauerstoff (O2) und Kohlendioxid gelangen durch das Nährmedium zu den Zellen. Nährstoff- und Gasversorgung erfolgen also durch Diffusion. Diese Diffusion ist jedoch oft unzureichend und kann schon in kurzer Zeit zu einer Hypoxie der Zellen führen. Dieses Problem soll durch Überlagerung mit einer Konvektion gelöst werden. Hierzu wurden Strömungskammern konstruiert und gefertigt, mit denen die Zellen definiert überströmt werden. Mit einer numerischen Strömungssimulation wurde für drei O2-Verbrauchsraten die Überströmung der Zellen berechnet. Das Gitter mit 1,2 Mio Zellen wurde in Gambit erstellt. Als Gleichungslöser wurde die Software Fluent verwendet. Der berechnete O2-Partialdruck ist für alle Stoffwechselraten homogen über die Zellen verteilt und stets im physiologischen Bereich. Die durch die Strömung auf die Zellen wirkenden Wandschubspannungen sind um Größenordnungen kleiner als in der physiologischen Umgebung. Die Ergebnisse zeigen, dass der Stofftransport mittels konvektiver Diffusion zu einer ausreichenden O2-Versorgung der Zellen bei gleichzeitig sehr niedrigen Wandschubspannungen führt.
BibTeX @inproceedings{Timmel2007, author = {Tobias Timmel and Leonid Goubergrits and Ulrich Kertzscher and Klaus Affeld}, title = {Definierte Überströmung von Monolayer-Zellkulturen}, booktitle = {41. DGBMT-Jahrestagung BMT 2007, Aachen, Germany, September 26--29}, journal = {Biomed Tech (Berl)}, year = {2007}, volume = {52 Suppl} }
2007 (06)	Goubergrits, L. ; Lange, L. ; Pöthke, J. ; Affeld, K. ; Kertzscher, U.: Materialauswahl für einen neuartigen Oxygenatoransatz. In: 41. DGBMT-Jahrestagung BMT 2007, Aachen, Germany, September 26–29. Biomed Tech (Berl) Volume 52 Suppl , 2007 [Abstract] [BibTeX] Article (PDF-file; 0.11 MB)
Abstract Oxygenatoren dienen zum Stoffaustausch zwischen Blut und einem Gasgemisch. Die Stoffübertragung kann durch eine bionische Vorgehensweise, also der Orientierung an biologischen Vorbildern, optimiert werden. Als Vorbild wird die Säugetierlunge gewählt, bei der das Blut um die Alveolen herumgeführt wird. Dazu ist in dieser Arbeit eine Oberfläche mit alveolenähnlichen Ausstülpungen entwickelt worden. Diese werden aus einer Naturkautschukmembran von etwa 80 µm Stärke gebildet, die mittels Druck durch Bohrungen einer Lochplatte (Durchmesser 200 µm, Lochabstände von 500 µm) gepresst wird. Das nichtlineare Materialverhalten ermöglicht die Entstehung von mehreren kommunizierenden Bläschen bis zu einem Durchmesser von 1 mm. Damit wird die Austauschfläche vergrößert, das Primingvolumen verringert und das Blut wird stärker durchmischt. Die Entwicklung kleinerer Oxygenatoren, die auch implantiert werden können, ist mit diesem Ansatz möglich.
BibTeX @inproceedings{Goubergrits2007a, author = {L. Goubergrits and L. Lange and J. Pöthke and K. Affeld and U. Kertzscher}, title = {Materialauswahl für einen neuartigen Oxygenatoransatz}, booktitle = {41. DGBMT-Jahrestagung BMT 2007, Aachen, Germany, September 26--29}, journal = {Biomed Tech (Berl)}, year = {2007}, volume = {52 Suppl} }
2007 (05)	Berthe, A. ; Kondermann, D. ; Christensen, C. ; Goubergrits, L. ; Kertzscher, U.: Using single particles for the validation of a 3D-3C near wall measurement technique. In: Proceedings of the 7th International Symposium Particle Image Velocimetry, Roma, Italy, September 11–14. , 2007 [BibTeX]
BibTeX @inproceedings{Berthe2007, author = {A. Berthe and D. Kondermann and C. Christensen and L. Goubergrits and U. Kertzscher}, title = {Using single particles for the validation of a 3D-3C near wall measurement technique}, booktitle = {Proceedings of the 7th International Symposium Particle Image Velocimetry, Roma, Italy, September 11--14}, year = {2007} }
2007 (04)	Berthe, A. ; Kertzscher, U. ; Goubergrits, L. ; Christensen, C. ; Affeld, K.: Development of a shear stress measurement technique for ventricular assist devices. In: 34th European Society for Artificial Organs Congress, Krems, Austria, September 5-?8. , 2007 [Abstract] [BibTeX]
Abstract Aim: Thromboembolic complications often limit the clinical application of ventricular assist devices (VAD). Thrombi are generated through the interaction of blood, of the wall of the artificial organ, and finally of the flow. Thereby the measurement of the flow close to the wall, especially of the wall shear stress, is a precondition to avoid thrombus generation in artificial organs. Up to now, there is no adequate measurement technique with spatial and temporal resolution for the investigation of flow fields close to instationary vaulted walls. The successive development and validation of such a measurement technique will be described up to the first application on a VAD model. Methods: Light emitting diodes (LEDs) are mounted in front of the transparent VAD wall. The total illumination of the volume is limited to the first micrometers next to the wall due to a molecular dye in the fluid with a high absorption coefficient for the incoming wavelength. The thickness of the visible sheet can be calibrated. Tracers passing the light sheet are captured in different gray scales by a CCD device. Thereby flow field and shear stress can be concluded from a time resolving three dimensional reconstruction. Results: Investigations of different flow channels proved the applicability of the new method to complex and instationary flows. For VADs no references assuring measurement results exist; new validation methods were set up successfully. Conclusion: For the investigation of shear stresses near vaulted, instationary walls, such as in VADs, a new measurement technique is being developed. It has been shown that it is applicable to instationary and vaulted walls. Validation techniques testify the quality of measurements without direct references.
BibTeX @inproceedings{Berthe2007a, author = {A. Berthe and U. Kertzscher and L. Goubergrits and C. Christensen and K. Affeld}, title = {Development of a shear stress measurement technique for ventricular assist devices}, booktitle = {34th European Society for Artificial Organs Congress, Krems, Austria, September 5-?8}, year = {2007} }
2007 (03)	Schirrmann, K. ; Kertzscher, U. ; Goubergrits, L. ; Kübler, W. ; Affeld, K.: A liquid-liquid-system as a model for blood flow in capillaries. In: 34th European Society for Artificial Organs Congress, Krems, Austria, September 5–8. , 2007 [Abstract] [BibTeX]
Abstract Aim: Understanding blood flow in natural and artificial capillaries is essential for the design of artificial organs. However, the blood flow in capillary networks is still not completely understood. We present a blood model suitable for mode ling the flow distribution at junctions and in capillary networks. Methods: A liquid-liquid-system comprising colored water and oil is used as a blood model. The water droplets, which are formed in the oil through the action of surface tension function as erythrocytes and the oil models the plasma. The chosen enlarged scale of about 360 to 1 results in a capillary diameter of 2.5 mm. The similarities of the model and blood flowing in capillaries are analyzed by ex periments examining the haematocrit, the pressure drop in a long straight tube and the behavior at junctions. Results: The volume fraction of water is smaller than the flow fraction of water. The pressure drop in straight tubes increases when any of the following increases: flow fraction of water, flow and drop volume. In the branches following a junction, we see an S-shaped flow fraction/flow relationship with given flows. The flow at a bifurcation with a given pressure difference in the branches is not regular for some conditions. Conclusion: The performance of the blood model is similar to that of blood flow in capillaries in all points mentioned, but the deformation of the red blood cell membrane cannot be modeled correctly. The ir regularities at a junction with given pressure drops is sup posed to model a mechanism which influences the blood distribution in pulmonary capillary networks.
BibTeX @inproceedings{Schirrmann2007a, author = {K. Schirrmann and U. Kertzscher and L. Goubergrits and W.M. Kübler and K. Affeld}, title = {A liquid-liquid-system as a model for blood flow in capillaries}, booktitle = {34th European Society for Artificial Organs Congress, Krems, Austria, September 5--8}, year = {2007} }
2007 (02)	Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: Numerical modeling and visualization of blood damage in three standard mechanical valves. In: 34th European Society for Artificial Organs Congress, Krems, Austria, September 5–8. , 2007 [Abstract] [BibTeX]
Abstract Aim: The reduction of blood damage is still the main goal for the development of the new generation artificial organs, the functionality of which has already been proven. The models of blood damage fulfill the requirement of the principle of causality, which means reduction of the blood damage due to decreasing shear stress t; reproduce the known experimental data for uniform mechanical loading; and take into account the dependence of the blood damage from the load history for time-dependent loading. The last requirement results in an integration of the blood damage along the path lines, which is a Lagrangian approach. Methods: We propose to use Eulers? formulation, since this approach is more convenient for the visualization and analysis of the results. This means that we have to solve the mass transport equation for the cost, including convection, diffusion, and the non-linear time-dependent source term. Some physical variable P, such as either free released hemoglobin or activated platelets, should be used as a cost. The proposed method was realized in the CFD software FLUENT. A visualization of the blood damage was realized using the program AMIRA. The new approach was applied to three standard mechanical valves placed in the aortic root: mono-, bi-leaflet and caged ball valve. Results: Blood damage in three mechanical heart valves was calculated and visualized separately for laminar and turbulent stresses for a period of 100 ms. Results show clearly differences in regions of sources and regions of transportation of the damaged blood. Conclusion(s): The proposed method fulfills all of the requirements for blood damage modeling and allows visualization of the regions producing blood damage and of the region of transportation of the destroyed blood cells.
BibTeX @inproceedings{Goubergrits2007b, author = {L. Goubergrits and U. Kertzscher and K. Affeld}, title = {Numerical modeling and visualization of blood damage in three standard mechanical valves}, booktitle = {34th European Society for Artificial Organs Congress, Krems, Austria, September 5--8}, year = {2007} }
2007 (01)	Hänggi, D. ; Stock, M. ; Galdeano, J. ; Affeld, K. ; Steiger, H.-J. ; Liepsch, D.: Visualisation of cisternal flow patterns after subarachnoid haemorrhage in a silicon rubber model and improving mobilisation of mock blood clot by means of external motion (head-shaking method). In: 58. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie e.V. (DGNC). Leipzig, April 26–29. German Medical Science GMS Publishing House, 2007 [Abstract] [BibTeX]
Abstract Objective: Cerebral vasospasm remains the major complication after subarachnoid haemorrhage (SAH). Recent clinical publications suggested that head-shaking might attenuate cerebral vasospasm after SAH due to facilitated wash-out and therefore increased clot clearance rate. The goal of this study was to construct an in vitro subarachnoid haemorrhage model, to visualise the flow dynamics after induced SAH and to analyse the clot clearance rate in relation to externally applied motion. Methods: We constructed a silicon rubber model of the cranial subarachnoid space of a healthy volunteer. This model was based on digital data of a thin layer CISS-MRT sequence. The model was connected to flow simulator and perfused with physiological pulsatile flow rates. First, basic flow patterns of artificial CSF were visualised by adding tracer particles (silver-coated hollow glass spheres (S-HGS) mean particle size of 15 µm) and using a video camera. In a second step SAH was simulated by adding a bulk load of particles. Flow patterns were compared with the base line flow pattern and mobilisation rate of the particle mass was defined. In a third step the model was moved with a rotational pattern (head-shaking simulation) and the influence on CSF flow and clearance rate were visualised and analysed. Results: Flow patterns in the basal cisterns of the model could be qualitatively defined with the particle tracing method. Particle deposits could imitate some aspects of subarachnoid clots, i. e. flow dependent and delayed mobilisation. The application of a rotational motion pattern caused deformations of subarachnoid fluid flow and accelerated mobilisation of particle deposits in a rate and amplitude dependent fashion. Conclusions: For the first time, experimental fluid dynamics was applied to cisternal flow in the context of subarachnoid haemorrhage. The set-up allowed defining basic cisternal flow patterns and the influence of flow and pulse rates, and external motion on mobilisation of intracisternal particle deposits. In general external motion accelerated clearance rate in an intensity dependent way.
BibTeX @inproceedings{Hanggi2007, author = {Hänggi, D. and Stock, M. and Galdeano, J. and Affeld, K. and Steiger, H.-J. and Liepsch, D.}, title = {Visualisation of cisternal flow patterns after subarachnoid haemorrhage in a silicon rubber model and improving mobilisation of mock blood clot by means of external motion (head-shaking method)}, booktitle = {58. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie e.V. (DGNC). Leipzig, April 26--29}, publisher = {German Medical Science GMS Publishing House}, year = {2007}, url = {http://www.egms.de/en/meetings/dgnc2007/07dgnc009.shtml} }
2006 (15)	Jehle, M. ; Jähne, B. ; Kertzscher, U.: Direct Estimation of the Wall Shear Rate using Parametric Motion Models in 3D. In: Pattern Recognition: Proceedings of the 28th DAGM Symposium, Berlin, Germany, September 12–14. Lecture Notes in Computer Science Volume 4174 Springer, 2006, pp. 434–443. [BibTeX] [DOI ]
BibTeX @inproceedings{Jehle2006, author = {Markus Jehle and Bernd Jähne and Ulrich Kertzscher}, title = {Direct Estimation of the Wall Shear Rate using Parametric Motion Models in 3D}, booktitle = {Pattern Recognition: Proceedings of the 28th DAGM Symposium, Berlin, Germany, September 12--14}, journal = {Lecture Notes in Computer Science}, publisher = {Springer}, year = {2006}, volume = {4174}, pages = {434--443}, doi = {http://dx.doi.org/10.1007/11861898_44} }
2006 (14)	Berthe, A. ; Christensen, C. ; Debaene, P. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: Further development of an image-based optical measurement technique for complex near-wall flows. In: Proceedings of the 12th International Symposium on Flow Visualization, Göttingen, Germany, September 10–14. , 2006 [Abstract] [BibTeX]
Abstract This project focuses on improving a non-invasive, image based measurement technique for flow velocities. It will provide a high-resolution analysis of complex, shear-flows near vaulted, mobile surfaces. Improvement takes place through separating error analysis for data acquisition from data processing. Artificial datasets and experiments are applied.
BibTeX @inproceedings{Berthe2006, author = {A. Berthe and C. Christensen and P. Debaene and L. Goubergrits and U. Kertzscher and K. Affeld}, title = {Further development of an image-based optical measurement technique for complex near-wall flows}, booktitle = {Proceedings of the 12th International Symposium on Flow Visualization, Göttingen, Germany, September 10--14}, year = {2006} }
2006 (13)	Goubergrits, L. ; Kertzscher, U. ; Affeld, K. ; Nayeri, C.N. ; Paschereit, C.O.: An idea for a new measurement technique for direct assessment of the 3D shear stress field using birefringence fluid. In: Proceedings of the 12th International Symposium on Flow Visualization, Göttingen, Germany, September 10–14. , 2006 [Abstract] [BibTeX]
Abstract Measurement technique for shear stress field assessment is proposed. The method is based on the streaming birefringence in liquids, which becomes birefringent under the action of shear force in flow. The effect is visualized by light sheet generated in fluid with reflecting particles that is acquired by two opposite cameras.
BibTeX @inproceedings{Goubergrits2006d, author = {L. Goubergrits and U. Kertzscher and K. Affeld and C. N. Nayeri and C. O. Paschereit}, title = {An idea for a new measurement technique for direct assessment of the 3D shear stress field using birefringence fluid}, booktitle = {Proceedings of the 12th International Symposium on Flow Visualization, Göttingen, Germany, September 10--14}, year = {2006} }
2006 (12)	Goubergrits, L. ; Wellnhofer, E. ; Kertzscher, U. ; Affeld, K.: Wall shear stress profiling of the coronary flow: Choosing a parameter of flow characterization. In: 5th World Congress of Biomechanics, München, Germany, July 29 – August 4. , 2006 [Abstract] [BibTeX] [DOI ]
Abstract Clinical studies suggest that local wall shear stress (WSS) patterns influence the site and the progression of atherosclerotic lesions. Computational fluid dynamics methods based on in-vivo three-dimensional (3D) vessel reconstructions have been recently shown to provide prognostically relevant WSS data. One of the questions that have to be solved for such studies is ? Which method or parameters may be used for WSS characterisation? The method should allow a comparison between different vessels with different geometries. Different geometries imply that a point by point comparison between two different WSS distributions is not feasible. Mean values are not sufficient to characterize complex WSS patterns. We propose to generate distribution histograms to quantify differences between resulting WSS distributions. The whole range of calculated wall shear stress values is divided into 100 classes. For each class the area with respect to the WSS range is calculated and normalized as percent of the total wall surface area. Cross-correlations and Chi-square tests may be used to compare these distribution histograms. Furthermore, histograms may be characterized by mean and peak values, median and skew. This method of WSS characterization was applied to three different right coronary arteries: one normal coronary artery, one with ?obstructive? and one with ?dilated? coronary atherosclerosis were compared. The geometries were reconstructed from a previously validated angiographic 3D reconstruction. The numerical solution of Navier-Stokes equations governing the fluid motion under defined boundary conditions was solved in FLUENT 6 (Fluent Inc., USA). The results show that WSS histograms within whole segments or vessels might identify different patterns of remodeling associated with characteristic changes in the distribution of WSS and quantify the extent and diffuseness of coronary artery disease.
BibTeX @inproceedings{Goubergrits2006e, author = {L. Goubergrits and E. Wellnhofer and U. Kertzscher and K. Affeld}, title = {Wall shear stress profiling of the coronary flow: Choosing a parameter of flow characterization}, booktitle = {5th World Congress of Biomechanics, München, Germany, July 29 -- August 4}, year = {2006}, doi = {http://dx.doi.org/10.1016/S0021-9290(06)85547-8} }
2006 (11)	Goubergrits, L. ; Bartz, F. ; Nayeri, C. ; Paschereit, C. ; Kertzscher, U. ; Affeld, K.: Validation of the numerical coronary flow simulation through LDA-measurements. In: 5th World Congress of Biomechanics, München, Germany, July 29 – August 4. , 2006 [Abstract] [BibTeX] [DOI ]
Abstract Assessing flow parameters, especially the distribution of the wall shear stress, in arteries is extremely important for the analysis of pathological changes in the vessel wall (e.g. atherosclerosis), as well as for the investigation of the atherosclerotic lesions genesis. Numerical flow simulations using realistic clinical data (e.g. MRI, angiography, CT) could be very helpful or even the only possible research method for clinically relevant studies. A fundamental or preliminary question is to validate the numerical flow computations. In this study, two 2.5-fold enlarged models of the left coronary vessel made of transparent silicon rubber were used to validate the flow computations. The first model is a simplified model of the main bifurcation of the left coronary artery generated according to the literature data. The second model was produced on the basis of a real vessel cast. Numerically, the flow was simulated with the program FLUENT6 (Fluent Inc., USA) under the same boundary conditions as the experimental tests. Initially, the mesh independence of the solution was examined. The results show that in order to ascertain the near wall flow and the wall shear stress correctly a very high near wall mesh resolution is needed (at least 1/1000th of the vessel diameter). Experimentally, the stationary and pulsatile flows in both models were measured at six separate cross-sections with the help of a two-component-LDA-system from the firm DANTEC. A glycerine/water mixture was used for the adjustment of the silicone refraction index n = 1.4. The resulting kinematic viscosity of the mixture at a room temperature of 23°C was 3.55×10-6 m²/s. The velocity profiles were then compared to the numerical results. The results showed a very good correlation between experimental and numerical results with a mean deviation of about 5%.
BibTeX @inproceedings{Goubergrits2006f, author = {L. Goubergrits and F.O. Bartz and Ch.N. Nayeri and C.O. Paschereit and U. Kertzscher and K. Affeld}, title = {Validation of the numerical coronary flow simulation through LDA-measurements}, booktitle = {5th World Congress of Biomechanics, München, Germany, July 29 -- August 4}, year = {2006}, doi = {http://dx.doi.org/10.1016/S0021-9290(06)85546-6} }
2006 (10)	Hänggi, D. ; Stock, M. ; Galdeano, J. ; Affeld, K. ; Steiger, H.-J. ; Liepsch, D.: Visualization of basic flow pattern in a subarachnoid hemorrhage model and measurement of influence due to variant kinetic applications. In: 5th World Congress of Biomechanics, München, Germany, July 29 – August 4. Journal of Biomechanics Volume 39 , 2006(1), pp. 368. [BibTeX] [DOI ]
BibTeX @inproceedings{Hanggi2006, author = {Hänggi, D. and Stock, M. and Galdeano, J. and Affeld, K. and Steiger, H.-J. and Liepsch, D.}, title = {Visualization of basic flow pattern in a subarachnoid hemorrhage model and measurement of influence due to variant kinetic applications}, booktitle = {5th World Congress of Biomechanics, München, Germany, July 29 -- August 4}, journal = {Journal of Biomechanics}, year = {2006}, volume = {39}, number = {1}, pages = {368}, url = {http://www.jbiomech.com/article/S0021-9290(06)84477-5}, doi = {http://dx.doi.org/10.1016/S0021-9290(06)84477-5} }
2006 (09)	Kertzscher, U. ; Goubergrits, L. ; Affeld, K. ; Doll, U.: Assessment of flow velocity and hematocrit distribution in a model of a fish gill. In: 5th World Congress of Biomechanics, München, Germany, July 29 – August 4. , 2006 [Abstract] [BibTeX] [DOI ]
Abstract The main task of lungs and gills is a sufficient gas exchange. Despite the fact that the oxygen content is low in water in comparison to air, fishes can extract oxygen very effectively from the water and with very low energy consumption. The aim of this project is to investigate the cause for this capability. We performed measurement in an enlarged model of a fish gill filament lamellae with a one-phase and a two-phase fluid. The latter is intended to model the blood (plasma and erythrocytes). The fluid was realized by a mixture of 50% oil and 50% water, which formed drops in oil. This drops model the red blood cells (erythrocytes). According to blood we call the percentage of the drops from the whole fluid volume the hematocrit value, in this case 50%. The flow was investigated with Particle Image Velocimetry (PIV) and image recording tools. From the results is concluded that the effective gas exchange is due to a combined effect of pillar-like structures in the gills and erythrocytes. The pillars deform the erythrocytes and hinder their motion and consecutively the motion of the plasma. Therefore the motion of the plasma is not as uniform as in a pure plasma flow and the transversal exchange is increased. The deformation of the erythrocytes from more or less spheres to stretched entities causes an increased gas exchange area. Finally the local hematocrit is increased due to the hindrance of the erythrocytes at the pillars, which leads again to an increase of the gas exchange area. The low energy consumption is probably due to the decrease of velocity in the gills. The gills works like a diffuser.
BibTeX @inproceedings{Kertzscher2006a, author = {U. Kertzscher and L. Goubergrits and K. Affeld and U. Doll}, title = {Assessment of flow velocity and hematocrit distribution in a model of a fish gill}, booktitle = {5th World Congress of Biomechanics, München, Germany, July 29 -- August 4}, year = {2006}, doi = {http://dx.doi.org/10.1016/S0021-9290(06)85595-8} }
2006 (08)	Spuler, A. ; Goubergrits, L. ; Kertzscher, U. ; Kiwit, J. ; Affeld, K.: Neurosurgery and biomechanics of cerebral aneurysms. In: 5th World Congress of Biomechanics, München, Germany, July 29 – August 4. , 2006 [Abstract] [BibTeX] [DOI ]
Abstract The risk of rupture for cerebral aneurysms has traditionally been estimated by simple morphological criteria such as size, shape and location of the aneurysm. Blood flow inside an aneurysm, however, another important parameter cannot be appreciated by morphological analysis alone. Blood interacts with the aneurysmal wall evoking mechanical and biological reactions of its constituents. Furthermore, there are aneurysms which can not be treated easily e.g. due to complicating features of the neck region. Therefore, some aneurysms can not be excluded from the blood circulation by complete mechanical occlusion. This paper provides an overview of different methods used to simulate blood flow and to visualize biofluidmechanical parameters inside and around cerebral aneurysms. These simulations can identify instable regions of the aneuysmal wall. It also appears possible that simulated dye washout experiments can be applied to test different treatment modalities and different treatment strategies. In the future, a sophisticated management of cerebral aneurysms will depend on biomechanical fluid analysis.
BibTeX @inproceedings{Spuler2006, author = {A. Spuler and L. Goubergrits and U. Kertzscher and J. Kiwit and K. Affeld}, title = {Neurosurgery and biomechanics of cerebral aneurysms}, booktitle = {5th World Congress of Biomechanics, München, Germany, July 29 -- August 4}, year = {2006}, doi = {http://dx.doi.org/10.1016/S0021-9290(06)84452-0} }
2006 (07)	Kertzscher, U. ; Goubergrits, L. ; Affeld, K. ; Guido, I. ; Scharfschwerdt, P. ; Hengstler, J.: Development of a standardised bioreactor with 3D capillary membrane structure. In: 5th World Congress of Biomechanics, München, Germany, July 29 – August 4. , 2006 [Abstract] [BibTeX] [DOI ]
Abstract All cells in bioreactors have to live without the natural network of capillaries, arteries and veins. In single layer cell cultures the mass flow of gases and nutrients can be achieved by diffusion alone. If, however, a higher cell volume requires a three dimensional structure, transport by diffusion alone will not suffice. One needs to introduce a convective transport. In nature, this is very effectively achieved by a network of capillaries. The next best we have in comparison to natural capillaries carrying blood are artificial capillaries carrying an appropriate gas or fluid. These artificial capillaries usually have pores, which permit the passage of the molecules needed by the cells. The aim of the project is the development of a standardized bioreactor with a 3D capillary structure which is easy to fabricate. In addition the bioreactor should be scalable to permit the culture of a larger or smaller cell mass and a window for microscopy is needed. For hepatocyte research we designed and fabricated four different sizes of bioreactors: 0.07, 4, 10, and 400 ml. Purpose of the big cell chamber is an approach to a clinical useful size. The smallest bioreactor has superior transparency for microscopic use: It permits a 3D arrangement of cells; however the thickness still permits the microscopic observation. To enhance the transparency capillaries made of cellulose are used for the smallest bioreactor. In addition the mass transfer inside the bioreactors was calculated using methods of computational fluid dynamics and investigated by experimental methods. The experiments confirmed the numerical results. Future scientific aim is the possibility to manipulate different parameters in the bioreactor. With these manipulations it is possible to investigate the cell reaction to low oxygen supply, changing pH-value, not optimal temperature, oxidative stress caused by light and so on.
BibTeX @inproceedings{Kertzscher2006, author = {U. Kertzscher and L. Goubergrits and K. Affeld and I. Guido and P. Scharfschwerdt and J. Hengstler}, title = {Development of a standardised bioreactor with 3D capillary membrane structure}, booktitle = {5th World Congress of Biomechanics, München, Germany, July 29 -- August 4}, year = {2006}, doi = {http://dx.doi.org/10.1016/S0021-9290(06)83958-8} }
2006 (06)	Seshadhri, S. ; Goubergrits, L. ; Timmel, T. ; Affeld, K.: Experimental and numerical dye washout flow visualization in an artificial heart valve. In: 33rd European Society for Artificial Organs Congress, Umeå, Sweden, June 21–24. , 2006 [Abstract] [BibTeX]
Abstract Flow visualization in realistic models is very important for the study of blood flow in artificial heart valves. However, the numerical methods do not visualize the results as does the dye washout method ? a method often used in flow studies. In this study we present the dye washout visualization of CFD results and compare these results with the conventional dye washout experiments in the same heart valve model under steady flow conditions. The investigation was carried out on a trileaflet biological valve prosthesis. For both the experimental and the numerical investigation, the flow was set to steady state conditions due to reasons of comparability. Before washout the bulbus was completely filled with the dye. The washout process was digitally recorded by a CCD camera. The numerical dye washout is based on the time dependent flow simulation using the solver FLUENT. The washout was implemented with the species transport model simulating the mixing of species (dye and pure water) without reactions. The data resulting from the species fraction distribution are used as input data for the dye washout visualization implemented in the program AMIRA that was developed by Zuse Institute of Berlin. The experimentally and numerically derived data of the washout process are currently processed. The comparison of the washout is based on the time course of the normalized grey value in defined regions of interest (ROI) that is quantified by a half dye time parameter.
BibTeX @inproceedings{Seshadhri2006a, author = {S. Seshadhri and L. Goubergrits and T. Timmel and K. Affeld}, title = {Experimental and numerical dye washout flow visualization in an artificial heart valve}, booktitle = {33rd European Society for Artificial Organs Congress, Umeå, Sweden, June 21--24}, year = {2006} }
2006 (05)	Schirrmann, K. ; Damerow, T. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: An experimental model for simulating blood flow in capillary networks. In: 33rd European Society for Artificial Organs Congress, Umeå, Sweden, June 21–24. , 2006 [Abstract] [BibTeX]
Abstract Understanding natural blood flow is essential for the design of artificial organs. However, blood flow in capillary networks is still not completely understood. An adequate blood model for the kinematics of red blood cells (RBCs) does not exist. The objective is to find a fluid suitable for modelling the interaction of plasma and RBCs. Proposed is a two phase fluid of two immiscible fluids. Such a mixture causes one of the components to form droplets within the other. The interfacial tension between the two fluids acts as the membrane of the RBCs. However, the shape of the RBC cannot be modeled since tension minimizes the surface of the droplet. In contrast to that, the membrane of the RBC flexes but retains a constant surface. The fluids used were colored water and oil. An enlarged scale of about 360 to 1 was chosen, which results in a capillary diameter of 2.5 mm. The material of the capillaries is oleophilic, which defines the oil as the plasma model. The blood model was produced by injecting the fluids by means of infusion pumps into the capillary via a Y-joint. Uniform droplets form at the junction. Different Y-joints were used to generate droplets of different diameters, ranging from 1.5 to 7 mm. The equivalent of a hematocrit of 0.50 is generated by pumping equal volumes of the fluids. This model will next be used to simulate blood flow through simple elements of a capillary network, such as bifurcations with different geometries.
BibTeX @inproceedings{Schirrmann2006, author = {K. Schirrmann and T. Damerow and L. Goubergrits and U. Kertzscher and K. Affeld}, title = {An experimental model for simulating blood flow in capillary networks}, booktitle = {33rd European Society for Artificial Organs Congress, Umeå, Sweden, June 21--24}, year = {2006} }
2006 (04)	Goubergrits, L. ; Affeld, K.: Numerical modeling of blood trauma in artificial organs. In: 33rd European Society for Artificial Organs Congress, Umea, Sweden, June 21–24. , 2006 [Abstract] [BibTeX]
Abstract Despite many years of research, many artificial organs still damage the blod. They cause hemolysis and platelet lysis. This damage is generated by hemodynamic forces. In our earlier work we proposed a numerical model of the lysis of a blood cell along a path line. This numerical model was based on experimental data, which describe the relations between blood damage, shear stress and exposure time. The model calculates an accumulated lysis index for time dependent shear stress in Lagrangian coordinates and under consideration of the shear stress history. This model was applied to compute the damage caused by three mechanical valves: monoleaflet, bileaflet and caged-ball valve. Objective was to include the Reynolds stresses in the model and compare new computation of the HI (hemolysis index) with earlier results, which were valid only for laminar shear stress. The modified model was applied to the flow through the three valves. The valve's flow was simulated with a CFD program FLUENT. The calculation of lysis was implemented into FLUENT using the user defined function and done automatically. HI was estimated by averaging of HI's calculated for nearly 5000 path lines in each valve. The results show significant impact of the turbulence for blood damage estimation. HI was about 30 times higher in the new model. The proposed model fulfills the requirements for physical consistence of the blood damage prediction. However, experiments, which discriminate the effects of laminar and turbulent shear stresses, are needed to confirm this theoretical model.
BibTeX @inproceedings{Goubergrits2006c, author = {L. Goubergrits and K. Affeld}, title = {Numerical modeling of blood trauma in artificial organs}, booktitle = {33rd European Society for Artificial Organs Congress, Umea, Sweden, June 21--24}, year = {2006} }
2006 (03)	Gabel, G. ; Affeld, K. ; Kertzscher, U.: A new anti-infective catheter concept. In: 33rd European Society for Artificial Organs Congress, Umea, Sweden, June 21–24. , 2006 [Abstract] [BibTeX]
Abstract Many efforts are being made to fight the spreading of multi-resistant bacteria. Catheters with bioactive substances either lead to the development of antibiotic resistance, which makes them effective for only a short period of time, or have other contraindications. The impact of biofilms on many fields within modern therapeutic concepts presents a challenge. New strategies are needed to fight and/or prevent biofilms, especially on widelyused artificial surfaces. A small scale biofilm reactor consisting of a multi-layer design is presented here. It is intended to test the feasibility of the concept of attacking the biofilm and/or attached bacteria from below. Perfusable microporous surface structures mimic nature's anti-infective defensive mechanisms. An example from nature is the Grey Treefrog, which has a skin that excretes antimicrobial peptides (AMPs). These are toxic to bacteria. Preliminary studies were conducted using fluorescence-in-situ hybridisation (FISH) technique to examine different biofilm behaviours on glass surfaces. Clinical strains of Staphylococcus epidermidis were used for inoculation together with a tryptic soy broth + glucose culture medium. In the centre of a round float glass plate, a porous glass filter (pore diameter 1.0-1.6 um) was glued using polysiloxane. This filter structure was perfused using a linear actuator to move the plunger of the attached glass syringes. Different agents were chosen for perfusion and the following comparison.
BibTeX @inproceedings{Gabel2006, author = {G. Gabel and K. Affeld and U. Kertzscher}, title = {A new anti-infective catheter concept}, booktitle = {33rd European Society for Artificial Organs Congress, Umea, Sweden, June 21--24}, year = {2006} }
2006 (02)	Goubergrits, L. ; Kertzscher, U. ; Affeld, K. ; Petz, C. ; Stalling, D. ; Hege, H.-C.: Numerical dye washout method as a tool to characterize the heart valve flow. In: 52nd ASAIO Congress, Chicago, Illinois, USA, June 8–10. , 2006 [Abstract] [BibTeX]
Abstract CFD methods are widely used for the development and optimization of artificial heart valves. CFD allows flow investigations with significant time and cost reductions when compared to experimental methods. However, choosing the proper flow parameters to characterize the flow to predict the heart valve function in vivo, is still a big challenge in modern studies. There is a set of parameters, which are used for flow characterization: pressure drop, maximal velocity magnitude and secondary velocity, characterization of the wall shear stress, shear stress and turbulence intencity by maximal values or by histogramms and calculation of the residence time along path lines. We propose to use the numerical simulation of the experimental dye washout method for flow characterization. This method allows the assessment of regions with a long or short residence time and therefore predicts the regions of high or low thrombus risk. This successful experimental method is modeled now numerically. This allows a 3D-resolved flow characterization and a possibility to validate the results experimentally. In order to simulate the dye washout, an unsteady flow simulation is performed with the flow solver FLUENT. Furthermore, a species transport model simulating the convective diffusion mixing of species (entering/outflowing blood) without reaction is applied. The results are distributions of the fluid fraction (entering/outflowing blood) for different time steps. These data were used for the dye washout visualization, which was realized using the software AMIRA. Results of these visualizations are images on the computer display, which represent the projection of the absorbed light intensity. The analysis of the washout process was done by quantifying the time course of the gray value. This method was applied in three standard mechanical heart valves (Björk-Shiley, St-Jude Medical and Starr Edwards caged-ball valve) positioned in the aortic root geometry and two valves designed for use in VAD?s. The results show that dye washout flow characterization seems to be a very useful parameter for flow characterization.
BibTeX @inproceedings{Goubergrits2006g, author = {L. Goubergrits and U. Kertzscher and K. Affeld and Ch. Petz and D. Stalling and H.-Ch. Hege}, title = {Numerical dye washout method as a tool to characterize the heart valve flow}, booktitle = {52nd ASAIO Congress, Chicago, Illinois, USA, June 8--10}, year = {2006} }
2006 (01)	Linneweber, J. ; Dohmen, P. ; Pietzner, K. ; Affeld, K. ; Kertzscher, U. ; Konertz, W.: Development and initial in-vitro and in-vivo testing of a valved stent for percutaneous valve replacement. In: 52nd Annual Conference of ASAIO, Chicago, USA, June 8–10. ASAIO J Volume 52 , 2006(2), pp. 9A. [BibTeX]
BibTeX @inproceedings{Linneweber2006, author = {Linneweber, J. and Dohmen, P.M. and Pietzner, K. and Affeld, K. and Kertzscher, U. and Konertz, W.}, title = {Development and initial in-vitro and in-vivo testing of a valved stent for percutaneous valve replacement}, booktitle = {52nd Annual Conference of ASAIO, Chicago, USA, June 8--10}, journal = {ASAIO J}, year = {2006}, volume = {52}, number = {2}, pages = {9A}, url = {http://journals.lww.com/asaiojournal/Citation/2006/03000/Development_and_Initial_in_Vitro_and_in_Vivo.55.aspx} }
2005 (05)	Affeld, K. ; Aguilera, D. ; Debaene, P. ; Goubergrits, L. ; Kertzscher, U. ; Timmel, T.: Flow in Artificial Valves and Blood Pumps. In: Blood Flow – Modelling and Diagnostics, Advanced Course and Workshop, June 20–23, Warsaw, Poland. Institute of Fundamental Technological Research, 2005 Warsaw., pp. 135–162. [BibTeX]
BibTeX @inproceedings{Affeld2005, author = {Affeld, K. and Aguilera, D. and Debaene, P. and Goubergrits, L. and Kertzscher, U. and Timmel, T.}, title = {Flow in Artificial Valves and Blood Pumps}, booktitle = {Blood Flow -- Modelling and Diagnostics, Advanced Course and Workshop, June 20--23, Warsaw, Poland}, publisher = {Institute of Fundamental Technological Research}, year = {2005}, pages = {135--162} }
2005 (04)	Kertzscher, U. ; Debaene, P. ; Goubergrits, L. ; Affeld, K.: Experimental assessment of wall shear flow. In: Blood Flow – Modelling and Diagnostics, Advanced Course and Workshop, June 20–23, Warsaw, Poland. Institute of Fundamental Technological Research, 2005, pp. 109–134. [Abstract] [BibTeX]
Abstract The assessment of wall shear flow is of interest for different technical and scientific fields. One of the research fields is biofluidmechanics, where a close relationship is assumed between flow and biological phenomena. Special problems are encountered when assessing the wall shear flow in biofluidmechanics. The flow is often pulsatile, the walls are curved and even vaulted, sometimes the walls are flexible and the wall shear flow should also be assessed with a high spatial and temporal resolution. An overview is given about existing methods to assess the wall shear flow. Some of these methods are point methods, others obtain a field. All of these methods have special advantages but also drawbacks. We therefore developed a new measurement method to investigate the flow close to a wall. This method is applicable at curved and vaulted walls, in unsteady flows, is non-intrusive, and obtains flow fields with spatial and temporal resolution. The new method was validated in a steady and unsteady laminar flow in a rectangular duct and in a rectangular U-shaped duct with a backward facing step. The last validation step was in an U-shaped duct with a lenticular cross section and a backward facing step. The results correspond closely with either the analytical or the numerical solution.
BibTeX @inproceedings{Kertzscher2005, author = {U. Kertzscher and P. Debaene and L. Goubergrits and K. Affeld}, title = {Experimental assessment of wall shear flow}, booktitle = {Blood Flow -- Modelling and Diagnostics, Advanced Course and Workshop, June 20--23, Warsaw, Poland}, publisher = {Institute of Fundamental Technological Research}, year = {2005}, pages = {109--134} }
2005 (03)	Timmel, T. ; Goubergrits, L. ; Affeld, K.: Tri-Leaflet valve with a purge flow for cardiac assist devices. In: Proceedings of the 3rd European Medical & Biological Engineering Conference. IFMBE proceedings Volume 11 , 2005 [Abstract] [BibTeX]
Abstract Purpose of this study is the optimization of an improved valve for cardiac assist systems. Clinical applications of these systems still suffer from thromboembolic complications. The problem often originates from thrombus formation behind the valve's leaflets. A thrombus is likely to form wherever the blood flow is stagnant. Especially in the sinuses of the valves stagnation areas are found. The valve design of the study presented here avoids the formation of the stagnation zone behind the leaflets by a purge flow during systole. This purge flow is separated from the valve's main flow by a flow divider directing a part of the main flow into the sinus behind the leaflet. The optimization in the present study was performed on a tri-leaflet valve. Two approaches were shown depending on whether the valve ships with a housing or not. In the latter case the housing and the flow divider can be designed freely. With a housing included, the flow divider's design is bound to the housing's geometry. The optimization was carried out numerically and experimentally. The results show that a sinus purge flow increases fluid exchange and thus minimizes stagnation areas in the sinus.
BibTeX @inproceedings{Timmel2005, author = {Tobias Timmel and Leonid Goubergrits and Klaus Affeld}, title = {Tri-Leaflet valve with a purge flow for cardiac assist devices}, booktitle = {Proceedings of the 3rd European Medical & Biological Engineering Conference}, journal = {IFMBE proceedings}, year = {2005}, volume = {11} }
2005 (02)	Affeld, K. ; Debaene, P. ; Goubergrits, L. ; Gabel, G. ; Affeld, F.: Injection of Sand as a Countermeasure to Subsidence – Model Experiments. In: Proceedings of the 7th International Symposium on Land Subsidence, Shanghai, China. Land Subsidence Volume 2 Shanghai Scientific & Technical Publishers, 2005, pp. 851–858. [Abstract] [BibTeX]
Abstract Subsidence of land is caused by volume sinks in layers below the land surface. There are many causes for these volume sinks, but very few countermeasures are known. One way to counter the sink is with a volume source. The volume source can be a fluid. Usually the fluid used is made of water mixed with fine particles ? grout. However, only a small fraction of the injected fluid volume is effective for a lift, because the fluid goes mostly into the inter-granular space. The injection of coarser particles such as sand would be more effective. However, granular matter such as sand resists pumping through tubes. The objective of this research is the injection of granular matter. With the help of several methods, forces and movements of grains were visualized. Force-chains and arches in a two-dimensional granular matter model were visualized with polarized light and photo-elastic material. From this, the geometry of a sand injector was derived and tested in a model with real sand. The movement of the injected sand grains was visualized on a glass plate in a half-space model of the ground. With the particle image velocimetry (PIV) method the vector field of the movement and the field of the resulting shear rate were assessed. In yet another model, the injection of sand was performed against a soil pressure. The required injection pressure was assessed. Lifting of areas or buildings to counter subsidence through the method of injecting granular material such as sand into the ground appears feasible.
BibTeX @inproceedings{Affeld2005a, author = {K. Affeld and P. Debaene and L. Goubergrits and G. Gabel and F. Affeld}, title = {Injection of Sand as a Countermeasure to Subsidence -- Model Experiments}, booktitle = {Proceedings of the 7th International Symposium on Land Subsidence, Shanghai, China}, journal = {Land Subsidence}, publisher = {Shanghai Scientific & Technical Publishers}, year = {2005}, volume = {2}, pages = {851--858} }
2005 (01)	Goubergrits, L. ; Bartz, F. ; Nayeri, C. ; Paschereit, C. ; Kertzscher, U. ; Affeld, K.: Validierung der numerischen Berechnungen durch LDA-Messungen in Koronargefäßen. In: Lasermethoden in der Strömungsmesstechnik, 13. Fachtagung 2005, Cottbus, Deutschland. , 2005 [Abstract] [BibTeX]
Abstract Die Erfassung von Strömungsparametern und insbesondere der Wandschubspannungsverteilung in Arterien ist von enormer Bedeutung für die Analyse pathologischer Gefäßwandveränderungen (z.B. Atherosklerose) sowie für die Untersuchung ihrer Ursachen. Numerische Strömungsberechnungen mit realen klinischen Ausgangsdaten können für die klinisch relevanten Studien mit mehreren Gefäßen sehr hilfreich bzw. die einzig durchführbare Untersuchungsmethode sein. Es stellt sich allerdings grundsätzlich die Frage nach der Validierung der numerischen Strömungsberechnungen. In der vorliegenden Arbeit wurden zur Validierung der Strömungsberechnungen in Koronarien zwei 2,5fach vergrößerte Modelle des linken Koronargefäßes - ein vereinfachtes Modell und ein Modell auf Basis eines realen Gefäßausgusses - aus transparentem Silikon hergestellt. Die stationäre Strömung in beiden Modellen wurde mit Hilfe einer 2-Komponenten-LDA-Anlage der Firma DANTEC in jeweils 6 verschiedenen Querschnitten erfasst. Die Geschwindigkeitsprofile wurden dann mit den numerischen Ergebnissen verglichen. Die numerischen Strömungssimulationen wurden mit dem Programm FLUENT durchgeführt. Die Ergebnisse zeigten eine sehr gute Übereinstimmung zwischen experimentellen und numerischen Geschwindigkeiten mit einer mittleren Differenz unter 5%.
BibTeX @inproceedings{Goubergrits2005a, author = {L. Goubergrits and F.O. Bartz and Ch.N. Nayeri and C.O. Paschereit and U. Kertzscher and K. Affeld}, title = {Validierung der numerischen Berechnungen durch LDA-Messungen in Koronargefäßen}, booktitle = {Lasermethoden in der Strömungsmesstechnik, 13. Fachtagung 2005, Cottbus, Deutschland}, year = {2005} }
2004 (05)	Hennig, C. ; Timmel, T. ; Bruck, S. ; Affeld, K.: Fahrradergometer für den Sport und für die Rehabilitation. In: 38. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 22–24, Ilmenau. Biomed Tech (Berl) Volume 49 Suppl 2 , 2004, pp. 514–515. [Abstract] [BibTeX]
Abstract In sports and in patients that are in rehabilitation the physical ability is measured with stationary cyclce ergometers. A new ergometer that can be attached easily to a bicycle, allows the mobile measurement independent of the location. The principle is based on the simultaneous measurement of chain force and chain velocity. One component of the chain force is measured, that is generated by the change of the chain s direction by gliders. The velocity of the chain is measured by a digital light barrier. The measured values are digitized, numerically processed and recorded. Through a GSM-Modem these data are transmitted to a remote central host computer and allow the control/evaluation of the sportsmen s and patient s performance.
BibTeX @inproceedings{Hennig2004, author = {Hennig, Chr. and Timmel, T. and Bruck, S. and Affeld, K.}, title = {Fahrradergometer für den Sport und für die Rehabilitation}, booktitle = {38. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 22--24, Ilmenau}, journal = {Biomed Tech (Berl)}, year = {2004}, volume = {49 Suppl 2}, pages = {514--515} }
2004 (04)	Debaene, P. ; Kertzscher, U. ; Goubergrits, L. ; Affeld, K.: Erfassung der wandnahen Strömung in komplexen Modellen als Entwicklungswerkzeug für die Medizintechnik. In: 38. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 22–24, Ilmenau. Biomedizinische Technik Volume 49 (Ergänzungsbd.2) , 2004, pp. 462–463. [Abstract] [BibTeX]
Abstract We propose a new method with which to investigate flow fields close to curved walls with spatial and temporal resolution. This kind of visualization is important for flows in the field of biofluidmechanics, since a close relationship is known between flow and biological phenomena. The new method is based on the observation and digital recording of neutrally buoyant, light reflecting particles suspended in the fluid. It can be considered as a special development of the classical Particle Image Velocimetry (PIV). The new method is non-intrusive, and is also applicable for unsteady flows. It has been used to investigate the steady and the unsteady laminar flow in a rectangular duct and in a rectangular U-shaped duct with a backward facing step. The results correspond closely with the analytical or numerical solution.
BibTeX @inproceedings{Debaene2004, author = {P. Debaene and U. Kertzscher and L. Goubergrits and K. Affeld}, title = {Erfassung der wandnahen Strömung in komplexen Modellen als Entwicklungswerkzeug für die Medizintechnik}, booktitle = {38. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 22--24, Ilmenau}, journal = {Biomedizinische Technik}, year = {2004}, volume = {49 (Ergänzungsbd.2)}, pages = {462--463} }
2004 (03)	Aguilera, D. ; Goubergrits, L. ; Affeld, K.: Strömungsvisualisierung mittels Farberosionsmethode. In: 38. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 22–24, Ilmenau. Biomed Tech (Berl) Volume 49 Suppl 2 , 2004, pp. 200–201. [Abstract] [BibTeX]
Abstract Clinical applications of ventricular assist devices (VAD) still suffer from a severe problem - thromboembolic complications too often limit the application of these system. One parameter, which is influencing the formation of thrombi is the wall shear rate. This parameter can be qualitatively measured by the paint erosion method, where a paint is applied to the investigated surface and the erosion with the flow is observed. Purpose of this study is to find a calibration between the amount of eroded paint and the wall shear rate, with other words, to quantify the method. As a calibration flow, the stagnation point flow was chosen. With Computational Fluid Dynamics (CFD) a model with a linear shear rate distribution was developed and than produced. The numerical results of the wall shear rate distribution were verified with experiments. Now it is possible connect the magnitude of wall shear rate and the rate of disappearance of the paint.
BibTeX @inproceedings{Aguilera2004, author = {Aguilera, D. and Goubergrits, L. and Affeld, K.}, title = {Strömungsvisualisierung mittels Farberosionsmethode}, booktitle = {38. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 22--24, Ilmenau}, journal = {Biomed Tech (Berl)}, year = {2004}, volume = {49 Suppl 2}, pages = {200--201} }
2004 (02)	Timmel, T. ; Goubergrits, L. ; Affeld, K.: Künstliche Herzklappe für Herzunterstützungssysteme mit einem Spülstrom. In: 38. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 22–24, Ilmenau. Biomed Tech (Berl) Volume 49 Suppl 2 , 2004, pp. 502–504. [Abstract] [BibTeX]
Abstract Purpose of this study is the optimization of an improved valve for cardiac assist systems. Clinical applications of these systems still suffer from thromboembolic complications. The problem originates mainly from thrombus formation behind the valves leaflets. A thrombus is likely to form wherever the blood flow is stagnant. Especially in the sinuses of the valves stagnation areas are found. The valve design of the study presented here avoids the formation of the stagnation zone behind the leaflets by a purge flow during systole. This purge flow is separated from the valves main flow by a flow divider directing a part of the main flow into the sinus behind the leaflet. Due to the simple geometry first investigations were carried out with a monoleaflet heart valve prosthesis. Based on these results the optimization in the present study was performed on a trileaflet valve in two steps. First, the flow was calculated using methods of computational fluid dynamics. Second, the models were investigated with a computer controlled valve tester. Physiological parameters were measured and the washout of a dye filled in the sinus was observed. The washout process was digitized and analyzed. The numerical and the experimental results were compared. The results of the numerical and experimental investigation show that a sinus purge flow increases fluid exchange and thus minimizes stagnation areas in the sinus. The effect is espected to avoid thrombus formation.
BibTeX @inproceedings{Timmel2004, author = {Timmel, T. and Goubergrits, L. and Affeld, K.}, title = {Künstliche Herzklappe für Herzunterstützungssysteme mit einem Spülstrom}, booktitle = {38. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 22--24, Ilmenau}, journal = {Biomed Tech (Berl)}, year = {2004}, volume = {49 Suppl 2}, pages = {502--504} }
2004 (01)	Petz, C. ; Stalling, D. ; Goubergrits, L. ; Affeld, K. ; Spuler, A.: Validierung von Strömungssimulationen in kardiovaskulären Anwendungen. In: Proceedings des Workshops Bildverarbeitung für die Medizin. , 2004, pp. 356–360. [Abstract] [BibTeX]
Abstract Die Strömungseigenschaften in Blutgefäßen sind nur sehr schwer zugänglich, bzw. einige Eigenschaften sind auch gar nicht exakt messbar. Theoretische Strömungsmodelle und Berechnungen sind daher ein wertvolles Hilfsmittel für deren Erforschung. Die Strömungsberechnung ist sehr komplex und die Korrektheit der Berechnung ist von vielen Parametern abhängig. In diesem Beitrag stellen wir ein Verfahren vor, mit dem wir die berechnete Blutströmung in einem Gefäßsystem durch einen experimentellen Versuchsaufbau verifizieren. Der Vergleich von Experiment und Simulation erfolgt auf der Basis von Bildsequenzen, die mit Methoden der wissenschaftlichen Visualisierung aus der Simulation erzeugt werden.
BibTeX @inproceedings{Petz2004, author = {Ch Petz and D Stalling and L Goubergrits and K Affeld and A Spuler}, title = {Validierung von Strömungssimulationen in kardiovaskulären Anwendungen}, booktitle = {Proceedings des Workshops Bildverarbeitung für die Medizin}, year = {2004}, pages = {356--360} }
2003 (05)	Goubergrits, L. ; Spuler, A. ; Affeld, K. ; Kertzscher, U.: Beeinflussung der Strömung in zerebralen Aneurysmen durch Coiling und Clipping. In: 37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24–27, Salzburg, Österreich. Biomed Tech (Berl) Volume 48 Suppl 1 , 2003 [Abstract] [BibTeX]
Abstract Cerebral aneurysms are potentially life threatening. The main threat of the aneurysm is rupture. Growth rate and risk of rupture seem to depend on the blood pressure and the wall shear stresses exerted upon the aneurysmal wall. The therapeutic options are either surgical clipping or endovascular embolization. The basic principle of both therapeutic options is a cut off the aneurysm from the blood circulation. However, the complete cut off is not always possible. Therefore the knowledge of the real aneurysm flow may help in treatment decisions. Raw data of the computer tomography were used for 3-D reconstruction of the aneurysm using image program AMIRA. The computer model was used to fabricate an aneurysm mold and then a transparent silicone rubber model. The dye wash out method was applied to visualize and quantify the aneurysm flow before and after therapeutic consideration. The results showed comparable aneurysm flow reduction after endovascular embolization and incomplete clipping.
BibTeX @inproceedings{Goubergrits2003b, author = {Goubergrits, L. and Spuler, A. and Affeld, K. and Kertzscher, U.}, title = {Beeinflussung der Strömung in zerebralen Aneurysmen durch Coiling und Clipping}, booktitle = {37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24--27, Salzburg, Österreich}, journal = {Biomed Tech (Berl)}, year = {2003}, volume = {48 Suppl 1} }
2003 (04)	Kertzscher, U. ; Debaene, P. ; Goubergrits, L. ; Affeld, K.: Weiterentwicklung eines Verfahrens zur Untersuchung wandnaher Strömung in Blutpumpen und Gefäßmodellen. In: 37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24–27, Salzburg, Österreich. Biomedizinische Technik Volume 48, Ergänzungsband 1 , 2003 [Abstract] [BibTeX]
Abstract In medicine, flow properties in vessels are of special interest, since a close relationship between the flow close to the wall and lesions of the vessel wall is assumed. A new method to visualize the flow close to the wall is proposed. Light reflecting particles in a dyed fluid which is flowing in a channel with transparent walls are illuminated. As particles close to the transparent wall are brighter than particles further inside the flow, the particles can be discriminated in different layers parallel to the wall. For each layer the velocity field can be assessed. The results of the experiments in a rectangular duct show the viability of the method. It was possible to measure the velocity close to the wall with an accuracy of ten percent. The characteristics of the new method are: touch free, assessment of the flow velocity field and the shear force field close to the wall, applicable in unsteady flows and with movable walls.
BibTeX @inproceedings{Kertzscher2003, author = {U. Kertzscher and P. Debaene and L. Goubergrits and K. Affeld}, title = {Weiterentwicklung eines Verfahrens zur Untersuchung wandnaher Strömung in Blutpumpen und Gefäßmodellen}, booktitle = {37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24--27, Salzburg, Österreich}, journal = {Biomedizinische Technik}, year = {2003}, volume = {48, Ergänzungsband 1} }
2003 (03)	Timmel, T. ; Bagheri, M. ; Sprung, C. ; Bruck, S. ; Sever, Ü. ; Affeld, K.: Neuartiges Messgerät zur ambulanten Messung des intrakraniellen Drucks bei Patienten mit Liquordrainagesystem (Shunt). In: 37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24–27, Salzburg, Österreich. Biomed Tech (Berl) Volume 48 Suppl 1 , 2003 [Abstract] [BibTeX]
Abstract The cerebrospinal fluid (CSF) drainage has been established as the standard method for the treatment of hydrocephalus. Complications after implantation of a drainage system (shunt) indicate the measurement of the intracranial pressure (ICP) in order to verify the function of the shunt. Normally an open catheter is used for this purpose. This method is imprecise and dangerous for the patient. Because of the connection between the cerebral ventricles and the air there is a danger of infection. The new ICP measurement device avoids these disadvantages. An implanted port (Rickham-Reservoir) that is part of the shunt system is punctured by a needle. Through the needle the pressure is passed via a catheter filled with isotonic NaCl-Solution to a pressure sensor. The sensor is mounted to a headset. There is no fluid motion between the patient's drainage system and the environment. Thus no bacteria can get into the ventricles. The measurement of the pressure does not depend on the position of the puncture needle because the sensor is positioned to a zero basing point (Foramen monroi). Standard sterile single-use components provide a simple ambulant measurement method. The pressure is displayed and stored in a separate device. Currently the ICP device is tested in a clinical study.
BibTeX @inproceedings{Timmel2003, author = {Timmel, T. and Bagheri, M. and Sprung, C. and Bruck, S. and Sever, Ü. and Affeld, K.}, title = {Neuartiges Messgerät zur ambulanten Messung des intrakraniellen Drucks bei Patienten mit Liquordrainagesystem (Shunt)}, booktitle = {37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24--27, Salzburg, Österreich}, journal = {Biomed Tech (Berl)}, year = {2003}, volume = {48 Suppl 1} }
2003 (02)	Binder, R. ; Goubergrits, L. ; Affeld, K.: Entwicklung eines Schlauchmodells mit den Volumenelastizitätseigenschaften von Arterien. In: 37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24–27, Salzburg, Österreich. Biomed Tech (Berl) Volume 48 Suppl 1 , 2003 [Abstract] [BibTeX]
Abstract In order to prepare a model for evaluation of pressure, flow and pulse wave velocity in human arteries, we developed a new flat, flexible tube from Polyurethane. The goal was to achieve the elastic properties of the human aorta, especially the Volume-Pressure-nonlinearity. These properties are not found in commercial available tubing in the range we were interested in. Our tubing was made by gluing a thin PU-foil onto an U-shaped Body made from stiff PU. By avoiding the circular shape, the pressure changes nonlinear with increasing volume. The final tube has properties regarding flow and pulse wave velocities very close to human values.
BibTeX @inproceedings{Binder2003, author = {Binder, R. and Goubergrits, L. and Affeld, K.}, title = {Entwicklung eines Schlauchmodells mit den Volumenelastizitätseigenschaften von Arterien}, booktitle = {37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24--27, Salzburg, Österreich}, journal = {Biomed Tech (Berl)}, year = {2003}, volume = {48 Suppl 1} }
2003 (01)	Aguilera, D. ; Guido, I. ; Goubergrits, L. ; Lederer, C. ; Affeld, K.: Strömungsvisualisierung durch eine neu entwickelte Kugelklappe für ein Herzunterstützungssystem. In: 37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24–27, Salzburg, Österreich. Biomed Tech (Berl) Volume 48 Suppl 1 , 2003 [Abstract] [BibTeX]
Abstract Clinical applications of ventricular assist devices still suffer from a severe problem -thromboembolic complications too often limit the application of these system. The main cause of thrombi are flow separations at the valves. A new ball valve for ventricular assist devices is developed. Its advantage is the good washout of the area around the ball during systole. The ball can rotate in all the directions, so every point on the ball surface has the same probability to be stagnation point but only for a short time. The model is been initially developed to overcome this drawback by minimising pressure drops, shear rates, and areas of recirculation or stagnation. The hemodynamic charcteristics through the valve was investigated with Computational Fluid Dynamics. The numerical results were verified with experiments using digital particle image velocimetry and paint erosion method.The final design version of the valve reduces the flow separations and in consequence as well the thromboembolic complications.
BibTeX @inproceedings{Aguilera2003, author = {Aguilera, D. and Guido, I. and Goubergrits, L. and Lederer, C. and Affeld, K.}, title = {Strömungsvisualisierung durch eine neu entwickelte Kugelklappe für ein Herzunterstützungssystem}, booktitle = {37. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 24--27, Salzburg, Österreich}, journal = {Biomed Tech (Berl)}, year = {2003}, volume = {48 Suppl 1} }
2002 (07)	Aguilera, D. ; Guido, I. ; Affeld, K.: Visualization of Wall Shear Stress in Blood Pumps with the Paint Erosion Method. In: Proceedings of the 2nd European Medical & Biological Engineering Conference. IFMBE Proceedings Volume 3 , 2002(1), pp. 1044–1045. [Abstract] [BibTeX]
Abstract Purpose of this study is to gain a better understanding of the inflow and outflow into an artificial ventricle. We applied the paint erosion method to analyze the washout and thus the wall shear rate in the blood pump. Especially at the wall in areas with low and alternating wall shear stress thrombi may generate. Prior to the experiment the entire inner surface of a blood pump is coated. The paint is exposed to the flow and the erosion can be observed. A digital video camera records the process of paint erosion. The quantitative evaluation of the washout effect is based on the calculation of the residual ratio of the paint on the inner surface. The direction of wall shear flow is seen as streak lines on the paint, whereas the magnitude of wall shear stress is reflected by the rate of disappearance of the paint.
BibTeX @inproceedings{Aguilera2002a, author = {D Aguilera and I Guido and K Affeld}, title = {Visualization of Wall Shear Stress in Blood Pumps with the Paint Erosion Method}, booktitle = {Proceedings of the 2nd European Medical & Biological Engineering Conference}, journal = {IFMBE Proceedings}, year = {2002}, volume = {3}, number = {1}, pages = {1044--1045} }
2002 (06)	Goubergrits, L. ; Affeld, K. ; Lederer, C. ; Aguilera, D. ; Strowich, S.: Development of a novel ball heart valve for use in ventricular assist devices. In: Proceedings of the 2nd European Medical & Biological Engineering Conference. IFMBE Proceedings Volume 3 , 2002(1), pp. 62–63. [Abstract] [BibTeX]
Abstract The clinical use of cardiac assist systems is still limited by a severe problem thromboembolic complications due to thrombus formation in the valves. The main causes of thrombi are flow separations and stagnation areas at the valves. A novel valve is proposed for ventricular assist devices. This valve uses the ball valve principle, which was used for many years but is nearly abandoned today. The design of the novel valve avoids flow separations on the valve housing by a careful control of the cross section of the duct. This design goal was achieved by use of computational fluid dynamics (CFD). Eleven models were designed and numerically investigated. The results of the numerical investigations were validated in experiments using the particle image velocimetry (PIV).
BibTeX @inproceedings{Goubergrits2002c, author = {L Goubergrits and K Affeld and Ch Lederer and D Aguilera and S Strowich}, title = {Development of a novel ball heart valve for use in ventricular assist devices}, booktitle = {Proceedings of the 2nd European Medical & Biological Engineering Conference}, journal = {IFMBE Proceedings}, year = {2002}, volume = {3}, number = {1}, pages = {62--63} }
2002 (05)	Timmel, T. ; Goubergrits, L. ; Affeld, K.: Optimization and investigation of a cardiac assist device valve with a purge flow. In: Proceedings of the 2nd European Medical & Biological Engineering Conference. IFMBE Proceedings Volume 3 , 2002(2), pp. 1042–1043. [Abstract] [BibTeX]
Abstract Objective of this study is the systematic optimisation of an artificial heart valve for ventricular assist systems (VAD). Clinical applications of these systems still suffer from thromboembolic complications. The problem often originates from thrombus formation behind the valve's leaflets. A thrombus is likely to form wherever the blood flow is stagnant. Especially in the sinuses of the valves stagnation areas are found. The valve design of the presented study reduces the formation of the stagnation zone behind the leaflets by a purge flow during systole. This purge flow is diverted from the valve's main flow by a flow divider directing a part of the main flow into the sinuses behind the leaflets. The purge flow effect was investigated using Particle Image Velocimetry (PIV). It was shown that a flow divider can minimise stagnation areas. Its effectiveness depends on the optimal combination of the geometric parameters.
BibTeX @inproceedings{Timmel2002a, author = {Tobias Timmel and Leonid Goubergrits and Klaus Affeld}, title = {Optimization and investigation of a cardiac assist device valve with a purge flow}, booktitle = {Proceedings of the 2nd European Medical & Biological Engineering Conference}, journal = {IFMBE Proceedings}, year = {2002}, volume = {3}, number = {2}, pages = {1042--1043} }
2002 (04)	Aguilera, D. ; Affeld, K. ; Lederer, C. ; Goubergrits, L.: Strömung durch eine neu entwickelte Kugelklappe für ein Herzunterstützungssystem. In: 36. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 25–27, Karlsruhe, Deutschland. Biomed Tech (Berl) Volume 47 , 2002(Suppl 1 Pt 1), pp. 154–157. [Abstract] [BibTeX]
Abstract Objective of the present study is the hemodynamic investigation of the fluidmechanics a ball valve developed for ventricular assist devices with improved parameters. The flow was investigated using Digital Particle Image Velocimetry with an enlarged model of the valve (2.8:1). The flow was recorded using a high speed video camera with 250 fps and analyzed by a cross-correlation method implemented in the software DaVis by LaVision. The results confirmed the improvement of the ball valve performed by a numerical study. The flow separations on the ball valve housing observed in the first design version was eliminated in the final design of the novel valve. Hence a valve of this design applied in ventricular assist devices can be expected to have a lower rate of thromboembolic complications.
BibTeX @inproceedings{Aguilera2002, author = {Aguilera, D. and Affeld, K. and Lederer, C. and Goubergrits, L.}, title = {Strömung durch eine neu entwickelte Kugelklappe für ein Herzunterstützungssystem}, booktitle = {36. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, September 25--27, Karlsruhe, Deutschland}, journal = {Biomed Tech (Berl)}, year = {2002}, volume = {47}, number = {Suppl 1 Pt 1}, pages = {154--157} }
2002 (03)	Kertzscher, U. ; Goubergrits, L. ; Spuler, A. ; Affeld, K.: Strömung in zerebralen Aneurysmen. In: 36. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Karlsruhe, September 25–27. Biomed Tech (Berl) Volume 47 , 2002(Suppl 1 Pt 1), pp. 289–291. [Abstract] [BibTeX] [PMID ]
Abstract Saccular aneurysm of the cerebral arteries occur in 1 to 5% of the population; the major risk of this disease is aneurysm rupture causing subarachnoid hemorrhage associated with a mortality rate of 50 to 60 Two methods exist to treat cerebral aneurysms: neurosurgical clipping at the base of the aneurysm and endovascular introduction of a platin coils. Both methods have advantages and disadvantages. With the knowledge of the flow in an aneurysm it is easier to choose the appropriate method. In this study we simulated the flow in four different aneurysms. The shape of the aneurysms are gained from computertomographic data. The simulated flow in four aneurysms shows the great variability of possible flow patterns.
BibTeX @inproceedings{Kertzscher2002, author = {U. Kertzscher and L. Goubergrits and A. Spuler and K. Affeld}, title = {Strömung in zerebralen Aneurysmen}, booktitle = {36. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Karlsruhe, September 25--27}, journal = {Biomed Tech (Berl)}, year = {2002}, volume = {47}, number = {Suppl 1 Pt 1}, pages = {289--291} }
2002 (02)	Debaene, P. ; Aguilera, D. ; Kertzscher, U. ; Affeld, K.: Bestimmung der Wandschubspannung in künstlichen Blutpumpen von Herzunterstützungssystemen. In: 36. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Karlsruhe, September 25–27. Biomed Tech (Berl) Volume 47 , 2002(Suppl 1 Pt 1), pp. 140–141. [Abstract] [BibTeX] [DOI ]
Abstract The walls in blood pumps are made of artificial material and thus are thrombogenic to a lesser or larger degree. Also the flow plays a role: a blood flow with no flow separations and stagnation zones is required to avoid the generation of thrombi. A precondition for solving this problem is the assessment of the wall shear rate. However this parameter is difficult to assess because of the deformability of the walls and the pulsation of the flow. Two methods are proposed to estimate the wall shear stress in bloodpumps. The paint erosion method allows a characterisation of the flow near the wall. The second method is a special development of standard Particle Image Velocimetry (PIV). A vector field of the flow close to the wall results. Both methods should permit the assessment of the wall shear stress in bloodpumps.
BibTeX @inproceedings{Debaene2002, author = {P. Debaene and D. Aguilera and U. Kertzscher and K. Affeld}, title = {Bestimmung der Wandschubspannung in künstlichen Blutpumpen von Herzunterstützungssystemen}, booktitle = {36. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Karlsruhe, September 25--27}, journal = {Biomed Tech (Berl)}, year = {2002}, volume = {47}, number = {Suppl 1 Pt 1}, pages = {140--141}, doi = {http://dx.doi.org/10.1515/bmte.2002.47.s1a.140} }
2002 (01)	Timmel, T. ; Bruck, S. ; Affeld, K.: Fahrradergometer für die Rehabilitation. In: 36. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Karlsruhe, September 25–27. Biomed Tech (Berl) Volume 47 , 2002(Suppl 1 Pt 2), pp. 712–713. [Abstract] [BibTeX] [PMID ]
Abstract In patients that are in rehabilitation the physical ability is measured with stationary cycle ergometers. A new ergometer, that can be mounted easily to a bicycle, allows the mobile measurement independent of the location. The principle is based on the simultaneous measurement of chain force and chain velocity. One component of the chain force is measured, that is generated by the change of the chain's direction by pulleys. The velocity of the chain is measured by the rotational speed of one of the pulleys. The new ergometer is easy to attach and remove. The measured values are digitized, numerically processed and recorded. Through a GSM-Modem these data are transmitted to a remote central host computer and allow the control/evaluation of the patient's performance.
BibTeX @inproceedings{Timmel2002, author = {T. Timmel and S. Bruck and K. Affeld}, title = {Fahrradergometer für die Rehabilitation}, booktitle = {36. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Karlsruhe, September 25--27}, journal = {Biomed Tech (Berl)}, year = {2002}, volume = {47}, number = {Suppl 1 Pt 2}, pages = {712--713} }
2001 (13)	Sever, Ü. ; Bruck, S. ; Affeld, K.: Entwicklung einer Software für den Empfang und die Auswertung von Gerätemessdaten via Modem. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomedizinische Technik Volume 46 , 2001(Ergänzungsband 1), pp. 406–407. [Abstract] [BibTeX]
Abstract Das Hauptproblem bei der Behandlung von schwer herzkranke Patienten besteht darin, daß nicht immer genügend Spenderorgane vorhanden ist. Zur Überbrückung der Wartezeiten bis zur Implantation werden immer häufiger Linksherzunterstützungssysteme ( Left Ventricular Assist Device = LVAD ) eingesetzt. Dabei spielt fehlerfreie Funktion solcher Systeme eine lebenswichtige Rolle. Deswegen müssen einige technische Parameter wie beispielsweise Druck, Frequenz, Stromstärke und Leistung ständig überwacht werden. Es soll eine Methode entwickelt werden, die einerseits ohne aktive Teilnahme der Patienten funktioniert andererseits die für die Patienten lästige ständige Kontrolle im Klinikum erspart. Dafür wird ein Meßsystem entwickelt, das per GSM-Netz die Daten überträgt, per Festnetz-Modem empfängt und mit Hilfe einer Software übermittelte Daten speichert, überwacht und auswertet. Es wird mit der graphische Programmiersprache LabVIEW eine Software als Teil dieses Meßsystems für den Empfang von Meßdaten per Festnetz- Modem sowie deren Darstellung ( Tabelle, Grafik, Zeitverlauf ) und Auswertung entwickelt. Die Software stellt in erste Linie die Kommunikation zwischen dem Modem und der serielle Schnittstelle von PC sicher. Anschließend werden per Modem übertragenen Meßdaten Empfangen und gespeichert. Zur Auswertung und Überwachung der Parameter werden diese Daten gelesen und in geeigneter Form dargestellt. Desweiterem werden von Herzfrequenzmeßgerät gewonnene Langzeitmeßwerte in Form von sog. Lorenz- Plot Wolke dargestellt ( 3D-Darstellung ), um zuverlässigere Aussagen zu bekommen. Außerdem wird es mit Hilfe der Software eine Leistungskurve von pneumatischen Antrieb erstellt zum Überwachen des Gerätes erstellt. Zum Schluß werden alle erstellten und empfangenen Werte und Grafiken überprüft, ob sie vorgegebenen Grenzwerte überschreiten. Wenn dies der Fall ist wird ein Alarmsignal ausgegeben. Bewegen sich die Meßwerte innerhalb der vorgegebenen Grenzwerte, so werden sie in bestimmten Intervallen gespeichert. Mit Hilfe dieser Methode wird die Ortsunabhängigkeit der Patienten ermöglicht. Außerdem durch regelmäßigen Überwachung und Auswertung einiger Parameter kann vor Ort ( in Klinikum ) über den Gesundheitszustand der Patienten ermittelt werden. Deswegen ist die Methode eine Ergänzung der Herzunterstützungssysteme.
BibTeX @inproceedings{Sever2001, author = {Ü. Sever and S. Bruck and K. Affeld}, title = {Entwicklung einer Software für den Empfang und die Auswertung von Gerätemessdaten via Modem}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomedizinische Technik}, year = {2001}, volume = {46}, number = {Ergänzungsband 1}, pages = {406--407} }
2001 (12)	Bayran, M. ; Bruck, S. ; Affeld, K.: Entwicklung eines Systems zur Übermittlung von Patientenmeßdaten durch ein GSM-Modem. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomedizinische Technik Volume 46 , 2001(Ergänzungsband 1), pp. 404–405. [Abstract] [BibTeX]
Abstract Zur Therapie von schwer herzinsuffizienten Patienten werden aufgrund des ständigen Spenderorganmangels immer häufiger Linksherzunterstützungsysteme (Left Ventricular Assist Device = LVAD) eingesetzt. Um eine fehlerfreie Funktion solcher LVAD zu gewährleisten, sollten einzelne technische Parameter überwacht werden. Damit dem Patienten ständige Kontrollen im Klinikum erspart bleiben, ist es notwendig die LVAD ortsunabhängig überwachen zu können. Dafür eignet sich die Datenfernübertragung via GSM-Netz. Das Kernstück des Systems bildet ein Mikroprozessor. Er hat die Aufgabe, die technischen Größen zu erfassen und das GSM-Modem zu steuern. Es sollen Daten wie Druck, Stromstärke und Pumpfrequenz überwacht und gleichzeitig aufgezeichnet werden. Dabei erfolgt die Überwachung kontinuierlich und die Aufzeichnung in einem vorgegebenen Zeitintervall. Dabei nehmen Sensoren die Meßwerte auf, die mit AD-Wandlern in digitale Signale umgewandelt werden. Liegen die erfaßten Werte außerhalb vorgegebener Grenzwerte, so wird ein Alarm ausgelöst. Hierbei wird sofort mit dem GSM-Modem ein entsprechender Rechner in der Klinik angewählt. Dort wird dem Personal eine diesbezügliche Fehlermeldung angezeigt. Bewegen sich die Meßwerte innerhalb der vorgegebenen Grenzen, so werden sie in bestimmten Zeitabständen gespeichert. Ein bis vier mal täglich werden diese Daten zur Dokumentation an die Klinik übermittelt. Eine spezielle Software stellt die Meßdaten in geeigneter Form dar. Somit kann man sich einen Überblick über den technischen Zustand des LVAD verschaffen. Sind hier Abweichungen von Normalfunktionen erkennbar, so kann der Patient zu einer genaueren Überprüfung bestellt werden. Die Technik wurde bei Langzeitmessungen an einem in vitro-Modell eines LVAD getestet. Über diesen Zeitraum konnten die genannten Parameter lückenlos dokumentiert werden. Bei weiteren Tests wurden durch aktive Manipulation der Meßsignale Alarmrufe provoziert. Die jeweilige Fehlfunktion wurde am daraufhin angewählten Rechner korrekt angezeigt. Das System stellt eine sinnvolle Ergänzung der technischen Beobachtung eines LVAD dar. Durch die kontinuierliche Kontrolle bestimmter Parameter kann die Sicherheit erhöht werden. Dabei arbeitet das System völlig autonom, so daß eine aktive Mitarbeit des Patienten nicht erforderlich ist.
BibTeX @inproceedings{Bayran2001, author = {M. Bayran and S. Bruck and K. Affeld}, title = {Entwicklung eines Systems zur Übermittlung von Patientenmeßdaten durch ein GSM-Modem}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomedizinische Technik}, year = {2001}, volume = {46}, number = {Ergänzungsband 1}, pages = {404--405} }
2001 (11)	Goubergrits, L. ; Affeld, K. ; Lederer, C.: Numerische Berechnung der Hämolyse bei einer Björk-Shiley Klappe und einer neuartigen S-Klappe für den Herzunterstützungssysteme. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomedizinische Technik Volume 46 , 2001(Ergänzungsband 1), pp. 156-157. [Abstract] [BibTeX]
Abstract Herzunterstützungssysteme haben heute einen festen Platz in der klinischen Praxis gefunden. Jedoch treten häufig Komplikationen auf, zu denen verstärkte schubspannungsbedingte Hämolyse und Thrombenbildung zählen. In Strömungsuntersuchungen wurden bis zu 10-fach größere Schubspannungen in künstlichen Klappen gegenüber natürlichen nachgewiesen. Tromben bilden sich bevorzugt in Gebieten mit Stagnation oder Rückströmungen, die sich z. B. im Bereich der Schließkörper der Björk-Shiley Klappe befinden. Im Rahmen einer vorangegangenen Studie wurde eine neue Herzklappe entworfen, die diese Thrombengefahr verringert. Im Rahmen dieser Arbeit soll die strömungsbedingte Hämolyse dieser Klappe untersucht werden. Bei der neuen Klappe handelt es sich um die S-Klappe, die das bewährte Funktionsprinzip der Björk-Shiley Klappe benutzt und verbessert. Da die Benutzung der Klappe in einem Herzunterstützungssystem den Einbau der Klappe in einem Kanal erfordert, wurde die Strömung durch die Gestaltung der Kanalgeometrie optimiert. Die Kanaloptimierung resultierte in einen S-förmig gekrümmten Kanal, in dem der Schließkörper während der Systole sich nahezu parallel zur Anströmung befindet. Frühere Strömungsuntersuchungen haben gezeigt, daß die Strömung in dieser neuartige S-Klappe nur einen sehr kleinen Bereich mit Rückströmungen aufweist, was eine Reduzierung der Thrombengefahr erwarten läßt. Normalerweise wird die durch künstliche Organe induzierte Blutschädigung in in-vitro Versuchen mit menschlichem oder tierischem Blut ermittelt. Allerdings führen große biologische Variabilität des Blutes und verschiedene Anfangsbedingungen der Versuche zu nicht reproduzierbaren Ergebnissen. In dieser Arbeit wurde die klappeninduzierte Hämolyse anhand einer numerischen Methode abgeschätzt. Die Methode basiert auf die Berechnung des Hämolyseindexes (HI) entlang der Partikelbahnen im Strömungsfeld der Klappen. Die Schubspannungsbedingte Hämolyse basiert auf bekannten Experimenten, die eine Korrelation zwischen Hämolyseindex, Schubspannung und Verweilzeit beschreiben. Das Modell berechnet den akkumulierten HI für zeitabhängige Schubspannungen in Lagrangschen Koordinaten. Das Modell berücksichtigt den Alterungsprozess des Blutes. Die Berechnung der Hämolyse erfordert jedoch eine vorherige Berechnung des Strömungsfeldes. Die Strömung durch diese Klappen wurde mit der Methode der CFD (Computational Fluid Dynamics) berechnet. Die Strömungsberechnungen wurden mit dem Programmpaket FLUENT5 der Firma Fluent Inc. durchgeführt. Dieses ist ein "Control Volume Finite Element Method"-Programm, die ein unstrukturiertes tetraedisches Gitter generiert. Die Basis für die Strömungssimulationen bilden die dreidimensionalen Navier-Stokes-Gleichungen für stationäre Strömungen mit inkompressiblen Fluiden und verschiedenen Turbulenzmodellen. Die Geometrien der Klappen, die mit dem 3D-Computer-Aided-Design Programm SolidWorks generiert wurden, wurden in den Preprozessor Gambit der Firma Fluent Inc. importiert. Mit diesem Preprozessor wurde das innere Gitter aus 300.000 bis 400.000 Tetraedern generiert. Als Eingangsbedingung wurde ein zeitkonstantes rechteckiges Geschwindigkeitsprofil mit V = 1 m/s definiert. Mit der kinematischen Viskosität des Blutes und dem Klappendurchmesser D = 0,022 m ergibt das eine Reynoldszahl von Re = 6300. Es wurde eine Turbulenz von 10% angenommen und das Standard k-e Turbulenzmodell angewendet. Das Blut wurde als newtonsches Fluid angenommen. Das Modell der strömungsbedingte Hämolyse wurde als "user defined function" in FLUENT implementiert und berechnet automatisch das HI entlang einer Partikelbahn. Für jeder Klappe wurden die HI von ungefähr 350 Partikelbahnen berechnet. Die resultierende Hämolyseindex für einen Durchgang des Blutes durch die Klappe wurde als über alle Partikelbahnen gemittelter HI berechnet. Die Ergebnisse haben gezeigt, daß die neuartige Klappe einen zweimal kleineren Hämolyseindex (HI=0,00048 %) im Vergleich zur Björk-Shiley Klappe (HI=0,001 %) aufweist.
BibTeX @inproceedings{Goubergrits2001c, author = {L. Goubergrits and K. Affeld and Ch. Lederer}, title = {Numerische Berechnung der Hämolyse bei einer Björk-Shiley Klappe und einer neuartigen S-Klappe für den Herzunterstützungssysteme}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomedizinische Technik}, year = {2001}, volume = {46}, number = {Ergänzungsband 1}, pages = {156-157} }
2001 (10)	Aguilera, D.: Sichtbarmachung der Wandschubspannung mit der Farberosionsmethode. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomedizinische Technik Volume 46 , 2001(Ergänzungsband 1), pp. 140–141. [Abstract] [BibTeX]
Abstract Herzunterstützungssysteme sind mechanische Pumpen, die Blut parallel zum Herzen pumpen und dieses dadurch entlasten. Es gibt zwei verschiedene Pumpentypen: radiale oder axiale Pumpen, die das Blut kontinuierlich fördern und Pumpen, die pulsatile fördern. Letztere sind dem natürlichen Herzen nachgebildet. Alle Pumpen haben jedoch eine mehr oder weniger großeTendenz zur Thrombenbildung, weil alle gegenwärtigen verfügbaren Materialien, aus denen Blutpumpe hergestellt werden, thrombogen sind. Wenn das Blut in Kontakt zu diesen Materialien kommt, werden gerinnungsaktive Subtanzen freigesetzt. Ist jedoch die Strömung in der Wandnähe schnell genug, so werden diese Stoffe rasch verdünnt, so dass es nicht zur Gerrinung kommt. Aus diesem Grund ist nicht nur das Material wichtig, sondern auch die Strömung. Eine Strömung geringer Geschwindigkeit, inbesondere mit Rückströmung und Totwassergebieten, kann die Thrombenbildung fördern. Die Geschwindigkeit der Strömung entscheidet über die Güte der Auswaschung der Blutpumpe. In dieser Arbeit soll diese Auswaschung untersucht werden, um die Thrombogengefahr in einer Blutpumpe zu verringern. Wir haben hierzu die Farberosionsmethode angewendet. Mit dieser Methode können wir die Wandschubspannung abschätzen. Dazu wird die ganze Innenfläche der Blutkammern mit Farbe bestrichen. Nach dem Einschalten der Pumpe wird das Abwaschen der Farbe beobachtet. Die Beziehung zwischen der Wandschubsspannung und der Farberosion wurde bereits in anderen Untersuchungen demonstriert. Es wurde Ruß in Pulverform und flüssiger Form als Farbstoff verwendet. Als Bindemittel wurde Polyäthylenglykol (PEG) vom PEG-Typ 8.000 bis PEG-Typ 30.000 verwendet. PEG mit niedrigem molekularen Gewicht von 8000 bis 20000 hatte eine schlechte Adhäsion auf der Wandung der Blutpumpe, die aus PVC gefertigt war. PEG mit hohem molekularem Gewicht von 30000 hatte hingegen eine gute Adhäsion. Messungen bei der Verwendung von Ruß in Pulverform zeigten, dass dieser einen Fleck auf der Oberfläche der Blutkammern hinterlässt, der nicht entfernt werden konnte. Bei Ruß in hydrophiler Form war das nicht der Fall. Ruß in Pulverform wurde daher nicht weiter verwendet. Die optimale Mischung zwischen Bindemischung und Farbstoff war PEG mit höherem molekularen Gewicht von 30000 und hydrophilem Ruß. Mit dieser Mischung wurde die ganze Innenfläche bedeckt und sie zeigte eine gute Adhäsion auf PVC. Diese Mischung wurde auch gut abgewaschen. Allerdings ist die Homogenität der Schichtdicke der Mischung noch nicht optimal. Die Farberosionsmethode ist eine neue Methode zur Sichtbarmachung der Strömung an den Wänden von Blutpumpen. Mit dieser Methode kann man die Stärke der Wandschubspannung gut beurteilen.
BibTeX @inproceedings{Aguilera2001, author = {D. Aguilera}, title = {Sichtbarmachung der Wandschubspannung mit der Farberosionsmethode}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomedizinische Technik}, year = {2001}, volume = {46}, number = {Ergänzungsband 1}, pages = {140--141} }
2001 (09)	Kertzscher, U. ; Debaene, P. ; Klein, C. ; Affeld, K.: Sichtbarmachung und Messung der Wandschubspannung in Blutpumpen. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomedizinische Technik Volume 46 , 2001(Ergänzungsband 1), pp. 154–155. [Abstract] [BibTeX]
Abstract In der Medizin ist die Erfassung von Strömungseigenschaften von besonderem Interesse, weil eine enge Beziehung zwischen Schädigungen an der Wand und der Strömung angenommen wird. Insbesondere die Wandschubspannung wird als wichtige Einflußgröße angesehen. Es ist zwar bekannt, daß in arteriellen Gefäßen kleine oder alternierende Wandschubspannungen zu Wandschädigungen gefolgt von Atherosklerose oder zu Thromben führen können, aber die genaue Beziehung zwischen der Wandschubspannung und der Einfluß auf die Wand ist noch unbekannt. Eine Voraussetzung zur Lösung dieses Problems ist die exakte Bestimmung der Wandschubspannung. In den künstlichen Blutpumpen von Herzunterstützungssystemen entwickeln sich häufig Thromben, die das Leben des Patienten gefährden. Die Lage dieser Thromben ist bekannt, nicht aber die Strömung in Wandnähe und insbesondere die Wandschubspannung. Es gibt erhebliche Probleme, diese Größe in Blutpumpen zu messen, da sich die Wand von Blutpumpen verformt. Weiterhin ist die Grundströmung pulsatil. Deswegen wird eine neue Methode zur Sichtbarmachung und Messung der Wandschubspannung in künstlichen Blutpumpen vorgestellt. Die neue Methode zur Messung der Wandschubspannung basiert auf der Beobachtung von lichtreflektierenden Partikeln, die sich in der Strömung befinden. Es ist eine spezielle Weiterentwicklung der standardmäßig eingesetzten Strömungssichtbarmachung. Während bei letzterer ein Lichtschnitt einen Querschnitt der Strömung beleuchtet, werden bei der neuen Methode nur die Partikel in der Nähe der Wand beleuchtet. Dies wird durch die Verwendung eines stark gefärbten Fluides erreicht, das verhindert, daß das Licht tief in die Strömung eindringt. Ein transparentes Strömungsmodell wird durch eine diffuse Lichtquelle beleuchtet. Als Strömungsmedium wird ein Tusche-Wasser-Gemisch verwendet, in das das Licht etwa einen Millimeter eindringen kann. Reflektierende Kunststoffkugeln mit einem Durchmesser von 500 Mikrometern werden als Partikel verwendet. Durch die Limitierung der Eindringtiefe des Lichtes, werden nur die Partikel in der Nähe der Wand beleuchtet. Diese Partikel visualisieren die Strömung in Wandnähe und können für die Particle Image Velocimetry genutzt werden. Zur Evaluation der Methode wurden erfolgreich Messungen zur Ermittlung der Wiederanlegelänge nach einer plötzlichen Rohrerweiterung durchgeführt. Die Ergebnisse der Strömungsuntersuchungen zeigen die Anwendbarkeit des Verfahrens. Die Richtung der Strömung in Wandnähe kann wie die Lage von Staulinien und Ablösegebieten sehr genau ermittelt werden. Da solche Bereiche mit der Bildung von Thromben in einen engen Zusammenhang stehen, kann die neue Methode ein wichtiges Hilfsmittel zur Lösung der durch die Strömung hervorgerufenen Probleme in künstlichen Organen mit Blutkontakt werden.
BibTeX @inproceedings{Kertzscher2001a, author = {U. Kertzscher and P. Debaene and C. Klein and K. Affeld}, title = {Sichtbarmachung und Messung der Wandschubspannung in Blutpumpen}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomedizinische Technik}, year = {2001}, volume = {46}, number = {Ergänzungsband 1}, pages = {154--155} }
2001 (08)	Klein, C. ; Affeld, K.: Modelluntersuchung zum Einströmvorgang in den künstlichen Ventrikel. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomedizinische Technik Volume 46 , 2001(Ergänzungsband 1), pp. 158–159. [Abstract] [BibTeX]
Abstract Die Blutströmung in einem künstlichen Ventrikeln ist sehr komplex. Die Strömung ist instationär, turbulent und die Geometrie ist veränderlich. Um diese Strömung besser zu verstehen, wurde ein Modell entwickelt, das sehr gut definiert ist. Es modelliert den Vorgang zu Beginn der Diastole des künstlichen Ventrikels und es gestattet die Sichtbarmachung der Strömung. Insbesondere ermöglicht es die Beobachtung und Erfassung der Strömung in Wandnähe. In der klinischen Praxis kommt es in der Nähe der Wand bei bei niedrigen und alternierenden Wandschubspannungen zur Thrombenbildung. Die Untersuchung der Wandschubspannungen hat deshalb eine große praktische Bedeutung. Der Einströmvorgang dauert nur etwa 300 Millisekunden. Dieser kurze Vorgang wird durch einen schwerkraftgetriebenen Fallstrom erzeugt. Dies geschieht dadurch, daß in einem Gefäßsystem eine Spiegelhöhendifferenz erzeugt wird, die sich gezielt ausgleichen kann. Es handelt sich also im Prinzip um zwei kommunizierende Röhren mit anfänglich unterschiedlichem Wasserspiegel. Das Gefäß mit dem höheren Flüssigkeitsspiegel ist über eine axialsymmetrische Düse mit der zweiten verbunden. Bei Ausgleich wird ein instationärer axialer Freistrahl erzeugt, der auf eine Wand gerichtet wird. Letztere stellt die Wand des künstlichen Ventrikels dar. Es treten Geschwindigkeiten von maximal 2 m pro Sekunde auf. Mit diesem Modell wurden folgende Messungen durchgeführt: Die Strömung wird in der Strahlachse und in Ebenen parallel zur Wand mit der Partikel Image Velocimetrie (PIV) erfaßt und analysiert. Die Wahl der Ebenen erfolgt durch entsprechende Lichtschnitte. Die Strömung wird in Wandnähe durch ein neues Verfahren erfaßt und analysiert. Es werden ebenfalls Partikelbewegungen erfaßt. Die wandnahe Strömung wird erfaßt, indem die wandfernen Bereiche durch Beifügung einer Farbe zum Fluid ausgeblendet werden. Die Strömung wird hier diffus beleuchtet. Die Aufnahme erfolgt beide Male mit einer Hochgeschwindigkeitsvideokamera mit einer Bildfrequenz von bis zu 500 Bildern pro Sekunde. Die Auswertung erfolgt mit entsprechenden PIV Analyseprogrammen. Die Aufnahmen zeigen, daß die Strömung den Einströmvorgang in einem künstlichen Ventrikel gut abbildet. Der Strömungsvorgang ist sehr gut reproduzierbar. Der Vorgang kann gut sichtbar gemacht werden. Die instationäre Entwicklung der Wandschubspannung wird in einer Serie von Vektorfeldern erfaßt. Der instationäre Freistrahl, der auf eine Wand gerichtet ist, ist die größtmögliche Vereinfachung des Einströmvorgangs. Ist dieser ausreichend untersucht, soll die ebene Wand durch eine gekrümmte Wand ersetzt werden, die der Geometrie eines künstlichen Ventrikels nahe kommt.
BibTeX @inproceedings{Klein2001, author = {Ch. Klein and K. Affeld}, title = {Modelluntersuchung zum Einströmvorgang in den künstlichen Ventrikel}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomedizinische Technik}, year = {2001}, volume = {46}, number = {Ergänzungsband 1}, pages = {158--159} }
2001 (07)	Timmel, T. ; Goubergrits, L. ; Affeld, K.: Konstruktion und experimentelle Untersuchung einer neuartigen Herzklappe für Herzunterstützungssysteme.. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomed Tech (Berl) Volume 46 Suppl 1 , 2001, pp. 128–129. [BibTeX]
BibTeX @inproceedings{Timmel2001b, author = {Tobias Timmel and Leonid Goubergrits and Klaus Affeld}, title = {Konstruktion und experimentelle Untersuchung einer neuartigen Herzklappe für Herzunterstützungssysteme.}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomed Tech (Berl)}, year = {2001}, volume = {46 Suppl 1}, pages = {128--129} }
2001 (06)	Scheckel, M. ; Affeld, K.: Modellstudie einer Blutströmung durch einen Stent in der Aortenbifurkation. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomedizinische Technik Volume 46, Ergänzungsband 1 , 2001, pp. 296–297. [Abstract] [BibTeX]
Abstract In der modernen Industriellen Gesellschaft spielen Verschlußkrankheiten peripherer Gefäße eine wichtige Rolle. Fünf Prozent der Bevölkerung über 50 Jahre sind davon betroffen. Die Mehrheit dieser Patienten klagt über Schmerzen in der Hüfte bzw. in den Beinen. Artheriosklerose ist der Hauptgrund für die chronische Gefäßverengung. Die arterielle Verengung der Gefäße verursacht einen verminderten Blutfluß zu den unteren Gliedmaßen, deren Muskulatur dadurch nicht ausreichend mit Sauerstoff versorgt wird. Die Gefäße im Bereich der Verengungen werden erweitert und mit Stents - metallischen Gitterstrukturen - offengehalten. Damit wird wieder ein normaler Blutfluß erreicht. In der vorliegenden Studie wurde der Einfluß der Modifikation eines Aortenstents auf die Blutströmung untersucht. Der betrachtete Stent ist ein neuer Nitinolstent, Luminexx?, welcher von der Fa. C.R. BARD®/ Angiomed, Karlsruhe entwickelt worden ist. Die Enden des Luminexx? stellen hoch radiopaque Tantalmarker dar. Diese Marker sollen die Sichtbarkeit des Stents im Röntgenbild verbessern. Das Ziel dieser Studie war es herauszufinden ob und in welchem Umfang die Blutströmung durch den modifizierten Stent beeinflußt und ob dadurch die Gefahr der Bildung von Thromben entsteht. Die Blutströmung wurde in einem fünffach vergrößerten Modell der Aortenbifurkation sichtbar gemacht. Die geometrischen Werte für das Modell der Aortenbifurkation wurden auf der Basis von anatomischen Messungen an Versuchspersonen bestimmt. Das Modell des Stents sowie die Tiefziehform für die Aortenbifurkation wurden im Maßstab fünf zu eins mit einer CNC-Maschine hergestellt. Das Modell wurde danach aus transparentem Kunstoff im Tiefziehverfahren hergestellt. Die Vergrößerung erlaubte die Beobachtung und die Dokumentation der Strömung mit einer Videokamera. Die Modellströmung hatte die gleiche Reynoldszahl wie die reale Blutströmung. Sechs verschiedene Positionen der Stents wurden untersucht. Das Modell wurde mit einem Farbstoff gefüllt und während der Durchströmung wird dieser Farbstoff durch Wasser ausgetauscht. Damit erhält man einen charakteristischen Wert für die Verweilzeit des Blutes im untersuchten Modell. Eine spezielle Analyse der Bilder der Blutströmung in der Nähe der Stentstruktur - mithilfe der Grauwertanalyse - erlaubte die Quantifizierung der Experimente. Die Ergebnisse lassen den Schluß zu, daß die neu eingeführten Marker des Stents die Blutströmung in der Aortenbifurkation nur unwesentlich beeinflussen. Die Bildung von Thromben in diesem Bereich erscheint unwahrscheinlich.
BibTeX @inproceedings{Scheckel2001, author = {M. Scheckel and K. Affeld}, title = {Modellstudie einer Blutströmung durch einen Stent in der Aortenbifurkation}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomedizinische Technik}, year = {2001}, volume = {46, Ergänzungsband 1}, pages = {296--297} }
2001 (05)	Goubergrits, L. ; Affeld, K. ; Timmel, T.: Optimierung einer neuartigen Klappe für Herzunterstützungssysteme mit einem Spülstrom des Klappensinus. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomedizinische Technik Volume 46, Ergänzungsband 1 , 2001, pp. 130–131. [Abstract] [BibTeX]
Abstract Herzunterstützungssysteme werden heutzutage häufig eingesetzt, um das kranke Herz des Patienten zu entlasten. Dieser Einsatz wird jedoch durch eine häufig auftretende Komplikation eingeschränkt. Es bilden sich Tromben in der Blutpumpe, die sich loslösen und das Leben des Patienten gefährden können. Diese Komplikationen werden vorwiegend von den künstlichen Herzklappen verursacht. Tromben bilden sich bevorzugt im Raum zwischen dem Klappensegel und der Gefäßwand, dem sogenannten Klappensinus. Dieser Raum wird wenig durchströmt und ist somit ein Stagnationsgebiet. Die Gefahr der Thrombenbildung kann man durch eine Verminderung dieses Stagnationsgebietes reduzieren. Dies erreicht man durch die Gestaltung der Strömungsführung in der Klappe. In dieser neuartigen Klappe wird ein Teil der Hauptströmung während der Durchströmphase (Systole) durch einen Strahlteiler abgeteilt und in den Raum hinter dem Segel geleitet. Dadurch wird die Verweilzeit von gerinnungsaktiven Substanzen (z. B. Thrombin, Adenosindiphosphat) in diesem Bereich verkürzt. Aufgabe der Optimierung der neuen Klappe war es, die Strömung im Raum hinter dem Segel durch die Gestaltung der Sinusgeometrie und der Strahlteiler zu intensivieren. Es wurden insgesamt 32 Variationen der Einsegelklappe mit dem 3D-Computer-Aided-Design- (CAD) Programm SolidWorks generiert. Die Einsegelklappe hat den Vorteil einer einfachen Geometrie und besitzt eine weniger komplexe Strömung als eine Klappe mit zwei oder drei Segeln. Folgende Klappenparameter wurden in diese Studie variiert: Größe und Gestaltung des Sinusraums, Größe und Position der Strahlteiler, und die Länge des Segels. Um die Anzahl der Klappenvariationen zu reduzieren, wurde eine aus dem Qualitätsmanagement bekannte Technik - die partielle Versuchsplanung nach Taguchi - angewendet. Bei Berücksichtigung aller Parameterkombinationen hätte man 188 Geometrien berechnen müssen. Mit der angewendeten Technik wurde die Wirkung aller variierten Parameter anhand von nur 32 Geometrien untersucht. Die Strömung durch diese Klappen wurde mit der Methode der CFD (Computational Fluid Dynamics) berechnet. Die Strömungsberechnungen wurden mit dem Programmpaket FLUENT5 der Firma Fluent Inc. durchgeführt. Dieses ist ein CVFEM- (Control Volume Finite Element Method) Programm und basiert auf der "pressure-segregated method", die ein unstrukturiertes tetraedisches Gitter generiert. Die Basis für die Strömungssimulationen bilden die dreidimensionalen Navier-Stokes-Gleichungen für stationäre Strömungen mit inkompressiblen Fluiden und verschiedenen Turbulenzmodellen. Die Geometrien der Klappen wurden in den Preprozessor Gambit der Firma Fluent Inc. importiert, um das innere Gitter aus 300.000 bis 400.000 Tetraedern zu generieren. Als Eingangsbedingung wurde ein zeitkonstantes rechteckiges Geschwindigkeitsprofil V = 1 m/s definiert. Mit der kinematischen Viskosität des Blutes und dem Klappendurchmesser D = 0,02 m ergibt das eine Reynoldszahl von Re = 6000. Es wurde eine Turbulenz von 10% angenommen und das Standard k-? Turbulenzmodell angewendet. Das Blut wurde als Newton'sches Fluid angenommen. Die Auswaschung des Sinusbereiches wurde auf der Basis der berechneten Wandschubspannungen beurteilt. In jeder Klappe wurde die integrale Fläche mit niedrigen Wandschubspannungen berechnet und miteinander verglichen. Es wurden zwei Bereiche als niedrigen Wandschubspannungen definiert: Wandschubspannungen zwischen 0 und 0,5 Pa und zwischen 0 und 1 Pa. Die Strömungsberechnungen zeigen eine sehr komplexe Strömung im Sinusraum, deren Eigenschaften noch nicht vollständig verstanden wurden. Alle variierten Parameter zeigen einen großen Einfluß auf die Strömung im Sinusraum. Daher ist es nötig, weitere Untersuchungen für die Optimierung der Spülströmung durchzuführen. Es wurden insgesamt 4 Einsegelklappen ausgewählt, deren Strömung eine bessere Auswaschung des Sinusraums aufweist. Außerdem wurde eine neue optimierte Klappe generiert, deren Geometrie die besten untersuchten Parameter besitzt. Diese 5 ausgewählten Klappen werden mit experimentellen Methoden in einem Herzklappenprüfstand weiter untersucht.
BibTeX @inproceedings{Goubergrits2001b, author = {L. Goubergrits and K. Affeld and T. Timmel}, title = {Optimierung einer neuartigen Klappe für Herzunterstützungssysteme mit einem Spülstrom des Klappensinus}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomedizinische Technik}, year = {2001}, volume = {46, Ergänzungsband 1}, pages = {130--131} }
2001 (04)	Debaene, P. ; Kertzscher, U. ; Affeld, K.: Untersuchung der Strömung in künstlichen Ventrikeln. In: 35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19–21. Biomedizinische Technik Volume 46, Ergänzungsband 1 , 2001, pp. 160–161. [Abstract] [BibTeX]
Abstract Eine der Gefahren, die beim Einsatz von Herzunterstützungssystemen auftreten, ist die durch die Aktivierung des Gerinnungssystems verursachte Thrombenbildung. Bei der klinischen Anwendung können sich diese Thromben loslösen und beim Patienten durch Verstopfung von Blutgefäßen eine Embolie verursachen. Die klinische Erfahrung mit künstlichen Ventrikeln hat gezeigt, daß die Thrombenbildung zum einen durch den Kontakt des Blutes mit Fremdoberflächen, zum anderen durch eine lange Verweilzeit des Blutes im Ventrikel bestimmt wird. Die Strömung beeinflußt diese Verweilzeit und somit sind strömungstechnische Untersuchung von künstlichen Ventrikeln für deren Verbesserung erforderlich. In dieser Arbeit wird eine weitere Untersuchung hierzu vorgestellt. Sie beschäftigt sich sich mit der Strömung innerhalb des künstlichen Ventrikels speziell im zentralen und im wandnahen Bereich. Es werden zwei unterschiedliche künstliche Ventrikel in einem Modellkreislauf untersucht. Die Beobachtung und Analyse der Strömung im zentralen Bereich erfolgt mittels PIV (Particle Image Velocimetry). Im wandnahen Bereich eine weiterentwickelte PIV-Methode durchgeführt. Bei beiden Metohoden werden lichtreflektierende Partikel, die der Strömung folgen, dem im Ventrikel strömende Modellfluid hinzugefügt und diese beobachtet. Der Ventrikel hat eine transparente Wandung. Bei dem Standard-PIV wird ein Lichtschnitt in der Mitte des Ventrikels erzeugt. Bei dem weiterentwickelten PIV-Verfahren wird der Ventrikel von außen durch diffuses Licht beleuchtet. Durch Verwendung eines gefärbten Modellfluids wird die Eindringtiefe des Lichtes so reduziert, daß nur die Partikel in Wandnähe sichtbar werden. Auf diese Weise wird die Partikelbewegung und damit die Strömung nur im wandnahen Bereich sichtbar gemacht. Eine Hochgeschwindigkeitskamera wird für die Bildaufnahme verwendet. Nach der Bildverarbeitung werden die Ergebnisse dargestellt und mit klinischen Befunden des Ventrikels verglichen. Aus der Untersuchung der Strömung in zwei Ventrikeln ergibt sich eine unregelmäßige Blutauswaschung. Die Stagnationsgebiete gestatten eine Abschätzung der Bereiche des Ventrikels, in denen die Bildung von Thromben zu erwarten ist.
BibTeX @inproceedings{Debaene2001, author = {P. Debaene and U. Kertzscher and K. Affeld}, title = {Untersuchung der Strömung in künstlichen Ventrikeln}, booktitle = {35. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Bochum, September 19--21}, journal = {Biomedizinische Technik}, year = {2001}, volume = {46, Ergänzungsband 1}, pages = {160--161} }
2001 (03)	Goubergrits, L. ; Affeld, K. ; Debaene, P.: Investigation of transport phenomena inside a microcapsule. In: 4th International Symposium on Particle Image Velocimetry, Göttingen, Germany, September 17–19. , 2001 [Abstract] [BibTeX] Article (PDF-file; 0.65 MB)
Abstract With a new approach the transport process within the microcapsule is accelerated by introduction of a convection. This is achieved by a movable body inside the microcapsule. It has a different density as the fluid within the microcapsule and can be moved relatively to the microcapsule by application of an external force through a magnet field or through an acceleration/deceleration. Two methods were applied to investigate the flow field generated by a motion of the body inside a microcapsule and the effect of transport improvement by this generated convective flow field. One method was the computational fluid dynamics (CFD) and the other the particle image velocimetry (PIV). The PIV method was used to investigate the flow field generated by a movable body inside a microcapsule. The averaged velocity of the fluid in the microcapsule was measured in order to calculate the Peclet number of the convective-diffusive mass transport inside the microcapsule. The effect of the transport improvement was investigated as a function of the Peclet number. The transport improvement was measured by decreasing of the period to achieve the 80 % saturation of the transported material inside the microcapsule. The results show that the period to achieve the 80 % saturation in the microcapsule was reduced by 60% with a movable body of the half diameter of the microcapsule and Peclet number Pe=600 compared with the mass transport in the microcapsule with a nonmovable body.
BibTeX @inproceedings{Goubergrits2001d, author = {L. Goubergrits and K. Affeld and P. Debaene}, title = {Investigation of transport phenomena inside a microcapsule}, booktitle = {4th International Symposium on Particle Image Velocimetry, Göttingen, Germany, September 17--19}, year = {2001} }
2001 (02)	Kertzscher, U. ; Debaene, P. ; Affeld, K.: New method to visualize and to measure the wall shear rate in blood pumps. In: 4th International Symposium on Particle Image Velocimetry, Göttingen, Germany, September 17–19. , 2001 [Abstract] [BibTeX] Article (PDF-file; 0.35 MB)
Abstract In medicine flow properties in vessels are of special interest, since a close relation between flow and lesions of the vessel wall is assumed. Especially the wall shear rate is important. A new method to visualize the wall shear rate is proposed. The new method is based on the observation of light reflecting particles, which are suspended in the fluid. The method can be considered as a special development of standard particle image velocimetry (PIV). Instead of having a light sheet illuminating a cross section of the flow, only particles near to the wall are illuminated. The selection is made by using a fluid, which does not permit the light to penetrate deeply into the fluid. To evaluate the method, we performed measurements in a sudden expansion flow to detect the reseparation region. Then the method has been used to assess the velocity field close to the wall of a blood pump of a cardiac assist device. The results are compared to the velocity distribution inside the blood pump. The results of the flow experiments show the viability of the method. The direction of the flow at the wall can be assessed very well, as well as the detection of the stagnation lines and flow separation zones. Additionally, it is possible to assess the flow structures encountered close to the wall.
BibTeX @inproceedings{Kertzscher2001, author = {U. Kertzscher and P. Debaene and K. Affeld}, title = {New method to visualize and to measure the wall shear rate in blood pumps}, booktitle = {4th International Symposium on Particle Image Velocimetry, Göttingen, Germany, September 17--19}, year = {2001} }
2001 (01)	Seeger, A. ; Affeld, K. ; Kertzscher, U. ; Goubergrits, L. ; Wellnhofer, E.: Assessment of Flow Structures in Bubble Columns by X-ray Based Particle Tracking Velocimetry. In: 4th International Symposium on Particle Image Velocimetry, Göttingen, Germany, September 17–19. , 2001 [Abstract] [BibTeX] Article (PDF-file; 1.93 MB)
Abstract For the investigation of flow structures in bubble columns it is necessary to measure the local liquid velocity. Common optical methods fail in a bubble flow with a large void fraction. The cause is the different refraction index of liquid phase and gaseous phase, which leads to reflection and dispersion. The new X-ray based Particle Tracking Velocimetry (PTV) ? called ?XPTV? ? presented here permits to obtain the liquid velocity three-dimensionally, touch-free and for any large void fraction. The problem of light reflection and light refraction on phase boundaries is solved by the use of X-rays instead of light. X-rays penetrate a gas/liquid flow in straight lines. The method can also be applied to opaque liquids, where optical methods fail.
BibTeX @inproceedings{Seeger2001a, author = {A. Seeger and K. Affeld and U. Kertzscher and L. Goubergrits and E. Wellnhofer}, title = {Assessment of Flow Structures in Bubble Columns by X-ray Based Particle Tracking Velocimetry}, booktitle = {4th International Symposium on Particle Image Velocimetry, Göttingen, Germany, September 17--19}, year = {2001} }
2000 (03)	Seeger, A. ; Kertzscher, U. ; Bruck, S. ; Affeld, K.: Bioimpedanzmessungen an hämoperfundierten Schweinenieren. In: 34. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Lübeck, September 28–30. Biomedizinische Technik Volume 45, Ergänzungsband 1 , 2000 [Abstract] [BibTeX]
Abstract Jährlich werden etwa 2000 Nierentransplantationen in der Bundesrepublik Deutschland durchgeführt. Diese transplantierten Nieren werden durch eine möglichen Abstoßungsreaktion des Körpers gefährdet. Diese Reaktion muß unter allen Umständen vermieden werden. Abstoßungsreaktionen können mit Hilfe von Immun-Suppressiva unterdrückt werden, die jedoch wiederum den Körper des Patienten schwächen und schwer zu dosieren sind. Bisher kann eine Abstoßungsreaktion nur durch eine Biopsie quantifiziert werden. Diese ist invasiv und schädigt zudem das Organ. Ziel ist es deshalb, das Organ ständig nicht-invasiv zu überwachen, um schnell und gezielt in eine mögliche Abstoßungsreaktion ein-greifen zu können. Ein möglicherweise geeigneter Indikator für die Abstoßungsreaktion ist eine Veränderung der Bioimpe-danz der Niere. Die Bioimpedanz kann Veränderun-gen der Zellen widerspiegeln, da die Zellwände und die Verteilung und Eigenschaften der intra- und extrazellulären Flüssigkeit einen entscheidenden Einfluß haben. Aus zahlreichen Untersuchungen ist bekannt, daß es mit Hilfe der Bioimpedanz möglich ist, zwischen ischämi-schem und gesundem Gewebe zu unterscheiden. Da es sich bei abgestoßenem Gewebe um ischämisches Gewebe handelt, liegt dieser Ansatz nahe. Abbildung 1 zeigt eine typische Impedanzveränderung einer Schweineniere, nachdem die Blutversorgung unterbrochen wurde. Die Veränderung der Phasenverschiebung ist nicht dargestellt. Typischerweise nimmt die Phasenver-schiebung ab bei sehr niedrigen Frequenzen (100 Hz) und zu bei höheren Frequenzen (50 kHz). Die Niere stammte von einem Schlachthofschwein und wurde vor dieser Messung mit Eigenblut perfundiert. Dieses Ergebnis deckt sich mit den Ergebnissen anderer Arbeiten.
BibTeX @inproceedings{Seeger2000, author = {A. Seeger and U. Kertzscher and S. Bruck and K. Affeld}, title = {Bioimpedanzmessungen an hämoperfundierten Schweinenieren}, booktitle = {34. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Lübeck, September 28--30}, journal = {Biomedizinische Technik}, year = {2000}, volume = {45, Ergänzungsband 1} }
2000 (02)	Kertzscher, U. ; Affeld, K. ; Goubergrits, L.: Messung der Wandschubspannung in Modellen von Blutgefäßen. In: 34. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Lübeck, September 28–30. Biomedizinische Technik Volume 45, Ergänzungsband 1 , 2000 [Abstract] [BibTeX]
Abstract In der Medizin ist die Erfassung von Strömungseigenschaften von besonderem Interesse, weil eine enge Beziehung zwischen Schädigungen an der Wand und der Strömung beobachtet worden ist. Insbesondere die Wandschubspannung wird als wichtige Einflußgröße angesehen [1]. Es ist zwar bekannt, daß kleine oder alternierende Wandschubspannungen zu Wandschädigungen gefolgt von Atherosklerose führen können, aber die genaue Beziehung zwischen der Wandschubspannung und den Wandschädigungen ist noch unbekannt. Eine Voraussetzung zur Lösung dieses Problems ist die Bestimmung der Wandschubspannung. Es existiert eine Vielzahl von Methoden zur Bestimmung dieser Größe [2]. Allerdings gibt es erhebliche Probleme, diese Größe in Modellen von Blutgefäßen zu messen, da die Gefäße gekrümmt sind und einen relativ kleinen Durchmesser besitzen. Außerdem ist die zu Grunde liegende Strömung pulsatil. Hierzu wird eine neue Methode zur Messung der Wandschubspannung vorgestellt.
BibTeX @inproceedings{Kertzscher2000, author = {U. Kertzscher and K. Affeld and L. Goubergrits}, title = {Messung der Wandschubspannung in Modellen von Blutgefäßen}, booktitle = {34. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Lübeck, September 28--30}, journal = {Biomedizinische Technik}, year = {2000}, volume = {45, Ergänzungsband 1} }
2000 (01)	Affeld, K. ; Goubergrits, L. ; Fernandez-Britto, J. ; Wellnhofer, E.: Use of Models in Blood Flow Investigation. In: Proceedings IFAC Conference Modelling and Control in Biomedical Systems. , 2000, pp. 203–206. [Abstract] [BibTeX]
Abstract Two different models of the blood flow are dealt with in this paper: one model is based on vessel casts, the other is based on angiograms. In both models the three dimensional geometry of the vessel is reconstructed. This geometry is the basis for the subsequent computation of the blood flow. This computation renders the flow in the lumen, but more important, the flow at the vessel wall and thus delivers the wall shear stress. This latter parameter is known to be of great influence for various pathological alterations of the vessel wall.
BibTeX @inproceedings{Affeld2000, author = {K Affeld and L Goubergrits and J Fernandez-Britto and E Wellnhofer}, title = {Use of Models in Blood Flow Investigation}, booktitle = {Proceedings IFAC Conference Modelling and Control in Biomedical Systems}, year = {2000}, pages = {203--206} }
1999 (02)	Kertzscher, U. ; Affeld, K. ; Goubergrits, L. ; Schade, M.: A new method to measure the wall shear rate in models of blood vessels. In: Proceedings of the European Medical & Biological Engineering Conference, Wien, Österreich, November 4–7. Biomed Tech (Berl) Volume 37 , 1999(Supplement 2), pp. 1412–1413. [BibTeX]
BibTeX @inproceedings{Kertzscher1999, author = {U. Kertzscher and K. Affeld and L. Goubergrits and M. Schade}, title = {A new method to measure the wall shear rate in models of blood vessels}, booktitle = {Proceedings of the European Medical & Biological Engineering Conference, Wien, Österreich, November 4--7}, journal = {Biomed Tech (Berl)}, year = {1999}, volume = {37}, number = {Supplement 2}, pages = {1412--1413} }
1999 (01)	Seeger, A. ; Goubergrits, L. ; Richard, N. ; Kertzscher, U. ; Wellnhofer, E.: X-ray based assessment of the three-dimensional velocity of the liquid phase in a bubble column. In: Proceedings of the Third International Workshop on PIV, Santa Barbara, California, September 16–18. , 1999, pp. 519–524. [BibTeX]
BibTeX @inproceedings{Seeger1999, author = {A. Seeger and L. Goubergrits and N. Richard and U. Kertzscher and E. Wellnhofer}, title = {X-ray based assessment of the three-dimensional velocity of the liquid phase in a bubble column}, booktitle = {Proceedings of the Third International Workshop on PIV, Santa Barbara, California, September 16--18}, year = {1999}, pages = {519--524} }
1998 (07)	Kertzscher, U. ; Affeld, K. ; Goubergrits, L. ; Ziemann, A.: Visualization of wall shear rate. In: Proceedings of the 8th International Symposium on Flow Visualization, Sorrento, Italy, September 1–4. , 1998 [Abstract] [BibTeX]
Abstract In Biofluidmechanics the blood flow in vessels is of special interest. Firstly, it is interesting for the fluiddynamicist because of the complicated structure of the flow, being three-dimensional and usually having flow separations. Secondly it is of interest for the medical scientist, who suspects a close relation between flow and lesions of the blood vessel wall. It is known, that a low wall shear rate at the wall causes the lesions, leading to the disease called atherosclerosis. The exact relation between wall shear rate and the lesions, however, is not known. A precondition for solving this problem is the assessment of the wall shear rate. A new method to visualize the latter is proposed. The method is based on the observation of light reflecting particles which are suspended in the fluid. The standard method of particle based flow visualization applies a light sheet through the flow. Only particles illuminated by the light sheet light up and are observed. A selection of the flow - a cross section - is visualized. The regions close to the wall comprise only a minor part of the image. The new method however, permits to look only at the flow close to the wall. The selection is made by using a fluid, which does not permit the light to penetrate deeply into the flow. The transparent flow model is illuminated by a diffusive light source. The light is illuminating only the viscous sublayer, so only the particles moving close to the wall are reflecting light. The surface flow can thus be visualized. Water is used as a model fluid. Black Indian ink is used to shield off the inner flow. The concentration is such, that the light penetrates only 10 micrometers. Hollow glass spheres with a mean diameter of 10 micrometers and a small standard deviation are used. The spheres are covered with aluminum for good reflectance. Note that the size of particles has to be the same order as the depth of light penetration. It is assumed, that the particles at the wall travel with a velocity = shear rate x diameter/2. This is used to compute the shear rate. The flow is recorded with a digital camera with a resolution of 1024 x 1024 pixel. The velocity field is subsequently computed using the cross-correlation method. For initial experiments a Hagen-Poiseuille flow was selected as a flow model. The tube has a cylindrical cross section and a diameter of 4 mm. It is made of a highly transparent silicone rubber. For this flow the wall shear rate is known and the method can be tested. Later the method was used to investigate the wall shear flow in a model of a branched blood vessel, the arteria carotis. Also this flow model was made of transparent silicone rubber. The results of the Hagen-Poiseuille flow experiment show the viability of the method. The assumption on the relation between wall shear rate and particle velocity was proved to be correct. The assessment of the wall shear rate in the arteria carotis flow is consistent with results achieved with other methods.
BibTeX @inproceedings{Kertzscher1998, author = {U Kertzscher and K Affeld and L Goubergrits and A Ziemann}, title = {Visualization of wall shear rate}, booktitle = {Proceedings of the 8th International Symposium on Flow Visualization, Sorrento, Italy, September 1--4}, year = {1998} }
1998 (06)	van der Hoeven, J.G. ; Kiliç, A. ; Vogel, P. ; Loudovici, D.A. ; Große-Siestrup, C. ; Affeld, K.: Vergleichende Untersuchung der Hämolyse von Blutpumpen verschiedener Bauart. In: 32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9–12. Biomed Tech (Berl) Volume 43 Suppl , 1998, pp. 332–334. [Abstract] [BibTeX] [PMID ]
Abstract In künstlichen Kreislaufsystemen können isolierte Organe einige Zeit am Leben erhalten werden. Besonders günstig ist es, diese Organe mit dem körpereigenen Blut zu perfundieren. Hierzu werden Blutpumpen benötigt, die aber bekanntlich das Blut traumatisieren. Deshalb wurden zwei neue Pumpen entwickelt und getestet. Diese Pumpen, als Wechselkammerpumpe und Pulspumpe bezeichnet, wurden mit drei kommerziell erhältliche Rollerpumpen von den Firmen Fresenius, Stöckert und Watson Marlow, verglichen. Als Kenngröße für die Bluttraumatisierung wurde die Freisetzung von Hämoglobins der Erithrozyten gewertet. Diese Hämolyse wurde als Index (Normalized Index of Hemolysis - NIH) auf das gepumpte Blutvolumen bezogen. Die Untersuchung ergab, daß für die neuen Blutpumpen der Index um 50 % bis 60 % niedriger lagen als bei den Rollerpumpen. Die neuen Blutpumpen sollen für ein künstliches Kreislaufsystem zum Ersatz von Tierversuchen eingesetzt werden. Anstelle der Versuchstiere werden Organe von Schlachthof untersucht.
BibTeX @inproceedings{Hoeven1998, author = {J. G. van der Hoeven and A. Kiliç and P. Vogel and D. A. Loudovici and C. Große-Siestrup and K. Affeld}, title = {Vergleichende Untersuchung der Hämolyse von Blutpumpen verschiedener Bauart}, booktitle = {32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9--12}, journal = {Biomed Tech (Berl)}, year = {1998}, volume = {43 Suppl}, pages = {332--334} }
1998 (05)	Seeger, A. ; Jaffrin, M.Y. ; Gourrir, A.L.: Messung der Bioimpedanz bei Dialysepatienten zur Bestimmung der Wassermenge in den einzelnen Flüssigkeitsräumen des Körpers. In: 32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9–12. Biomed Tech (Berl) Volume 43 Suppl , 1998, pp. 534–535. [BibTeX] [PMID ]
BibTeX @inproceedings{Seeger1998, author = {A. Seeger and M. Y. Jaffrin and A. Le Gourrir}, title = {Messung der Bioimpedanz bei Dialysepatienten zur Bestimmung der Wassermenge in den einzelnen Flüssigkeitsräumen des Körpers}, booktitle = {32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9--12}, journal = {Biomed Tech (Berl)}, year = {1998}, volume = {43 Suppl}, pages = {534--535} }
1998 (04)	Goubergrits, L. ; Affeld, K.: Berechnung der Strömung durch eine neuartige Einsegelklappe für Herzunterstützungssysteme. In: 32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9–12. Biomed Tech (Berl) Volume 43 Suppl , 1998, pp. 288–289. [Abstract] [BibTeX] [PMID ]
Abstract Herzunterstützungssysteme haben heute einen festen Platz in der klinischen Praxis gefunden. Allerdings wird ihr Einsatz durch thromboembolische Komplikationen eingeschränkt. Die Komplikationen werden vorwiegend von den Klappen verursacht. Diese Klappen sind vorwiegend Segelklappen. Sie werden bei manchen Systemen aus Polyurethan, bei anderen aus dem noch besser blutverträglichen Perikard gefertigt. Trotz der guten Blutverträglichkeit findet man häufig Thromben. Sie bilden sich bevorzugt an einem Ort - im Raum zwischen dem Segel und der Sinuswand. Dieser Ort ist für das Blut ein Stagnationsgebiet, das nur wenig durchströmt wird. Bei der neuen Klappe wird durch einen Strahlteiler ein Teil des Hauptstroms abgeteilt und in den Raum hinter dem Segel geleitet. Diese Strömung mit der Methode des CFD berechnet und es wird die Geometrie optimiert. Es kann eine bessere kontrollierbare Durchströmung erreicht werden.
BibTeX @inproceedings{Goubergrits1998, author = {L. Goubergrits and K. Affeld}, title = {Berechnung der Strömung durch eine neuartige Einsegelklappe für Herzunterstützungssysteme}, booktitle = {32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9--12}, journal = {Biomed Tech (Berl)}, year = {1998}, volume = {43 Suppl}, pages = {288--289} }
1998 (03)	Kiliç, A. ; van der Hoeven, J.G. ; Affeld, K. ; Loudovici, D.A. ; von Baeyer, H.: Weiterentwicklung eines Kreislaufmodells zur normothermen Organperfusion. In: 32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9–12. Biomed Tech (Berl) Volume 43 Suppl , 1998, pp. 500–503. [BibTeX] [PMID ]
BibTeX @inproceedings{Kilic1998, author = {A. Kiliç and J. G. van der Hoeven and K. Affeld and D. A. Loudovici and H. von Baeyer}, title = {Weiterentwicklung eines Kreislaufmodells zur normothermen Organperfusion}, booktitle = {32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9--12}, journal = {Biomed Tech (Berl)}, year = {1998}, volume = {43 Suppl}, pages = {500--503} }
1998 (02)	Lambertz, M. ; Affeld, K. ; Ziemann, A.: Untersuchung einer neuen Herzklappe für Herzunterstützungssysteme. In: 32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9–12. Biomed Tech (Berl) Volume 43 Suppl , 1998, pp. 514–515. [Abstract] [BibTeX] [PMID ]
Abstract Beim Einsatz von Herzunterstützungssystemen besteht die Gefahr der Thrombenbildung. Die Thromben bilden sich insbesondere leicht im Bereich der Herzklappen. Ziel der Arbeit war es, durch die Entwicklung einer neuen Herzklappe - dies ist die S-Klappe - die Thrombenbildung zu vermindern. Hierzu wurde die Strömung durch die S-Klappe mit einem zehnfach vergrößerten Modell untersucht. Die Strömungsuntersuchungen erfolgten mit der Farbstoffmethode mit fluoreszierenden Farben und mit der Methode der Digital Particle Image Velocimetry (DPIV). Die Versuche zeigten eine deutliche Verringerung der Strömungsablösungen gegenüber einer konventionellen Herzklappe. Mit weiteren Modifikationen konnten diese Strömungsablösungen dann vollständig vermieden werden. Damit kann erwartet werden, daß die Komplikationsrate bei einem klinischen Einsatz in einem Herzunterstützungssystem verringert sein wird.
BibTeX @inproceedings{Lambertz1998, author = {M. Lambertz and K. Affeld and A. Ziemann}, title = {Untersuchung einer neuen Herzklappe für Herzunterstützungssysteme}, booktitle = {32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9--12}, journal = {Biomed Tech (Berl)}, year = {1998}, volume = {43 Suppl}, pages = {514--515} }
1998 (01)	Seeger, A. ; Kertzscher, U. ; Gerhäusser, A. ; Krause, F. ; Sommer, G. ; Kolupa, J. ; Schäfer, H. ; Arnold, R. ; Affeld, K. ; Schaldach, M. ; Scheel, W. ; Orglmeister, R. ; Manck, O.: Ein implantierbares Telemetriesystem zur Impedanzspektroskopie. In: 32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9–12. Biomed Tech (Berl) Volume 43 Suppl 3 , 1998, pp. 117–122. [BibTeX] [PMID ]
BibTeX @inproceedings{Seeger1998a, author = {A. Seeger and U. Kertzscher and A. Gerhäusser and F. Krause and G. Sommer and J. Kolupa and H. Schäfer and R. Arnold and K. Affeld and M. Schaldach and W. Scheel and R. Orglmeister and O. Manck}, title = {Ein implantierbares Telemetriesystem zur Impedanzspektroskopie}, booktitle = {32. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Dresden, September 9--12}, journal = {Biomed Tech (Berl)}, year = {1998}, volume = {43 Suppl 3}, pages = {117--122} }
1994 (01)	Affeld, K. ; Gadischke, J.: Shear Rate And Thrombin Transport. In: 3rd International Symposium on Biofluid Mechanics, Munich, Germany, July 16–19. , 1994 [BibTeX]
BibTeX @inproceedings{Affeld1994a, author = {K. Affeld and J. Gadischke}, title = {Shear Rate And Thrombin Transport}, booktitle = {3rd International Symposium on Biofluid Mechanics, Munich, Germany, July 16--19}, year = {1994} }
1991 (02)	Affeld, K. ; Schichl, K. ; Ziemann, A.: Flow model studies of heart valves. In: Proceedings of a NATO Advanced Study Institute on New Frontiers in Cardiovascular Engineering, Malaga, Spain, December 4–14. Plenum Press, 1991 New York. [BibTeX]
BibTeX @inproceedings{Affeld1991a, author = {K. Affeld and K. Schichl and A. Ziemann}, title = {Flow model studies of heart valves}, booktitle = {Proceedings of a NATO Advanced Study Institute on New Frontiers in Cardiovascular Engineering, Malaga, Spain, December 4--14}, publisher = {Plenum Press}, year = {1991} }
1991 (01)	Affeld, K.: Model laws and fluid mechanics of bloodpumps. In: Topical Workshop of COMAC BME Concerted Action HEART, Aachen, Germany. , 1991, pp. 35–40. [BibTeX]
BibTeX @inproceedings{Affeld1991, author = {K. Affeld}, title = {Model laws and fluid mechanics of bloodpumps}, booktitle = {Topical Workshop of COMAC BME Concerted Action HEART, Aachen, Germany}, year = {1991}, pages = {35--40} }
1990 (01)	Affeld, K. ; Walker, P. ; Schichl, K.: A ten times enlarged model of artificial heart valve flow. In: 2nd International Symposium on Biofluid Mechanics and Biorheology. Springer, 1990 [BibTeX]
BibTeX @inproceedings{Affeld1990b, author = {Klaus Affeld and Peter Walker and Klaus Schichl}, title = {A ten times enlarged model of artificial heart valve flow}, booktitle = {2nd International Symposium on Biofluid Mechanics and Biorheology}, publisher = {Springer}, year = {1990} }
1989 (04)	Malaviya, A. ; Affeld, K. ; Walker, P. ; Schartl, M.: Simulation der Signale des Ultraschallfarbdopplers bei der Strömung durch künstliche Herzklappen. In: 23. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Kiel, August 31 – September 2. Biomed Tech (Berl) Volume 34 Suppl , 1989, pp. 115–116. [BibTeX] [PMID ]
BibTeX @inproceedings{Malaviya1989, author = {A. Malaviya and K. Affeld and P. Walker and M. Schartl}, title = {Simulation der Signale des Ultraschallfarbdopplers bei der Strömung durch künstliche Herzklappen}, booktitle = {23. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Kiel, August 31 -- September 2}, journal = {Biomed Tech (Berl)}, year = {1989}, volume = {34 Suppl}, pages = {115--116} }
1989 (03)	Rees, W. ; Schiessler, A. ; Hetzer, R. ; Affeld, K.: Fluidmechanische Untersuchungen einer pulsatilen Herz-Lungen-Maschine. In: 23. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Kiel, August 31 – September 2. Biomed Tech (Berl) Volume 34 Suppl , 1989, pp. 97–98. [BibTeX] [PMID ]
BibTeX @inproceedings{Rees1989, author = {W. Rees and A. Schiessler and R. Hetzer and K. Affeld}, title = {Fluidmechanische Untersuchungen einer pulsatilen Herz-Lungen-Maschine}, booktitle = {23. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Kiel, August 31 -- September 2}, journal = {Biomed Tech (Berl)}, year = {1989}, volume = {34 Suppl}, pages = {97--98} }
1989 (02)	Schichl, K. ; Affeld, K. ; Spiegelberg, A.: Ein rechnergesteuerter Prüfstand für künstliche Herzklappen. In: 23. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Kiel, August 31 – September 2. Biomed Tech (Berl) Volume 34 Suppl , 1989, pp. 95–96. [BibTeX] [PMID ]
BibTeX @inproceedings{Schichl1989, author = {K. Schichl and K. Affeld and A. Spiegelberg}, title = {Ein rechnergesteuerter Prüfstand für künstliche Herzklappen}, booktitle = {23. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Kiel, August 31 -- September 2}, journal = {Biomed Tech (Berl)}, year = {1989}, volume = {34 Suppl}, pages = {95--96} }
1989 (01)	Walker, P. ; Affeld, K. ; Schichl, K.: Bildverarbeitung bei der Strömung durch künstliche Herzklappen. In: 23. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Kiel, August 31 – September 2. Biomed Tech (Berl) Volume 34 Suppl , 1989, pp. 113–114. [BibTeX] [PMID ]
BibTeX @inproceedings{Walker1989, author = {P. Walker and K. Affeld and K. Schichl}, title = {Bildverarbeitung bei der Strömung durch künstliche Herzklappen}, booktitle = {23. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Kiel, August 31 -- September 2}, journal = {Biomed Tech (Berl)}, year = {1989}, volume = {34 Suppl}, pages = {113--114} }

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