Three‐dimensional distribution of wall shear stress and its gradient in red cell‐resolved computational modeling of blood flow in in vivo‐like microvascular networks

Restenosis resulting from neointimal hyperplasia (NH) limits the effectiveness of intravascular stents. Rates of restenosis vary with stent geometry, but whether stents affect spatial and temporal distributions of wall shear stress (WSS) in vivo is unknown. We tested the hypothesis that alterations in spatial WSS after stent implantation predict sites of NH in rabbit iliac arteries. Antegrade iliac artery stent implantation was performed under angiography, and blood flow was measured before casting 14 or 21 days after implantation. Iliac artery blood flow domains were obtained from three-dimensional microfocal X-ray computed tomography imaging and reconstruction of the arterial casts. Indexes of WSS were determined using three-dimensional computational fluid dynamics. Vascular histology was unchanged proximal and distal to the stent. Time-dependent NH was localized within the stented region and was greatest in regions exposed to low WSS and acute elevations in spatial WSS gradients. The lowest values of WSS spatially localized to the stented area of a theoretical artery progressively increased after 14 and 21 days as NH occurred within these regions. This NH abolished spatial disparity in distributions of WSS. The results suggest that stents may introduce spatial alterations in WSS that modulate NH in vivo.

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Design and Analysis of a Shear Stress Sensor for Microcirculation Investigations (Invited Paper)

Volume 2: Symposia, Parts A, B, and C ◽

10.1115/fedsm2003-45069 ◽

2003 ◽

Author(s):

Risa Robinson ◽

Lynn Fuller ◽

Harvey Palmer ◽

Mary Frame

Keyword(s):

Blood Flow ◽

Shear Stress ◽

Wall Shear Stress ◽

Computational Technique ◽

Flow Modification ◽

Stress Sensors ◽

Shear Stress Sensors ◽

Wall Shear

Blood flow regulation in the microvascular network has been investigated by means of computational fluid dynamics, in vivo particle tracking and microchannel models. It is evident from these studies that shear stress along the wall is a key factor in the communication network that results in blood flow modification, yet current methods for shear stress determination are acknowledged to be imprecise. Micromachining technology allows for the development of implantable shear stress sensors that will enable us to monitor wall shear stress at multiple locations in arteriole bifurcations. In this study, a microchannel was employed as an in vitro model of a microvessel. Thermal shear stress sensors were used to mimic the endothelial cells that line the vessel wall. A three dimensional computational model was created to simulate the system’s thermal response to the constant temperature control circuit and related wall shear stress. The model geometry included a silicon wafer section with all the fabrication layers — silicon dioxide, poly silicon resistor, silicon nitride — and a microchannel with cross section 17 μm × 17 μm. This computational technique was used to optimize the dimensions of the system for a 0.01 Reynolds number flow at room temperature in order to reduce the amount of heat lost to the substrate and to predict and maximize the signal response. Results of the design optimization are presented and the fabrication process discussed.

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Inflammatory Response of Endothelial Cells to Wall Shear Stress in Three Dimensional Stenotic Models

ASME 2009 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2009-206669 ◽

2009 ◽

Author(s):

Leonie Rouleau ◽

Joanna Rossi ◽

Jean-Claude Tardif ◽

Rosaire Mongrain ◽

Richard L. Leask

Keyword(s):

Endothelial Cells ◽

Shear Stress ◽

Wall Shear Stress ◽

Three Dimensional ◽

Realistic Model ◽

In Vitro Models ◽

Steady Flows ◽

Wall Shear

Endothelial cells (ECs) are believed to respond differentially to hemodynamic forces in the vascular tree. Once atherosclerotic plaque has formed in a vessel, the obstruction creates complex spatial gradients in wall shear stress (WSS). In vitro models have used mostly unrealistic and simplified geometries, which cannot reproduce accurately physiological conditions. The objective of this study was to expose ECs to the complex WSS pattern created by an asymmetric stenosis. Endothelial cells were grown and exposed for different times to physiological steady flows in straight dynamic controls and in idealized asymmetric stenosis models. Cell morphology was noticeably different in the regions with spatial WSS gradients, being more randomly oriented and of cobblestone shape. Inflammatory molecule expression was also altered by exposure to shear and endothelial nitric oxide synthase (eNOS) was upregulated by its presence. A regional response in terms of inflammation was observed through confocal microscopy. This work provides a more realistic model to study endothelial cell response to spatial and temporal WSS gradients that are present in vivo and is an important advancement towards a better understanding of the mechanisms involved in coronary artery disease.

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Measurements of the wall shear stress distribution in the outflow tract of an embryonic chicken heart

Journal of The Royal Society Interface ◽

10.1098/rsif.2009.0063 ◽

2009 ◽

Vol 7 (42) ◽

pp. 91-103 ◽

Cited By ~ 68

Author(s):

C. Poelma ◽

K. Van der Heiden ◽

B. P. Hierck ◽

R. E. Poelmann ◽

J. Westerweel

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Three Dimensional ◽

Outflow Tract ◽

Chicken Heart ◽

Embryonic Chicken ◽

Dimensional Reconstruction ◽

Wall Shear ◽

Embryo Heart

In order to study the role of blood–tissue interaction in the developing chicken embryo heart, detailed information about the haemodynamic forces is needed. In this study, we present the first in vivo measurements of the three-dimensional distribution of wall shear stress (WSS) in the outflow tract (OFT) of an embryonic chicken heart. The data are obtained in a two-step process: first, the three-dimensional flow fields are measured during the cardiac cycle using scanning microscopic particle image velocimetry; second, the location of the wall and the WSS are determined by post-processing flow velocity data (finding velocity gradients at locations where the flow approaches zero). The results are a three-dimensional reconstruction of the geometry, with a spatial resolution of 15–20 µm, and provides detailed information about the WSS in the OFT. The most significant error is the location of the wall, which results in an estimate of the uncertainty in the WSS values of 20 per cent.

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In-vivo blood flow parameters can predict at-risk aortic aneurysms and dissection: a comprehensive biomechanics model

European Heart Journal ◽

10.1093/ehjci/ehaa946.2339 ◽

2020 ◽

Vol 41 (Supplement_2) ◽

Author(s):

M Salmasi ◽

O.A Jarral ◽

S Pirola ◽

S Sasidharan ◽

J Pepper ◽

...

Keyword(s):

Blood Flow ◽

Shear Stress ◽

Wall Shear Stress ◽

Risk Prediction ◽

Aortic Wall ◽

Tissue Mechanics ◽

Aortic Aneurysms ◽

Funding Source ◽

Wall Shear

Abstract Background Abnormal blood flow patterns can alter the material properties of the thoracic aorta via altered vascular biology and tissue biomechanics. In-vivo haemodynamic assessment of the aorta is yet to penetrate clinical practice due to our limited understanding of its effect on aortic wall properties. The decision for surgical treatment is based on size thresholds, limited to a single measurement of aortic diameter from routine imaging, although many aortic dissections (40–60%) occur below these size thresholds. This multi-centre study aims to assess the clinical utility of biomechanics principles in thoracic aortic aneurysm (TAA) risk rupture prediction using a substantial sample size. Methods Fifty-five patients undergoing surgery for root or ascending TAA were recruited from five cardiac centres. Bicuspid aortic valves and connective tissue disease were excluded from this study.Haemodynamic assessment Pre-operative 4-dimensional flow magnetic resonance imaging (4D-MRI) were conducted. Direct 4D-flow analysis and computational fluid dynamics (CFD) were performed creating detailed wall shear stress (WSS) maps across the whole aneurysms. Aortic wall assessment The aneurysmal aortic sample was obtained from surgery and subjected to region specific uniaxial failure tests in the circumferential and longitudinal directions, as well as delamination testing within the aortic media. Whole aneurysm histological characterisation was also conducted using computational pathology techniques. Blood flow, tissue mechanics and microstructural properties were used to develop a risk prediction model with assessment of elastin, collagen and smooth muscle cell composition, as well as failure strain assessment and dissection energy function. Results Outcomes of mechanical properties were: Young's Elastic Modulus as a measure of aortic stiffness (0.85 MPa ±0.69), as well as maximal tensile strength (0.49 MPa ± 0.36), which demonstrated reduced aortic wall strength in the outer curvature. This correlated with increased wall shear stress (WSS) (up to 10 Pa) and flow velocity (up to 43 l/min). Regions of abnormal flow and tissue mechanics correlated significantly with degraded medial microstructure (elastin abundance: 34 vs 66%; collagen abundance 26 vs 57%, p<0.05). Conclusions CFD modelling has the potential to provide a risk prediction of acute events in TAA beyond the current size classification, as validated by altered aortic tissue properties. Future longitudinal studies are warranted to validate this methods in moderately enlarging thoracic aortas. Flow, mechanical, histology properties Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): NIHR Imperial College BRC

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Numerical Simulation of Fluid-Induced Vibration and Wall Shear Stress in Fusi/Form Cerebral Aneurysm: Newtonian and Non-Newtonian Fluid

Fluids Engineering ◽

10.1115/imece2006-14766 ◽

2006 ◽

Author(s):

Yong Hyun Kim ◽

Joon Sand Lee ◽

Xin Wu

Keyword(s):

Blood Flow ◽

Shear Stress ◽

Wall Shear Stress ◽

Newtonian Fluid ◽

Stress Gradient ◽

In Vivo Studies ◽

Rupture Area ◽

Study Results ◽

Wall Shear

Vascular techniques have been used for curing the aneurysm, but the reason for the occurrence of aneurysms can not be known using these techniques. These techniques are usually used for preventing a significant situation such as rupture of an aneurysm. In our study, blood flow effects with or without vascular techniques inside an aneurysm were analyzed with computational fluid dynamics (CFD). Important hemodynamic quantities like wall shear stress and pressure in vessel are difficult to measure in-vivo. Blood flow is assumed to be Newtonian fluid. But it actually consists of platelets, so it is also considered a non-Newtonian fluid in this study. Results of the numerical model were used to compare and analyze fluid characteristics with experimental data. Using the flow characteristics (wall shear stress (WSS), wall shear stress gradient (WSSG)), the rupture area was identified to be located in the distal area. However, the rupture area, in vivo studies, was observed to be present at a different location. During pulsatile flow, vibration induced by flow is implicated by weakening of the artery wall and affects more than shear stress. After adapting the fluid-induced vibration, the rupture area in aneurysm is found to be located in the same area as the in-vivo result. Since smaller inflow and low WSS provide the effect of the distal neck, the vibration provides more effects in dome area. In this study it has been found that the effect of shear stress on the rupture of aneurysm is less than the effect of vibration. In the case of non-Newtonian fluid, vibration induced by flow also has more effects than WSS and WSSG. The simulation results gave detailed information about hemodynamics under physiological pulsatile inlet condition.

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