In vivo blood flow and wall shear stress measurements in the vitelline network

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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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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Non-periodicity of blood flow and its influence on wall shear stress in the carotid artery bifurcation: An in vivo measurement-based computational study

Journal of Biomechanics ◽

10.1016/j.jbiomech.2020.109617 ◽

2020 ◽

Vol 101 ◽

pp. 109617 ◽

Cited By ~ 2

Author(s):

Xindong Zhou ◽

Lekang Yin ◽

Lijian Xu ◽

Fuyou Liang

Keyword(s):

Blood Flow ◽

Shear Stress ◽

Carotid Artery ◽

Wall Shear Stress ◽

Computational Study ◽

In Vivo Measurement ◽

Carotid Artery Bifurcation ◽

Wall Shear

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Alterations in wall shear stress predict sites of neointimal hyperplasia after stent implantation in rabbit iliac arteries

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.01107.2004 ◽

2005 ◽

Vol 288 (5) ◽

pp. H2465-H2475 ◽

Cited By ~ 107

Author(s):

John F. LaDisa ◽

Lars. E. Olson ◽

Robert C. Molthen ◽

Douglas A. Hettrick ◽

Phillip F. Pratt ◽

...

Keyword(s):

Blood Flow ◽

Shear Stress ◽

Wall Shear Stress ◽

Iliac Artery ◽

Stent Implantation ◽

Neointimal Hyperplasia ◽

Three Dimensional ◽

Iliac Arteries ◽

Wall Shear

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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