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1
Duncan, D. D., C. B. Bargeron, S. E. Borchardt, O. J. Deters, S. A. Gearhart, F. F. Mark, and M. H. Friedman. "The Effect of Compliance on Wall Shear in Casts of a Human Aortic Bifurcation." Journal of Biomechanical Engineering 112, no. 2 (May 1, 1990): 183–88. http://dx.doi.org/10.1115/1.2891170.
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Rigid and compliant casts of a human aortic bifurcation were subjected to physiologically realistic pulsatile fluid flows. At a number of sites near the wall in the approximate median plane of the bifurcation of these models, fluid velocity was measured with a laser Doppler velocimeter, and wall motion (in the case of the compliant cast) was determined with a Reticon linescan camera. The velocity and wall motion data were combined to estimate the instantaneous shear rates at the cast wall. Analysis showed that at the outer walls the cast compliance reduced shear rates, while at the walls of the flow divider the shear rate was increased.
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Deters, O. J., C. B. Bargeron, F. F. Mark, and M. H. Friedman. "Measurement of Wall Motion and Wall Shear in a Compliant Arterial Cast." Journal of Biomechanical Engineering 108, no. 4 (November 1, 1986): 355–58. http://dx.doi.org/10.1115/1.3138628.
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Initial measurements of the time-varying wall shear rate at two sites in a compliant cast of a human aortic bifurcation are presented. The shear rates were derived from flow velocities measured by laser Doppler velocimetry (LDV) near the moving walls of the cast. To derive these shear rate values, the distance from the velocimeter sampling volume to the cast wall must be known. The time variation of this distance was obtained from LDV measurements of the velocity of the wall itself.
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Stel, HV, KS Sakariassen, PG de Groot, JA van Mourik, and JJ Sixma. "Von Willebrand factor in the vessel wall mediates platelet adherence." Blood 65, no. 1 (January 1, 1985): 85–90. http://dx.doi.org/10.1182/blood.v65.1.85.85.
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Abstract A monoclonal antibody directed against the von Willebrand factor moiety (vWF) of factor VIII-von Willebrand factor (FVIII-vWF), which blocks ristocetin-induced platelet aggregation as well as the binding of FVIII- vWF to platelets in the presence of ristocetin, inhibited platelet adherence to human artery subendothelium when present in normal flowing blood. This monoclonal antibody, CLB-RAg 35, inhibited platelet adherence as a function of the shear rate. At wall shear rates below 500 s-1, platelet adherence was not affected, but at higher shear rates platelet adherence was gradually inhibited, reaching an average of 11% of the normal value at 2,500 s-1. Indirect immunofluorescence established the reactivity of CLB-RAg 35 with vWF present in artery subendothelium. Pretreatment of normal vessel walls with this antibody inhibited adherence of platelets in blood from a patient with severe homozygous von Willebrand's disease and in blood from normal individuals. The inhibition was shear-rate dependent and significant at high shear rates (2,500 s-1). By adding increasing amounts of purified FVIII-vWF to normal blood, the inhibition was gradually overcome. These data indicate that vWF present in the vessel wall contributes appreciably to platelet adherence. At high wall shear rates, platelet adherence is mediated virtually completely by both plasma FVIII-vWF and vWF in the vessel wall. At low wall shear rates (below 500 s-1), platelet adherence occurs independent of FVIII-vWF in plasma and vWF in the vessel wall.
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Stel, HV, KS Sakariassen, PG de Groot, JA van Mourik, and JJ Sixma. "Von Willebrand factor in the vessel wall mediates platelet adherence." Blood 65, no. 1 (January 1, 1985): 85–90. http://dx.doi.org/10.1182/blood.v65.1.85.bloodjournal65185.
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A monoclonal antibody directed against the von Willebrand factor moiety (vWF) of factor VIII-von Willebrand factor (FVIII-vWF), which blocks ristocetin-induced platelet aggregation as well as the binding of FVIII- vWF to platelets in the presence of ristocetin, inhibited platelet adherence to human artery subendothelium when present in normal flowing blood. This monoclonal antibody, CLB-RAg 35, inhibited platelet adherence as a function of the shear rate. At wall shear rates below 500 s-1, platelet adherence was not affected, but at higher shear rates platelet adherence was gradually inhibited, reaching an average of 11% of the normal value at 2,500 s-1. Indirect immunofluorescence established the reactivity of CLB-RAg 35 with vWF present in artery subendothelium. Pretreatment of normal vessel walls with this antibody inhibited adherence of platelets in blood from a patient with severe homozygous von Willebrand's disease and in blood from normal individuals. The inhibition was shear-rate dependent and significant at high shear rates (2,500 s-1). By adding increasing amounts of purified FVIII-vWF to normal blood, the inhibition was gradually overcome. These data indicate that vWF present in the vessel wall contributes appreciably to platelet adherence. At high wall shear rates, platelet adherence is mediated virtually completely by both plasma FVIII-vWF and vWF in the vessel wall. At low wall shear rates (below 500 s-1), platelet adherence occurs independent of FVIII-vWF in plasma and vWF in the vessel wall.
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Fatemi, Ray S., and Stanley E. Rittgers. "Derivation of Shear Rates From Near-Wall LDA Measurements Under Steady and Pulsatile Flow Conditions." Journal of Biomechanical Engineering 116, no. 3 (August 1, 1994): 361–68. http://dx.doi.org/10.1115/1.2895743.
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Atherosclerosis, thrombosis, and intimal hyperplasia are major forms of cardiovascular diseases in the United States. Previous studies indicate a significant correlation between hemodynamics, in particular, wall shear rate, and pathology of the arterial walls. While results of these studies implicate morphologic and functional changes related to wall shear rate magnitude, a standard technique for wall shear rate measurement has not been established. In this study, theoretical and in-vitro experimental fully developed steady and physiologic pulsatile flow waveforms have been used to obtain velocity profiles in the near-wall region. The estimated wall shear rates from these results are compared to the theoretical value to assess the accuracy of the approximating technique. Experimentally obtained results from LDA suggest that in order to minimize the error in velocity data, and subsequently, the wall shear rate, the first measured velocity has to be 500 μm away from the wall. While a linear approximation did not produce errors larger than 16.4 percent at peak systole, these errors substantially increased as the velocity magnitudes decreased during late systole and diastole. Overall, a third degree polynomial curve fit using four points produced the most accurate estimation of wall shear rate through out the cardiac cycle. Results of higher degree curve-fitting functions can be unpredictable due to potential oscillations of the function near the wall. Hence, based on the results of this study, use of a linear approximation is not recommended; a third degree curve-fitting polynomial, using four points provided the most accurate approximation for these flow waveforms.
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Wang, Shixin, Haiqing Liu, Yue Wang, Yizhi Qiao, Liang Wang, Jie Bai, Tim K. T. Tse, Cruz Y. Li, and Yunfei Fu. "Experimental Study on the Seismic Performance of Shear Walls with Different Coal Gangue Replacement Rates." Applied Sciences 12, no. 20 (October 20, 2022): 10622. http://dx.doi.org/10.3390/app122010622.
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To replace conventional concrete with coal gangue concrete in the construction industry, lateral cyclic loading tests were applied to three shear walls with different coal gangue replacement rates in this study, in which the replacement rate of coal gangue was 0%, 50%, and 100%. The load‒displacement hysteretic curves and backbone curves of the shear walls obtained from tests were analyzed to compare the failure process and seismic performance of each shear wall. The results indicate that the stress performance and failure morphology of coal gangue concrete shear walls and conventional concrete shear walls are extremely similar, and the characteristics of the hysteretic and backbone curves are approximately the same. With the increase in the coal gangue replacement rate, the bearing capacity and ductility of the three shear walls gradually decrease, the strength degradation gradually becomes significant, and the energy dissipation capacity becomes worse, but the difference is not obvious, and all of them can meet the requirements of seismic performance. In addition, with the increase in the coal gangue replacement rate, the stiffness degradation gradually slows, so it is feasible to construct a shear wall using coal gangue concrete instead of conventional concrete.
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Ben Driss, A., J. Benessiano, P. Poitevin, B. I. Levy, and J. B. Michel. "Arterial expansive remodeling induced by high flow rates." American Journal of Physiology-Heart and Circulatory Physiology 272, no. 2 (February 1, 1997): H851—H858. http://dx.doi.org/10.1152/ajpheart.1997.272.2.h851.
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The effects of chronic increase in aortic blood flow on arterial wall remodeling were investigated in vivo with the use of an aortocaval fistula (ACF) model in rats. Phasic hemodynamics and aortic wall structure upstream and downstream in 30 male Wistar rats with ACF and 30 sham-operated rats were compared immediately and 2 mo after the ACF was opened in anesthetized rats. Opening the ACF upstream acutely decreased aortic pressure (-30%, P < 0.001) and increased aortic blood velocity (x12, P < 0.001), blood flow (x9, P < 0.001), wall shear stress (x10, P < 0.001) and guanosine 3',5'-cyclic monophosphate (cGMP) wall content (+50%, P < 0.01). After 2 mo, aortic pressure decreased (-22%, P < 0.001) and aortic blood velocity, diameter, and blood flow increased (+114%, P < 0.001; +60%, P < 0.001; and +250%, P < 0.001; respectively) compared with the control group. Aortic wall shear stress and cGMP wall content dropped over time and tended to recover control values; aortic wall tensile stress was higher than in the control group (P < 0.05). Medial cross-sectional area and elastin and collagen contents increased (+38%, P < 0.01; +50%, P < 0.01; and +30%, P < 0.05, respectively) and were associated with smooth muscle cell hypertrophy) (+23%, P < 0.05), despite a decrease in arterial wall thickness (-13%, P < 0.01). Opening the ACF downstream acutely decreased aortic pressure (-30%, P < 0.001) without any change in aortic blood velocity, diameter, blood flow, shear stress, and cGMP wall content. After 2 mo, pressure, blood velocity, shear stress, and cGMP wall content decreased (-22%, P < 0.001; -31%, P < 0.01; -46%, P < 0.02; and -50%, P < 0.05; respectively) and diameter and blood flow were unchanged; smooth muscle cell hypertrophy and hypoplasia were the only observed changes in the aortic wall structure. These results suggest that both shear and tensile stresses are involved in the aortic wall remodeling. Increase in shear stress likely induces expansive remodeling in relation to flow-dependent vasodilation, whereas increase in tensile stress is responsible for medial hypertrophy and fibrosis.
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Bao, Quan, Xin Meng, Mingcheng Hu, Jian Xing, Dan Jin, He Liu, Jie Jiang, and Yanwei Yin. "Simulation analysis of aneurysm embolization surgery: Hemorheology of aneurysms with different embolization rates (CTA)." Bio-Medical Materials and Engineering 32, no. 5 (September 3, 2021): 295–308. http://dx.doi.org/10.3233/bme-211225.
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BACKGROUND: Embolization degree acts as an important factor affecting recurrence of aneurysm. OBJECTIVE: To analyze the role of hemodynamics parameters of different degrees of embolization in the occurrence, development and post-treatment of aneurysms, and to determine the specific factors causing the occurrence and recurrence of aneurysms after hemodynamics treatment. Our study provides a theoretical basis for the prevention and treatment of aneurysms. METHODS: Computed tomography angiography data of a patient with cerebral aneurysm was used to model 0%, 24%, 52%, 84% and 100% of endovascular embolization, respectively. The time average wall shear stress, time average wall shear stress, oscillatory shear index, hemodynamics formation index and relative retentive time were used to analyze the changes of hemodynamics indexes in different embolic models. RESULTS: With the increase of embolic rate, the values of time average wall shear stress, time average wall shear stress grade and aneurysm index formation gradually increased, and the values of relative retention time gradually decreased. Oscillatory shear index was higher in patients with incomplete embolization and decreased in patients with complete embolization. CONCLUSIONS: As the degree of embolization increased, the blood flow tended to stabilize, reducing the risk of cerebral aneurysm rupture, and finding that the wall of the vessel junction was susceptible to injury.
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McNally, Andrew, A. George Akingba, and Philippe Sucosky. "Effect of arteriovenous graft flow rate on vascular access hemodynamics in a novel modular anastomotic valve device." Journal of Vascular Access 19, no. 5 (March 1, 2018): 446–54. http://dx.doi.org/10.1177/1129729818758229.
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Purpose: Perturbed vascular access hemodynamics is considered a potential driver of intimal hyperplasia, the leading cause of vascular access failure. To improve vascular access patency, a modular anastomotic valve device has been designed to normalize venous flow between hemodialysis periods while providing normal vascular access during hemodialysis. The objective of this study was to quantify the effects of arteriovenous graft flow rate on modular anastomotic valve device vascular access hemodynamics under realistic hemodialysis conditions. Methods: Modular anastomotic valve device inlet and outlet flow conditions and velocity profiles were measured by ultrasound Doppler in a vascular access flow loop replicating arteriovenous graft flow rates of 800, 1000, and 1500 mL/min. Fluid–structure interaction simulations were performed to identify low wall shear stress regions on the vein wall and to characterize them in terms of temporal shear magnitude, oscillatory shear index, and relative residence time. The model was validated with respect to the Doppler measurements. Results: The low wall shear stress region generated downstream of the anastomosis under low and moderate arteriovenous graft flow rates was eliminated under the highest arteriovenous graft flow rate. Increase in arteriovenous graft flow rate from 800 to 1500 mL/min resulted in a substantial increase in wall shear stress magnitude (27-fold increase in temporal shear magnitude), the elimination of wall shear stress bidirectionality (0.20-point reduction in oscillatory shear index), and a reduction in flow stagnation (98% decrease in relative residence time). While the results suggest the ability of high arteriovenous graft flow rates to protect the venous wall from intimal hyperplasia–prone hemodynamics, they indicate their adverse impact on the degree of venous hemodynamic abnormality.
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Colace, Thomas Vincent, and Scott L. Diamond. "Direct Observation of Von Willebrand Factor Elongation and Fiber Formation On Collagen During Acute Whole Blood Exposure to Pathological Flow." Blood 120, no. 21 (November 16, 2012): 1070. http://dx.doi.org/10.1182/blood.v120.21.1070.1070.
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Abstract Abstract 1070 Under conditions of pathological shear rate, von Willebrand Factor (vWF) undergoes conformational changes and self aggregation. We sought to visualize this phenomenon using a novel microfluidic model of stenosis and understand its role in thrombus formation in elevated shear rate environments. In severe stenosis, vWF experiences millisecond exposures to pathological wall shear rates (gw). Distinct from shear experiments that last many seconds, we deployed microfluidic devices for single-pass perfusion of whole blood or platelet free plasma (PFP) over fibrillar type 1 collagen (< 50 msec transit time) at pathological gw or spatial wall shear rate gradient (grad gw). Using fluorescent anti-vWF, long thick vWF fibers (>20 mm) bound to collagen were visualized at constant gw > 30,000 s−1 during perfusion of PFP, a process enhanced by EDTA. Rapid acceleration or deceleration of EDTA-PFP at grad gw = ± 5.5 × 105 to 4.3 × 107 s−1/cm did not promote vWF deposition when gw < 30,000. At 19,400 s−1, EDTA-blood perfusion resulted in rolling vWF-platelet nets, while blood perfusion (normal Ca2+) generated large vWF/platelet deposits that repeatedly embolized and were blocked by anti-GP1b or the aIIbβ3 inhibitor GR144053 and did not require shear gradients. Blood perfusion at venous shear rate (200 s−1) produced a stable platelet deposit that was a substrate for massive but unstable vWF-platelet aggregates when flow was increased to 7800 s−1. Supported by collagen and enhanced by platelet GP1b and aIIbβ3, vWF fiber formation occurred during acute exposures to pathological gw but did not require wall shear rate gradients. Figure 1 A, Platelet free citrated-plasma was treated with 1 μg/mL fluorescently labeled anti-vWF and 5 mM EDTA. The plasma samples were perfused over a collagen type 1 surface at local wall shear rates of 30,000, 62,400 and 125,000 s−1 from left to right. Long fibers of vWF (>20 μm) appeared at shear rates above ∼30,000 s−1, with more fibers appearing at higher shear rates. The bar indicates 15 μm. Figure 1. A, Platelet free citrated-plasma was treated with 1 μg/mL fluorescently labeled anti-vWF and 5 mM EDTA. The plasma samples were perfused over a collagen type 1 surface at local wall shear rates of 30,000, 62,400 and 125,000 s−1 from left to right. Long fibers of vWF (>20 μm) appeared at shear rates above ∼30,000 s−1, with more fibers appearing at higher shear rates. The bar indicates 15 μm. Disclosures: No relevant conflicts of interest to declare.
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Talbot, L., and J. J. Steinert. "The Frequency Response of Electrochemical Wall Shear Probes in Pulsatile Flow." Journal of Biomechanical Engineering 109, no. 1 (February 1, 1987): 60–64. http://dx.doi.org/10.1115/1.3138643.
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The frequency response of surface-mounted electrochemical mass transfer probes used to deduce wall shear rates has been investigated experimentally for the case of fully developed laminar pulsatile flow in a straight tube. Generally good agreement is found with the asymptotic results obtained by Lighthill’s methods. The significance of the results with regard to the investigation of models of pulsatile flows of physiological interest is discussed. It is concluded that the frequency-dependent phase and amplitude corrections required to obtain accurate wall shear measurements are of such magnitudes as to render impractical the use of electrochemical probes to determine wall shear rates in these flows.
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HSU, H. Y., and N. A. PATANKAR. "A continuum approach to reproduce molecular-scale slip behaviour." Journal of Fluid Mechanics 645 (February 2, 2010): 59–80. http://dx.doi.org/10.1017/s0022112009992540.
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In this work we explore if it is possible to reproduce molecular-scale slip behaviour by using continuum equations. To that end it is noted that molecular-scale slip is affected by three factors: (i) near the wall, the fluid experiences a potential because of the wall; (ii) the fluid density responds to that potential, and hence, fluid compressibility is relevant; and (iii) the fluid can lose momentum to the wall. To incorporate these features we simulate shear flow of a compressible fluid between two walls in the presence of a potential. Compressibility effect is found to be important only in the near-wall region. The slip length is calculated from the mean velocity profile. The slip-length-versus-shear-rate trend is similar to that in molecular dynamic calculations. First, there is a constant value of the slip length at low shear rates. Then, the slip length increases beyond a critical shear rate. Lastly, the slip length reaches another constant value if the wall momentum loss parameter is non-zero. The scaling for the critical shear rate emerges from our results. The value of the slip length increases if the wall potential is less corrugated and if the momentum loss to the wall is low. An understanding of the overall force balance during various slip modes emerges from the governing equations.
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Siegel, John M., Christos P. Markou, David N. Ku, and S. R. Hanson. "A Scaling Law for Wall Shear Rate Through an Arterial Stenosis." Journal of Biomechanical Engineering 116, no. 4 (November 1, 1994): 446–51. http://dx.doi.org/10.1115/1.2895795.
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Atherosclerosis of the human arterial system produces major clinical symptoms when the plaque advances to create a high-grade stenosis. The hemodynamic shear rates produced in high-grade stenoses are important in the understanding of atheromatous plaque rupture and thrombosis. This study was designed to quantify the physiologic stress levels experienced by endothelial cells and platelets in the region of vascular stenoses. The steady hemodynamic flow field was solved for stenoses with percent area reductions of 50, 75, and 90 percent over a range of physiologic Reynolds numbers (100–400). The maximum wall shear rate in the throat region can be shown to vary by the square root of the Reynolds number. The shear rate results can be generalized to apply to a range of stenosis lengths and flow rates. Using dimensions typical for a human carotid or coronary artery, wall shear rates were found to vary from a maximum of 20,000 s−1 upstream of the throat to a minimum of −630 s−1 in the recirculation zone for a 90 percent stenosis. An example is given which illustrates how these values can be used to understand the relationship between hemodynamic shear and platelet deposition.
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Badimon, L., JJ Badimon, VT Turitto, and V. Fuster. "Role of von Willebrand factor in mediating platelet-vessel wall interaction at low shear rate; the importance of perfusion conditions." Blood 73, no. 4 (March 1, 1989): 961–67. http://dx.doi.org/10.1182/blood.v73.4.961.961.
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Abstract We have previously observed that von Willebrand factor (vWF) plays an important role in platelet deposition on subendothelium at low values of wall shear rate (200 to 400 seconds-1). In the present study, we have investigated the mechanism responsible for such a defect in platelet deposition at low shear rates in the absence of vWF. Blood from both normal and von Willebrand's disease (vWD) animals was exposed to de-endothelialized aorta from normal pigs for a range of shear rates (200 to 3,000 seconds-1) and exposure times (three to 30 minutes) in a tubular perfusion chamber. Variations in the method of inhibiting coagulation (none, heparin, citrate, hirudin, and EDTA) and of perfusing blood (in vitro v ex vivo) were compared by determining the influence of wall shear rate and vWF on the deposition of 111In-labeled platelets on subendothelium. Whereas platelet deposition was reduced in the absence of vWF for all experimental variations at high shear rates (greater than 850 seconds-1), a defect was observed at low shear rates only when heparinized blood was exposed by means of an ex vivo perfusion system. Maximum sensitivity of the measurement occurs under ex vivo perfusion conditions due to the reduced ability of platelets to deposit in normal blood when recirculated in vitro. Our results indicate that vWF mediates platelet-vessel wall interaction even at low shear rates and that such effect can only be observed in systems where platelet function is minimally affected by the experimental conditions.
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Badimon, L., JJ Badimon, VT Turitto, and V. Fuster. "Role of von Willebrand factor in mediating platelet-vessel wall interaction at low shear rate; the importance of perfusion conditions." Blood 73, no. 4 (March 1, 1989): 961–67. http://dx.doi.org/10.1182/blood.v73.4.961.bloodjournal734961.
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We have previously observed that von Willebrand factor (vWF) plays an important role in platelet deposition on subendothelium at low values of wall shear rate (200 to 400 seconds-1). In the present study, we have investigated the mechanism responsible for such a defect in platelet deposition at low shear rates in the absence of vWF. Blood from both normal and von Willebrand's disease (vWD) animals was exposed to de-endothelialized aorta from normal pigs for a range of shear rates (200 to 3,000 seconds-1) and exposure times (three to 30 minutes) in a tubular perfusion chamber. Variations in the method of inhibiting coagulation (none, heparin, citrate, hirudin, and EDTA) and of perfusing blood (in vitro v ex vivo) were compared by determining the influence of wall shear rate and vWF on the deposition of 111In-labeled platelets on subendothelium. Whereas platelet deposition was reduced in the absence of vWF for all experimental variations at high shear rates (greater than 850 seconds-1), a defect was observed at low shear rates only when heparinized blood was exposed by means of an ex vivo perfusion system. Maximum sensitivity of the measurement occurs under ex vivo perfusion conditions due to the reduced ability of platelets to deposit in normal blood when recirculated in vitro. Our results indicate that vWF mediates platelet-vessel wall interaction even at low shear rates and that such effect can only be observed in systems where platelet function is minimally affected by the experimental conditions.
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Wilms, Patrick, Jan Wieringa, Theo Blijdenstein, Kees van Malssen, and Reinhard Kohlus. "Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows." Rheologica Acta 60, no. 8 (June 30, 2021): 423–37. http://dx.doi.org/10.1007/s00397-021-01281-5.
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AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.
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Ngai, A. C., and H. R. Winn. "Estimation of shear and flow rates in pial arterioles during somatosensory stimulation." American Journal of Physiology-Heart and Circulatory Physiology 270, no. 5 (May 1, 1996): H1712—H1717. http://dx.doi.org/10.1152/ajpheart.1996.270.5.h1712.
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We tested the hypothesis that a shear stress-dependent mechanism is involved in the dilation of pial arterioles during somatosensory stimulation. In alpha-chloralose-anesthetized rats implanted with cranial windows, we simultaneously measured the diameter and flow velocity of pial arterioles with video and dual-slit methods. Stimulation (0.2-0.3 V, 5 Hz, 0.5 ms pulses for 20 s) of the contralateral sciatic nerve evoked consistent dilator responses in pial arterioles (36 +/- 1 micron diam) without affecting blood pressure. The dilator responses consisted of an initial transient peak dilation of 30 +/- 3%, followed by a sustained dilation of 13 +/- 1% (n = 11). Mean velocity increased by 16.4 +/- 5.7% at 5 s after stimulus onset. Wall shear rate and volume flow were calculated from diameter and velocity data by assuming a parabolic flow profile. There was no significant change in wall shear rate, whereas flow rate increased significantly during sciatic nerve stimulation. The present findings suggest that a flow (shear stress)-mediated mechanism does not play an important role in the dilator response of pial arterioles to sciatic nerve stimulation.
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Lui, Mathew, Elizabeth E. Gardiner, Jane F. Arthur, Isaac Pinar, Woei Ming Lee, Kris Ryan, Josie Carberry, and Robert K. Andrews. "Novel Stenotic Microchannels to Study Thrombus Formation in Shear Gradients: Influence of Shear Forces and Human Platelet-Related Factors." International Journal of Molecular Sciences 20, no. 12 (June 18, 2019): 2967. http://dx.doi.org/10.3390/ijms20122967.
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Thrombus formation in hemostasis or thrombotic disease is initiated by the rapid adhesion, activation, and aggregation of circulating platelets in flowing blood. At arterial or pathological shear rates, for example due to vascular stenosis or circulatory support devices, platelets may be exposed to highly pulsatile blood flow, while even under constant flow platelets are exposed to pulsation due to thrombus growth or changes in vessel geometry. The aim of this study is to investigate platelet thrombus formation dynamics within flow conditions consisting of either constant or variable shear. Human platelets in anticoagulated whole blood were exposed ex vivo to collagen type I-coated microchannels subjected to constant shear in straight channels or variable shear gradients using different stenosis geometries (50%, 70%, and 90% by area). Base wall shears between 1800 and 6600 s−1, and peak wall shears of 3700 to 29,000 s−1 within stenoses were investigated, representing arterial-pathological shear conditions. Computational flow-field simulations and stenosis platelet thrombi total volume, average volume, and surface coverage were analysed. Interestingly, shear gradients dramatically changed platelet thrombi formation compared to constant base shear alone. Such shear gradients extended the range of shear at which thrombi were formed, that is, platelets became hyperthrombotic within shear gradients. Furthermore, individual healthy donors displayed quantifiable differences in extent/formation of thrombi within shear gradients, with implications for future development and testing of antiplatelet agents. In conclusion, here, we demonstrate a specific contribution of blood flow shear gradients to thrombus formation, and provide a novel platform for platelet functional testing under shear conditions.
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Basri, Hasan, Jimmy Deswidawansyah Nasution, Ardiyansyah Syahrom, Mohd Ayub Sulong, Amir Putra Md. Saad, Akbar Teguh Prakoso, and Faisal Aminin. "The effect to flow rate characteristic on biodegradation of bone scaffold." Malaysian Journal of Fundamental and Applied Sciences 13, no. 4-2 (December 17, 2017): 546–52. http://dx.doi.org/10.11113/mjfas.v13n4-2.843.
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This paper proposes an improved modeling approach for bone scaffolds biodegradation. In this study, the numerical analysis procedure and computer-based simulation were performed for the bone scaffolds with varying porosities in determining the wall shear stresses and the permeabilities along with their influences on the scaffolds biodegradation process while the bio-fluids flow through within followed with the change in the flow rates. Based on the experimental study by immersion testing from 0 to 72 hours of the time period, the specimens with different morphologies of the commercial bone scaffolds were collected into three groups samples of 30%, 41%, and 55% porosities. As the representative of the cancellous bone morphology, the morphological degradation was observed by using 3-D CAD scaffold models based on microcomputed tomography images. By applying the boundary conditions to the computational fluid dynamics (CFD) and the fluid-structure interaction (FSI) models, the wall shear stresses within the scaffolds due to fluid flow rates variation had been simulated and determined before and after degradation. The increase of fluid flow rates tends to raise the pressure drop for scaffold models with porosities lower than 50% before degradation. As the porosities increases, the pressure drop decreases with an increase in permeability within the scaffold. The flow rates have significant effects on scaffolds with higher pressure drops by introducing the wall shear stresses with the highest values and lower permeability. These findings indicate the importance of using accurate computational models to estimate shear stress and determine experimental conditions in perfusion bioreactors for tissue engineering more accurate results will be achieved to indicate the natural distributions of fluid flow velocity, wall shear stress, and pressure.
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Shahid, Salman, Abdul Qader Hasan, Sharul Sham Dol, Mohamed S. Gadala, and Mohd Shiraz Aris. "Effects of Near-Wall Vortices on Wall Shear Stress in a Centrifugal Pump Impeller." WSEAS TRANSACTIONS ON FLUID MECHANICS 16 (March 5, 2021): 37–47. http://dx.doi.org/10.37394/232013.2021.16.5.
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Boundary layer separation and vortex formation cause unappealing deterioration of pump pressure head. The purpose of this research paper is to correlate formation of vortices with near-wall shear stresses resulting in a loss of pump pressure head. This phenomenon is observed at the centrifugal pump impeller tip at various flow rates and impeller rotational velocities through CFD (Computational Fluid Dynamic) analysis. This research paper investigates internal flow in a shrouded centrifugal impeller that is modelled under design flow rate conditions using ANSYS Fluent as its simulation bases solving built-in Navier-Stokes equation, and 𝑘 − 𝜔 SST turbulence model under steady conditions. Numerical results revealed an increase in wall shear stresses with increasing flow rate ranging from 314.2 Pa to 595.60 Pa at increments that pulsate per flow rate. Flow characteristics, such as evolution of vortices and flow turbulence enhance wall shear stresses increasing the wall skin-friction remarkably leading towards a loss in pressure head. This paper analyzes the vortices and turbulence in flow structures with regards to their influence upon the impeller performance.
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Williams, Dillon C., Mohamed A. Zayed, and Guy Genin. "RS23. Reduction of Wall Shear Strain Rates in Arteriovenous Graft Venous Anastomoses." Journal of Vascular Surgery 69, no. 6 (June 2019): e276-e277. http://dx.doi.org/10.1016/j.jvs.2019.04.426.
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Al-Masry, Waheed A., and Malik I. Al-Ahmed. "Effect of scale-up on wall shear rates in circulating bubble columns." Journal of Chemical Technology & Biotechnology 80, no. 11 (2005): 1230–35. http://dx.doi.org/10.1002/jctb.1309.
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Keynton, R. S., S. E. Rittgers, and M. C. S. Shu. "The Effect of Angle and Flow Rate Upon Hemodynamics in Distal Vascular Graft Anastomoses: An In Vitro Model Study." Journal of Biomechanical Engineering 113, no. 4 (November 1, 1991): 458–63. http://dx.doi.org/10.1115/1.2895427.
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A steady flow, in vitro model of distal arterial bypass graft junctions was used to examine the effects of junction angle and flow rate on the local velocity field. Three test sections were fabricated from Plexiglas™ tubing having anastomotic junction angles of either 30, 45, or 60 deg. Flow visualization revealed velocity profiles skewed toward the outer wall with a flow split around a clear stagnation point along the outer wall. Laser Doppler anemometry [LDA] measurements confirmed a distinct stagnation point at the outer wall and both reverse and forward shear were detected immediately upstream and downstream, respectively, of this site. Axial velocities and shear rates along the outer wall were higher than along the inner wall and occurred in the junction angle order: 45, 60, and 30 deg. This study clearly identified changes in wall shear which varied with the anastomotic angle and flow rate.
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Tangelder, G. J., D. W. Slaaf, T. Arts, and R. S. Reneman. "Wall shear rate in arterioles in vivo: least estimates from platelet velocity profiles." American Journal of Physiology-Heart and Circulatory Physiology 254, no. 6 (June 1, 1988): H1059—H1064. http://dx.doi.org/10.1152/ajpheart.1988.254.6.h1059.
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Velocity profiles, as determined in vivo in rabbit mesenteric arterioles with fluorescently labeled platelets as natural flow markers, were used to calculate least estimates of the actual wall shear rate in these microvessels (17–32 micron diam). The fit of the velocity data points described the profile as close to the wall as 0.5 micron. To satisfy the no-slip condition, a thin layer of fluid with a steep velocity gradient near the wall was assumed. Least estimates of wall shear rate, as calculated from the fitted platelet-velocity profiles and using the mean velocity gradient in this layer of fluid, ranged from 472 to 4,712 s-1 with a median value of 1,700 s-1. Red blood cell center-line velocities varied between 1.3 and 14.4 mm/s (median 3.4). The wall shear rates were at least 1.46–3.94 (median 2.12) times higher than expected on the basis of a parabolic velocity distribution but with the same volume flow in the vessel. Considerable spatial differences in wall shear rate might exist even within a short segment of a vessel.
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Lee, San Min, Won Chang, Hyo-Jin Kang, Su Joa Ahn, Jeong-Hoon Lee, and Jeong Min Lee. "Comparison of four different Shear Wave Elastography platforms according to abdominal wall thickness in liver fibrosis evaluation: a phantom study." Medical Ultrasonography 21, no. 1 (February 17, 2019): 22. http://dx.doi.org/10.11152/mu-1737.
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Aims: To compare the applicability, reliability and stiffness values of four different shear wave elastography (SWE) platforms and to determine the influence of abdominal wall thickness on those of four SWE platforms evaluating liver fibrosis. Material and methods: We used four different SWE platforms: transient elastography (TE), pSWE (S-shear wave), 2D SWE/ SSI (SuperSonic Imagine) and 2D SWE/GE (GE Health care). To identify the effect of abdominal wall thickness, five commercially available liver fibrosis phantoms were covered in 1.3 cm and 2.3 cm thick porcine abdominal walls, respectively. All measurements were performed by three observers. Absolute repeatability of each measurement was evaluated using coefficients of variation (CVs). Applicability rate, CVs and mean stiffness values were compared according to platforms and abdominal wall thickness.Results: Applicability rates were significantly different among the four SWE platforms (p<0.001): 2DSWE/SSI showed the lowest applicability rate (68.9%) compared with the other three platforms (TE, 95.6%, pSWE, 93.3%, 2D SWE/GE, 97.8%) due to higher technical failure rates in phantoms with thick wall. Repeatability was significantly different according to the platform and abdominal wall thickness. Stiffness values did not significantly differ according to abdominal wall thickness, even though the values were significantly different among four platforms in all phantoms.Conclusions: The applicability, repeatability, and stiffness value were different depending on SWE platforms. Further, the applicability and repeatability would be more affected by abdominal wall thickness. Thus, careful consideration should be given to an appropriate SWE platform, when evaluating liver fibrosis in patients with thick abdominal wall.
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Russell, Janice, Dianne Cooper, Anitaben Tailor, Karen Y. Stokes, and D. Neil Granger. "Low venular shear rates promote leukocyte-dependent recruitment of adherent platelets." American Journal of Physiology-Gastrointestinal and Liver Physiology 284, no. 1 (January 1, 2003): G123—G129. http://dx.doi.org/10.1152/ajpgi.00303.2002.
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The influence of reductions in venular shear rate on platelet-endothelial (P/E) cell adhesion has not been previously addressed. The objectives of this study were to define the effects of reductions in venular shear rate on P/E cell adhesion and to determine the interdependence of P/E cell adhesion and leukocyte-endothelial (L/E) cell adhesion at low shear rates. Intravital videomicroscopy was used to quantify P/E and L/E cell adhesion in rat mesenteric venules exposed to shear rates ranging between 118 ± 9 and 835 ± 44 s−1. Shear rate was altered in postcapillary venules by rapid, graded blood withdrawal, without retransfusion of shed blood. Reducing shear rate from >600 s−1to <200 s−1resulted in an eightfold increase in L/E cell adhesion, whereas P/E cell adhesion increased 18-fold. A blocking antibody directed against P-selectin blunted both the P/E and L/E cell adhesion elicited by low shear rates. Immunoneutralization of CD11/CD18 on leukocytes or rendering animals neutropenic also blocked the shear rate-dependent recruitment of both platelets and leukocytes. These findings indicate that 1) low shear rates promote P/E and L/E cell adhesion in mesenteric venules, and 2) adherent neutrophils (mediated by CD11/CD18) create a platform onto which platelets can bind to the venular wall at low shear rates.
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Demirel, S., D. Chen, Y. Mei, S. Partovi, H. von Tengg-Kobligk, M. Dadrich, D. Böckler, HU Kauczor, and M. Müller-Eschner. "Comparison of morphological and rheological conditions between conventional and eversion carotid endarterectomy using computational fluid dynamics – a pilot study." Vascular 23, no. 5 (October 8, 2014): 474–82. http://dx.doi.org/10.1177/1708538114552836.
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Purpose: To compare postoperative morphological and rheological conditions after eversion carotid endarterectomy versus conventional carotid endarterectomy using computational fluid dynamics. Basic methods: Hemodynamic metrics (velocity, wall shear stress, time-averaged wall shear stress and temporal gradient wall shear stress) in the carotid arteries were simulated in one patient after conventional carotid endarterectomy and one patient after eversion carotid endarterectomy by computational fluid dynamics analysis based on patient specific data. Principal findings: Systolic peak of the eversion carotid endarterectomy model showed a gradually decreased pressure along the stream path, the conventional carotid endarterectomy model revealed high pressure (about 180 Pa) at the carotid bulb. Regions of low wall shear stress in the conventional carotid endarterectomy model were much larger than that in the eversion carotid endarterectomy model and with lower time-averaged wall shear stress values (conventional carotid endarterectomy: 0.03–5.46 Pa vs. eversion carotid endarterectomy: 0.12–5.22 Pa). Conclusions: Computational fluid dynamics after conventional carotid endarterectomy and eversion carotid endarterectomy disclosed differences in hemodynamic patterns. Larger studies are necessary to assess whether these differences are consistent and might explain different rates of restenosis in both techniques.
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Wang, Haifeng, Klemens Uhlmann, Vijay Vedula, Daniel Balzani, and Fathollah Varnik. "Fluid-structure interaction simulation of tissue degradation and its effects on intra-aneurysm hemodynamics." Biomechanics and Modeling in Mechanobiology 21, no. 2 (January 13, 2022): 671–83. http://dx.doi.org/10.1007/s10237-022-01556-7.
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AbstractTissue degradation plays a crucial role in vascular diseases such as atherosclerosis and aneurysms. Computational modeling of vascular hemodynamics incorporating both arterial wall mechanics and tissue degradation has been a challenging task. In this study, we propose a novel finite element method-based approach to model the microscopic degradation of arterial walls and its interaction with blood flow. The model is applied to study the combined effects of pulsatile flow and tissue degradation on the deformation and intra-aneurysm hemodynamics. Our computational analysis reveals that tissue degradation leads to a weakening of the aneurysmal wall, which manifests itself in a larger deformation and a smaller von Mises stress. Moreover, simulation results for different heart rates, blood pressures and aneurysm geometries indicate consistently that, upon tissue degradation, wall shear stress increases near the flow-impingement region and decreases away from it. These findings are discussed in the context of recent reports regarding the role of both high and low wall shear stress for the progression and rupture of aneurysms.
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Baldwin, J. T., J. M. Tarbell, S. Deutsch, D. B. Geselowitz, and G. Rosenberg. "Hot-Film Wall Shear Probe Measurements Inside a Ventricular Assist Device." Journal of Biomechanical Engineering 110, no. 4 (November 1, 1988): 326–33. http://dx.doi.org/10.1115/1.3108449.
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Wall shear rates at eleven sites within the Penn State Electric Ventricular Assist Device (EVAD) were determined with the pump operating under conditions of 30 and 50 percent systolic duration and a mean flow rate of 5.8 L/min using a flush-mounted hot-film probe. Probe calibrations were performed with the hot-film in two orientations relative to the flow direction: a standard orientation and an orientation in which the hot-film was rotated by 90 deg from the standard orientation. The magnitude and direction of the wall shear stress at each site within the EVAD were estimated from ensemble averaged voltage data recorded for similar standard and rotated film orientations. The results indicate that, during diastole the wall shear stress direction around the pump’s periphery for both operating conditions is predominantly perpendicular to the inflow-outflow plane (in the direction of the pusher plate motion) and reaches a peak value of approximately 350 dynes/cm2. The highest wall shear stresses were found near the prosthetic aortic valve (inside the EVAD) under the 30 percent systolic duration condition and are estimated to be as high as 2700 dynes/cm2. Peak shear stress values of 1400 dynes/cm2 were observed in the vicinity of the prosthetic mitral valve under both operating conditions. The results suggested that the valve regions are substantially more hemolytic than other wall regions of the EVAD; the magnitudes of the wall shear stresses are sensitive to operating conditions; and that wall shear in the direction of pusher plate motion can be significant.
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Meghdadi, N., and H. Niroomand-Oscuii. "NUMERICAL SIMULATION OF THE EFFECT OF VENOUS NEEDLE'S FLOW RATE AND ANGLE ON FLOW PARAMETERS OF A HEMODIALYSIS GRAFT." Biomedical Engineering: Applications, Basis and Communications 27, no. 05 (October 2015): 1550048. http://dx.doi.org/10.4015/s1016237215500489.
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Arterio-Venous grafts, which are used for hemodialysis, frequently develop intimal hyperplasia in venous anastomosis which ultimately leads to graft failure. It is observed in different studies that the wall shear stress can be correlated to intimal hyperplasia development. Although high Arterio-Venous access blood flow has been implicated in the pathogenesis of graft stenosis, the role of needle's angle and flow rate during the hemodialysis procedure are relatively unexplored. Since the flow field in the region of the venous needle may be a source of damage, in the current study, a numerical investigation of the effect of venous needle's angle and flow rate on hemodynamic parameters of the flow inside a hemodialysis graft has been carried out. Five cases of different needle angles and flow rates with graft flow rate of 500 ml/min have been investigated. Results indicate that in lower angle and lower flow rates the risk of damage is less because of lower wall shear stress and more uniform shear stress distribution on graft wall.
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Lawler, Karen, Gerardene Meade, Gerald O'Sullivan, and Dermot Kenny. "Shear stress modulates the interaction of platelet-secreted matrix proteins with tumor cells through the integrin αvβ3." American Journal of Physiology-Cell Physiology 287, no. 5 (November 2004): C1320—C1327. http://dx.doi.org/10.1152/ajpcell.00159.2004.
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Interaction of tumor cells with the vascular wall is required for metastasis from the bloodstream. The precise interaction among metastatic cells, circulating platelets, the vessel wall, and physiological flow conditions remains to be determined. In this study, we investigated the interaction of shear on metastatic cell lines adherent to lipopolysaccharide (LPS)-treated endothelium. Tumor cells were perfused over LPS-treated human umbilical vein endothelial cells (HUVECs) at incremental venous shear rates from 50 to 800 s−1. At a venous shear rate of 400 s−1, 3% of adherent tumor cells formed pseudopodia under shear, a process we termed shear-induced activation. Because platelets promote tumor dissemination, we then investigated the effect of pretreating tumor cells with platelet releasate collected from activated platelet concentrate. We found that in the presence of platelet releasate, the number of tumor cells adhering to HUVECs increased and tumor “activation” occurred at a significantly lower shear rate of 50 s−1. This was inhibited with acetylsalicylic acid. Depletion of fibronectin or vitronectin from the platelet releasate resulted in significantly less adhesion at higher venous shear rates of 600 and 800 s−1. The integrin αvβ3has been shown to mediate cell adhesion primarily through vitronectin and fibronectin proteins. Inhibition of αvβ3, followed by the addition of platelet releasate to the tumor cells, resulted in significantly less adhesion at higher venous shear rates of 600 and 800 s−1. Collectively, our data suggest that αvβ3promotes the metastatic phenotype of tumor cells through interactions with the secreted platelet proteins vitronectin and fibronectin under venous shear conditions.
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Yeo, K. S., and A. P. Dowling. "The stability of inviscid flows over passive compliant walls." Journal of Fluid Mechanics 183 (October 1987): 265–92. http://dx.doi.org/10.1017/s0022112087002635.
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The linear temporal stability of incompressible semi-bounded inviscid parallel flows over passive compliant walls is studied. It is shown that some of the well-known classical results for inviscid parallel flows with rigid boundaries can, in fact, be extended in modified form to passive compliant walls. These include a result of Rayleigh (1880) which shows that the real part of the phase velocity of a non-neutral disturbance must lie within the range of the velocity distribution; the semi-circle theorem of Howard (1961) and a result of Høiland (1953) which places a bound on the temporal amplification rates of unstable disturbances. The bounds on the phase velocity and the temporal amplification rates of unstable two-dimensional disturbances provide useful guides for numerical studies.The results are valid for a large class of passive compliant walls. This generality is achieved through a variational-Lagrangian formulation of the essential dynamics of wall motion. A general treatment of the marginal stability of thin shear flows over general passive compliant walls is given. It represents a generalization of the analysis given by Benjamin (1963) for membrane and plate surfaces. Sufficient conditions for the stability of thin shear flows over passive compliant walls are deduced. The applications of the stability criteria to simple cases of compliant wall are described to illustrate the use and the effectiveness of these criteria.
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Uttam, Shubham, Piru Mohan Khan, Md Irshad Alam, and Somnath Roy. "BEHAVIOR OF WALL SHEAR STRESS NEAR CAROTID ARTERY BIFURCATION AT ELEVATED PULSE RATES." Journal of Flow Visualization and Image Processing 27, no. 3 (2020): 249–67. http://dx.doi.org/10.1615/jflowvisimageproc.2020031021.
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Dumont, Eric, Francine Fayolle, and Jack Legrand. "Flow regimes and wall shear rates determination within a scraped surface heat exchanger." Journal of Food Engineering 45, no. 4 (September 2000): 195–207. http://dx.doi.org/10.1016/s0260-8774(00)00056-x.
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Weydahl, Erlend S., and James E. Moore. "Dynamic curvature strongly affects wall shear rates in a coronary artery bifurcation model." Journal of Biomechanics 34, no. 9 (September 2001): 1189–96. http://dx.doi.org/10.1016/s0021-9290(01)00051-3.
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Awati, K. M., Y. Park, E. Weisser, and M. E. Mackay. "Wall slip and shear stresses of polymer melts at high shear rates without pressure and viscous heating effects." Journal of Non-Newtonian Fluid Mechanics 89, no. 1-2 (February 2000): 117–31. http://dx.doi.org/10.1016/s0377-0257(99)00037-3.
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Loosli, Christian, Stephan Rupp, Bente Thamsen, Mathias Rebholz, Gerald Kress, Mirko Meboldt, and Paolo Ermanni. "High-frequency operation of pulsatile ventricular assist devices: A computational study on circular and elliptically shaped pumps." International Journal of Artificial Organs 42, no. 12 (July 5, 2019): 725–34. http://dx.doi.org/10.1177/0391398819857442.
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Pulsatile positive displacement pumps as ventricular assist devices were gradually replaced by rotary devices due to their large volume and high adverse event rates. Nevertheless, pulsatile ventricular assist devices might be beneficial with regard to gastrointestinal bleeding and cardiac recovery. Therefore, aim of this study was to investigate the flow field in new pulsatile ventricular assist devices concepts with an increased pump frequency, which would allow lower stroke volumes to reduce the pump size. We developed a novel elliptically shaped pulsatile ventricular assist devices, which we compared to a design based on a circular shape. The pump size was adjusted to deliver similar flow rates at pump frequencies of 80, 160, and 240 bpm. Through a computational fluid dynamics study, we investigated flow patterns, residence times, and wall shear stresses for different frequencies and pump sizes. A pump size reduction by almost 50% is possible when using a threefold pump frequency. We show that flow patterns inside the circular pump are frequency dependent, while they remain similar for the elliptic pump. With slightly increased wall shear stresses for higher frequencies, maximum wall shear stresses on the pump housing are higher for the circular design (42.2 Pa vs 18.4 Pa). The calculated blood residence times within the pump decrease significantly with increasing pump rates. A smaller pump size leads to a slight increase of wall shear stresses and a significant improvement of residence times. Hence, high-frequency operation of pulsatile ventricular assist devices, especially in combination with an elliptical shape, might be a feasible mean to reduce the size, without any expectable disadvantages in terms of hemocompatibility.
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Nazemi, M., C. Kleinstreuer, J. P. Archie, and F. Y. Sorrell. "Fluid Flow and Plaque Formation in an Aortic Bifurcation." Journal of Biomechanical Engineering 111, no. 4 (November 1, 1989): 316–24. http://dx.doi.org/10.1115/1.3168385.
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Considering steady laminar flow in a two-dimensional symmetric branching channel with local occlusions, a finite element model has been developed to study velocity fields including reverse flow regions, pressure profiles and wall shear stress distributions for different Reynolds numbers, bifurcation angles and lumen reductions. The flow analysis has been extended to include a new submodel for the pseudo-transient formation of plaque at sites and deposition rates defined by the physical characteristics of the flow. Specifically, simulating the onset of atherosclerotic lesions, sinusoidal plaque layers have been placed in areas of critically low wall shear stresses, and simulating the growth of particle depositions, plaque layers have been added in a stepwise fashion in regions of critically high and low shear. Thus two somewhat conflicting hypothetical correlations between critical wall shear stress levels and atheroma have been tested and a solution has been postulated. The validated computer simulation model is a predictive tool for analyzing the effects of local changes in wall curvature due to surgical reconstruction and/or atherosclerotic lesions, and for investigating the design of aortic bifurcations which mitigate plaque formation.
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Moore,, James E., Erlend S. Weydahl, and Aland Santamarina. "Frequency Dependence of Dynamic Curvature Effects on Flow Through Coronary Arteries." Journal of Biomechanical Engineering 123, no. 2 (November 1, 2000): 129–33. http://dx.doi.org/10.1115/1.1351806.
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The flow through a curved tube model of a coronary artery was investigated computationally to determine the importance of time-varying curvature on flow patterns that have been associated with the development of atherosclerosis. The entry to the tube was fixed while the radius of curvature varied sinusoidally in time at a frequency of 1 or 5 Hz. Angiographic data from other studies suggest that the radius of curvature waveform contains significant spectral content up to 6 Hz. The overall flow patterns were similar to those observed in stationary curved tubes; velocity profile skewed toward the outer wall, secondary flow patterns, etc. The effects of time-varying curvature on the changes in wall shear rate were expressed by normalizing the wall shear rate amplitude with the shear rate calculated at the static mean radius of curvature. It was found that the wall shear rate varied as much as 94 percent of the mean wall shear rate at the mid wall of curvature for a mean curvature ratio of 0.08 and a 50 percent change in radius of curvature. The effects of 5 Hz deformation were not well predicted by a quasi-static approach. The maximum values of the normalized inner wall shear rate amplitude were found to scale well with a dimensionless parameter equivalent to the product of the mean curvature ratio (δ), normalized change in radius of curvature (ε), and a Womersley parameter (α). This parameter was less successful at predicting the amplitudes elsewhere in the tube, thus additional studies are necessary. The mean wall shear rate was well predicted with a static geometry. These results indicate that dynamic curvature plays an important role in determining the inner wall shear rates in coronary arteries that are subjected to deformation levels of εδα>0.05. The effects were not always predictable with a quasi-static approach. These results provide guidelines for constructing more realistic models of coronary artery flow for atherogenesis research.
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Wüstenhagen, Carolin, Sylvia Pfensig, Stefan Siewert, Sebastian Kaule, Niels Grabow, Klaus-Peter Schmitz, and Michael Stiehm. "Optimization of stent designs regarding the thrombosis risk using computational fluid dynamics." Current Directions in Biomedical Engineering 4, no. 1 (September 1, 2018): 93–96. http://dx.doi.org/10.1515/cdbme-2018-0024.
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AbstractIn-stent thrombosis is a major complication of stent implantations. Unlike pathological occurrences as in-stent restenosis for instance, thrombosis represents an acute event associated with high mortality rates. Experiments show that low wall shear stress promotes undirected endothelial cell coverage of the vessel wall and therefore increases the risk of thrombus formation. Stent design represents a crucial factor influencing the surface areas of low wall shear stress and thus the incidence of acute in-stent thrombosis. In this study, we present an optimization method for stent designs with minimized thrombosis risk. A generic stent design was developed, based on five different stent design parameters. Optimization was conducted based on computational fluid dynamics analysis and the gradient-free Nelder-Mead approach. For each optimization step, a numerical fluid simulation was performed in a vessel with a reference vessel diameter of 2.70 mm with stent-overexpansion ratio of 1.0:1.1. For each numerical fluid simulation a physiological Reynolds number of 250, resulting in a mean velocity of 0.331 m/s at the inlet and a laminar flow as well as stiff vessel walls were assumed. The impact of different stent designs was analyzed based on the wall shear stress distribution. As a basis for the comparison of different stent designs, a dimensionless thrombosis risk number was calculated from the area of low wall shear stress and the overall stented area. The first two optimization steps already provide a decrease of thrombosis risk of approximately 83%. In conclusion, computational fluid dynamic analyses and optimization methods usind the Nelder-Mead approach represent a useful tool for the development of hemodynamically optimized stent designs with minimized thrombosis risk.
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Rooman, Muhammad, Zahir Shah, Ebenezer Bonyah, Muhammad Asif Jan, and Wejdan Deebani. "Mathematical Modeling of Carreau Fluid Flow and Heat Transfer Characteristics in the Renal Tubule." Journal of Mathematics 2022 (May 10, 2022): 1–14. http://dx.doi.org/10.1155/2022/2517933.
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This study looks into the steady heat transfer issue of a flow of an incompressible Carreau fluid. Carreau fluid exhibits the shear thinning and thickening characteristics at low, moderate, and high shear rates. At the tubule wall, the fluid absorption is used as a function of pressure gradient and wall permeability through the tubule wall. Supposing the tubule radius considerably small in comparison to its length, the governing equations are considerably simplified. Significant quantities of interest are computed analytically by using perturbation, and the influence of emergent parameters is discussed through graphical results. The comparisons of results with existing data are set up to be good agreement.
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Kiesow, Robert O., and Michael W. Plesniak. "Modification of Near-Wall Structure in a Shear-Driven 3-D Turbulent Boundary Layer." Journal of Fluids Engineering 124, no. 1 (August 24, 2001): 118–26. http://dx.doi.org/10.1115/1.1431269.
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The near-wall physics of a planar, shear-driven, 3-D turbulent boundary layer with varying strengths of crossflow are examined. Flow visualization data reveals a reduction of mean streak length by as much as 50% with increasing spanwise shear. Power spectra of velocity confirm this shift towards higher temporal frequencies, corresponding to decreased streamwise length scales. PIV measurements indicate a significant modification of the inner region of the boundary layer with increasing spanwise shear. Streamwise velocity profiles exhibit an increasing velocity deficit with increased crossflow. Increased levels of the normal Reynolds stresses u′2¯ and v′2¯ and an increase in the −u′v′¯ Reynolds shear stress are also observed. Modifications in the spanwise and transverse vorticity were also observed at higher shear rates.
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Jiroušková, Markéta, Jan Evangelista Dyr, Jiří Suttnar, Karel Holada, and Bohuslava Trnková. "Platelet Adhesion to Fibrinogen, Fibrin Monomer, and Fibrin Protofibrils in Flowing Blood - The Effect of Fibrinogen Immobilization and Fibrin Formation." Thrombosis and Haemostasis 78, no. 03 (1997): 1125–31. http://dx.doi.org/10.1055/s-0038-1657698.
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SummaryPlatelet fibrin(ogen) adhesive interactions were investigated in whole citrated blood using the rectangular perfusion chamber at wall shear rates of 300 and 1600s1 with regard to the amount and structure of immobilized protein. Only single platelets adhered to adsorbed fibrinogen at both low and high surface fibrinogen concentrations and at 1600 s1 almost no adhesion was observed. When using spray-immobilized protein, platelet adhesion was significantly higher than to ad sorbed protein. Conversion of adsorbed fibrinogen to fibrin monomer resulted in the formation of pronounced platelets aggregates and with the elevation of wall shear rate 50% decrease of adhesion took place. Degree of platelet adhesion to fibrin monomer was significantly influenced by immobilized protein concentration at both shear rates. However, the morphology (small and dense platelet aggregates) and extent of platelets adhered to fibrin pentamer was nearly the same at both shear rates. Starting with surface-bound fibrinogen and alternating addition of thrombin and fibrinogen fibrin pentamer was prepared using the stepwise synthesis. This methodology is based on the observation that at low concentration immobilized fibrin monomer binds fibrinogen in 1:1 molar ratio. The gradually formed fibrin of a defined size and composition can be a useful tool in the further understanding of the role of fibrin architecture in the pathophysiology of thrombosis.
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Bahrami, Saeed, and Mahmood Norouzi. "Hemodynamic impacts of hematocrit level by two-way coupled FSI in the left coronary bifurcation." Clinical Hemorheology and Microcirculation 76, no. 1 (October 15, 2020): 9–26. http://dx.doi.org/10.3233/ch-200854.
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Cardiovascular disease is now under the influence of several factors that encourage researchers to investigate the flow of these vessels. Oscillation influences the blood circulation in the volume of red blood cells (RBC) strongly. Therefore, in this study, its effects have been considered on hemodynamic parameters in the elastic wall and coronary bifurcation. In this study, a 3D geometry of non-Newtonian and pulsatile blood circulation is considered in the left coronary artery bifurcation. The Casson model with various hematocrits is analyzed in elastic and rigid walls. The wall shear stress (WSS) cannot show the stenosis artery alone, therefore, the oscillatory shear index (OSI) is represented as a hemodynamic parameter of WSS individually of time. The results are determined using two-way fluid-structure interaction (FSI) coupling method using an arbitrary Lagrangian-Eulerian method. The most prominent difference in velocity happened in the bifurcation and at hematocrit 30 with yield stress 6.59E-04 Pa. The backflow and vortex flow in the LCx branch grown with increasing shear rates. The likelihood of plaque generation at the ending of the LM branch is observed in hematocrits 10 and 20, while the WSS magnitude is normal in the hematocrit 60 with the greatest yield stress in the bifurcation. The shear stress among the rigid and elastic models is the highest at the ending of the LM branch. The wall shear stress magnitude among the models decreased at most of 24.49% by dividing the flow. Time-independent results for models showed that there is the highest value of OSI at the bifurcation, which then quickly dropped.
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Ye, Huilin, Zhiqiang Shen, and Ying Li. "Shear rate dependent margination of sphere-like, oblate-like and prolate-like micro-particles within blood flow." Soft Matter 14, no. 36 (2018): 7401–19. http://dx.doi.org/10.1039/c8sm01304g.
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Sofialidis, D., and P. Prinos. "Wall Suction Effects on the Structure of Fully Developed Turbulent Pipe Flow." Journal of Fluids Engineering 118, no. 1 (March 1, 1996): 33–39. http://dx.doi.org/10.1115/1.2817507.
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The effects of wall suction on the structure of fully developed pipe flow are studied numerically by solving the Reynolds averaged Navier-Stokes equations. Linear and nonlinear k-ε or k-ω low-Re models of turbulence are used for “closing” the system of the governing equations. Computed results are compared satisfactorily against experimental measurements. Analytical results, based on boundary layer assumptions and the mixing length concept, provide a law of the wall for pipe flow under the influence of low suction rates. The analytical solution is found in satisfactory agreement with computed and experimental data for a suction rate of A = 0.46 percent. For the much higher rate of A = 2.53 percent the above assumptions are not valid and analytical velocities do not follow the computed and experimental profiles, especially in the near-wall region. Near-wall velocities, as well as the boundary shear stress, are increased with increasing suction rates. The excess wall shear stress, resulting from suction, is found to be 1.5 to 5.5 times the respective one with no suction. The turbulence levels are reduced with the presence of the wall suction. Computed results of the turbulent shear stress uv are in close agreement with experimental measurements. The distribution of the turbulent kinetic energy k is predicted better by the k-ω model of Wilcox (1993). Nonlinear models of the k-ε and k-ω type predict the reduction of the turbulence intensities u’, v’, w’, and the correct levels of v’ and w’ but they underpredict the level of u’.
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Van Buren, Tyler, Owen Williams, and Alexander J. Smits. "Turbulent boundary layer response to the introduction of stable stratification." Journal of Fluid Mechanics 811 (December 13, 2016): 569–81. http://dx.doi.org/10.1017/jfm.2016.775.
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The response of an initially neutral rough-wall turbulent boundary layer to a change in wall temperature is investigated experimentally. The change causes a localized peak in stable stratification that diffuses and moves away from the wall with downstream distance. The streamwise and wall-normal components of turbulent velocity fluctuations are damped at similar rates, even though the stratification only directly impacts the wall-normal component. The Reynolds shear profiles reveal the growth of an internal layer that scales approximately with the bulk Brunt–Väisälä frequency.
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Hochareon, Pramote, Keefe B. Manning, Arnold A. Fontaine, John M. Tarbell, and Steven Deutsch. "Wall Shear-Rate Estimation Within the 50cc Penn State Artificial Heart Using Particle Image Velocimetry." Journal of Biomechanical Engineering 126, no. 4 (August 1, 2004): 430–37. http://dx.doi.org/10.1115/1.1784477.
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Particle image velocimetry (PIV) has been gaining acceptance as a routine tool to evaluate the flow fields associated with fluid mechanical devices. We have developed algorithms to investigate the wall shear-rates within the 50cc Penn State artificial heart using low magnification, conventional particle image velocimetry (PIV). Wall shear has been implicated in clot formation, a major post-implant problem with artificial hearts. To address the issues of wall scattering and incomplete measurement volumes, associated with near wall measurements, we have introduced a zero masking and a fluid centroid shifting technique. Simulations using different velocity fields were conducted with the techniques to assess their viability. Subsequently, the techniques were applied to the experimental data collected. The results indicate that the size of the interrogation region should be chosen to be as small as possible to maximize resolution while large enough to ensure an adequate number of particles per region. In the current study, a 16×16 interrogation window performed well with good spatial resolution and particle density for the estimation of wall shear rate. The techniques developed with PIV allow wall shear-rate estimates to be obtained from a large number of sites at one time. Because a planar image of a flow field can be determined relatively rapidly, PIV may prove useful in any preliminary design procedure.
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Zaidi, TN, LV McIntire, DH Farrell, and P. Thiagarajan. "Adhesion of platelets to surface-bound fibrinogen under flow." Blood 88, no. 8 (October 15, 1996): 2967–72. http://dx.doi.org/10.1182/blood.v88.8.2967.bloodjournal8882967.
Full textAbstract:
After platelet activation, fibrinogen mediates platelet-platelet interactions leading to platelet aggregation. In addition, fibrinogen can also function as a cell adhesion molecule, providing a substratum for adhesion of platelets and endothelial cells. In this report, we studied the adhesion of platelets to surface-immobilized fibrinogen under flow in different shear rates. Heparinized whole blood containing mepacrine-labeled platelets was perfused for two minutes at various wall shear rates from 250 to 2,000 s-1 in a parallel plate flow chamber. The number of adherent fluorescent platelets was quantitated every 15 seconds with an epifluorescent videomicroscope and digital image processing system. When compared with platelet adhesion and aggregation seen on glass surfaces coated with type I bovine collagen, a significant increase in platelet adhesion was observed on immobilized fibrinogen up to wall shear rates of 800 s-1. The adherent platelets formed a single layer on fibrinogen-coated surfaces. Under identical conditions, no significant adhesion was observed on fibronectin- or vitronectin-coated surfaces. Although platelet adhesion to collagen was substantially inhibited by the platelet inhibitors prostaglandin E1 and theophylline, these inhibitors had no effect on platelet adhesion to fibrinogen. Platelets adhered to recombinant homodimeric wild-type (gamma 400–411) fibrinogen, but not to the recombinant homodimeric gamma' variant of fibrinogen. Platelet adhesion to recombinant fibrinogen with RGD to RGE mutations at positions alpha 95–97 and alpha 572–574 was similar to that with plasma-derived fibrinogen. These results show that platelets adhere to fibrinogen-coated surfaces under moderate wall shear rates, that the interaction is mediated by the fibrinogen 400–411 sequence at the carboxy-terminus of the gamma chain, and that the interaction is independent of platelet activation and the RGD sequences in the alpha chain.
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Hantgan, RR, G. Hindriks, RG Taylor, JJ Sixma, and PG de Groot. "Glycoprotein Ib, von Willebrand factor, and glycoprotein IIb:IIIa are all involved in platelet adhesion to fibrin in flowing whole blood." Blood 76, no. 2 (July 15, 1990): 345–53. http://dx.doi.org/10.1182/blood.v76.2.345.345.
Full textAbstract:
Abstract We have investigated the molecular basis of thrombus formation by measuring the extent of platelet deposition from flowing whole blood onto fibrin-coated glass coverslips under well-defined shear conditions in a rectangular perfusion chamber. Platelets readily and specifically adhered to fibrin-coated coverslips in 5 minute perfusion experiments done at either low (300 s-1) or high (1,300 s-1) wall shear rates. Scanning electron microscopic examination of fibrin-coated coverslips after perfusions showed surface coverage by a monolayer of adherent, partly spread platelets. Platelet adhesion to fibrin was effectively inhibited by a monoclonal antibody (MoAb) specific for glycoprotein (GP) IIb:IIIa. The dose-response curve for inhibition of adhesion by anti-GPIIb:IIIa at both shear rates paralleled that for inhibition of platelet aggregation. Platelet aggregation and adhesion to fibrin were also blocked by low concentrations of prostacyclin. In contrast, anti- GPIb reduced adhesion by 40% at 300 s-1 and by 70% at 1,300 s-1. A similar pattern of shear rate-dependent, incomplete inhibition resulted with a MoAb specific for the GPIb-recognition region of von Willebrand factor (vWF). Platelets from an individual with severe von Willebrand's disease, whose plasma and platelets contained essentially no vWF, exhibited defective adhesion to fibrin, especially at the higher shear rate. Addition of purified vWF restored adhesion to normal values. These results are consistent with a two-site model for platelet adhesion to fibrin, in which the GPIIb:IIIa complex is the primary receptor, with GPIb:vWF providing a secondary adhesion pathway that is especially important at high wall shear rates.