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Jahr	Titel
2013 (01)	Goubergrits, L. ; Schaller, J. ; Kertzscher, U. ; Petz, C. ; Hege, H.-C. ; Spuler, A.: Reproducibility of Image-Based Analysis of Cerebral Aneurysm Geometry and Hemodynamics: An In-Vitro Study of Magnetic Resonance Imaging, Computed Tomography and 3D Rotational Angiography. In: Journal of Neurological Surgery - Part A accepted (2013) [Zusammenfassung] [BibTeX]
Zusammenfassung Background and study aims: Image-based computational fluid dynamics (CFD) provides a means for analysis of biofluidmechanical parameters of cerebral aneurysms. This may enable patient-specific rupture risk analysis and facilitate treatment decisions. Application of different imaging methods may, however, alter the geometrical basis of these studies. The present study compares geometry and hemodynamics of an aneurysm phantom model acquired by means of magnetic resonance imaging (MRI), computed tomography (CT) and rotational angiography (3DRA). Materials and methods: The phantom model of a basilaris artery aneurysm was fabricated based on data generated by CT angiography. This model underwent imaging by means of CT, MRI, and 3DRA. We compared the geometrical reconstructions using the original dataset with those obtained from CT, MRI, and 3DRA. Similarly, CFD analyses were performed using the four reconstructions (3DRA, MRI, CT, and original dataset). Results: MRI and the 3DRA based reconstructions yield mean reconstruction errors of 0.097 mm and 0.1 mm which are by a factor of 2.5 better than the CT reconstruction. The maximal error for the aneurysm radius (7.11 mm) measurement was found in the 3DRA reconstruction and was 3.8% (0.28 mm). A comparison of calculated time-averaged wall shear stress (WSS) shows good correlations for the entire surface and separately for the surface of the aneurysmal sack. The maximal error of 8% of the mean WSS calculation of the whole surface was found for the CT reconstruction. The calculations of the aneurysmal sack mean WSS from the MRI reconstruction were estimated to have a maximal error of 7%. Conclusion: All three imaging techniques (CT, MRI, 3DRA) reproduce adequately aneurysm geometry and allow meaningful CFD analyses.
BibTeX @article{Goubergrits2013, author = {L. Goubergrits and J. Schaller and U. Kertzscher and Ch. Petz and H.-Ch. Hege and A. Spuler}, title = {Reproducibility of Image-Based Analysis of Cerebral Aneurysm Geometry and Hemodynamics: An In-Vitro Study of Magnetic Resonance Imaging, Computed Tomography and 3D Rotational Angiography}, journal = {Journal of Neurological Surgery - Part A}, year = {2013}, volume = {accepted} }
2012 (09)	Hildebrandt, T. ; Heppt, W. ; Kertzscher, U. ; Goubergrits, L.: The concept of rhino-respiratory homeostasis – a new approach to nasal breathing. In: Facial Plastic Surgery (2012 accepted) [Zusammenfassung] [BibTeX]
Zusammenfassung The suggested concept of Rhino-Respiratory Homeostasis is a new theoretical model for the discussion of physiological and physical principles of nasal breathing. This model is based on a comprehensive view of nasal functions that takes comparative animal physiology into account. Consequently, it has a universal cross-species character and emphasises the central role of nasal secretion. In contrast to the established view, the focus is transferred from the inspired air to the nasal wall. This concept considers the parietal effect of airflow represented by wall shear stress with special regard to the epithelial lining fluid. It delivers one possible mechanism of an inherent triggering of the nasal cycle. Furthermore, the issue of biological fluid-structure-interaction is introduced. The paper presents a rethinking of nasal breathing which was inspired by clinical experience and results of flow field investigations through CFD (Computational Fluid Dynamics).
BibTeX @article{Hildebrandt2012a, author = {T. Hildebrandt and W. Heppt and U. Kertzscher and L. Goubergrits}, title = {The concept of rhino-respiratory homeostasis -- a new approach to nasal breathing}, journal = {Facial Plastic Surgery}, year = {2012 accepted} }
2012 (08)	Hildebrandt, T. ; Goubergrits, L. ; Heppt, W. ; Bessler, S. ; Zachow, S.: Evaluation of the intranasal flow field through computational fluid dynamics (CFD). In: Facial Plastic Surgery (2012 accepted) [Zusammenfassung] [BibTeX]
Zusammenfassung A reliable and comprehensive assessment of nasal breathing is problematic and still a common issue in rhinosurgery. Impairments of nasal breathing need an objective approach. In this regard, currently rhinomanometry is the only standard diagnostic tool available and with various limitations. However, in the last decade Computational Fluid Dynamics (CFD) has become a promising method in facing the challenge of qualifying nasal breathing. The paper presents the CFD employment on a symptom-free subject and a symptomatic patient. Thereby, certain flow field features and changes before and after surgery were investigated. Moreover, the study outlines suggestions for concrete rhinological CFD applications.
BibTeX @article{Hildebrandt2012, author = {T. Hildebrandt and L. Goubergrits and W. Heppt and S. Bessler and S. Zachow}, title = {Evaluation of the intranasal flow field through computational fluid dynamics (CFD)}, journal = {Facial Plastic Surgery}, year = {2012 accepted} }
2012 (07)	Affeld, K. ; Goubergrits, L. ; Watanabe, N. ; Kertzscher, U.: Platelet Deposition to Collagen-Coated Surface at Low Shear Rates – Experimental Results and a Numerical Monte Carlo Model. In: Journal of Biomechanics (2012 accepted) [BibTeX]
BibTeX @article{Affeld2012a, author = {Klaus Affeld and Leonid Goubergrits and Nobuo Watanabe and Ulrich Kertzscher}, title = {Platelet Deposition to Collagen-Coated Surface at Low Shear Rates -- Experimental Results and a Numerical Monte Carlo Model}, journal = {Journal of Biomechanics}, year = {2012 accepted} }
2012 (06)	Kertzscher, U. ; Schneider, T. ; Goubergrits, L. ; Affeld, K. ; Hänggi, D. ; Spuler, A.: In vitro study of cerebrospinal fluid dynamics in a shaken basal cistern after experimental subarachnoid hemorrhage. In: PLoS ONE 7 (2012), Nr. 8, S. e41677 [Zusammenfassung] [BibTeX] [DOI ]
Zusammenfassung Introduction: Cerebral arterial vasospasm leads to delayed cerebral ischemia and constitutes the major delayed complication following aneurysmal subarachnoid hemorrhage. Cerebral vasospasm can be reduced by increased blood clearance from the subarachnoid space. Clinical pilot studies allow the hypothesis that the clearance of subarachnoid blood is facilitated by means of head shaking. A major obstacle for meaningful clinical studies is the lack of data on appropriate parameters of head shaking. Our in vitro study aims to provide these essential parameters. Materials and methods: A model of the basal cerebral cistern was derived from human magnetic resonance imaging data. Subarachnoid hemorrhage was simulated by addition of dyed experimental blood to transparent experimental cerebrospinal fluid (CSF) filling the model of the basal cerebral cistern. Effects of various head positions and head motion settings (shaking angle amplitudes and shaking frequencies) on blood clearance were investigated using the quantitative dye washout method. Results and discussion: Blood washout can be divided into two phases: Blood/CSF mixing and clearance. The major effect of shaking consists in better mixing of blood and CSF thereby increasing clearance rate. Without shaking, blood/CSF mixing and blood clearance in the basal cerebral cistern are hampered by differences in density and viscosity of blood and CSF. Blood clearance increases with decreased shaking frequency and with increased shaking angle amplitude. Head shaking facilitates clearance by varying the direction of gravitational force. Conclusion: From this in vitro study can be inferred that patient or head shaking with large shaking angles at low frequency is a promising therapeutic strategy to increase blood clearance from the subarachnoid space.
BibTeX @article{Kertzscher2012, author = {U. Kertzscher and T. Schneider and L. Goubergrits and K. Affeld and D. Hänggi and A. Spuler}, title = {In vitro study of cerebrospinal fluid dynamics in a shaken basal cistern after experimental subarachnoid hemorrhage}, journal = {PLoS ONE}, year = {2012}, volume = {7}, number = {8}, pages = {e41677}, doi = {http://dx.doi.org/10.1371/journal.pone.0041677} }
2012 (05)	Affeld, K. ; Grosshauser, J. ; Goubergrits, L. ; Kertzscher, U.: Percutaneous devices: a review of applications, problems and possible solutions. In: Expert Review of Medical Devices 9 (2012), Nr. 4, S. 389–399 [Zusammenfassung] [BibTeX]
Zusammenfassung Percutaneous devices enable the transfer of mass, energy and forces through the skin. There is a wide clinical need for this which is not likely to disappear. Emerging new artificial organs, such as wearable kidneys or lungs, will increase the demand. Any application lasting longer than days or weeks is endangered by infections entering the body via the exit site. A care-free solution has been found solely for an exit site placed on the skull where it can be securely immobilized. For the majority of the locations on the abdomen or chest, no solution for an infection-free device has been found. A solution may be possible with a better understanding of the physiology of the keratinocytes as a barrier for microbes.
BibTeX @article{Affeld2012, author = {Klaus Affeld and Johannes Grosshauser and Leonid Goubergrits and Ulrich Kertzscher}, title = {Percutaneous devices: a review of applications, problems and possible solutions}, journal = {Expert Review of Medical Devices}, year = {2012}, volume = {9}, number = {4}, pages = {389--399} }
2012 (04)	Berthe, A. ; Gärtlein, S. ; Lederer, C. ; Kertzscher, U. ; Affeld, K. ; Goubergrits, L.: Flow field of a novel implantable valveless counterpulsation heart assist device. In: Annals of Biomedical Engineering 40 (2012), Nr. 9, S. 1982–1995 [Zusammenfassung] [BibTeX] [DOI ]
Zusammenfassung Flow fields are one of the key factors associated with the life threatening formation of thrombi in artificial organs. Therefore, knowledge of flow field is crucial for the design and optimization of a long-term blood pump performance. The blood chamber flow of a novel counterpulsation heart assist device (CPD) has been investigated using laser doppler velocimetry (LDV), particle image velocimetry (PIV) and near-wall PIV (wall-PIV). The wall-PIV is an in-house developed technique assessing wall shear rates (WSR). These experimental techniques analyzed complex transient three-dimensional (3D) flow fields including major and secondary structures during the whole CPD cycle (ejection, filling and hold time). PIV measurements in the central plane investigated an evolution (development and destruction) of the blood chamber fully filling vortex as the major CPD flow structure. The wall-PIV measurements identified areas of blood stagnation (vortex center and jet impingements) and quantified WSR at the front housing. Maximal mean WSR of 2045+605s-1 were found at the end of the filling. The LDV, which identified helical flow structure at the outer region of the pump, was used to complete 3D flow analysis and to combine PIV and wall-PIV results. The results suggest good washing behavior of the CPD regarding thrombus formation.
BibTeX @article{Berthe2012, author = {A. Berthe and S. Gärtlein and Ch. Lederer and U. Kertzscher and K. Affeld and L. Goubergrits}, title = {Flow field of a novel implantable valveless counterpulsation heart assist device}, journal = {Annals of Biomedical Engineering}, year = {2012}, volume = {40}, number = {9}, pages = {1982--1995}, doi = {http://dx.doi.org/10.1007/s10439-012-0569-5} }
2012 (03)	Schneider, T. ; Goubergrits, L. ; Paschereit, C. ; Kertzscher, U. ; Affeld, K.: Spannungsoptik-Tomographie zur Messung der Scherung in Strömungen. In: tm - Technisches Messen 79 (2012), Nr. 6, S. 304–309 [BibTeX]
BibTeX @article{Schneider2012, author = {Schneider, T. and Goubergrits, L. and Paschereit, C.O. and Kertzscher, U. and Affeld, K.}, title = {Spannungsoptik-Tomographie zur Messung der Scherung in Strömungen}, journal = {tm - Technisches Messen}, year = {2012}, volume = {79}, number = {6}, pages = {304--309} }
2012 (02)	Goubergrits, L. ; Schaller, J. ; Kertzscher, U. ; van den Bruck, N. ; Poethkow, K. ; Petz, C. ; Hege, H.-C. ; Spuler, A.: Statistical wall shear stress maps of ruptured and unruptured middle cerebral artery aneurysms.. In: J R Soc Interface 9 (2012), Nr. 69, S. 677–688 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung Haemodynamics and morphology play an important role in the genesis, growth and rupture of cerebral aneurysms. The goal of this study was to generate and analyse statistical wall shear stress (WSS) distributions and shapes in middle cerebral artery (MCA) saccular aneurysms. Unsteady flow was simulated in seven ruptured and 15 unruptured MCA aneurysms. In order to compare these results, all geometries must be brought in a uniform coordinate system. For this, aneurysms with corresponding WSS data were transformed into a uniform spherical shape; then, all geometries were uniformly aligned in three-dimensional space. Subsequently, we compared statistical WSS maps and surfaces of ruptured and unruptured aneurysms. No significant (p > 0.05) differences exist between ruptured and unruptured aneurysms regarding radius and mean WSS. In unruptured aneurysms, statistical WSS map relates regions with high (greater than 3 Pa) WSS to the neck region. In ruptured aneurysms, additional areas with high WSS contiguous to regions of low (less than 1 Pa) WSS are found in the dome region. In ruptured aneurysms, we found significantly lower WSS. The averaged aneurysm surface of unruptured aneurysms is round shaped, whereas the averaged surface of ruptured cases is multi-lobular. Our results confirm the hypothesis of low WSS and irregular shape as the essential rupture risk parameters.
BibTeX @article{Goubergrits2012, author = {Goubergrits, L. and Schaller, J. and Kertzscher, U. and van den Bruck, N. and Poethkow, K. and Petz, Ch and Hege, H-Ch and Spuler, A.}, title = {Statistical wall shear stress maps of ruptured and unruptured middle cerebral artery aneurysms}, journal = {J R Soc Interface}, year = {2012}, volume = {9}, number = {69}, pages = {677--688}, doi = {http://dx.doi.org/10.1098/rsif.2011.0490}, pmid = {21957117} }
2012 (01)	Timmel, T. ; Seshadri, S. ; Goubergrits, L. ; Affeld, K. ; Kertzscher, U.: Tri-leaflet valve design with a purge flow for heart-assist devices: an in vitro optimization study.. In: Artif Organs 36 (2012), Nr. 1, S. 42–48 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung The objective of this study is to assess the effect of a purge flow on valves of pulsatile heart-assist devices. Clinical applications of these devices are still limited because of frequent thromboembolic complications. These complications often originate at the valves and the unavoidable flow separation regions that are found behind the leaflets. The flow separations cause a long residence time of blood that is considered particularly detrimental. To solve this problem, a valve with a purge flow is proposed. A purge flow is a jet, which is separated from the main blood flow and directed behind the leaflets into the sinus to flush it. Even though the purge flow does not prevent a flow separation, it shortens the residence time of the blood in the sinus. Thus, the purge flow improves the periodic washout of the blood in the region of flow separation. The complex purge flow was investigated in a tri-leaflet valve. The geometrical parameters of the valve were varied systematically. A statistical technique--the Taguchi method--was used to reduce the number of investigated models to 12. The flows through the resulting valve models were numerically simulated and analyzed. The evaluated models with the best results were subsequently investigated experimentally using different methods: hemodynamic tests in a valve tester and flow visualization using the dye washout method. It was shown that the purge flow can effectively wash out the sinus. Therefore, the purge flow valve reduces the potential of a thrombus formation normally associated with the valve.
BibTeX @article{Timmel2012, author = {Timmel, Tobias and Seshadri, Santhosh and Goubergrits, Leonid and Affeld, Klaus and Kertzscher, Ulrich}, title = {Tri-leaflet valve design with a purge flow for heart-assist devices: an in vitro optimization study.}, journal = {Artif Organs}, year = {2012}, volume = {36}, number = {1}, pages = {42--48}, doi = {http://dx.doi.org/10.1111/j.1525-1594.2011.01308.x}, pmid = {21955182} }
2011 (05)	Schirrmann, K. ; Mertens, M. ; Kertzscher, U. ; Affeld, K. ; Kuebler, W.M.: Cell Physiology and Fluid Mechanics in the Pulmonary Alveolus and its Capillaries. In: Fundamental Medical and Engineering Investigations on Protective Artificial Respiration. A Collection of Papers from the DFG funded Research Program PAR 116 (2011), S. 49–65 [BibTeX]
BibTeX @inbook{PAR2011, author = {Kerstin Schirrmann and Michael Mertens and Ulrich Kertzscher and Klaus Affeld and Wolfgang M. Kuebler}, title = {Cell Physiology and Fluid Mechanics in the Pulmonary Alveolus and its Capillaries}, booktitle = {Fundamental Medical and Engineering Investigations on Protective Artificial Respiration. A Collection of Papers from the DFG funded Research Program PAR}, publisher = {Springer Verlag Berlin Heidelberg}, year = {2011}, volume = {116}, pages = {49--65} }
2011 (04)	Watanabe, N. ; Affeld, K. ; Schaller, J. ; Schmitmeier, S. ; Reininger, A.J. ; Goubergrits, L. ; Kertzscher, U.: Investigation of human platelet adhesion under low shear conditions in a rotational flow chamber. In: Journal of Biorheology 25 (2011), S. 64–70 [Zusammenfassung] [BibTeX] [DOI ]
Zusammenfassung Even though blood pumps became into the clinical usage, thrombo-embolic complications still pose a major problem and their process has been not yet clarified and quantified. However, it is known that the basis of thrombus formation is platelet adhesion, which is supposed to be tightly associated with the shear rate. Therefore, our current interest focuses on the effect of the shear condition on platelet adhesion. We have designed and fabricated an experimental setup allowing a fluorescent microscopy of whole blood within a rotational viscometer under the controllable shear condition. A small area of the bottom plate was coated with collagen type-I, which provides a model of the injured vessel as a target for platelets to adhere. Using this setup, the time course of platelet adhesion under several different shear rates, ranging between 127 and 723s-1, was studied. Platelets adhesion increased along with shear rates up to 283s-1, followed by its gradual decrease when the shear rate exceeded above 346s-1. The adhesion amounts were statistically significant between 283 and 173 (p=0.02), 173 and 127 (p=0.035), and 283 and 503s-1 (p=0.03), respectively. This result suggests that there is an optimal shear condition around 300s-1 for platelet adhesion to collagen type-I.
BibTeX @article{Watanabe2011, author = {Nobuo Watanabe and Klaus Affeld and Jens Schaller and Stephanie Schmitmeier and Armin J. Reininger and Leonid Goubergrits and Ulrich Kertzscher}, title = {Investigation of human platelet adhesion under low shear conditions in a rotational flow chamber}, journal = {Journal of Biorheology}, year = {2011}, volume = {25}, pages = {64--70}, doi = {http://dx.doi.org/10.1007/s12573-011-0039-y} }
2011 (03)	Affeld, K. ; Grosshauser, J. ; Reiter, K. ; Grosse-Siestrup, C. ; Kertzscher, U.: How can we achieve infection-resistant percutaneous energy transfer?. In: Artif Organs 35 (2011), Nr. 8, S. 800–806 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung Clinical records show ever increasing functional times of rotary blood pumps implanted in patients. With longer functional time, the problem of driveline infection is becoming more urgent. No material or scaffold has been found, which allows a permanent and stable ingrowth of skin cells that would prevent (pathogenic) germs entering the body. Usually, the epithelial cells die at the exit site and new cells form a sulcus around the driveline, which grows deeper and finally becomes infected. The purpose of this project is to present a solution to this problem by elaborating a new mechanism, the active skin-penetrating device. The device is composed of a tube with a 5-mm diameter, a protective sleeve that surrounds the catheter exit site, and an active traction device. The protective sleeve is made of thin polyurethane covered with polyethylenterephtalat (PET, i.e. Dacron) fibers to permit the attachment of keratinocytes, similar to the standard driveline. The active traction device exerts a constant pull on the protective sleeve. The ingrown keratinocytes slowly give way and the protective sleeve gradually moves out of the body at a rate of a few millimeters per week. Meanwhile, the keratinocytes transform into horny cells and are then shed as in natural skin. Therefore, the formation of a sulcus is avoided, and the protective sleeve remains infection-free. In a first proof of the concept, four of the new devices and 10 control devices were implanted in goats. The devices remained infection-free for a period of 420 days, whereas four of the 10 control devices became infected. On the basis of these experiments, the active skin-penetrating device has been further developed and is being tested again in goats in a refined version. The results so far indicate that with the active-skin penetrating device an infection-resistant percutaneous energy transfer can be achieved for a prolonged period of time.
BibTeX @article{Affeld2011, author = {Affeld, Klaus and Grosshauser, Johannes and Reiter, Katja and Grosse-Siestrup, Christian and Kertzscher, Ulrich}, title = {How can we achieve infection-resistant percutaneous energy transfer?}, journal = {Artif Organs}, year = {2011}, volume = {35}, number = {8}, pages = {800--806}, doi = {http://dx.doi.org/10.1111/j.1525-1594.2011.01329.x}, pmid = {21843295} }
2011 (02)	Giridharan, G.A. ; Lederer, C. ; Berthe, A. ; Goubergrits, L. ; Hutzenlaub, J. ; Slaughter, M.S. ; Dowling, R.D. ; Spence, P.A. ; Koenig, S.C.: Flow dynamics of a novel counterpulsation device characterized by CFD and PIV modeling. In: Med Eng Phys 33 (2011), Nr. 10, S. 1193–1202 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung BACKGROUND: Historically, single port valveless pneumatic blood pumps have had a high incidence of thrombus formation due to areas of blood stagnation and hemolysis due to areas of high shear stress. METHODS: To ensure minimal hemolysis and favorable blood washing characteristics, particle image velocimetry (PIV) and computational fluid dynamics (CFD) were used to evaluate the design of a new single port, valveless counterpulsation device (Symphony). The Symphony design was tested in 6-h acute (n=8), 5-day (n=8) and 30-day (n=2) chronic experiments in a calf model (Jersey, 76kg). Venous blood samples were collected during acute (hourly) and chronic (weekly) time courses to analyze for temporal changes in biochemical markers and quantify plasma free hemoglobin. At the end of the study, animals were euthanized and the Symphony and end-organs (brain, liver, kidney, lungs, heart, and spleen) were examined for thrombus formations. RESULTS: Both the PIV and the CFD showed the development of a strong moving vortex during filling phase and that blood exited the Symphony uniformly from all areas during ejection phase. The laminar shear stresses estimated by CFD remained well below the hemolysis threshold of 400Pa inside the Symphony throughout filling and ejection phases. No areas of persistent blood stagnation or flow separation were observed. The maximum plasma free hemoglobin (<10mg/dl), average platelet count (pre-implant=473±56K/µl and post-implant=331±62K/µl), and average hematocrit (pre-implant=31±2% and post-implant=29±2 were normal at all measured time-points for each test animal in acute and chronic experiments. There were no changes in measures of hepatic function (ALP, ALT) or renal function (creatinine) from pre-Symphony implantation values. The necropsy examination showed no signs of thrombus formation in the Symphony or end organs. CONCLUSIONS: These data suggest that the designed Symphony has good washing characteristics without persistent areas of blood stagnation sites during the entire pump cycle, and has a low risk of hemolysis and thrombus formations.
BibTeX @article{Giridharan2011, author = {Giridharan, G. A. and Lederer, C. and Berthe, A. and Goubergrits, L. and Hutzenlaub, J. and Slaughter, M. S. and Dowling, R. D. and Spence, P. A. and Koenig, S. C.}, title = {Flow dynamics of a novel counterpulsation device characterized by CFD and PIV modeling}, journal = {Med Eng Phys}, year = {2011}, volume = {33}, number = {10}, pages = {1193--1202}, doi = {http://dx.doi.org/10.1016/j.medengphy.2011.05.008}, pmid = {21680224} }
2011 (01)	Wellnhofer, E. ; Osman, J. ; Kertzscher, U. ; Affeld, K. ; Fleck, E. ; Goubergrits, L.: Non-dimensional modeling in flow simulation studies of coronary arteries including side-branches: A novel diagnostic tool in coronary artery disease.. In: Atherosclerosis 216 (2011), Nr. 2, S. 277–282 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung Blood flow, vascular shape and size and local remodeling of the vascular wall are linked through wall shear stress (WSS) signaling. Inter-individual comparison of shape and WSS is hampered by large differences in size of flow and shape. We performed non-dimensional modeling to discriminate different types of coronary artery remodeling based on WSS patterns and vessel morphology.Blood flow was simulated in three-dimensional reconstructed right coronary artery trees from seven controls, five patients with coronary artery disease (CAD) and five patients with aneurysmatic CAD (AnCAD) classified by expert visual diagnosis. A discriminant model using low WSS area, a remodeling index, and cross-correlation of WSS in main trunks and complete trees (K) as non-dimensional parameters classified CAD and AnCAD correctly and identified three patients with high risk profile and functional disease in controls. The new model was compared with discriminant analysis of identical cases simulated without side-branches. The inclusion of K (information from side-branches) and replacement of the mean diameter by a non-dimensional remodeling index improved the model. We found significant (p<0.005) gender differences in the remodeling index.The combination of non-dimensional modeling and WSS profiling should be further investigated as a novel diagnostic tool in CAD beyond local stenosis.
BibTeX @article{Wellnhofer2011, author = {Ernst Wellnhofer and Jan Osman and Ulrich Kertzscher and Klaus Affeld and Eckart Fleck and Leonid Goubergrits}, title = {Non-dimensional modeling in flow simulation studies of coronary arteries including side-branches: A novel diagnostic tool in coronary artery disease.}, journal = {Atherosclerosis}, year = {2011}, volume = {216}, number = {2}, pages = {277--282}, doi = {http://dx.doi.org/10.1016/j.atherosclerosis.2010.12.027}, pmid = {21333992} }
2010 (05)	Wellnhofer, E. ; Osman, J. ; Kertzscher, U. ; Affeld, K. ; Fleck, E. ; Goubergrits, L.: Flow simulation studies in coronary arteries – impact of side-branches. In: Atherosclerosis 213 (2010), Nr. 2, S. 475–481 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung AIMS: Wall shear stress (WSS) may induce local remodeling of the vascular wall and the WSS pattern in turn depends on vascular geometry. We aimed to elucidate the impact of side-branches on local WSS. METHODS AND RESULTS: Steady numerical flow simulation studies were performed in three-dimensional reconstructed right coronary artery (RCA) trees. RCA from seven controls, five patients with coronary artery disease (CAD) and five patients with aneurysmatic CAD (AnCAD) classified by expert visual diagnosis were studied. Then three transient flow simulations were performed with cases representative for each group in order to evaluate the impact of pulsatile flow simulation. As vascular size and flow rates vary considerably between patients, non-dimensional approaches were applied for group comparison. A point-to-point comparison of the WSS in the same tree with and without side-branches revealed local differences in WSS of up to 12.0Pa. This was caused by a reduction of volume flow of up to 78.7% in the trunk. Differences are not only limited to bifurcation sites but also affect local narrowings and strongly curved segments. The point-to-point comparison of steady and transient simulations found an average increase of WSS of below 7% in transient simulations. No significant differences were found between histograms of pulsatile and steady simulations, showing a high cross-correlation of >0.97. CONCLUSION: Side-branches must not be neglected in numerical flow simulation (steady and transient) studies. Steady simulations are valid for an assessment of time-averaged WSS distributions.
BibTeX @article{Wellnhofer2010, author = {Ernst Wellnhofer and Jan Osman and Ulrich Kertzscher and Klaus Affeld and Eckart Fleck and Leonid Goubergrits}, title = {Flow simulation studies in coronary arteries -- impact of side-branches}, journal = {Atherosclerosis}, year = {2010}, volume = {213}, number = {2}, pages = {475--481}, doi = {http://dx.doi.org/10.1016/j.atherosclerosis.2010.09.007}, pmid = {20934704} }
2010 (04)	Hoehme, S. ; Brulport, M. ; Bauer, A. ; Bedawy, E. ; Schormann, W. ; Hermes, M. ; Puppe, V. ; Gebhardt, R. ; Zellmer, S. ; Schwarz, M. ; Bockamp, E. ; Timmel, T. ; Hengstler, J.G. ; Drasdo, D.: Prediction and validation of cell alignment along microvessels as order principle to restore tissue architecture in liver regeneration. In: Proc Natl Acad Sci USA 107 (2010), Nr. 23, S. 10371–10376 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung Only little is known about how cells coordinately behave to establish functional tissue structure and restore microarchitecture during regeneration. Research in this field is hampered by a lack of techniques that allow quantification of tissue architecture and its development. To bridge this gap, we have established a procedure based on confocal laser scans, image processing, and three-dimensional tissue reconstruction, as well as quantitative mathematical modeling. As a proof of principle, we reconstructed and modeled liver regeneration in mice after damage by CCl(4), a prototypical inducer of pericentral liver damage. We have chosen the regenerating liver as an example because of the tight link between liver architecture and function: the complex microarchitecture formed by hepatocytes and microvessels, i.e. sinusoids, ensures optimal exchange of metabolites between blood and hepatocytes. Our model captures all hepatocytes and sinusoids of a liver lobule during a 16 days regeneration process. The model unambiguously predicted a so-far unrecognized mechanism as essential for liver regeneration, whereby daughter hepatocytes align along the orientation of the closest sinusoid, a process which we named "hepatocyte-sinusoid alignment" (HSA). The simulated tissue architecture was only in agreement with the experimentally obtained data when HSA was included into the model and, moreover, no other likely mechanism could replace it. In order to experimentally validate the model of prediction of HSA, we analyzed the three-dimensional orientation of daughter hepatocytes in relation to the sinusoids. The results of this analysis clearly confirmed the model prediction. We believe our procedure is widely applicable in the systems biology of tissues.
BibTeX @article{Hoehme2010, author = {Stefan Hoehme and Marc Brulport and Alexander Bauer and Essam Bedawy and Wiebke Schormann and Matthias Hermes and Verena Puppe and Rolf Gebhardt and Sebastian Zellmer and Michael Schwarz and Ernesto Bockamp and Tobias Timmel and Jan G Hengstler and Dirk Drasdo}, title = {Prediction and validation of cell alignment along microvessels as order principle to restore tissue architecture in liver regeneration}, journal = {Proc Natl Acad Sci USA}, year = {2010}, volume = {107}, number = {23}, pages = {10371--10376}, doi = {http://dx.doi.org/10.1073/pnas.0909374107}, pmid = {20484673} }
2010 (03)	Goubergrits, L. ; Thamsen, B. ; Berthe, A. ; Poethke, J. ; Kertzscher, U. ; Affeld, K. ; Petz, C. ; Hege, H.-C. ; Hoch, H. ; Spuler, A.: In Vitro Study of Near-Wall Flow in a Cerebral Aneurysm Model with and without Coils.. In: AJNR Am J Neuroradiol 31 (2010), Nr. 8, S. 1521–1528 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung BACKGROUND AND PURPOSE: Coil embolization procedures change the flow conditions in the cerebral aneurysm and, therefore, in the near-wall region. Knowledge of these flow changes may be helpful to optimize therapy. The goal of this study was to investigate the effect of the coil-packing attenuation on the near-wall flow and its variability due to differences in the coil structure. MATERIALS AND METHODS: An enlarged transparent model of an ACA aneurysm was fabricated on the basis of CT angiography. The near-wall flow was visualized by using a recently proposed technique called Wall-PIV. Coil-packing attenuation of 10 15 and 20% were investigated and compared with an aneurysmal flow without coils. Then the flow variability due to the coil introduction was analyzed in 10 experiments by using a packing attenuation of 15 RESULTS: A small packing attenuation of 10% already alters the near-wall flow significantly in a large part of the aneurysmal sac. These flow changes are characterized by a slow flow with short (interrupted) path lines. An increased packing attenuation expands the wall area exposed to the altered flow conditions. This area, however, depends on the coil position and/or on the 3D coil structure in the aneurysm. CONCLUSIONS: To our knowledge, this is the first time the near-wall flow changes caused by coils in an aneurysm model have been visualized. It can be concluded that future hydrodynamic studies of coil therapy should include an investigation of the coil structure in addition to the coil-packing attenuation.
BibTeX @article{Goubergrits2010a, author = {L. Goubergrits and B. Thamsen and A. Berthe and J. Poethke and U. Kertzscher and K. Affeld and C. Petz and H-C. Hege and H. Hoch and A. Spuler}, title = {In Vitro Study of Near-Wall Flow in a Cerebral Aneurysm Model with and without Coils.}, journal = {AJNR Am J Neuroradiol}, year = {2010}, volume = {31}, number = {8}, pages = {1521--1528}, doi = {http://dx.doi.org/10.3174/ajnr.A2121}, pmid = {20488901} }
2010 (02)	Berthe, A. ; Kondermann, D. ; Christensen, C. ; Goubergrits, L. ; Garbe, C. ; Affeld, K. ; Kertzscher, U.: Three-dimensional, three-component wall-PIV. In: Experiments in Fluids 48 (2010), Nr. 6, S. 983–997 [Zusammenfassung] [BibTeX] [DOI ]
Zusammenfassung This paper describes a new time-resolved three-dimensional, three-component (3D-3C) measurement technique called wall-PIV. It was developed to assess near wall flow fields and shear rates near non-planar surfaces. The method is based on light absorption according to Beer?Lambert?s law. The fluid containing a molecular dye and seeded with buoyant particles is illuminated by a monochromatic, diffuse light. Due to the dye, the depth of view is limited to the near wall layer. The three-dimensional particle positions can be reconstructed by the intensities of the particle?s projection on an image sensor. The flow estimation is performed by a new algorithm, based on learned particle trajectories. Possible sources of measurement errors related to the wall-PIV technique are analyzed. The accuracy analysis was based on single particle experiments and a three-dimensional artificial data set simulating a rotating sphere.
BibTeX @article{Berthe2010, author = {André Berthe and Daniel Kondermann and Carolyn Christensen and Leonid Goubergrits and Christoph Garbe and Klaus Affeld and Ulrich Kertzscher}, title = {Three-dimensional, three-component wall-PIV}, journal = {Experiments in Fluids}, year = {2010}, volume = {48}, number = {6}, pages = {983--997}, doi = {http://dx.doi.org/10.1007/s00348-009-0777-4} }
2010 (01)	Schirrmann, K. ; Mertens, M. ; Kertzscher, U. ; Kuebler, W.M. ; Affeld, K.: Theoretical modeling of the interaction between alveoli during inflation and deflation in normal and diseased lungs. In: J Biomech 43 (2010), Nr. 6, S. 1202–1207 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung Alveolar recruitment is a central strategy in the ventilation of patients with acute lung injury and other lung diseases associated with alveolar collapse and atelectasis. However, biomechanical insights into the opening and collapse of individual alveoli are still limited. A better understanding of alveolar recruitment and the interaction between alveoli in intact and injured lungs is of crucial relevance for the evaluation of the potential efficacy of ventilation strategies. We simulated human alveolar biomechanics in normal and injured lungs. We used a basic simulation model for the biomechanical behavior of virtual single alveoli to compute parameterized pressure-volume curves. Based on these curves, we analyzed the interaction and stability in a system composed of two alveoli. We introduced different values for surface tension and tissue properties to simulate different forms of lung injury. The data obtained predict that alveoli with identical properties can coexist with both different volumes and with equal volumes depending on the pressure. Alveoli in injured lungs with increased surface tension will collapse at normal breathing pressures. However, recruitment maneuvers and positive endexpiratory pressure can stabilize those alveoli, but coexisting unaffected alveoli might be overdistended. In injured alveoli with reduced compliance collapse is less likely, alveoli are expected to remain open, but with a smaller volume. Expanding them to normal size would overdistend coexisting unaffected alveoli. The present simulation model yields novel insights into the interaction between alveoli and may thus increase our understanding of the prospects of recruitment maneuvers in different forms of lung injury.
BibTeX @article{Schirrmann2009, author = {Kerstin Schirrmann and Michael Mertens and Ulrich Kertzscher and Wolfgang M Kuebler and Klaus Affeld}, title = {Theoretical modeling of the interaction between alveoli during inflation and deflation in normal and diseased lungs}, journal = {J Biomech}, year = {2010}, volume = {43}, number = {6}, pages = {1202--1207}, doi = {http://dx.doi.org/10.1016/j.jbiomech.2009.11.025}, pmid = {20031137} }
2009 (05)	Mertens, M. ; Tabuchi, A. ; Meissner, S. ; Krueger, A. ; Schirrmann, K. ; Kertzscher, U. ; Pries, A.R. ; Slutsky, A.S. ; Koch, E. ; Kuebler, W.M.: Alveolar dynamics in acute lung injury: heterogeneous distension rather than cyclic opening and collapse. In: Crit Care Med 37 (2009), Nr. 9, S. 2604–2611 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung OBJECTIVES:: To analyze alveolar dynamics in healthy and acid-injured lungs of ventilated mice. Protective ventilation is potentially lifesaving in patients with acute lung injury. However, optimization of ventilation strategies is hampered by an incomplete understanding of the effects of mechanical ventilation at the alveolar level. DESIGN:: In anesthetized and ventilated Balb/c mice, subpleural alveoli were visualized by darkfield intravital microscopy and optical coherence tomography. SETTING:: Animal research laboratory. SUBJECTS:: Male Balb/c mice. INTERVENTIONS:: Lung injury was induced by intratracheal instillation of hydrochloric acid. In control animals and mice with lung injury, ventilation pressures were varied between 0 and 24 cm H2O at baseline, 60 mins, and 120 mins, and alveolar distension and cyclic opening and collapse of alveolar clusters were analyzed. MEASUREMENTS AND MAIN RESULTS:: In normal lungs, alveolar clusters distend with increasing ventilation pressure in a sigmoid relationship. Although an increase in ventilation pressure from 0 to 24 cm H2O increases alveolar size by 41.5 +/- 2.3% in normal lungs, alveolar distension is reduced to 20.6 +/- 2.2% 120 mins after induction of lung injury by acid aspiration. Cyclic opening and collapse of alveolar clusters are neither observed in normal nor acid-injured lungs. Alveolar compliance is highest in small and distensible alveolar clusters, which are also most prone to acid-induced injury. CONCLUSIONS:: Over the applied pressure range, volume changes in control and acid-injured mouse lungs result predominantly from alveolar distension rather than cyclic opening and collapse of alveolar clusters. Preferential loss of compliance in small alveolar clusters redistributes tidal volume to larger alveoli, which increases spatial heterogeneity in alveolar inflation and may promote alveolar overdistension.
BibTeX @article{Mertens2009, author = {Michael Mertens and Arata Tabuchi and Sven Meissner and Alexander Krueger and Kerstin Schirrmann and Ulrich Kertzscher and Axel R Pries and Arthur S Slutsky and Edmund Koch and Wolfgang M Kuebler}, title = {Alveolar dynamics in acute lung injury: heterogeneous distension rather than cyclic opening and collapse}, journal = {Crit Care Med}, year = {2009}, volume = {37}, number = {9}, pages = {2604--2611}, doi = {http://dx.doi.org/10.1097/CCM.0b013e3181a5544d}, pmid = {19623041} }
2009 (04)	Goubergrits, L. ; Weber, S. ; Petz, C. ; Hege, H.-C. ; Spuler, A. ; Poethke, J. ; Berthe, A. ; Kertzscher, U.: Wall-PIV as a near wall flow validation tool for CFD: application in a pathologic vessel enlargement (aneurysm). In: J Vis 12 (2009), Nr. 3, S. 241–250 [BibTeX]
BibTeX @article{Goubergrits2009c, author = {Goubergrits, L. and Weber, S. and Petz, Ch. and Hege, H-Ch. and Spuler, A. and Poethke, J. and Berthe, A. and Kertzscher, U.}, title = {Wall-PIV as a near wall flow validation tool for CFD: application in a pathologic vessel enlargement (aneurysm)}, journal = {J Vis}, publisher = {IOS Press}, year = {2009}, volume = {12}, number = {3}, pages = {241--250} }
2009 (03)	Berthe, A. ; Kondermann, D. ; Garbe, C. ; Affeld, K. ; Jähne, B. ; Kertzscher, U.: The wall-PIV measurement technique for near wall flow fields in biofluid mechanics. In: Imaging Measurement Methods for Flow Analysis 106/2009 (2009), S. 11–20 [Zusammenfassung] [BibTeX] [DOI ]
Zusammenfassung This chapter describes the development of a new time resolved 3D PIV technique for near wall flow field measurements. This measurement technique, called wall-PIV, is based on Beer-Lambert?s law. It substitutes the classical PIV laser sheet by a diffuse, monochromatic full-field illumination that is limited to the near wall region by an absorbing molecular dye in the fluid. Aimed range of applications is the investigation of flow fields next to one- or two dimensionally curved, possibly flexing surfaces. The three dimensional three component flow estimation uses a new optical flow algorithm, based on particle trajectories. Results of the measurement technique?s application on a displacement pediatric blood pump are presented.
BibTeX @incollection{Berthe2009, author = {A. Berthe and D. Kondermann and Ch. Garbe and K. Affeld and B. Jähne and U. Kertzscher}, title = {The wall-PIV measurement technique for near wall flow fields in biofluid mechanics}, booktitle = {Imaging Measurement Methods for Flow Analysis}, publisher = {Springer Berlin / Heidelberg}, year = {2009}, volume = {106/2009}, pages = {11--20}, doi = {http://dx.doi.org/10.1007/978-3-642-01106-1_2} }
2009 (02)	Goubergrits, L. ; Wellnhofer, E. ; Kertzscher, U. ; Affeld, K. ; Petz, C. ; Hege, H.-C.: Coronary artery WSS profiling using a geometry reconstruction based on biplane angiography. In: Ann Biomed Eng 37 (2009), Nr. 4, S. 682–691 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung Computational fluid dynamics (CFD) methods based on three-dimensional (3D) vessel reconstructions have recently been shown to provide prognostically relevant hemodynamic data. However, the geometry reconstruction and the assessment of clinically relevant hemodynamic parameters may depend on the used imaging modality. In this study, the silicon model of the left coronary artery (LCA) was acquired with a biplane angiography. The geometry reconstruction was done using commercial CAAS 5.2 QCA 3D software and compared with an original geometry. The original model is an optically digitized post-mortem vessel cast. The biplane angiography reconstruction achieved a Hausdorff surface distance of 0.236 mm to the original geometry that is comparable with results obtained in our earlier study for computed tomography (CT) and magnetic resonance imaging (MRI) reconstructions. Steady flow simulations were performed with a commercial CFD program FLUENT. A comparison of the calculated wall shear stress (WSS) shows good correlation for histograms (r=0.97) and good agreement among the four modalities with a mean WSS of 0.65 Pa in the original model, of 0.68 Pa in the CT-based model, of 0.67 Pa in the MRI based model, and of 0.69 Pa in the biplane angiography-based model. We can conclude that the biplane angiography-based reconstructions can be used for the WSS profiling of the coronary arteries.
BibTeX @article{Goubergrits2009, author = {Leonid Goubergrits and Ernst Wellnhofer and Ulrich Kertzscher and Klaus Affeld and Christoph Petz and Hans-Christian Hege}, title = {Coronary artery WSS profiling using a geometry reconstruction based on biplane angiography}, journal = {Ann Biomed Eng}, year = {2009}, volume = {37}, number = {4}, pages = {682--691}, doi = {http://dx.doi.org/10.1007/s10439-009-9656-7}, pmid = {19229618} }
2009 (01)	Wellnhofer, E. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K. ; Fleck, E.: Novel non-dimensional approach to comparison of wall shear stress distributions in coronary arteries of different groups of patients. In: Atherosclerosis 202 (2009), Nr. 2, S. 483–490 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung BACKGROUND: Local wall shear stress (WSS) has an impact on local remodelling of the vessel wall. WSS in turn strongly depends on local geometry. Our aim was to characterize patterns of local wall shear stress associated with distinct types of remodelling in coronary arteries. Vessel size and flow rates are different between patients, however. To compare distribution patterns of WSS in analogy to fluid-dynamic modelling, non-dimensional WSS/area functions are calculated. METHODS: Right coronary arteries from seven controls, five patients with coronary artery disease (CAD) and five patients with aneurysmatic CAD (AnCAD) were analyzed. Flow simulations were performed in three-dimensionally reconstructed coronary vessels from biplane angiographic projections. Local WSS was normalized as percentage of maximum value in a histogram (100 classes) and corresponding area was expressed as percentage of total area. RESULTS: The normalized WSS distribution was characterized by a single peak with a large lower tie in controls, a loss of the single peak and a stochastic distribution in AnCAD and a narrowing of the lower tie in CAD. Correct classification of 16/17 coronary arteries was feasible by Fisher's discriminant functions based on median WSS, mean diameter, percentage of area with WSS ≤0.4 Pa and with WSS ≥15 Pa. CONCLUSION: Normalized WSS distribution might be an efficient tool in comparing wall shear stress between different patient groups. Whether normalized WSS distribution curves are apt to grade severity of disease remains to be investigated.
BibTeX @article{Wellnhofer2009, author = {E. Wellnhofer and L. Goubergrits and U. Kertzscher and K. Affeld and E. Fleck}, title = {Novel non-dimensional approach to comparison of wall shear stress distributions in coronary arteries of different groups of patients}, journal = {Atherosclerosis}, year = {2009}, volume = {202}, number = {2}, pages = {483--490}, doi = {http://dx.doi.org/10.1016/j.atherosclerosis.2008.05.044}, pmid = {18617176} }
2008 (05)	Kertzscher, U. ; Goubergrits, L. ; Doll, U. ; Gabel, G. ; Affeld, K.: Enhanced oxygen transport in fish gills – flow measurements in a model. In: Design & Nature and Ecodynamics 3 (2008), Nr. 3 [Zusammenfassung] [BibTeX]
Zusammenfassung Fish are able to extract oxygen from water effectively and with low energy consumption. In order to understand this trait, we investigated the flow in a fish gill model. We performed particle image velocimetry measurements on an enlarged simplified model of a fish gill. Two fluid models were used in the experiments: a one-phase and a two-phase flow, the latter of which models blood flow. The local hematocrit value distribution was investigated for the two-phase flow. In addition, the flow was visualized by dye injection for both fluid models. It was concluded from the results that the effective gas exchange is due to an enhanced transversal exchange within the gill with a two-phase flow, a deformation of the erythrocytes, and a local increase in hematocrit.
BibTeX @article{Kertzscher2008b, author = {U. Kertzscher and L. Goubergrits and U. Doll and G. Gabel and K. Affeld}, title = {Enhanced oxygen transport in fish gills -- flow measurements in a model}, journal = {Design & Nature and Ecodynamics}, year = {2008}, volume = {3}, number = {3} }
2008 (04)	Linneweber, J. ; Dohmen, P. ; Kertzscher, U. ; Affeld, K. ; Konertz, W.: Local glycoprotein IIb/IIIa receptor inhibitor delivery from the pump surface attenuates platelet adhesion in continuous flow ventricular assist devices. In: Artif Organs 32 (2008), Nr. 10, S. 792–799 [Zusammenfassung] [BibTeX]
Zusammenfassung Shear-induced platelet activation (SIPA) has been identified to induce platelet adhesion and thrombus formation in continuous flow left ventricular assist devices (LVAD). Platelet glycoprotein (GP) IIb/IIIa receptor inhibitors are effective to prevent SIPA. However, systemic GP IIb/IIIa receptor inhibitor application is associated with severe bleeding complications. The aim of the study was to evaluate (i) the feasibility of absorption and elution of the GP IIb/IIIa receptor blocker TAK-029 from the Ti6Al4V surface of the pump; and (ii) the effect of local GP IIb/IIIa receptor blocker delivery regarding platelet adhesion on the surface of a continuous flow VAD model. Saturating concentrations of TAK-029 were adsorbed on the surface of a centrifugal pump. Whole human blood was perfused in circulatory mock loops using untreated (control), albumin-coated, or TAK-029-coated pumps. Peripheral resistance of the circulatory systems were adjusted accordingly to generate 5 L flow per min with impeller rotational speeds of 3500 (high-shear group) and 1500 rpm (low-shear group), respectively. Platelet adhesions on the respective impellers were quantified by ELISA and scanning electron microscopy (SEM). TAK-029 elution and half-life time were determined by ELISA. Compared with control, albumin-coated pumps showed 64 and 20% less platelet adhesions in the high- and low-shear group, respectively. TAK-029 coated pumps reduced platelet adhesion by additional 33 and 65%, respectively, compared with the albumin group. Elution of TAK 029 was initially very rapid and continued slowly. The results show that it is possible to adsorb and elute a small molecular weight GP IIb/IIIa receptor blocker from the pump surface. This drug elution reduced platelet adhesion on the pump significantly. Further studies are necessary to find a suitable drug bonding that will prolong the antiplatelet effect and preclude any bleeding complication caused by this procedure.
BibTeX @article{Linneweber2008, author = {J. Linneweber and P.M. Dohmen and U. Kertzscher and K. Affeld and W. Konertz}, title = {Local glycoprotein IIb/IIIa receptor inhibitor delivery from the pump surface attenuates platelet adhesion in continuous flow ventricular assist devices}, journal = {Artif Organs}, year = {2008}, volume = {32}, number = {10}, pages = {792--799} }
2008 (03)	Kertzscher, U. ; Berthe, A. ; Goubergrits, L. ; Affeld, K.: Particle image velocimetry of a flow at a vaulted wall. In: Proc Inst Mech Eng H 222 (2008), Nr. 4, S. 465–473 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung The assessment of flow along a vaulted wall (with two main finite radii of curvature) is of general interest; in biofluid mechanics, it is of special interest. Unlike the geometry of flows in engineering, flow geometry in nature is often determined by vaulted walls. Specifically the flow adjacent to the wall of blood vessels is particularly interesting since this is where either thrombi are formed or atherosclerosis develops. Current measurement methods have problems assessing the flow along vaulted walls. In contrast with conventional particle image velocimetry (PIV), this new method, called wall PIV, allows the investigation of a flow adjacent to transparent flexible surfaces with two finite radii of curvature. Using an optical method which allows the observation of particles up to a predefined depth enables the visualization solely of the boundary layer flow. This is accomplished by adding a specific dye to the fluid which absorbs the monochromatic light used to illuminate the region of observation. The obtained images can be analysed with the methods of conventional PIV and result in a vector field of the velocities along the wall. With wall PIV, the steady flow adjacent to the vaulted wall of a blood pump was investigated and the resulting velocity field as well as the velocity fluctuations were assessed.
BibTeX @article{Kertzscher2008c, author = {U. Kertzscher and A. Berthe and L. Goubergrits and K. Affeld}, title = {Particle image velocimetry of a flow at a vaulted wall}, journal = {Proc Inst Mech Eng H}, year = {2008}, volume = {222}, number = {4}, pages = {465--473}, pmid = {18595358} }
2008 (02)	Goubergrits, L. ; Kertzscher, U. ; Schöneberg, B. ; Wellnhofer, E. ; Petz, C. ; Hege, H.-C.: CFD analysis in an anatomically realistic coronary artery model based on non-invasive 3D imaging: comparison of magnetic resonance imaging with computed tomography. In: Int J Cardiovasc Imaging 24 (2008), Nr. 4, S. 411–421 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung Computational fluid dynamics (CFD) methods based on in vivo three-dimensional vessel reconstructions have recently been shown to provide prognostically relevant hemodynamic data. However, the geometry reconstruction and the assessment of clinically relevant hemodynamic parameters may depend on the used imaging modality. This study compares geometric reconstruction and calculated wall shear stress (WSS) values based on magnetic resonance imaging (MRI) and computed tomography (CT). Both imaging methods were applied to a same 2.5-fold upscale silicon model of the left coronary artery (LCA) main bifurcation. The original model is an optically digitized post mortem vessel cast. This digitized geometry is considered as a "gold standard" or original geometry for the MRI versus CT comparative study. The use of the upscale model allowed generating a high resolution CT raw data set with voxel size of 0.156 x 0.156 x 0.36 mm(3) and a high resolution MRI data set with an equivalent voxel size of 0.196 x 0.196 x 0.196 mm(3) for corresponding in vivo conditions. MRI based reconstruction achieved a mean Hausdorff surface distance of 0.1 mm to the original geometry. This is 2.5 times better than CT based reconstruction with mean Hausdorff surface distance of 0.252 mm. A comparison of the calculated mean WSS shows good correlation (r = 0.97) and good agreement among the three modalities with a WSS of 0.65 Pa in the original model, of 0.68 Pa in the CT based model and of 0.67 Pa in the MRI based model.
BibTeX @article{Goubergrits2008a, author = {Leonid Goubergrits and Ulrich Kertzscher and Bastian Schöneberg and Ernst Wellnhofer and Christoph Petz and Hans-Christian Hege}, title = {CFD analysis in an anatomically realistic coronary artery model based on non-invasive 3D imaging: comparison of magnetic resonance imaging with computed tomography}, journal = {Int J Cardiovasc Imaging}, year = {2008}, volume = {24}, number = {4}, pages = {411--421}, doi = {http://dx.doi.org/10.1007/s10554-007-9275-z}, pmid = {17955344} }
2008 (01)	Goubergrits, L. ; Kertzscher, U. ; Affeld, K. ; Petz, C. ; Stalling, D. ; Hege, H.-C.: Numerical Dye Washout Method as a Tool for Characterizing the Heart Valve Flow: Study of Three Standard Mechanical Heart Valves. In: ASAIO J 54 (2008), Nr. 1, S. 50–57 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung To date, no ideal heart valve prosthesis for the replacement of a diseased natural valve or for use in ventricular assist devices exists. Valves still cause thromboembolic complications originating from thrombus formations in the valve's stagnant and recirculation zones. Optimization of valve design requires detailed flow field investigations. Usually, the regions that are more prone to thrombus formation can be estimated using a dye washout experiment. This successful experimental method was simulated using numerical methods. The proposed method was applied to three standard mechanical heart valves-Björk-Shiley, St-Jude, and Starr-Edwards valve. The dye washout was characterized by a time course of the gray value averaged over a defined region of interest. Finally, these curves were quantified by a half dye time (HDT), which characterizes the blood residence time. The HDT in the best valve, the Starr-Edwards valve, was 0.0747 s. The HDT in the worst valve, the Björk-Shiley, was 0.0942 s. The analysis of the hemodynamic valve parameters (pressure drop, velocity magnitudes and turbulence) revealed that the best valve is the St-Jude valve. The Starr-Edwards valve displayed the worst hemodynamic parameters. This study shows that the proposed numerical method of dye washout visualization can be used as an additional tool for the flow characterization.
BibTeX @article{Goubergrits2008, author = {Leonid Goubergrits and Ulrich Kertzscher and Klaus Affeld and Christoph Petz and Detlev Stalling and Hans-Christian Hege}, title = {Numerical Dye Washout Method as a Tool for Characterizing the Heart Valve Flow: Study of Three Standard Mechanical Heart Valves}, journal = {ASAIO J}, year = {2008}, volume = {54}, number = {1}, pages = {50--57}, doi = {http://dx.doi.org/10.1097/MAT.0b013e31815c5e38}, pmid = {18204316} }
2007 (02)	Linneweber, J. ; Dohmen, P.M. ; Kertzscher, U. ; Affeld, K. ; Nosé, Y. ; Konertz, W.: The effect of surface roughness on activation of the coagulation system and platelet adhesion in rotary blood pumps. In: Artif Organs 31 (2007), Nr. 5, S. 345–351 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung The surface roughness of left ventricular assist devices (LVADs) is important for the biocompatibility of blood pumps. However, little is known about the effect of surface roughness on the antithrombogenicity of the device. The present study investigated the effect of surface roughness on the activation of the coagulation system and platelet adhesion in an impeller-type blood pump. Three identical Baylor Gyro 710 centrifugal blood pumps (Baylor College of Medicine, Houston, TX, USA) were manufactured with impeller surface roughness of 0.05, 0.2, and 0.4 microm, respectively, as determined by a stylus profilometer and by scanning electron microscopy. Whole blood was anticoagulated (1-IU heparin/mL, ACT 250 s) and circulated for 60 min in an artificial circulatory system, simulating LVAD perfusion (5-L/min flow against 100 mm Hg). Enzyme-linked immunosorbent assays were developed to quantify fibrinogen- and von Willebrand factor (vWf) adsorption as well as platelet adhesion directly on the impellers of the pumps. Levels of prothrombin fragment F1.2 and thrombin-antithrombin (TAT) complex were measured in order to quantify activation of coagulation. Compared with the 0.05-microm surface, platelet adhesion was 40 and 76% higher on the 0.2- and 0.4-microm surface, respectively (P < 0.01). The evaluation of adsorbed fibrinogen and vWf showed significant higher protein antigen levels on the rougher surfaces (P < 0.01). Furthermore, nonpulsatile perfusion activated the coagulation system. By contrast, the surface roughness had no significant influence on plasma prothrombin F1.2 fragment- and TAT concentrations. Antithrombogenicity was significantly reduced in pumps with inferior metal-finishing quality.
BibTeX @article{Linneweber2007, author = {Jörg Linneweber and Pascal Maria Dohmen and Ulrich Kertzscher and Klaus Affeld and Yukihiko Nosé and Wolfgang Konertz}, title = {The effect of surface roughness on activation of the coagulation system and platelet adhesion in rotary blood pumps}, journal = {Artif Organs}, year = {2007}, volume = {31}, number = {5}, pages = {345--351}, doi = {http://dx.doi.org/10.1111/j.1525-1594.2007.00391.x}, pmid = {17470203} }
2007 (01)	Kertzscher, U. ; Goubergrits, L. ; Affeld, K.: Flow separations in blood flow – its significance in the human circulation and in artificial organs. In: Flow Phenomena in Nature Volume 2: Inspiration, Learning and Applications (2007), S. 505–528 [Zusammenfassung] [BibTeX]
Zusammenfassung Flow separations are ubiquitous in daily life and engineering. In most cases, they are unwelcome and impede the performance of the devices in which they occur. The flow separates inevitably behind bluff bodies. This increases the drag. In aircraft flow separation at the wings may even lead to a loss of stability and a catastrophic crash. In pumps and turbines vibrations may occur, while in tubing systems a loss of energy is observed. How does nature handle this flow phenomenon? Specifically, how is the circulatory system of the human body adapted? In the human body, the blood leaves the heart and enters the circulatory loop with a velocity of about 1 m/s. At the other end, in the capillaries, the blood moves at a speed of only 1 mm/s. This is achieved by the increase of the total cross-section area of the vessels. This enormous deceleration occurs in the major part of the blood circulation without flow separations. The reason is that area enlargement occurs normally at bifurcations. However, at some vessels and bifurcations, some flow separations with large areas of low wall shear stress still do occur. The combination of low wall shear stress -- as it occurs in flow separation -- and certain blood components cause the wall of the blood vessel to change its nature. These changes make the inner surface rough and decrease the cross section, a process called arteriosclerosis. A host of impairments result from these changes of the vessel wall. This affects a large number of people in modern western society. The eminent German pathologist R. Virchow discovered the interaction of flow, blood contents and the vessel wall more than 150 years ago. To date, the ?Virchow?s Triad? is not completely understood. Using modern tools in experimental and numerical fluid mechanics great progress has been made in the elucidation of pathological events. At the core of it, a low wall shear stress, mostly caused by a flow separation, is always found.
BibTeX @incollection{Kertzscher2007, author = {Ulrich Kertzscher and Leonid Goubergrits and Klaus Affeld}, title = {Flow separations in blood flow -- its significance in the human circulation and in artificial organs}, booktitle = {Flow Phenomena in Nature Volume 2: Inspiration, Learning and Applications}, publisher = {WIT Press}, year = {2007}, pages = {505--528} }
2006 (05)	Goubergrits, L.: Numerical modeling of blood damage: current status, challenges and future prospects. In: Expert Rev Med Devices 3 (2006), Nr. 5, S. 527–531 [BibTeX] [DOI ] [PMID ]
BibTeX @article{Goubergrits2006, author = {Leonid Goubergrits}, title = {Numerical modeling of blood damage: current status, challenges and future prospects}, journal = {Expert Rev Med Devices}, year = {2006}, volume = {3}, number = {5}, pages = {527--531}, doi = {http://dx.doi.org/10.1586/17434440.3.5.527}, pmid = {17064236} }
2006 (04)	Kertzscher, U. ; Goubergrits, L. ; Affeld, K.: Flow in artificial valves and pulsatile blood pumps. In: ERCOFTAC Bulletin Bulletin 68 (2006), S. 29–32 [Zusammenfassung] [BibTeX]
Zusammenfassung The function of pulsatile blood pumps is very similar to that of the natural heart: the blood chamber expands and contracts analog to the ventricle while inflow and outflow valves direct the blood flow. Initially, the valves used in blood pumps were the valves that were being developed for the replacement of the diseased natural valves. The patient with an implanted artificial valve is often endangered by thrombo-embolic complications. These complications are caused by a complex interaction between blood, material of the valve and the flow. The specific causal flow phenomenon is flow separation. In flow separation, the platelets, the thrombus generating blood cells, come into extended contact with the foreign material and may deposit and aggregate to a thrombus. Therefore the avoidance of flow separation is the objective of valve design. The danger of thrombo-embolic complications is even greater for a patient with an implanted blood pump, which contains two artificial valves. In the case of a valve replacement, the artificial valve is implanted in a vessel whose geometry may only be roughly determined and which is different for each patient. The vessel forms the duct, which has a great influence on the flow through the valve. In the blood pump, however, there is an engineering advantage: the duct can be dimensioned to the will of the designer, while in the body the size and the shape of the duct are given. An attempt to make use of this design freedom is demonstrated by the S-valve, shown in figure 1. It has a disk shaped occluder, which can tilt in order to open and close. In fact it is a Björk-Shiley valve, which is at an incline relative to the direction of the main flow, instead of the normal position, which is at a right angle to it. With this incline, one can achieve that the plane of the disk is in line with the incoming flow ? the angle of attack is now zero. In this way, a flow separation at the disk can be reduced. In a straight duct, a disk in this position would not close as a result of flow reversal and for this reason the angle of attack is kept at around 30°. In the S-shaped duct the disk closes, because when the flow reverses its initial flow lines are parallel to the S-shaped duct walls and therefore inclined towards the disk plane. In the open position a flow contraction and a flow diffuser are formed. This can be designed in way that the objective, avoiding of a flow separation, is met. Figure 2 shows the results of an experiment, in which the flow and its effect on residence time and flow separation are made visible.
BibTeX @article{Kertzscher2006b, author = {U. Kertzscher and L. Goubergrits and K. Affeld}, title = {Flow in artificial valves and pulsatile blood pumps}, journal = {ERCOFTAC Bulletin}, year = {2006}, volume = {Bulletin 68}, pages = {29--32} }
2006 (03)	Goubergrits, L. ; Timmel, T. ; Affeld, K. ; Petz, C. ; Stalling, D. ; Hege, H.C.: Characterization of an artificial valve flow using the numerical dye washout visualization technique: application to the monoleaflet valve with purged flow. In: Artif Organs 30 (2006), Nr. 8, S. 642–650 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung Until today, no ideal heart valve prosthesis for the replacement of a diseased natural valve or for use in ventricular assist devices exists. Valves still cause thromboembolic complications originating from thrombus formations in the valve's stagnant zones. Optimization of valve design involves avoiding stagnation zones and zones of high shear stresses. This requires detailed flow field investigations. Usually, the regions which are more prone to thrombus formation can be estimated using a dye washout experiment. The method allows an assessment of regions with a high or low residence time that may in turn predict regions with a corresponding thrombus risk. This successful experimental method was simulated using numerical methods with a combination of the computational fluid dynamics program FLUENT (Fluent Inc., Lebanon, NH, USA) and of the visualization tool AMIRA (TGS Inc., San Diego, CA, USA). The numerical dye washout visualization was applied to four monoleaflet valves with varying valve housing geometries. The results show a significant difference in the washout processes of the examined valves. The dye washout was characterized by a time course of the gray value averaged over a defined region of interest. Finally, these curves were quantified by a half dye time. The half dye time in the best optimized valve was only 0.2753 s. The same time in the original valve was 0.6834 s. This study shows that the proposed numerical method of dye washout visualization can be used as an additional tool of the flow characterization in artificial organs.
BibTeX @article{Goubergrits2006a, author = {Leonid Goubergrits and Tobias Timmel and Klaus Affeld and Christoph Petz and Detlev Stalling and Hans Christian Hege}, title = {Characterization of an artificial valve flow using the numerical dye washout visualization technique: application to the monoleaflet valve with purged flow}, journal = {Artif Organs}, year = {2006}, volume = {30}, number = {8}, pages = {642--650}, doi = {http://dx.doi.org/10.1111/j.1525-1594.2006.00277.x}, pmid = {16911322} }
2006 (02)	Wellnhofer, E. ; Goubergrits, L. ; Kertzscher, U. ; Affeld, K.: In-vivo coronary flow profiling based on biplane angiograms: influence of geometric simplifications on the three-dimensional reconstruction and wall shear stress calculation. In: Biomed Eng Online 5 (2006), S. 39 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung BACKGROUND: Clinical studies suggest that local wall shear stress (WSS) patterns modulate the site and the progression of atherosclerotic lesions. Computational fluid dynamics (CFD) methods based on in-vivo three-dimensional vessel reconstructions have recently been shown to provide prognostically relevant WSS data. This approach is, however, complex and time-consuming. Methodological simplifications are desirable in porting this approach from bench to bedside. The impact of such simplifications on the accuracy of geometry and wall shear stress calculations has to be investigated. METHODS: We investigated the influence of two methods of lumen reconstruction, assuming circular versus elliptical cross-sections and using different resolutions for the cross-section reconstructions along the vessel axis. Three right coronary arteries were used, of which one represented a normal coronary artery, one with "obstructive", and one with "dilated" coronary atherosclerosis. The vessel volume reconstruction was performed with three-dimensional (3D) data from a previously validated 3D angiographic reconstruction of vessel cross-sections and vessel axis. RESULTS: The difference between the two vessel volumes calculated using the two evaluated methods is less than 1 The difference, of the calculated pressure loss, was between 2.5% and 8.5% for the evaluated methods. The distributions of the WSS histograms were nearly identical and strongly cross-correlated (0.91-0.95). The good agreement of the results was confirmed by a Chi-square test. CONCLUSION: A simplified approach to the reconstruction of coronary vessel lumina, using circular cross-sections and a reduced axial resolution of about 0.8 mm along the vessel axis, yields sufficiently accurate calculations of WSS.
BibTeX @article{Wellnhofer2006, author = {Ernst Wellnhofer and Leonid Goubergrits and Ulrich Kertzscher and Klaus Affeld}, title = {In-vivo coronary flow profiling based on biplane angiograms: influence of geometric simplifications on the three-dimensional reconstruction and wall shear stress calculation}, journal = {Biomed Eng Online}, year = {2006}, volume = {5}, pages = {39}, doi = {http://dx.doi.org/10.1186/1475-925X-5-39}, pmid = {16774680} }
2006 (01)	Affeld, K. ; Affeld, F. ; Debaene, P. ; Goubergrits, L.: Injection of granular material: visualization of stress and grain flow. In: Journal of Visualization 9 (2006), Nr. 1, S. 31–38 [Zusammenfassung] [BibTeX]
Zusammenfassung Some civil engineering projects require the injection of granular matter such as sand into the ground. However, granular matter resists pumping through tubes and thus it is difficult to inject such matter into the ground. 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. The movement of sand grains was visualized on a glass plate in a half-space ground model. With the particle image velocimetry (PIV) method the vector field of the movement and the field of the resulting shear rate were assessed. In this way a new method for the injection of granular material, such as, sand into the ground was devised. The method appears to be applicable to lift a building to counter subsidence.
BibTeX @article{Affeld2006, author = {K. Affeld and F. Affeld and P. Debaene and L. Goubergrits}, title = {Injection of granular material: visualization of stress and grain flow}, journal = {Journal of Visualization}, year = {2006}, volume = {9}, number = {1}, pages = {31--38} }
2005 (02)	Debaene, P. ; Kertzscher, U. ; Goubergrits, L. ; Affeld, K.: Visualization of a Wall Shear Flow: Development of a New Particle Image Interrogation Method. In: Journal of Visualization 8 (2005), Nr. 4, S. 305–314 [Zusammenfassung] [BibTeX]
Zusammenfassung In this paper we propose a new method which might be useful to investigate the flow fields close to vaulted walls with spatial and temporal resolution. This kind of flow visualization is important in the field of biofluid mechanics, since a close relationship is assumed between flow and biological phenomena. This new method is non-invasive, and is also applicable for unsteady flows. It has been used to investigate the steady and the unsteady laminar flow in a rectangular duct, as well as the steady, laminar flow in two different U-shaped ducts, both with a backward facing step, one having a rectangular cross-section, the other a nearly elliptical cross-section. The results concurred well with analytical or numerical solutions.
BibTeX @article{Debaene2005, author = {P. Debaene and U. Kertzscher and L. Goubergrits and K. Affeld}, title = {Visualization of a Wall Shear Flow: Development of a New Particle Image Interrogation Method}, journal = {Journal of Visualization}, year = {2005}, volume = {8}, number = {4}, pages = {305--314} }
2005 (01)	Goubergrits, L. ; Affeld, K. ; Kertzscher, U.: Innovative developments of the heart valves designed for use in ventricular assist devices. In: Expert Rev Med Devices 2 (2005), Nr. 1, S. 61–71 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung Prosthetic heart valves are routinely used for replacing diseased natural heart valves. Even today, after five decades of prosthetic heart valve development, in the authors opinion the main problem associated with these valves is the risk of thromboembolic complications caused by unnatural hemodynamics. Further growing application of prosthetic heart valves is their use in the pulsatile ventricular assist devices (VADs). VADs may provide life-saving solutions to patients with severe cardiovascular diseases and are superior to drug therapy for patients with severe heart failure. However, the clinical applications of VADs still suffer from thromboembolic complications due to thrombus formations in the vicinity of the valves. Wherever the flow is stagnant or flow separation occurs, a thrombus is likely to form. The design of the heart valves with flow avoiding the formation of stagnant zones is one of the main goals in the development of new valves. This article reviews some innovative design approaches of the valves specially designed for use in VADs. Three design concepts are presented; one is based on the tilting disk valve, the second on the natural valve geometry and the third on the ball valve principle. However, these three different concepts have one common basic idea; the use of the freedom of the valve-housing design. This additional design freedom, which is available in VADs, is a key factor in the development of new valves with optimal hemodynamic performance.
BibTeX @article{Goubergrits2005, author = {Leonid Goubergrits and Klaus Affeld and Ulrich Kertzscher}, title = {Innovative developments of the heart valves designed for use in ventricular assist devices}, journal = {Expert Rev Med Devices}, year = {2005}, volume = {2}, number = {1}, pages = {61--71}, doi = {http://dx.doi.org/10.1586/17434440.2.1.61}, pmid = {16293030} }
2004 (10)	Kertzscher, U. ; Dimitroff, G. ; Binsteiner, M. ; Affeld, K. ; Goubergrits, L. ; Seeger, A. ; Wellnhofer, E.: X-ray based measurements of the local solid phase content in a three-phase flow of a bubble column: statistical significance. In: Experiments in Fluids 37 (2004), S. 923–928 [Zusammenfassung] [BibTeX]
Zusammenfassung Information regarding the flow properties in bubble columns with a three-phase flow is of great interest for research into its performance, as well as for the validation of computer models. In an earlier paper we proposed an X-ray based Particle Tracking Velocimetry (PTV) - called XPTV. This method allows not only the measurement of the velocities of both solid and fluid phases in a three-phase flow, but also the assessment of the time averaged local solid phase content. In this paper we are concerned with the statistical significance of the obtained measurements.
BibTeX @article{Kertzscher2004, author = {U. Kertzscher and G. Dimitroff and M. Binsteiner and K. Affeld and L. Goubergrits and A. Seeger and E. Wellnhofer}, title = {X-ray based measurements of the local solid phase content in a three-phase flow of a bubble column: statistical significance}, journal = {Experiments in Fluids}, year = {2004}, volume = {37}, pages = {923--928} }
2004 (09)	Bluestein, D. ; Yin, W. ; Affeld, K. ; Jesty, J.: Flow-induced platelet activation in mechanical heart valves. In: J Heart Valve Dis 13 (2004), Nr. 3, S. 501–508 [Zusammenfassung] [BibTeX]
Zusammenfassung BACKGROUND AND AIM OF THE STUDY: A study was conducted to measure in vitro the procoagulant properties of platelets induced by flow through mechanical heart valves. METHODS: The procoagulant activity of platelets was measured using a real-time assay of platelet activation state (PAS), which was based on a modification of the prothrombinase method. Acetylated prothrombin was used instead of normal prothrombin in this assay in order to eliminate the positive feedback effect of thrombin. This enabled a direct comparison between thrombin generation rates in the assay and the flow stresses that induce platelet activation. Gel-filtered platelets (10(5) per microliters) were circulated through a left ventricular assist device with two Bjork-Shiley mono-leaflet mechanical heart valves mounted in opposition, and platelet activation state was measured over 30-min time courses. The results were compared with two configurations in which the leaflet motion of one of the valves was restricted (severely restricted and mildly restricted), mimicking defective function of a compromised valve in vivo, and with a control lacking valves. RESULTS: The severely restricted valve activated the platelets at a rate eight-fold higher than with unrestricted valves, and three-fold higher than with mildly restricted valves. Both restricted valves activated platelets at rates significantly higher than either the control (no valves) or the unrestricted valve. CONCLUSION: Flow through compromised mechanical heart valves causes platelet activation, which can be measured with a modified prothrombinase assay system. The ability to perform sensitive quantitative measurements in cardiovascular devices in vitro may have a significant impact on the design and development of these devices.
BibTeX @article{Bluestein2004, author = {Bluestein, D. and Yin, W. and Affeld, K. and Jesty, J.}, title = {Flow-induced platelet activation in mechanical heart valves}, journal = {J Heart Valve Dis}, year = {2004}, volume = {13}, number = {3}, pages = {501--508} }
2004 (08)	Yin, W. ; Alemu, Y. ; Affeld, K. ; Jesty, J. ; Bluestein, D.: Flow-induced platelet activation in bileaflet and monoleaflet mechanical heart valves. In: Ann Biomed Eng 32 (2004), Nr. 8, S. 1058–1066 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung A study was conducted to measure in vitro the procoagulant properties of platelets induced by flow through Carbomedics bileaflet and Bjork-Shiley monoleaflet mechanical heart valves (MHVs). Valves were mounted in a left ventricular assist device, and platelets were circulated through them under pulsatile flow. Platelet activation states (PAS) were measured during circulation using a modified prothrombinase method. Computational fluid dynamics (CFD) simulations of turbulent, transient, and non-Newtonian blood flow patterns generated by the two valve designs were done using the Wilcox k - w turbulence model, and platelet shear-stress histories (the integral of shear-stress exposure with respect to time) through the two MHVs were calculated. PAS measurements indicated that the bileaflet MHV activated platelets at a rate more than twice that observed with the monoleaflet MHV. Turbulent flow patterns were evident in CFD simulations for both valves, and corroborated the PAS observations, showing that, for particles close to the leaflet(s), shear-stress exposure in the bileaflet MHV can be more than four times that in the monoleaflet valve.
BibTeX @article{Yin2004, author = {Wei Yin and Yared Alemu and Klaus Affeld and Jolyon Jesty and Danny Bluestein}, title = {Flow-induced platelet activation in bileaflet and monoleaflet mechanical heart valves}, journal = {Ann Biomed Eng}, year = {2004}, volume = {32}, number = {8}, pages = {1058--1066}, pmid = {15446502} }
2004 (07)	Affeld, K. ; Goubergrits, L. ; Kertzscher, U. ; Gadischke, J. ; Reininger, A.: Mathematical model of platelet deposition under flow conditions. In: Int J Artif Organs 27 (2004), Nr. 8, S. 699–708 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Platelet deposition in resting blood is well researched and understood. However, the influence of hemodynamic parameters such as wall shear rate is less clear. Clinical experience and experiments show an interaction between flow and platelet deposition. But a complete understanding of the flow influence and hence a quantification has not yet been achieved. A well defined experiment of flow dependant platelet depositions is the stagnation point flow. This kind of flow is ubiquitous in the circulatory system, to be found in every bifurcation and recirculation region. These are the areas where thrombus formations are likely to occur if other conditions are also met. First, experiments were performed in a stagnation point flow chamber. A simplified blood model, platelet rich plasma, was used as a test fluid. With a microscope the platelet deposition was observed and recorded. Platelets deposit in a characteristic pattern showing the influence of the flow. An analysis of this pattern is the objective of this study and is achieved with the help of a numerical model, which is based on a convective diffusive transport. The model results in a platelet deposition pattern, which in its shape and temporal development is very similar to experimental results. Hence it is concluded that the assumed transport processes are causal for platelet depositions and thrombus formation.
BibTeX @article{Affeld2004, author = {K. Affeld and L. Goubergrits and U. Kertzscher and J. Gadischke and A. Reininger}, title = {Mathematical model of platelet deposition under flow conditions}, journal = {Int J Artif Organs}, year = {2004}, volume = {27}, number = {8}, pages = {699--708}, pmid = {15478541} }
2004 (06)	Goubergrits, L. ; Petz, C. ; Stalling, D. ; Affeld, K.: Experimental and numerical dye washout flow visualization. In: Journal of Visualization 7(3) (2004), S. 233–240 [Zusammenfassung] [BibTeX]
Zusammenfassung Flow visualization in realistic models is very important for the study of pathological vessel enlargements (aneurysms). Furthermore, flow visualization may help in treatment decisions. However, the most interesting parameter, the wall shear stress, is difficult to measure in vivo. This parameter can be provided by computational fluid dynamics. However, the numerical methods don't visualize the results as does of the dye washout method - a method often used in flow studies. This experimental method simulates the cine angiograms acquired during contrast agent injection used in medicine. In this paper we present the dye washout visualization of CFD results and compare these results with the conventional dye washout experiments in the same aneurysm model under steady flow conditions.
BibTeX @article{Goubergrits2004a, author = {L. Goubergrits and C. Petz and D. Stalling and K. Affeld}, title = {Experimental and numerical dye washout flow visualization}, journal = {Journal of Visualization}, year = {2004}, volume = {7(3)}, pages = {233--240} }
2004 (05)	Kertzscher, U. ; Seeger, A. ; Affeld, K. ; Goubergrits, L. ; Wellnhofer, E.: X-ray based particle tracking velocimetry – a measurement technique for multi-phase flows and flows without optical access. In: Flow Measurement and Instrumentation 15 (2004), S. 199–206 [Zusammenfassung] [BibTeX]
Zusammenfassung Information regarding the flow in multi-phase systems, such as bubble columns, is necessary for the design of improved devices, as well as for the validation of computer models. Common optical methods are limited in bubble columns with a large void fraction. The reason that this should be is the difference in the refraction indices of liquid and gaseous phases, which leads to reflection and refraction of light. In addition, in flows without optical access, optical methods cannot be used. The method proposed by these authors in their previous paper regarding X-ray based Particle Tracking Velocimetry (PTV) - called XPTV - resolves these problems. It allows us to measure the velocity three-dimensionally, non invasive, and in devices without optical access. In bubble columns, X-rays are neither reflected nor refracted at the phase boundaries and the flow is penetrated in straight lines. Therefore, it works independently from the void fraction. This has been proved to be a reliable and useful measurement technique, circumventing the limitations of optical methods. This paper reports the latest improvements in the algorithms designed to track and reconstruct particles, a feature which is explained here in detail. The improved algorithms are applied to measure the hydrodynamic parameters in a bubble column under two different flow conditions.
BibTeX @article{Kertzscher2004a, author = {U. Kertzscher and A. Seeger and K. Affeld and L. Goubergrits and E. Wellnhofer}, title = {X-ray based particle tracking velocimetry -- a measurement technique for multi-phase flows and flows without optical access}, journal = {Flow Measurement and Instrumentation}, year = {2004}, volume = {15}, pages = {199--206} }
2004 (04)	Goubergrits, L. ; Affeld, K. ; Fernandez-Britto, J. ; Falcon, L.: Hemodynamic study in 26 authentic carotid bifurcations. In: Technology and Health Care 12 (2004), Nr. 2, S. 188–190 [BibTeX]
BibTeX @article{Goubergrits2004b, author = {L. Goubergrits and K. Affeld and J. Fernandez-Britto and L. Falcon}, title = {Hemodynamic study in 26 authentic carotid bifurcations}, journal = {Technology and Health Care}, year = {2004}, volume = {12}, number = {2}, pages = {188--190} }
2004 (03)	Goubergrits, L. ; Affeld, K.: Numerical estimation of blood damage in artificial organs. In: Artif Organs 28 (2004), Nr. 5, S. 499–507 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung The aim of this study was to determine a method for the numerical estimation of blood damage. Normally, human or animal blood is used for in vitro evaluation of lysis by artificial organs. However, blood has some disadvantages: large biological variability and different initial test conditions lead to nonreproducible test results. For that reason, it would be an advantage to have a numerical method for blood damage estimation. This proposed method is based on the calculation of an integrated hemolysis and platelet lysis index along the path line in the flow field of the artificial organ. The time-dependent shear stress related lysis is based on known experimental data. In order to calibrate these data, the method was first applied to blood circulation in the human body. The results showed that the known data overestimate hemolysis by a factor of approximately 25. Next, the method was applied to a standard BjÃ?Æ?Ã?Â¶rk-Shiley valve. The flow through a valve was simulated with the computational fluid dynamics program FLUENT. The calculation of lysis was added into FLUENT and done automatically. The results showed that the BjÃ?Æ?Ã?Â¶rk-Shiley valve increased the hemolysis index by 7% if implanted in the human body circulation.
BibTeX @article{Goubergrits2004, author = {Leonid Goubergrits and Klaus Affeld}, title = {Numerical estimation of blood damage in artificial organs}, journal = {Artif Organs}, year = {2004}, volume = {28}, number = {5}, pages = {499--507}, doi = {http://dx.doi.org/10.1111/j.1525-1594.2004.07265.x}, pmid = {15113346} }
2004 (02)	Seeger, A. ; Kertzscher, U. ; Affeld, K. ; Goubergrits, L. ; Wellnhofer, E.: X-ray based particle tracking velocimetry for bubble columns with high void fraction. In: Bubbly flows: analysis, modelling and calculation (2004) [BibTeX]
BibTeX @incollection{Seeger2004, author = {A. Seeger and U. Kertzscher and K. Affeld and L. Goubergrits and E. Wellnhofer}, title = {X-ray based particle tracking velocimetry for bubble columns with high void fraction}, booktitle = {Bubbly flows: analysis, modelling and calculation}, publisher = {Springer}, year = {2004} }
2004 (01)	Kertzscher, U. ; Seeger, A. ; Affeld, K. ; Wellnhofer, E.: Measurement of the local liquid and the local solid velocity simultaneously. In: Bubbly flows: analysis, modelling and calculation (2004) [BibTeX]
BibTeX @incollection{Kertzscher2004b, author = {U. Kertzscher and A. Seeger and K. Affeld and E. Wellnhofer}, title = {Measurement of the local liquid and the local solid velocity simultaneously}, booktitle = {Bubbly flows: analysis, modelling and calculation}, publisher = {Springer}, year = {2004} }
2003 (04)	von Baeyer, H. ; Hopfenmüller, W. ; Riedel, E. ; Affeld, K.: Atherosclerosis: current concepts of pathophysiology and pharmacological intervention based on trial outcomes. In: Clin Nephrol 60 Suppl 1 (2003), S. S31–S48 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Atherosclerosis related cardiovascular diseases are the leading cause of death in western societies. The clinical manifestations are chronic arterial obstructions or acute arterial occlusions in various vascular territories. The pathogenesis is only understood in part as yet. Arterial wall abnormalities, blood composition abnormalities and hemodynamic alterations are generally accepted to be causative (Virchow's triad). The key role is played by macrophages in the subendothelial space that are activated immunologically by oxidized LDL particles via the scavenger receptor pathway. Recently, endothelial dysfunction due to oxidative stress was identified as a priming factor in the course of the development of atherosclerotic plaques. Shear stress-induced microinjuries of the endothelium in hemodynamically compromised regions together with local coagulation activation associated with microinflammation of the plaque are currently thought to cause plaque rupture. This event is the reason for local clot formation and ultimate organ infarction. Treatment success is still insufficient, however some progress during the last decade is reflected by the improving outcome of atherosclerosis associated cardiovascular diseases. Evidence from clinical trials supports the efficacy of statins, antiplatelet agents, antihypertensive agents if necessary and omega-fatty acids in patients with overt atherosclerosis. The reduction of mortality achieved by those drugs amounts to: omega-fatty acids -21 statins -16 anti-platelet agents -14 treatment of hypertension -13 It is impossible to calculate the combined effect of these modalities since in each trial participants received co-medication containing agents tested in other trials.
BibTeX @article{Baeyer2003, author = {H. von Baeyer and W. Hopfenmüller and E. Riedel and K. Affeld}, title = {Atherosclerosis: current concepts of pathophysiology and pharmacological intervention based on trial outcomes}, journal = {Clin Nephrol}, year = {2003}, volume = {60 Suppl 1}, pages = {S31--S48}, pmid = {12940532} }
2003 (03)	Goubergrits, L. ; Affeld, K. ; Fernandez-Britto, J. ; Falcon, L.: Investigation of geometry and atherosclerosis in the human carotid bifurcations. In: Journal of Mechanics in Medicine and Biology 3 (2003), Nr. 1, S. 31–48 [Zusammenfassung] [BibTeX]
Zusammenfassung The common carotid artery bifurcation has attracted a special interest because atherosclerotic wall alterations are often found in this artery and, because of its unique shape, which influences the flow field and, hence, the location of wall alterations. However, current knowledge of its geometry is insufficient by a determination and quantification of the "geometric risk factors". At post mortem the 86 arteries from sixty-four autopsy subjects were excised and filled with a special resin at the proper transmural pressure. Eighty-six vessel casts of the carotid artery were fabricated and some etiologic factors such as age, sex and disease were collected. Furthermore, the arteries were processed according to the methods established by the World Health Organization in 1958 and the locations and level of the atherosclerotic lesions (fatty streaks, fibrous and severe plaques) were assessed. The following selected geometric parameters of these arteries were measured: the diameters of the main branches of the carotid bifurcation (common, external and internal carotid arteries), the angles between these main branches, the enlargement of the carotid sinus and the enlargement of the carotid bifurcation. Furthermore, 26 vessel casts were digitized and three-dimensional computer models were generated. These models were than used to assess other geometrical features such as curvature of the branches and non-planarity of the bifurcation. The analysis of the relationship between measured geometric parameters, etiologic factors and atherosclerotic lesions was performed. The geometric parameters vary considerably, presumably contributing to a corresponding variability in the distribution and level of the atherosclerotic lesions and local hemodynamic.
BibTeX @article{Goubergrits2003a, author = {L. Goubergrits and K. Affeld and J. Fernandez-Britto and L. Falcon}, title = {Investigation of geometry and atherosclerosis in the human carotid bifurcations}, journal = {Journal of Mechanics in Medicine and Biology}, year = {2003}, volume = {3}, number = {1}, pages = {31--48} }
2003 (02)	Goubergrits, L. ; Leirner, A. ; Affeld, K.: Trileaflet valve for VAD use with purged sinus. In: Artif Organs 27 (2003), Nr. 6, S. 586–591 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Clinical applications of ventricle assist devices continue to be problematic due to thromboembolic complications. The problem originates mainly at the valves, which are usually made of an antithrombogenic material, such as cross-linked bovine pericardium. However, wherever the blood flow is stagnant or forms a recirculation region, a thrombus is likely to form. A similar blood flow is found in the space between the housing of the valve and the leaflets, the so-called valve sinus. Consequently, thrombi are often generated in this region. The novel valve design presented in this article avoids the formation of stagnant flow in the valve sinus during systole by a purge flow. This flow is taken from the main flow through the valve and is directed into each sinus region. The effect is achieved by perforation of the valve sinus with a small orifice at the bottom of the sinus. The purge flow effect is investigated with the computational fluid dynamics (CFD) method. The simulation shows that the purge flow effectively increases flow in the valve sinuses.
BibTeX @article{Goubergrits2003, author = {L. Goubergrits and A. Leirner and K. Affeld}, title = {Trileaflet valve for VAD use with purged sinus}, journal = {Artif Organs}, year = {2003}, volume = {27}, number = {6}, pages = {586--591}, pmid = {12780516} }
2003 (01)	Seeger, A. ; Kertzscher, U. ; Affeld, K. ; Wellnhofer, E.: Measurement of the local velocity of the solid phase and the local solid hold-up in a three-phase flow by X-ray based particle tracking velocimetry (XPTV). In: Chemical Engineering Science 58 (2003), Nr. 9, S. 1721–1729 [Zusammenfassung] [BibTeX] [DOI ]
Zusammenfassung The measurement of the local solid velocity and the local solid hold-up in three-phase flows (gas, liquid, solid) is of great interest with regard to the design of three-phase reactors. Moreover, such measurements are necessary for the validation of flow simulations of three-phase flows. The optical methods usually applied for velocity measurements such as particle image velocimetry do not work in three-phase flows. This is due to the opacity of the solid phase or/and because of the reflections and refractions that occur on phase boundaries. Other measurement methods are intrusive and very time consuming. The measurement of the local solid hold-up is even more difficult. The new X-ray based particle tracking velocimetry (XPTV), described in this paper, measures the solid velocity and the solid content simultaneously. This fast working and non-intrusive technique has already been successfully applied in a bubble column to measure the liquid velocity. XPTV is a three-dimensional three-component method. It works independently from void fraction and solid hold-up.
BibTeX @article{Seeger2003, author = {A. Seeger and U. Kertzscher and K. Affeld and E. Wellnhofer}, title = {Measurement of the local velocity of the solid phase and the local solid hold-up in a three-phase flow by X-ray based particle tracking velocimetry (XPTV)}, journal = {Chemical Engineering Science}, year = {2003}, volume = {58}, number = {9}, pages = {1721--1729}, doi = {http://dx.doi.org/10.1016/S0009-2509(03)00010-1} }
2002 (08)	Kertzscher, U. ; Affeld, K. ; Scheckel, M.: Model study of blood flow through a stent in the aorto-iliac bifurcation. In: Int J Artif Organs 25 (2002), Nr. 12, S. 1153–1159 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Atherosclerotic ailments play a major role in industrial societies. Atherosclerotic disease causes stenotic narrowing of the arterial vessel system. These narrow passages can be widened with balloon angioplasty and stents are introduced to keep the passage open. In this study, stents designed for the aorto-iliac bifurcation are considered. Most of these stents used in peripheral arteries are self-expanding stents made from Nitinol, a thermo-reactive alloy. The insertion is done under radiographic control. However, the delicate metallic structure of the stent usually casts only a weak radiographic shadow and thus is difficult to detect. A stent with an innovative radio opaque tantalum marker (Luminexx, C.R. BARD--Angiomed, Karlsruhe), overcomes this problem. However, the markers extend into the blood flow and the question arises whether the markers may cause the generation of thrombi. In a model study in an enlarged model of the aorto-iliac bifurcation with an inserted stent the flow was visualized. The enlarged scale permits the observation and video recording of the flow in great detail. The Reynolds similarity is kept. A subsequent analysis of the flow in the vicinity of the markers shows a short residence time. These results indicate that the additional markers do not increase the risk of thrombus generation.
BibTeX @article{Kertzscher2002a, author = {U. Kertzscher and K. Affeld and M. Scheckel}, title = {Model study of blood flow through a stent in the aorto-iliac bifurcation}, journal = {Int J Artif Organs}, year = {2002}, volume = {25}, number = {12}, pages = {1153--1159}, pmid = {12518959} }
2002 (07)	Dohmen, P. ; Scheckel, M. ; Stein-Konertz, M. ; Erdbruegger, W. ; Affeld, K. ; Konertz, W.: In vitro hydrodynamics of a decellularized pulmonary porcine valve, compared with a glutaraldehyde and polyurethane heart valve. In: Int J Artif Organs 25 (2002), Nr. 11, S. 1089–1094 [Zusammenfassung] [BibTeX]
Zusammenfassung BACKGROUND: Hydrodynamic performance of a decellularized pulmonary porcine valve was evaluated with a computer versatile pulse duplicator and compared to glutaraldehyde fixated stentless porcine bioprosthesis and a polyurethane heart valve. METHODS: Decellularized pulmonary porcine matrices (Group I, n = 5) were treated chemically to become cell-free collagen matrices. The findings of this heart valve were compared with aortic glutaraldehyde treated porcine prostheses (Group II, n = 5) and polyurethane three leaflet valve prostheses (Group III, n = 1). Measurements were performed in 0.9% saline test fluid at room temperature. Measurements compared were closing time, closing volume, systemic pressure difference and energy losses. Each valve was measured 6 times with 70 beats/minute, a stroke volume of 70 ml corresponds to a cardiac output of 4.9 L/minute. RESULTS: Group I and group III showed no significant differences between parameters. The measured closing time was significantly different (p < 0.001) between group I and II, respectively 24.333 and 53.600 ms and group II and III respectively 53.600 and 24.000. Difference in closing volume was significant (p < 0.05) between groups II and I respectively 3.67 and 0.68 ms and group II and III respectively 3.67 and 0.71. Systolic mean pressure gradient was 18.25 +/- 1.04 mm Hg in group II which was significantly different (p < 0.001) from groups I and III, respectively 10.65 +/- 0.29 mm Hg and 7.70 +/- 0.30 mm Hg. CONCLUSIONS: Decellularized pulmonary porcine valves showed the same excellent performance as polyurethane valve prosthesis, which are superior to the investigated glutaraldehyde fixed xenograft.
BibTeX @article{Dohmen2002, author = {Dohmen, P.M. and Scheckel, M. and Stein-Konertz, M. and Erdbruegger, W. and Affeld, K. and Konertz, W.}, title = {In vitro hydrodynamics of a decellularized pulmonary porcine valve, compared with a glutaraldehyde and polyurethane heart valve}, journal = {Int J Artif Organs}, year = {2002}, volume = {25}, number = {11}, pages = {1089--1094} }
2002 (06)	Goubergrits, L. ; Affeld, K. ; Debaene, P. ; Kertzscher, U.: Investigation of transport phenomena inside a microcapsule. In: Ann N Y Acad Sci 972 (2002), S. 200–205 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Mass transfer within a microcapsule is enhanced by convection, achieved by introducing a movable body inside the microcapsule. This body has a different density from the fluid within the microcapsule and can be moved relative to the microcapsule by application of an external force, such as a magnetic field or acceleration/deceleration. The effect of the transport improvement was investigated as a function of the Peclet number (Pe) by using computational fluid dynamics and particle image velocimetry. The results show that the period to achieve 80% saturation in the microcapsule was reduced by 60% with a movable body with half of the diameter of the microcapsule and Pe = 600, compared to the mass transport in the microcapsule with a non-movable body.
BibTeX @article{Goubergrits2002, author = {Leonid Goubergrits and Klaus Affeld and Perrine Debaene and Ulrich Kertzscher}, title = {Investigation of transport phenomena inside a microcapsule}, journal = {Ann N Y Acad Sci}, year = {2002}, volume = {972}, pages = {200--205}, pmid = {12496018} }
2002 (05)	Seeger, A. ; Affeld, K. ; Goubergrits, L. ; Kertzscher, U. ; Wellnhofer, E. ; Delfos, R.: X-ray-based flow visualization and measurement: application in multiphase flows. In: Ann N Y Acad Sci 972 (2002), S. 247–253 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Information concerning continuous or discreet phase flow in multiphase systems is desired for various practical and analytical applications. The potential of X-ray-based flow visualization and measurement of multiphase flow is demonstrated here by two non-intrusive methods: (1) Measurement of the three-dimensional (3D) velocity field of the continuous liquid phase in a bubble column by X-ray-based particle tracking velocimetry (PTV) of seeded particles. (2) Liquid flow visualization in a bubble column by injecting an X-ray absorbing liquid into the bubble column. X-rays have the advantage that they are not affected by the various refraction indices of the multiphase system and penetrate the multiphase flow in undistorted straight lines. Hence, in contrast to optical methods, both of these X-ray-based methods are independent of the void fraction and are applicable to opaque liquids.
BibTeX @article{Seeger2002, author = {Axel Seeger and Klaus Affeld and Leonid Goubergrits and Ulrich Kertzscher and Ernst Wellnhofer and Rene Delfos}, title = {X-ray-based flow visualization and measurement: application in multiphase flows}, journal = {Ann N Y Acad Sci}, year = {2002}, volume = {972}, pages = {247--253}, pmid = {12496025} }
2002 (04)	Goubergrits, L. ; Affeld, K. ; Fernandez-Britto, J. ; Falcon, L.: Geometry of the human common carotid artery. A vessel cast study of 86 specimens. In: Pathol Res Pract 198 (2002), Nr. 8, S. 543–551 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung The carotid artery is of special interest for the pathologist because of its frequent depositions, and for the fluidmechanician because of its complex flow properties. However, there is a distinct lack in current knowledge of its geometry. Therefore, a vessel cast study was undertaken. At post mortem, the arteries are excised and filled with a special resin at the proper transmural pressure. Eighty-six vessel casts of the carotid artery were performed, and some etiological factors of atherosclerosis, such as age, sex and disease, were collected. The following selected geometric parameters of these vessel casts were measured in this study: the diameters of the main branches of carotid bifurcation (common, internal and external arteries), and the angles between internal, external and common carotid arteries. The averaged geometric parameters and their variability over 86 vessel casts of the carotid artery were investigated. Furthermore, the relationship between these measured parameters and the etiological factors age, sex and disease was analyzed. The geometric parameters varied considerably, presumably contributing to a corresponding variability in the local hemodynamic and distribution of the atherosclerotic lesions.
BibTeX @article{Goubergrits2002a, author = {L. Goubergrits and K. Affeld and J. Fernandez-Britto and L. Falcon}, title = {Geometry of the human common carotid artery. A vessel cast study of 86 specimens}, journal = {Pathol Res Pract}, year = {2002}, volume = {198}, number = {8}, pages = {543--551}, pmid = {12389998} }
2002 (03)	Affeld, K. ; Kertzscher, U. ; Goubergrits, L.: Experimental assessment of wall shear flow in models. In: Biorheology 39 (2002), Nr. 3-4, S. 485–489 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung The blood flow immediately adjacent to the wall of a blood vessel or an artificial surface is of great interest. This flow defines the shear stress at the wall and is known to have a great physiological importance. The use of models is a viable method to investigate this flow. However, even in models the shear stress at the wall is difficult to assess. A new optical method is based on transparent models and uses particles in the model fluid, which are only visible near the wall. This is achieved with a model fluid having a defined opacity. This fluid obscures particles in the center of the models, but permits the observation and recording of particles close to the wall. The method has been applied for Hagen-Poiseuille flow and for the likewise well researched flow in a tube with a sudden expansion.
BibTeX @article{Affeld2002, author = {K. Affeld and U. Kertzscher and L. Goubergrits}, title = {Experimental assessment of wall shear flow in models}, journal = {Biorheology}, year = {2002}, volume = {39}, number = {3-4}, pages = {485--489}, pmid = {12122270} }
2002 (02)	Goubergrits, L. ; Affeld, K. ; Fernandez-Britto, J. ; Falcon, L.: Atherosclerosis and flow in carotid arteries with authentic geometries. In: Biorheology 39 (2002), Nr. 3-4, S. 519–524 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung The influence of blood flow on the depositions and development of atherosclerotic lesions have been observed and described since the 19th century. Observations have shown that depositions correlate with regions of low wall shear stress. However, the exact correlations between depositions, vessel geometry and flow parameters are not yet known. The purpose of this study was the quantification of atherosclerosis risk factors in carotid bifurcation. This artery has attracted particular interest because lesions are often found in this bifurcation. Post mortem, the arteries are excised and vessel casts are produced. Afterwards, the arteries are analyzed morphometrically. The vessel casts are used for the assessment of some geometrical parameters. 31 carotid bifurcations were analyzed in this study. Eight vessel casts were digitized and rendered three-dimensional mathematical models of the arteries. These data were imported by the computational fluid dynamics program FLUENT. Further, the blood flow was reconstructed in a computer model based on the individual vessel geometry. The flow parameters, such as velocity, pressure and wall shear stress were computed. At the same time the geometrical parameters and wall alterations are known. This permits the comparison of the anatomical shape and its flow with the distribution and level of the wall alterations.
BibTeX @article{Goubergrits2002b, author = {L. Goubergrits and K. Affeld and J. Fernandez-Britto and L. Falcon}, title = {Atherosclerosis and flow in carotid arteries with authentic geometries}, journal = {Biorheology}, year = {2002}, volume = {39}, number = {3-4}, pages = {519--524}, pmid = {12122275} }
2002 (01)	Sartori-Montecroce, O. ; Goubergrits, L. ; Affeld, K.: Investigation of the flow performance of a nutating blood pump by computational fluid dynamics. In: Artif Organs 26 (2002), Nr. 4, S. 392–396 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung In centrifugal blood pumps, blood is moved into a circular path with the help of an impeller. In a nutating pump, the nutating body takes over the role of the impeller. Since the nutating body itself does not rotate, this pump needs no seal, no blood contacting, and no magnetic bearings. To examine the suitability of the nutating pump principle for mechanical heart assist, the flow performance of different nutating pump models was investigated by computational fluid dynamics. The geometrical parameters of the pump were varied and flow-pressure curves were calculated for 12 models at different rotation frequencies. All models showed satisfactory flow-pressure curves. One model was computed minutely at 1 flow configuration to examine shear stresses within the fluid. A flow of 5 L/min and a frequency of 3,300 rotations per min (rpm) resulted in a differential pressure of 85 mm Hg. The maximum shear stress in the fluid at this flow was estimated to be 193 Pa which is considered to be an acceptable value for a blood pump.
BibTeX @article{Sartori-Montecroce2002, author = {Oliver Sartori-Montecroce and Leonid Goubergrits and Klaus Affeld}, title = {Investigation of the flow performance of a nutating blood pump by computational fluid dynamics}, journal = {Artif Organs}, year = {2002}, volume = {26}, number = {4}, pages = {392--396}, pmid = {11952514} }
2001 (05)	Timmel, T. ; Goubergrits, L. ; Affeld, K.: Optimization and investigation of a novel cardiac assist valve with a purge flow. In: Int J Artif Organs 24 (2001), Nr. 11, S. 777–783 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Clinical applications of cardiac assist systems still suffer from thromboembolic complications due to thrombus formation behind the valve's leaflets. Wherever the flow is stagnant such as in the sinus, a thrombus is likely to form. The valve design in this study avoids stagnation zones 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 was performed on a monoleaflet valve because of its simple geometry. Relevant geometric parameters were systematically varied. Thirty-two models were designed and numerically investigated. The models with the best results were preselected and investigated in a computer-controlled valve tester. The washout of a dye filled in the sinus was digitally recorded and quantified. The results show that a sinus purge flow minimizes stagnation areas in the sinus and thus may avoid thrombus formation.
BibTeX @article{Timmel2001, author = {T. Timmel and L. Goubergrits and K. Affeld}, title = {Optimization and investigation of a novel cardiac assist valve with a purge flow}, journal = {Int J Artif Organs}, year = {2001}, volume = {24}, number = {11}, pages = {777--783}, pmid = {11797847} }
2001 (04)	Leirner, A. ; Hayashida, S. ; Maizato, M. ; Silva, de-L, M. ; Cestari, I. ; Affeld, K.: Pulsatile ventricular assist device with pericardial inner lining. In: Artif Organs 25 (2001), Nr. 11, S. 907–911 [Zusammenfassung] [BibTeX]
Zusammenfassung Preserved pericardium in contact with blood is not thrombogenic, therefore avoiding the use of anticoagulants, and has excellent mechanical properties. Our objective is to take advantage of these characteristics and build a pulsatile ventricular assist device (VAD) with pericardium used as the inner lining of the blood chamber. A mold is used for the tanning of the pericardium, rendering it with an exact shape. A flexible polymeric structure is designed to serve as a base for the pericardium, guiding it and limiting its rate of strain. It consists of two halves, which when outfitted with the interior pericardium lining and connected to each other, form the blood chamber. This assembly is housed in rigid polyvinyl chloride (PVC) shells making up the air chamber for the pneumatic activation. Valves are likewise made of pericardium. Sealing of the chambers was tested statically up to 300 mm Hg with no air or fluid leakage. The device was tested for 60 continuous days in a mock loop, demonstrating hydrodynamic performance adequate for ventricular assist. Micrographs (confocal laser and scanning electron microscopy) were obtained of several pericardium areas, especially on the flexing regions that are a transition between the wet and dry regions. No sign of damage to the pericardium was observed either with the naked eye or at the microscopic level. From the hydraulic performance and materials viewpoints, a completely pericardium-lined pulsatile VAD displaying a polymeric structure that avoids unpredictable bending and limits strain is feasible. The results warrant further studies regarding biocompatibility and strength advantages.
BibTeX @article{Leirner2001, author = {Leirner, A.A. and Hayashida, S.A. and Maizato, M.J. and Silva, de-L, M. and Cestari, I.A. and Affeld, K.}, title = {Pulsatile ventricular assist device with pericardial inner lining}, journal = {Artif Organs}, year = {2001}, volume = {25}, number = {11}, pages = {907--911} }
2001 (03)	Goubergrits, L. ; Affeld, K. ; Fernandez-Britto, J. ; Falcon, L.: Atherosclerosis in the human common carotid artery. A morphometric study of 31 specimens. In: Pathol Res Pract 197 (2001), Nr. 12, S. 803–809 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung The carotid artery bifurcation is of special interest to both the pathologist because of its frequent atherosclerotic depositions, and to the fluidmechanicist because of its complex flow properties. However, current knowledge is incomplete regarding the level and position of atherosclerotic plaques in the carotid bifurcation and their quantitative correlation with its geometry. The study presented here is intended to fill that knowledge gap and try to quantify the geometrical risk factors. During the post-mortem the arteries were excised and filled with a resin at the proper transmural pressure of 80 mm Hg. Thirty-one vessel casts of the carotid artery from twenty-three autopsied individuals were made. The vessel casts were used to measure several geometrical parameters. After fabrication of the vessel casts each artery was investigated according to pathomorphological procedure. An atherometric system (AS) indicating the level of atherosclerotic lesions was applied. The specimens were divided into three groups according to the level of atherosclerosis. The comparison was made between the level of wall alteration of the main branches of the carotid bifurcation (common, internal and external carotid branch), and between these three groups themselves. Further, we conducted a comparison of the averaged geometric parameters in different groups to define the correlations between atherosclerotic lesions and geometric parameters. The results show that the most advanced lesions (fibrous and severe plaques) with about 70% of all lesions were mainly found in the internal and the external carotid branches, compared with only 25% for the common carotid branch. The comparative analysis showed that a relatively high carotid sinus enlargement of > 1.2 of the common carotid branch diameter is a most significant geometric risk factor among those investigated, whereas there was no correlation between branch angles and atherosclerosis. In conclusion, the quantification of atherosclerotic risk factors is very important in the investigation of atherosclerotic disease development.
BibTeX @article{Goubergrits2001, author = {L. Goubergrits and K. Affeld and J. Fernandez-Britto and L. Falcon}, title = {Atherosclerosis in the human common carotid artery. A morphometric study of 31 specimens}, journal = {Pathol Res Pract}, year = {2001}, volume = {197}, number = {12}, pages = {803--809}, pmid = {11795827} }
2001 (02)	Seeger, A. ; Affeld, K. ; Goubergrits, L. ; Kertzscher, U. ; Wellnhofer, E.: X-ray-based assessment of the three-dimensional velocity of the liquid phase in a bubble column. In: Experiments in Fluids 31 (2001), Nr. 2, S. 193–201 [Zusammenfassung] [BibTeX]
Zusammenfassung Information regarding the local liquid velocity in bubble columns is of great interest for research into its performance. Common optical methods fail in bubble flows having large void fractions because of the different refraction indices of liquid phase and gaseous phases. The new X-ray Particle Tracking Velocimetry (XPTV) described here, solves the problem by the use of x-rays instead of light. X-rays penetrate a gas/liquid flow in straight lines. XPTV enables us to measure the three-dimensional velocity of the liquid phase. This method was applied and validated in two bubble columns. The same method is also applicable to opaque liquids.
BibTeX @article{Seeger2001, author = {A. Seeger and K. Affeld and L. Goubergrits and U. Kertzscher and E. Wellnhofer}, title = {X-ray-based assessment of the three-dimensional velocity of the liquid phase in a bubble column}, journal = {Experiments in Fluids}, year = {2001}, volume = {31}, number = {2}, pages = {193--201} }
2001 (01)	Goubergrits, L. ; Affeld, K. ; Wellnhofer, E. ; Zurbrügg, R. ; Holmer, T.: Estimation of wall shear stress in bypass grafts with computational fluid dynamics method. In: Int J Artif Organs 24 (2001), Nr. 3, S. 145–151 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Coronary artery bypass graft (CABG) operation for coronary artery disease with different types of grafts has a large clinical application world wide. Immediately after this operation patients are usually relieved of their chest pain and have improved cardiac function. However, after a while, these bypass grafts may fail due to for example, neointimal hyperplasia or thrombosis. One of the causes for this bypass graft failure is assumed to be the blood flow with low wall shear stress. The aim of this research is to estimate the wall shear stress in a graft and thus to locate areas were wall shear stress is low. This was done with the help of a blood flow computer model. Post-operative biplane angiograms of the graft were recorded, and from these the three-dimensional geometry of the graft was reconstructed and imported into the computational fluid dynamics (CFD) program FLUENT. The stationary diastolic flow through the grafts was calculated, and the wall shear stress distribution was estimated. This procedure was carried out for one native vessel and two different types of bypass grafts. One bypass graft was a saphenous vein and the other one was a varicose saphenous vein encased in a fine, flexible metal mesh. The mesh was attached to give the graft a defined diameter. The computational results show that each graft has distinct areas of low wall shear stress. The graft with the metal mesh has an area of low wall shear stress (< 1 Pa, stationary flow), which is four times smaller than the respective areas in the other graft and in the native vessel. This is thought to be caused by the smaller and more uniform diameter of the metal mesh-reinforced graft.
BibTeX @article{Goubergrits2001a, author = {L. Goubergrits and K. Affeld and E. Wellnhofer and R. Zurbrügg and T. Holmer}, title = {Estimation of wall shear stress in bypass grafts with computational fluid dynamics method}, journal = {Int J Artif Organs}, year = {2001}, volume = {24}, number = {3}, pages = {145--151}, pmid = {11314808} }
2000 (01)	Zimmer, R. ; Steegers, A. ; Paul, R. ; Affeld, K. ; Reul, H.: Velocities, shear stresses and blood damage potential of the leakage jets of the Medtronic Parallel bileaflet valve. In: Int J Artif Organs 23 (2000), Nr. 1, S. 41–48 [Zusammenfassung] [BibTeX]
Zusammenfassung Even nowadays, the essential problem of mechanical heart valve prostheses is the risk of thromboembolic events mainly caused by unnatural hemodynamics, e.g. just a few years ago the Medtronic Parallel (MP) showed unsatisfactory clinical results caused by thrombi. Therefore, in vitro investigations of the whole leakage jets were performed at the MP in mitral position by means of a pulse duplicator using a two channel laser Doppler anemometer. From the measured data, mean velocity profiles and the distribution of Reynolds shear stresses, as a function of the location within the jet, were calculated. From this data the potential of blood damage is evaluated computing a Blood Damage Index (BDI) of hemolysis and platelet damage. Four regurgitant free jets right above the hinges were observed during systole at the inflow side of the MP. The peak velocities at the origin of the jets were in the order of 1.6-2.1 m/s. Two jets experienced maximum turbulent shear stresses around 100 N/m2 within this area. The BDI for platelets of the MP is around ten times higher than the BDI of the St.-Jude-Medical. The study shows that besides the flow structure within the hinges of a mechanical heart valve, the whole regurgitant jet has a large blood damage potential. This potential is measurable, respectively calculable and seems to be (on account of it's support of the clinical outcome) one piece of the puzzle that explains the negative trials of the MP.
BibTeX @article{Zimmer2000, author = {Zimmer, R. and Steegers, A. and Paul, R. and Affeld, K. and Reul, H.}, title = {Velocities, shear stresses and blood damage potential of the leakage jets of the Medtronic Parallel bileaflet valve}, journal = {Int J Artif Organs}, year = {2000}, volume = {23}, number = {1}, pages = {41--48} }
1998 (06)	Fernandez-Britto, J. ; Wong, R. ; Campos, R. ; Falcon, L. ; Affeld, K. ; Guski, H.: Atherosclerotic lesions, myocardial damage and lipidograms: a multiarterial study applying an atherometric system and canonical correlation. In: Gen Diagn Pathol 143 (1998), Nr. 5-6, S. 311–316 [Zusammenfassung] [BibTeX]
Zusammenfassung 472 autopsy subjects were examined with the following aims: to study the association pattern of atherosclerotic lesions between different arterial sectors, the impact of serum lipid disorders (total cholesterol, HDL-c, LDL-c, VLDL-c, and triglycerides were analyzed) and the association pattern between the atherosclerotic lesions in different arterial sectors and the degree of heart damage. For morphometric analysis of the vessels (aorta, circle of Willis, coronary, renal, iliac, and femoral arteris) the atherometric system was used. The most relevant results were as follows: the lipid disorders show their greatest impact in the heart, coronary and femoral arteries and abdominal aorta, whereas the strongest correlations between the atherosclerotic lesions in different arterial sectors were found in those with anatomical continuity.
BibTeX @article{Fernandez-Britto1998, author = {Fernandez-Britto, J.E. and Wong, R. and Campos, R. and Falcon, L. and Affeld, K. and Guski, H.}, title = {Atherosclerotic lesions, myocardial damage and lipidograms: a multiarterial study applying an atherometric system and canonical correlation}, journal = {Gen Diagn Pathol}, year = {1998}, volume = {143}, number = {5-6}, pages = {311--316} }
1998 (05)	Affeld, K.: Cardiac valves and cardiac assist systems. In: VKI Lecture Series 1998-04: Fluid Dynamics and Biological Flows 4 (1998), S. F1–F73 [BibTeX]
BibTeX @incollection{Affeld1998c, author = {Affeld, K.}, title = {Cardiac valves and cardiac assist systems}, booktitle = {VKI Lecture Series 1998-04: Fluid Dynamics and Biological Flows}, publisher = {van Karman Institute}, year = {1998}, volume = {4}, pages = {F1--F73} }
1998 (04)	Affeld, K. ; Goubergrits, L. ; Fernandez-Britto, J. ; Falcon, L.: Variability of the geometry of the human common carotid artery – A vessel cast study of 31 specimens. In: Pathol Res Pract 194 (1998), Nr. 9, S. 597–602 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung The carotid artery is of special interest both for the pathologist because of its frequent depositions and for the fluid mechanic because of its complex flow properties. However, current knowledge of its geometry is insufficient. Therefore, a vessel cast study was undertaken and a method to fabricate vessel casts was developed. At post mortem the arteries are excised and filled with a resin at the proper transmural pressure. Thirty-one vessel casts of the carotid artery were performed and the following selected geometric parameters of these vessel casts were measured: the diameters of the main branches of carotid bifurcation (common, internal and external arteries) and the angles between internal, external and common carotid arteries. The geometric parameters vary considerably and may contribute to a corresponding variability in local hemodynamics.
BibTeX @article{Affeld1998a, author = {K. Affeld and L. Goubergrits and J. Fernandez-Britto and L. Falcon}, title = {Variability of the geometry of the human common carotid artery -- A vessel cast study of 31 specimens}, journal = {Pathol Res Pract}, year = {1998}, volume = {194}, number = {9}, pages = {597--602}, pmid = {9793957} }
1998 (03)	Affeld, K. ; Goubergrits, L. ; Holberndt, O.: Novel cardiac assist valve with a purge flow in the valve sinus. In: ASAIO J 44 (1998), Nr. 5, S. M642–M647 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Clinical applications of cardiac assist systems continue to have a severe problem, that of thromboembolic complications. The problem originates mainly at the valves, which are usually made of a antithrombogenic material, such as bovine pericardium. However, the valve housing is made of a less suitable material, and wherever the blood flow is stagnant, a thrombus is likely to form. Such stagnant blood flow is found in the space between the housing of the valve and the leaflets, in the sinuses. Consequently, thrombi often are generated in the sinuses. The novel valve design presented in this article avoids the formation of the stagnation zone in the sinuses by a purge flow. This flow is taken from the main flow through the valve and is directed into each sinus of the res purges the sinuses. The purge flow effect is investigated with an experimental method in which the sinus is filled with dye, and washout during the valve action is observed and recorded on videotape, which is compared with washout in a valve without a purge flow. In addition, the purge flow effect is investigated by computational fluid dynamics. Both methods show that the purge flow effectively increases fluid exchange in the sinuses.
BibTeX @article{Affeld1998, author = {K. Affeld and L. Goubergrits and O. Holberndt}, title = {Novel cardiac assist valve with a purge flow in the valve sinus}, journal = {ASAIO J}, year = {1998}, volume = {44}, number = {5}, pages = {M642--M647}, pmid = {9804514} }
1998 (02)	Schichl, K. ; Affeld, K. ; Dreysse, S.: Test procedure for artificial mitral valves. In: Int J Artif Organs 21 (1998), Nr. 1, S. 37–42 [Zusammenfassung] [BibTeX]
Zusammenfassung The flow curve of a valve-tester has a great influence on the performance of a valve. Usually the flow curve of the aorta is used. However, the mitral valve flow curve differs greatly from the flow curve of the aortic valve. It varies with the pulse rate and is further changed in patients with certain heart diseases. To investigate the different mitral flow conditions, ultrasonic flow curves from patients with a mechanical artificial mitral valve were analyzed. The curves show that a mitral valve prosthesis has not only to work under physiological flow conditions, but also in pathologically deviant flows. According to these results three different characteristic flow curves were selected and used to test several valves with a computer controlled valve-tester. The mean diastolic pressure difference and the whole closing behavior were influenced by the flow curve; and the differences in energy losses were particularly great. This indicates, that the flow curve must be adjusted appropriately.
BibTeX @article{Schichl1998, author = {Schichl, K. and Affeld, K. and Dreysse, S.}, title = {Test procedure for artificial mitral valves}, journal = {Int J Artif Organs}, year = {1998}, volume = {21}, number = {1}, pages = {37--42} }
1998 (01)	Affeld, K.: Valvular Dynamics. In: Intra and Extracorporeal Cardiovascular Fluid Dynamics (1998), S. 257 [BibTeX]
BibTeX @incollection{Affeld1998d, author = {Affeld, K.}, title = {Valvular Dynamics}, booktitle = {Intra and Extracorporeal Cardiovascular Fluid Dynamics}, publisher = {Computational Mechanics Publications}, year = {1998}, pages = {257} }
1997 (03)	Mussivand, T. ; Kung, R. ; McCarthy, P. ; Poirier, V. ; Arabia, F. ; Portner, P. ; Affeld, K.: Cost effectiveness of artificial organ technologies versus conventional therapy. In: ASAIO J 43 (1997), Nr. 3, S. 230–236 [BibTeX]
BibTeX @article{Mussivand1997, author = {Mussivand, T. and Kung, R.T. and McCarthy, P.M. and Poirier, V.L. and Arabia, F.A. and Portner, P. and Affeld, K.}, title = {Cost effectiveness of artificial organ technologies versus conventional therapy}, journal = {ASAIO J}, year = {1997}, volume = {43}, number = {3}, pages = {230--236} }
1997 (02)	von Baeyer, H. ; Stahl, K. ; Häusler, M. ; Meissler, M. ; Unger, V. ; Frank, J. ; Große-Siestrup, C. ; Kaczmarczyk, G. ; Affeld, K. ; Flaig, H.J. ; Steinbach, B.: [A new method of ex vivo whole blood perfusion of isolated mammalian organs, exemplified by the kidney of swine]. In: Biomed Tech (Berl) 42 (1997), Nr. 3, S. 61–68 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung A new method for the ex vivo perfusion of organs from large mammals is described. Gas exchange and dialysis are carried out simultaneously with a low-flux polysulfon dialysis module. The dialysate (e.g. Tyrode solution) is aerated with a mixture of oxygen and carbon dioxide to ensure gas exchange with the blood. Dialysis is carried out in a closed thermostatically controlled system. Monitoring of ultrafiltration is maintained by continuously weighing the blood reservoir and adjusting an afferent and efferent blood pump. Initial results obtained with isolated pig kidneys demonstrate the suitability of the new method for use as a model for the replacement of animal experiments. Theoretically, clinical application in the area of in vivo regional organ perfusion may also be possible.
BibTeX @article{Baeyer1997, author = {H. von Baeyer and K. Stahl and M. Häusler and M. Meissler and V. Unger and J. Frank and C. Große-Siestrup and G. Kaczmarczyk and K. Affeld and H. J. Flaig and B. Steinbach}, title = {[A new method of ex vivo whole blood perfusion of isolated mammalian organs, exemplified by the kidney of swine]}, journal = {Biomed Tech (Berl)}, year = {1997}, volume = {42}, number = {3}, pages = {61--68}, pmid = {9181830} }
1997 (01)	Affeld, K. ; Ziemann, A. ; Goubergrits, L.: Technical obstacles on the road towards a permanent left ventricular assist device. In: Heart Vessels Suppl 12 (1997), S. 28–30 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung After many years of research, various left ventricular assist systems (LVADs) are now entering clinical practice and are exposed to wider application. Currently, we are seeing a change in concept: after the successful application of LVADs as a bridge to transplant, today the permanent use of these devices is attracting the attention of the scientific community. LVADs based on pulsatile blood pumps necessarily contain many discrete elements. However, by integration of parts they can be made fairly simple and safe. Thrombo-embolic complications can be reduced by better design of the valves, avoiding stagnant flow altogether.
BibTeX @article{Affeld1997, author = {K. Affeld and A. Ziemann and L. Goubergrits}, title = {Technical obstacles on the road towards a permanent left ventricular assist device}, journal = {Heart Vessels}, year = {1997}, volume = {Suppl 12}, pages = {28--30}, pmid = {9476537} }
1996 (02)	Affeld, K. ; Goubergrits, L. ; Bender, A. ; Kilic, A.: Strömung in einem Aneurysma eines Blutgefäßes. In: Humboldt Spectrum 4 (1996), S. 16–18 [Zusammenfassung] [BibTeX]
Zusammenfassung An den Arterien im Schädelinneren, die das Gehirn mit Blut versorgen, können sackartige Ausstülpungen - sog. Aneurysmen - auftreten. Solche Aneurysmen können unter dem Druck des in den Arterien strömenden Blutes platzen (N. Akkas 1990) und so zu Blutungen an der Hirnoberfläche oder auch im Gehirn führen. Solche Blutungen können schwere Störungen verursachen und auch tödliche Folgen haben, insbesondere, wenn die Aneurysmen, was nicht selten ist, nach einer ersten Blutung erneut reißen und zu wiederholten Blutungen führen (J. A. Jane/ N. F. Kassel/ J. C. Turner/ H. R. Winn 1985). An einem Strömungsmodell wird sichtbar gemacht, wie die über einen Katheter in das Aneurysma eingebrachten kleinen Drahtspiralen die Blutströmung im Aneurysma beeinflussen und die Blutungsgefahr deutlich verringern.
BibTeX @article{Affeld1996a, author = {Klaus Affeld and Leonid Goubergrits and Andreas Bender and Ali Kilic}, title = {Strömung in einem Aneurysma eines Blutgefäßes}, journal = {Humboldt Spectrum}, year = {1996}, volume = {4}, pages = {16--18} }
1996 (01)	Affeld, K.: Centrifugal pumps or pulsatile pumps: which have the greater potential for a chronic cardiac assist system?. In: Int J Artif Organs 19 (1996), Nr. 11, S. 627–629 [BibTeX] [PMID ]
BibTeX @article{Affeld1996, author = {K. Affeld}, title = {Centrifugal pumps or pulsatile pumps: which have the greater potential for a chronic cardiac assist system?}, journal = {Int J Artif Organs}, year = {1996}, volume = {19}, number = {11}, pages = {627--629}, pmid = {8970828} }
1995 (01)	Affeld, K. ; Reininger, A. ; Gadischke, J. ; Grunert, K. ; Schmidt, S. ; Thiele, F.: Fluid mechanics of the stagnation point flow chamber and its platelet deposition. In: Artif Organs 19 (1995), Nr. 7, S. 597–602 [Zusammenfassung] [BibTeX]
Zusammenfassung The interaction of flow and thrombus generation often is a crucial question for the engineer working in the field of artificial organs. However, this interaction is only incompletely known, and quantitative data under well-defined experimental conditions are especially rare. These can be attained with the stagnation point flow chamber. This flow model applies platelet-rich plasma (PRP) as fluid. Its flow conditions are assessed with the help of computational fluid mechanics. In addition, the concept of the boundary layer is introduced, which permits assessment of the platelet flow along the wall. The results of the experiment indicate that platelets are deposited at a defined shear rate.
BibTeX @article{Affeld1995, author = {Affeld, K. and Reininger, A.J. and Gadischke, J. and Grunert, K. and Schmidt, S. and Thiele, F.}, title = {Fluid mechanics of the stagnation point flow chamber and its platelet deposition}, journal = {Artif Organs}, year = {1995}, volume = {19}, number = {7}, pages = {597--602} }
1994 (03)	Miethke, C. ; Affeld, K.: A new valve for the treatment of hydrocephalus – Ein neues Ventil zur Behandlung des Hydrocephalus. In: Biomed Tech (Berl) 39 (1994), Nr. 7-8, S. 181–187 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Presently available hydrocephalus valves still are not perfect. There are two major drawbacks: They have a tendency to clog and do not take into account the posture of the patient. The latter results in an intracranial pressure which is either too high or too low. To avoid these problems a new valve was designed which is described in this article. It introduces a pressure control: The force on the actual valve seat is augmented and balanced by a powerful spring. The large forces generated this way are able to overcome sticking forces due to fibrin or cellular debris. The valve functions well even with viscous and sticky cerebrospinal fluid (CSF). This mechanism maintains the pressure almost independent of the composition of the CSF. A valve insensitive to the posture of the patient can create an overdrainage, causing related problems such as subdural hygromas, slit ventricle syndrome, and consecutive proximal catheter obstruction. This is avoided by the valve presented here. It has two different pressure controllers: one designed for the supine position and another designed for the upright position of the patient. When the patient stands up or sits up, the pressure controller for the horizontal position is shut off by a gravity-activated sphere, and the drainage of CSF is directed into the appropriate controller for the upright position. In this way, the change of the hydrostatic differential pressure between the ventricles and the peritoneal cavity is taken into account and the intracranial pressure remains within physiological values. Laboratory investigations have shown that the new valve performs as designed.
BibTeX @article{Miethke1994, author = {C. Miethke and K. Affeld}, title = {A new valve for the treatment of hydrocephalus -- Ein neues Ventil zur Behandlung des Hydrocephalus}, journal = {Biomed Tech (Berl)}, year = {1994}, volume = {39}, number = {7-8}, pages = {181--187}, pmid = {7948661} }
1994 (02)	Affeld, K. ; Bailleu, A. ; Buss, A. ; Diluweit, J. ; Friedrichsen, U. ; Gadischke, J. ; Hanitsch, R. ; Hetzer, R. ; Huber, A. ; Kahler, J. ; et al.: A new electrohydraulic energy converter for a left ventricular assist device. In: Artif Organs 18 (1994), Nr. 7, S. 479–483 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung An energy converting system that can function for years without maintenance is required for the drive of a left ventricular assist device (LVAD). To meet the requirements of safety, the energy converter should have a simple design with few moving elements. The design applied herein has only one moving part and thus has greater inherent safety than competing systems. The only moving part is the rotor unit, comprised of the impeller of a centrifugal pump, the rotor of an electric motor, and the rotor of an electric axial actuator. A reversal of flow of the transmitter fluid can be achieved with an axial shift of this rotor unit. This fluid acts on the outer surface of a blood chamber and enables it to draw in blood and to expel it. Valves direct the flow of blood. The energy converter performs a flow of 12 L/min at a motor speed of 6,000 rpm against a pressure head of 115 mm Hg according to an output of the pulsatile blood pump of 5 L/min.
BibTeX @article{Affeld1994, author = {Affeld, K. and Bailleu, A. and Buss, A. and Diluweit, J. and Friedrichsen, U. and Gadischke, J. and Hanitsch, R. and Hetzer, R. and Huber, A. and Kahler, J. and et al.}, title = {A new electrohydraulic energy converter for a left ventricular assist device}, journal = {Artif Organs}, year = {1994}, volume = {18}, number = {7}, pages = {479--483}, pmid = {7980089} }
1994 (01)	Shtengold, E. ; Godin, E. ; Affeld, K.: Biomechanical tissue properties as an indicator of organ vitality prior to transplantations. In: Int J Artif Organs 17 (1994), Nr. 7, S. 408–411 [Zusammenfassung] [BibTeX]
Zusammenfassung An organ's vitality prior to transplantation can be evaluated by analysis of its mechanical properties. A new apparatus was designed to measure these properties. The organ to be tested is placed in a reservoir with saline and submitted to the load of a cylindrical element. The load is applied in a stepwise mode and results in a small local deformation of the organ. This deformation is identical to the displacement of the cylinder and is measured as a function of time. This is compared to a theoretical analysis of the deformation of a viscoelastic halfspace. This theory was used to interpret the results of experiments which were carried out on eight rabbit kidneys. The instantaneous modulus of elasticity reaches a maximum within 15 minutes, then decreases and reaches a steady state after 30 minutes of warm ischemia. The method is easy to apply and appears to be useful for the quantification of an organ's vitality and in particular recognizes the level of the organ's edema before transplantation.
BibTeX @article{Shtengold1994, author = {Shtengold, E. and Godin, E. and Affeld, K.}, title = {Biomechanical tissue properties as an indicator of organ vitality prior to transplantations}, journal = {Int J Artif Organs}, year = {1994}, volume = {17}, number = {7}, pages = {408--411} }
1993 (05)	Schichl, K. ; Affeld, K.: A computer controlled versatile pulse duplicator for precision testing of artificial heart valves. In: Int J Artif Organs 16 (1993), Nr. 10, S. 722–728 [Zusammenfassung] [BibTeX]
Zusammenfassung Numerous devices and mock circulations have been described for the measurement of pressure loss, closure time, closing and leakage volumes and energy loss in artificial heart valves. However, all the devices have been troubled with difficulties in generating and assessing the precise flow through the valve, and problems in defining the arterial load, i.e. the artificial aorta. The new test device follows a radically different approach: a computer controlled piston forces the fluid through the test valve only--with no afterload. During systole, outflow follows a physiological curve which is identical for all types of heart valves of a given size. During diastole a mathematically defined physiological pressure difference curve is followed. Consequently, the measurements are independent of the individual machine, the lab where testing takes place, the scientist who executes the test, the time when measurements are taken and all other external influences.
BibTeX @article{Schichl1993, author = {Schichl, K. and Affeld, K.}, title = {A computer controlled versatile pulse duplicator for precision testing of artificial heart valves}, journal = {Int J Artif Organs}, year = {1993}, volume = {16}, number = {10}, pages = {722--728} }
1993 (04)	Affeld, K. ; Schichl, K. ; Ziemann, A.: Assessment of rowing efficiency. In: Int J Sports Med 14 Suppl 1 (1993), S. S39–S41 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung Between one-fourth and one-third of the energy in rowing is lost to the flow of water around the blade which decreases efficiency, i.e., the ratio of effective energy to expended energy. Hitherto the assessment of this hydrodynamic rowing efficiency was difficult and could not be achieved as a function of rowing angle and time. By recording the path of the blade and the forces acting on the blade a method was found, which is practical to use and renders the hydrodynamic efficiency at each instant of the rowing action. The assessment is based on the measurement of boat velocity, angular velocity of the oar or scull, and moment exerted by the rower. These parameters are measured, digitized, and stored in the boat for later computation on shore.
BibTeX @article{Affeld1993, author = {K. Affeld and K. Schichl and A. Ziemann}, title = {Assessment of rowing efficiency}, journal = {Int J Sports Med}, year = {1993}, volume = {14 Suppl 1}, pages = {S39--S41}, pmid = {8262707} }
1993 (03)	Lerche, D. ; Vlastos, G. ; Koch, B. ; Pohl, M. ; Affeld, K.: Viscoelastic behaviour of human blood and polyacrylamide model fluids for heart valve testing. In: Journal de Physique III France 3 (1993), S. 1283–1289 [Zusammenfassung] [BibTeX]
Zusammenfassung New heart valves and other cardiovascular assist systems have to be tested for hydrodynamic performance. In place of human blood simple model fluids like glycerol solutions are employed often due to ethical and practical reasons. But blood exhibits complex non-Newtonian and viscoelastic behaviour. Rheological blood properties are reviewed based on literature and own experimental results. Furthermore we studied polymer solutions with respect to blood-like flow behaviour. Rheology was assessed by means of the low shear rotational viscometer (LS 40, Mettler-Toledo, Switzerland) under stationary and dynamic shear conditions (variation of frequency and angular displacement).
BibTeX @article{Lerche1993, author = {Lerche, D. and Vlastos, G. and Koch, B. and Pohl, M. and Affeld, K.}, title = {Viscoelastic behaviour of human blood and polyacrylamide model fluids for heart valve testing}, journal = {Journal de Physique III France}, year = {1993}, volume = {3}, pages = {1283--1289} }
1993 (02)	Affeld, K. ; Schichl, K. ; Ziemann, A.: Rudern als Strömungsproblem. In: Forschung Aktuell 39-41 (1993), S. 25–30 [BibTeX]
BibTeX @article{Affeld1993a, author = {K. Affeld and K. Schichl and A. Ziemann}, title = {Rudern als Strömungsproblem}, journal = {Forschung Aktuell}, year = {1993}, volume = {39-41}, pages = {25--30} }
1993 (01)	Affeld, K. ; Ziemann, A. ; Schichl, K.: Flow separation in artificial heart valves. In: Notes on Numerical Fluid Mechanics (1993), S. 184–191 [BibTeX]
BibTeX @incollection{Affeld1993b, author = {Klaus Affeld and Andreas Ziemann and Klaus Schichl}, title = {Flow separation in artificial heart valves}, booktitle = {Notes on Numerical Fluid Mechanics}, publisher = {Vieweg}, year = {1993}, pages = {184--191} }
1990 (03)	Affeld, K. ; Schichl, K.: Ein rechnergesteuertes Testverfahren für künstliche Herzklappen. In: Spektrum der Wissenschaft 7 (1990), S. 22–24 [BibTeX]
BibTeX @article{Affeld1990, author = {K. Affeld and K. Schichl}, title = {Ein rechnergesteuertes Testverfahren für künstliche Herzklappen}, journal = {Spektrum der Wissenschaft}, year = {1990}, volume = {7}, pages = {22--24} }
1990 (02)	Affeld, K. ; Treiber-Molkentin, J. ; Walker, P.: An Enlarged Model of Stenotic Coronary Artery Flow. In: Preventive Cardiology (1990), S. 159–166 [BibTeX]
BibTeX @article{Affeld1990a, author = {K. Affeld and J. Treiber-Molkentin and P. Walker}, title = {An Enlarged Model of Stenotic Coronary Artery Flow}, journal = {Preventive Cardiology}, year = {1990}, pages = {159--166} }
1990 (01)	Gerlach, J. ; Vienken, J. ; Walker, P. ; Affeld, K.: Computer aided time-lapse video analysis of hepatocyte morphology during adhesion to cellulose membranes. In: Int J Artif Organs 13 (1990), Nr. 6, S. 365–369 [Zusammenfassung] [BibTeX]
Zusammenfassung An investigation was performed to demonstrate that time-lapse cinematography and computer aided video analysis of cell morphology is suitable to study and compare the characteristics of hepatocytes during the adhesion process to membranes. We chose to compare ordinary cellulose Cuprophan membranes and membranes coated with collagen or fibronectin. Striking differences between uncoated cellulose and fibronectin or collagen coating were seen in the cell count per square millimeter and adhesion behaviour. On the investigated uncoated Cuprophan the hepatocytes were found to attach but not to spread whilst on collagen coated Cuprophan most of the cells spread spherically, and on fibronectin coated membranes most of the cells flattened spherically or polygonally. Time-lapse video microscopy seems to be a valuable technique for assessing the morphologic behaviour of cells in a detailed and quantitative manner in order to improve the hepatocyte culture technique in bioreactors for hybrid systems.
BibTeX @article{Gerlach1990, author = {Gerlach, J. and Vienken, J. and Walker, P. and Affeld, K.}, title = {Computer aided time-lapse video analysis of hepatocyte morphology during adhesion to cellulose membranes}, journal = {Int J Artif Organs}, year = {1990}, volume = {13}, number = {6}, pages = {365--369} }
1989 (01)	Affeld, K. ; Walker, P. ; Schichl, K.: The use of image processing in the investigation of artificial heart valve flow.. In: ASAIO Trans 35 (1989), Nr. 3, S. 294–298 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung A circulation model enlarged ten times with a likewise enlarged model of the artificial heartvalve leads to a very slow motion of the fluid. Many methods of flow visualization can therefore be applied. The particle method has been chosen as the most appropriate for further processing. The flow is videotaped, two consecutive frames are selected and with the help of image processing the vector field, the streamlines and the velocity profiles are computed and drawn.
BibTeX @article{Affeld1989, author = {K. Affeld and P. Walker and K. Schichl}, title = {The use of image processing in the investigation of artificial heart valve flow.}, journal = {ASAIO Trans}, year = {1989}, volume = {35}, number = {3}, pages = {294--298}, pmid = {2597467} }
1987 (02)	Becker, H. ; Schurig, R. ; Gahl, G.M. ; Große-Siestrup, C. ; Affeld, K. ; Weihermüller, K. ; Hain, H.: Design criteria for artificial percutaneous leads, with emphasis on the comparison between the Tenckhoff catheter and the Berlin catheter. In: Contrib Nephrol 57 (1987), S. 136–146 [BibTeX] [PMID ]
BibTeX @article{Becker1987, author = {H. Becker and R. Schurig and G. M. Gahl and C. Große-Siestrup and K. Affeld and K. Weihermüller and H. Hain}, title = {Design criteria for artificial percutaneous leads, with emphasis on the comparison between the Tenckhoff catheter and the Berlin catheter}, journal = {Contrib Nephrol}, year = {1987}, volume = {57}, pages = {136--146}, pmid = {3677687} }
1987 (01)	Kitamura, T. ; Affeld, K. ; Mohnhaupt, A.: Design of a new pulse duplicator system for prosthetic heart valves. In: J Biomech Eng 109 (1987), Nr. 1, S. 43–47 [Zusammenfassung] [BibTeX] [PMID ]
Zusammenfassung This paper discusses results of a computer simulation for designing a new pulse duplicator system for mechanical heart valves. The design objective of the system is to obtain a compact, efficient pulse duplicator system capable of accurately measuring the volume flow rate across a valve. The volume flow rate is determined as the derivative of the volume displacement of an actuator piston which directly drives the fluid. The system does not need any circulatory loop, since the piston is controlled on-line to follow command signals representing an aortic impedance. The results of the computer simulation show: the designed PI-controllers of the actuator can precisely control valve motion to follow given command signals, the eigenvalues of the controllers have to be carefully chosen to prevent unstable behaviors of a valve in diastole, and the dimensions of the actuator is optimized by minimizing a cost function of the total efficiency of the system.
BibTeX @article{Kitamura1987, author = {T. Kitamura and K. Affeld and A. Mohnhaupt}, title = {Design of a new pulse duplicator system for prosthetic heart valves}, journal = {J Biomech Eng}, year = {1987}, volume = {109}, number = {1}, pages = {43--47}, pmid = {3560878} }
1986 (02)	von Scheel, J. ; Affeld, K.: [The Kümmel and Beck puncture of the frontal sinus]. In: Laryngol Rhinol Otol (Stuttg) 65 (1986), Nr. 1, S. 40–41 [BibTeX] [PMID ]
BibTeX @article{Scheel1986, author = {J. von Scheel and K. Affeld}, title = {[The Kümmel and Beck puncture of the frontal sinus]}, journal = {Laryngol Rhinol Otol (Stuttg)}, year = {1986}, volume = {65}, number = {1}, pages = {40--41}, pmid = {3951296} }
1986 (01)	Affeld, K. ; Schichl, K. ; Yoganathan, A.: Investigation of the flow in a centrifugal blood pump. In: ASAIO Trans 32 (1986), Nr. 1, S. 269–273 [BibTeX] [PMID ]
BibTeX @article{Affeld1986, author = {K. Affeld and K. Schichl and A. Yoganathan}, title = {Investigation of the flow in a centrifugal blood pump}, journal = {ASAIO Trans}, year = {1986}, volume = {32}, number = {1}, pages = {269--273}, pmid = {2946310} }
1984 (01)	Große-Siestrup, C. ; Affeld, K.: Design criteria for percutaneous devices. In: J Biomed Mater Res 18 (1984), Nr. 4, S. 357–382 [Zusammenfassung] [BibTeX] [DOI ] [PMID ]
Zusammenfassung A theoretical model of a percutaneous device is described. The model is split into several components, each with its own function. Special structures such as horns, hair, feathers, fingernails, hoofs , teeth, and antlers are taken as examples where nature has solved the problems of "percutaneous devices." These structures have been regarded in relation to dimensional and structural differences of epidermis, dermis, and subcutis. Theoretical guidelines are described for the design of a prosthetic percutaneous device.
BibTeX @article{Grosse-Siestrup1984, author = {C. Große-Siestrup and K. Affeld}, title = {Design criteria for percutaneous devices}, journal = {J Biomed Mater Res}, year = {1984}, volume = {18}, number = {4}, pages = {357--382}, doi = {http://dx.doi.org/10.1002/jbm.820180405}, pmid = {6736073} }

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