A Numerical Study of Blood Flow Patterns in Anatomically Realistic and Simplified End-to-Side Anastomoses

1999 ◽  
Vol 121 (3) ◽  
pp. 265-272 ◽  
Author(s):  
J. A. Moore ◽  
D. A. Steinman ◽  
S. Prakash ◽  
K. W. Johnston ◽  
C. R. Ethier
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Patterns ◽  
Geometric Features ◽  
Simplified Models ◽  
Out Of Plane ◽  
Wall Shear ◽  
Blood Flow Patterns ◽  
Stress Patterns

Purpose: Recently, some numerical and experimental studies of blood flow in large arteries have attempted to accurately replicate in vivo arterial geometries, while others have utilized simplified models. The objective of this study was to determine how much an anatomically realistic geometry can be simplified without the loss of significant hemodynamic information. Method: A human femoral-popliteal bypass graft was used to reconstruct an anatomically faithful finite element model of an end-to-side anastomosis. Nonideal geometric features of the model were removed in sequential steps to produce a series of successively simplified models. Blood flow patterns were numerically computed for each geometry, and the flow and wall shear stress fields were analyzed to determine the significance of each level of geometric simplification. Results: The removal of small local surface features and out-of-plane curvature did not significantly change the flow and wall shear stress distributions in the end-to-side anastomosis. Local changes in arterial caliber played a more significant role, depending upon the location and extent of the change. The graft-to-host artery diameter ratio was found to be a strong determinant of wall shear stress patterns in regions that are typically associated with disease processes. Conclusions: For the specific case of an end-to-side anastomosis, simplified models provide sufficient information for comparing hemodynamics with qualitative or averaged disease locations, provided the “primary” geometric features are well replicated. The ratio of the graft-to-host artery diameter was shown to be the most important geometric feature. “Secondary” geometric features such as local arterial caliber changes, out-of-plane curvature, and small-scale surface topology are less important determinants of the wall shear stress patterns. However, if patient-specific disease information is available for the same arterial geometry, accurate replication of both primary and secondary geometric features is likely required.

Wall Deformation, Wall Shear Stress and Atherosclerosis Around the Intercostal Ostia of C57 Mice

2007 ◽  
Author(s):  
Jin Suo ◽  
Dardo E. Ferrara ◽  
Robert E. Guldberg ◽  
Robert W. Taylor ◽  
Don P. Giddens
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Patterns ◽  
Laser Scanning Microscopy ◽  
Upstream Region ◽  
Disturbed Flow ◽  
Wall Deformation ◽  
Wall Shear ◽  
Blood Flow Patterns

Dorsal surfaces and upstream regions around ostia of aortic branches are favored sites of atherosclerosis. Both asymmetrical stresses in branch walls and disturbed flow patterns have been suggested as contributing to this localization. In the present study, fluorescence images of the thoracic aortic tree of C57 mice were obtained using quantum dot (Qdot) bioconjugate markers for vascular cell adhesion molecule-1 (VCAM-1) and two-photon excitation laser scanning microscopy. The images show that dorsal surfaces and upstream regions of intercostal ostia have a higher intensity of VCAM-1 than the downstream region. We also investigated blood flow patterns and wall shear stress (WSS) in the descending aorta and proximal intercostal branches of C57 mice using micro-CT imaging and ultrasound velocity measurements, combined with computational fluid dynamics (CFD). The latter investigation showed that dynamical wall deformation caused by pulsatile pressure around the ostia induces blood flow patterns which create lower and oscillating WSS in the upstream region and dorsal surface than in the distal region. Comparisons of the Qdot marker and CFD studies demonstrate that the distribution of greater expression of VCAM-1 corresponds with lower and oscillating WSS around the branch ostia. Thus, local wall deformation may contribute to disturbed flow patterns that are known to be associated with increased VCAM-1 expression.

scholarly journals Effects of Disturbed Flow on Vascular Endothelium: Pathophysiological Basis and Clinical Perspectives

2011 ◽  
Vol 91 (1) ◽  
pp. 327-387 ◽  
Author(s):  
Jeng-Jiann Chiu ◽  
Shu Chien
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Patterns ◽  
Arterial Tree ◽  
Disturbed Flow ◽  
Hemodynamic Forces ◽  
Venous Diseases ◽  
Wall Shear

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

Non-Newtonian Flow Patterns Associated With an Arterial Stenosis

1992 ◽  
Vol 114 (4) ◽  
pp. 512-514 ◽  
Author(s):  
X. Y. Luo ◽  
Z. B. Kuang
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Constitutive Equation ◽  
Wall Shear Stress ◽  
Velocity Profile ◽  
Pressure Gradient ◽  
Flow Patterns ◽  
Arterial Stenosis ◽  
Newtonian Flow ◽  
Wall Shear

A non-Newtonian constitutive equation for blood has been introduced in this paper. Using this equation, blood flow attributes such as velocity profiles, flowrate, pressure gradient, and wall shear stress in both straight and stenotic (constricted) tubes have been examined. Results showed that compared with Newtonian flow at the same flowrate, the non-Newtonian normally features larger pressure gradient, higher wall shear stress, and different velocity profile, especially in stenotic tube. In addition, the non-Newtonian stenotic flow appears to be more stable than Newtonian flow.

Basic study on estimation method of wall shear stress in common carotid artery using blood flow imaging

2020 ◽  
Vol 59 (SK) ◽  
pp. SKKE16 ◽  
Author(s):  
Ryo Nagaoka ◽  
Kazuma Ishikawa ◽  
Michiya Mozumi ◽  
Magnus Cinthio ◽  
Hideyuki Hasegawa
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Carotid Artery ◽  
Wall Shear Stress ◽  
Common Carotid Artery ◽  
Estimation Method ◽  
Flow Imaging ◽  
Basic Study ◽  
Blood Flow Imaging ◽  
Wall Shear

Mathematical analysis of two-phase blood flow through a stenosed curved artery with hematocrit and temperature dependent viscosity

2021 ◽  
Author(s):  
Chandan Kumawat ◽  
Bhupendra Kumar Sharma ◽  
Khalid Saad Mekheimer
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Mathematical Study ◽  
Temperature Dependent ◽  
Two Phase ◽  
Temperature Dependent Viscosity ◽  
Linear Temperature ◽  
Wall Shear ◽  
Dependent Viscosity

Abstract A two-phase blood flow model is considered to analyze the fluid flow and heat transfer in a curved tube with time-variant stenosis. In both core and plasma regions, the variable viscosity model ( Hematocrit and non linear temperature-dependent, respectively) is considered. A toroidal coordinate system is considered to describe the governing equations. The perturbation technique in terms of perturbation parameter ε is used to obtain the temperature profile of blood flow. In order to find the velocity, wall shear stress and impedance profiles, a second-order finite difference method is employed with the accuracy of 10−6 in the each iteration. Under the conditions of fully-developed flow and mild stenosis, the significance of various physical parameters on the blood velocity, temperature, wall shear stress (WSS) and impedance are investigated with the help of graphs. A validation of our results has been presented and comparison has been made with the previously published work and present study, and it revels the good agreement with published work. The present mathematical study suggested that arterial curvature increase the fear of deposition of plaque (atherosclerosis), while, the use of thermal radiation in heat therapies lowers this risk. The positive add in the value of λ1 causes to increase in plasma viscosity; as a result, blood flow velocity in the stenosed artery decreases due to the assumption of temperature-dependent viscosity of the plasma region. Clinical researchers and biologists can adopt the present mathematical study to lower the risk of lipid deposition, predict cardiovascular disease risk and current state of disease by understanding the symptomatic spectrum, and then diagnose patients based on the risk.

The Effect of Wall Distensibility on Flow in a Two-Dimensional End-to-Side Anastomosis

1994 ◽  
Vol 116 (3) ◽  
pp. 294-301 ◽  
Author(s):  
D. A. Steinman ◽  
C. Ross Ethier
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Intimal Hyperplasia ◽  
Bypass Graft ◽  
Numerical Approach ◽  
Flow Patterns ◽  
Temporal Variations ◽  
Model Studies ◽  
Wall Shear ◽  
Wall Distensibility

The development of intimal hyperplasia at the distal anastomosis is the major cause of long-term bypass graft failure. To evaluate the suspected role of hemodynamic factors in the pathogenesis of distal intimal hyperplasia, an understanding of anastomotic flow patterns is essential. Due to the complexity of arterial flow, model studies typically make simplifying assumptions, such as treating the artery and graft walls as rigid. In the present study this restriction is relaxed to consider the effects of vessel wall distensibility on anastomotic flow patterns. Flow was simulated in an idealized 2-D distensible end-to-side anastomosis model, using parameters appropriate for the distal circulation and assuming a purely elastic artery wall. A novel numerical approach was developed in which the wall velocities are solved simultaneously with the fluid and pressure fields, while the wall displacements are treated via an iterative update. Both the rigid and distensible cases indicated the presence of elevated temporal variations and low average magnitudes of wall shear stress at sites known to be susceptible to the development of intimal hyperplasia. At these same sites, large spatial gradients of wall shear stress were also noted. Comparison between distensible-walled and corresponding rigid-walled simulations showed moderate changes in wall shear stress at isolated locations, primarily the bed, toe and heel. For example, in the case of a distensible geometry and a physiologic pressure waveform, the heel experienced a 38 percent increase in cycle-averaged shear stress, with a corresponding 15 percent reduction in shear stress variability, both relative to the corresponding values in the rigid-walled case. However, other than at these isolated locations, only minor changes in overall wall shear stress patterns were observed. While the physiological implications of such changes in wall shear stress are not known, it is suspected that the effects of wall distensibility are less pronounced than those brought about by changes in arterial geometry and flow conditions.

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