Evaluation of 3D blood flow patterns and wall shear stress in the normal and dilated thoracic aorta using flow-sensitive 4D CMR

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.

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

Journal of Biomechanical Engineering ◽

10.1115/1.2798319 ◽

1999 ◽

Vol 121 (3) ◽

pp. 265-272 ◽

Cited By ~ 69

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.

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ESTIMATION OF WALL SHEAR STRESS USING 4D FLOW CARDIOVASCULAR MRI AND COMPUTATIONAL FLUID DYNAMICS

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519417500464 ◽

2016 ◽

Vol 17 (03) ◽

pp. 1750046 ◽

Cited By ~ 4

Author(s):

E. SOUDAH ◽

J. CASACUBERTA ◽

P. J. GAMEZ-MONTERO ◽

J. S. PÉREZ ◽

M. RODRÍGUEZ-CANCIO ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Blood Flow ◽

Shear Stress ◽

Cardiovascular Magnetic Resonance ◽

Magnetic Resonance ◽

Wall Shear Stress ◽

Thoracic Aorta ◽

4D Flow ◽

Wall Shear

In the last few years, wall shear stress (WSS) has arisen as a new diagnostic indicator in patients with arterial disease. There is a substantial evidence that the WSS plays a significant role, together with hemodynamic indicators, in initiation and progression of the vascular diseases. Estimation of WSS values, therefore, may be of clinical significance and the methods employed for its measurement are crucial for clinical community. Recently, four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has been widely used in a number of applications for visualization and quantification of blood flow, and although the sensitivity to blood flow measurement has increased, it is not yet able to provide an accurate three-dimensional (3D) WSS distribution. The aim of this work is to evaluate the aortic blood flow features and the associated WSS by the combination of 4D flow cardiovascular magnetic resonance (4D CMR) and computational fluid dynamics technique. In particular, in this work, we used the 4D CMR to obtain the spatial domain and the boundary conditions needed to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. Similar WSS distributions were found for cases simulated. A sensitivity analysis was done to check the accuracy of the method. 4D CMR begins to be a reliable tool to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. The combination of both techniques may provide the ideal tool to help tackle these and other problems related to wall shear estimation.

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

Physiological Reviews ◽

10.1152/physrev.00047.2009 ◽

2011 ◽

Vol 91 (1) ◽

pp. 327-387 ◽

Cited By ~ 999

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.

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ESTIMATION OF WALL SHEAR STRESS OF COMPLIANT THORACIC AORTA WITH ANEURYSM

Journal of Mechanics in Medicine and Biology ◽

10.1142/s021951942050013x ◽

2020 ◽

Vol 20 (03) ◽

pp. 2050013

Author(s):

AHMED BAKHIT ALANAZI ◽

MOHAMED YACIN SIKKANDAR ◽

MOHAMED IBRAHIM WALY

Keyword(s):

Blood Flow ◽

Shear Stress ◽

Wall Shear Stress ◽

Flow Pattern ◽

Thoracic Aorta ◽

Mass Flow ◽

Tangential Force ◽

Patient Specific ◽

Hemodynamic Pattern ◽

Wall Shear

In this paper, a numerical estimation of wall shear stress (WSS) in a compliant Thoracic Aorta (TA) with aneurysm is modeled and the hemodynamic pattern is studied using Computational Fluid Dynamics (CFD). Thoracic Aortic Aneurysm (TAA) is an excessively localized enlargement of TA caused by weakness in the arterial wall and it can rupture the inner wall intima and continue on to the outer wall adventitia. WSS is a tangential force exerted by blood flow on the vessel wall, and its estimation is clinically very important because any change in WSS is considered as a vital cue in the onset of aneurysm. In this work, a three-dimensional (3D) model of a TAA reconstructed from computed tomography (CT) images comprising of 600 slices with 1-mm resolution from neck to hip is considered and patient-specific simulations have been carried out in compliant TA under rest and exercise conditions. The findings show that the change in wall geometry was marginal due to variation in pressure forces inside and is not the primary source for expansion of an aneurysm. It was inferred that expansion was rather due to thinning of the wall, owing to damage caused to the inner lining of the tissues, at regions of high WSS. It was found that the geometry extraction is important as any change in length causes a corresponding variation in mass flow through it. Although mass conservation is maintained irrespective of the length, it does affect the rate of flow due to shifting in the pressure boundary conditions with the length as it varies the pressure inside the system. Modeling of the geometry is very important as the change in mass flow will affect the outlet velocity and strength of vortices. Surprisingly, the split-up of flow is consistent but the geometric change in the model has no effect on WSS values and flow pattern. The results of this study provide important information such as blood flow pattern and pressure drops in the compliant TA on WSS estimations with TAA diseases.

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Influence of Geometric Changes in the Thoracic Aorta due to Arterial Switch Operations on the Wall Shear Stress Distribution

The Open Biomedical Engineering Journal ◽

10.2174/1874120701711010009 ◽

2017 ◽

Vol 11 (1) ◽

pp. 9-16 ◽

Cited By ~ 5

Author(s):

Tomohiro Fukui ◽

Hiroaki Asama ◽

Manabu Kimura ◽

Toshiyuki Itoi ◽

Koji Morinishi

Keyword(s):

Blood Flow ◽

Shear Stress ◽

Wall Shear Stress ◽

Thoracic Aorta ◽

Aortic Root ◽

Heart Diseases ◽

Arterial Switch ◽

Wall Shear ◽

Curvature And Torsion ◽

Geometric Changes

Background:The transposition of the great arteries (TGA) is one of the most severe congenital heart diseases. The arterial switch operation (ASO) is the preferred procedure to treat TGA. Although numerous reports have shown good results after ASOs, some patients suffer from circulatory system problems following the procedure. One reason for problems post-ASO is the local changes in the curvature and torsion of the thoracic aorta.Objective:The influence of these geometric changes on the blood flow field needs to be investigated in detail to consider possible cardiovascular problems after an ASO.Method:In this study, we conduct blood flow simulations in the thoracic aorta post-ASO, evaluate geometric changes in the aorta due to the ASO in terms of curvature and torsion, and consider the effect of geometric changes on blood flow in the aorta.Results:It was found that a large curvature near the aortic root causes an increase in the maximal wall shear stress value in the middle systole. Moreover, a large torsion results in a circumferential change in the maximal wall shear stress region. It was also found that the maximal wall shear stress in the post-ASO models is significantly higher than that in the normal models. This indicates that the aortic aneurysm initiation risk for a post-ASO artery may be higher than that of a normal artery.Conclusion:To reduce the risk of initiating an aneurism, it is suggested that the curvature near the aortic root should be decreased during the ASO.

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Non-Newtonian Flow Patterns Associated With an Arterial Stenosis

Journal of Biomechanical Engineering ◽

10.1115/1.2894103 ◽

1992 ◽

Vol 114 (4) ◽

pp. 512-514 ◽

Cited By ~ 10

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.

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