scholarly journals The Influence of the Anastomosis Angle on the Hemodynamics in the Distal Anastomosis in the Infrainguinal Bypass: an In Vitro Study

2016 ◽  
pp. 591-595 ◽  
Author(s):  
T. GRUS ◽  
G. GRUSOVÁ ◽  
L. LAMBERT ◽  
R. BANERJEE ◽  
J. MATĚCHA ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Intimal Hyperplasia ◽  
Similarity Theory ◽  
Experimental Models ◽  
Distal Anastomosis ◽  
Infrainguinal Bypass ◽  
Wall Shear

The geometric shape of the distal anastomosis in an infrainguinal bypass has an influence on its durability. In this article, we compared three different angles of the anastomosis with regard to the hemodynamics. Three experimental models of the distal infrainguinal anastomosis with angles of 25°, 45°, and 60° respectively were constructed according to the similarity theory to assess flow in the anastomoses using particle image velocimetry and computational fluid dynamics. In the toe, heel, and floor of the anastomosis that correspond to the locations worst affected by intimal hyperplasia, adverse blood flow and wall shear stress were observed in the 45° and 60° models. In the 25° model, laminar blood flow was apparent more peripherally from the anastomosis. In conclusions, decreasing the distal anastomosis angle in a femoropopliteal bypass results in more favorable hemodynamics including the flow pattern and wall shear stress in locations susceptible to intimal hyperplasia.

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

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.

scholarly journals In-Vitro Simulation of the Blood Flow in an Axisymmetric Abdominal Aortic Aneurysm

2019 ◽  
Vol 9 (21) ◽  
pp. 4560
Author(s):  
Espa ◽  
Moroni ◽  
Boniforti
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Shear Stress ◽  
Particle Tracking ◽  
Classical Particle ◽  
Abdominal Aortic ◽  
Wall Shear

We investigated the blood flow patterns and the hemodynamics associated with an abdominal aortic aneurysm detected in an in vitro measurement campaign performed in a laboratory model of an aneurysm with rigid walls and an axisymmetric shape. Experiments were run in steady flow conditions and by varying the Reynolds number in the range 410 < Re < 2650. High spatial and temporal resolution 2D optical measurements of the velocity field were obtained through a particle tracking technique known as Hybrid Lagrangian Particle Tracking. Conversely to classical Particle Image Velocimetry, both the fluid particle trajectories and the instantaneous and time-averaged velocity fields are provided without constraints on the grid size and very close to the vessel boundary. All the most relevant quantities needed to investigate the flow features were evaluated, and in particular, we focused on the wall shear stress distribution both in the healthy aortic portion and within the aneurysm. Results show that the recirculation zone in correspondence of the cavity moves downstream, and this displacement is found to increase with Re. Very low wall shear stress values are recovered in correspondence of the aneurysmal cavity, while a sharp peak occurs in correspondence of the reattachment point. In agreement with the literature data, the peak value is found to decrease with Re and to be about equal to twice the upstream value.

scholarly journals In vitro blood flow model with physiological wall shear stress for hemocompatibility testing—An example of coronary stent testing

2016 ◽  
Vol 11 (3) ◽  
pp. 031004 ◽  
Author(s):  
Gerwin Erik Engels ◽  
Sjoerd Leendert Johannes Blok ◽  
Willem van Oeveren
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Model ◽  
Coronary Stent ◽  
Wall Shear ◽  
Blood Flow Model

Pulsatile Flow in an End-to-Side Vascular Graft Model: Comparison of Computations With Experimental Data

2000 ◽  
Vol 123 (1) ◽  
pp. 80-87 ◽  
Author(s):  
M. Lei ◽  
D. P. Giddens ◽  
S. A. Jones ◽  
F. Loth ◽  
H. Bassiouny
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Intimal Hyperplasia ◽  
Vascular Graft ◽  
Small Diameter ◽  
Shear Stresses ◽  
Wall Shear

Various hemodynamic factors have been implicated in vascular graft intimal hyperplasia, the major mechanism contributing to chronic failure of small-diameter grafts. However, a thorough knowledge of the graft flow field is needed in order to determine the role of hemodynamics and how these factors affect the underlying biological processes. Computational fluid dynamics offers much more versatility and resolution than in vitro or in vivo methods, yet computations must be validated by careful comparison with experimental data. Whereas numerous numerical and in vitro simulations of arterial geometries have been reported, direct point-by-point comparisons of the two techniques are rare in the literature. We have conducted finite element computational analyses for a model of an end-to-side vascular graft and compared the results with experimental data obtained using laser-Doppler velocimetry. Agreement for velocity profiles is found to be good, with some clear differences near the recirculation zones during the deceleration and reverse-flow segments of the flow waveform. Wall shear stresses are determined from velocity gradients, whether by computational or experimental methods, and hence the agreement for this quantity, while still good, is less consistent than for velocity itself. From the wall shear stress numerical results, we computed four variables that have been cited in the development of intimal hyperplasia—the time-averaged wall shear stress, an oscillating shear index, and spatial and temporal wall shear stress gradients—in order to illustrate the versatility of numerical methods. We conclude that the computational approach is a valid alternative to the experimental approach for quantitative hemodynamic studies. Where differences in velocity were found by the two methods, it was generally attributed to the inability of the numerical method to model the fluid dynamics when flow conditions are destabilizing. Differences in wall shear, in the absence of destabilizing phenomena, were more likely to be caused by difficulties in calculating wall shear from relatively low resolution in vitro data.

Alteration of Mean Wall Shear Stress Near an Oscillating Stagnation Point

1998 ◽  
Vol 120 (2) ◽  
pp. 227-237 ◽  
Author(s):  
A. L. Hazel ◽  
T. J. Pedley
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Stagnation Point ◽  
Intimal Hyperplasia ◽  
Bypass Surgery ◽  
Carotid Sinus ◽  
Time Varying ◽  
The Mean ◽  
Wall Shear

The site opposite an end-to-side anastomosis, resulting from femoral bypass surgery, and the carotid sinus are two regions well known to be prone to fibrous intimal hyperplasia or atherogenesis, respectively. The blood flow at these two sites features a stagnation point, which oscillates in strength and position. Mathematical models are used to determine some of the features of such a flow; in particular, the mean wall shear stress is calculated. The positional oscillations cause a significant change in the distribution and magnitude of the mean wall shear stress from that of the well-studied case of a stagnation point that oscillates only in strength. It is therefore proposed that the recorded effect of time dependence in the flow upon atherogenesis could still be a result of the distribution of the mean and not the time-varying components of the wall shear stress.

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

scholarly journals Investigation of Wall Shear Stress in Cardiovascular Research and in Clinical Practice—From Bench to Bedside

2021 ◽  
Vol 22 (11) ◽  
pp. 5635
Author(s):  
Katharina Urschel ◽  
Miyuki Tauchi ◽  
Stephan Achenbach ◽  
Barbara Dietel
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Cell Function ◽  
Computational Techniques ◽  
Apical Surface ◽  
Cardiovascular Research ◽  
Endothelial Cell Function ◽  
Wall Shear

In the 1900s, researchers established animal models experimentally to induce atherosclerosis by feeding them with a cholesterol-rich diet. It is now accepted that high circulating cholesterol is one of the main causes of atherosclerosis; however, plaque localization cannot be explained solely by hyperlipidemia. A tremendous amount of studies has demonstrated that hemodynamic forces modify endothelial athero-susceptibility phenotypes. Endothelial cells possess mechanosensors on the apical surface to detect a blood stream-induced force on the vessel wall, known as “wall shear stress (WSS)”, and induce cellular and molecular responses. Investigations to elucidate the mechanisms of this process are on-going: on the one hand, hemodynamics in complex vessel systems have been described in detail, owing to the recent progress in imaging and computational techniques. On the other hand, investigations using unique in vitro chamber systems with various flow applications have enhanced the understanding of WSS-induced changes in endothelial cell function and the involvement of the glycocalyx, the apical surface layer of endothelial cells, in this process. In the clinical setting, attempts have been made to measure WSS and/or glycocalyx degradation non-invasively, for the purpose of their diagnostic utilization. An increasing body of evidence shows that WSS, as well as serum glycocalyx components, can serve as a predicting factor for atherosclerosis development and, most importantly, for the rupture of plaques in patients with high risk of coronary heart disease.

P044 A new method to determine wall shear stress distributions in in-vitro flow models of arterial flow

1998 ◽  
Vol 31 ◽  
pp. 77 ◽  
Author(s):  
F.N. van de Vosse ◽  
F.J.H. Gijsen
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
New Method ◽  
Arterial Flow ◽  
Stress Distributions ◽  
Flow Models ◽  
Wall Shear

Runge-Kutta method for wall shear stress of blood flow in stenosed artery

2014 ◽  
Author(s):  
Izyan Syazana Awaludin ◽  
Rokiah@Rozita Ahmad
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Kutta Method ◽  
Runge Kutta Method ◽  
Stenosed Artery ◽  
Runge Kutta ◽  
Wall Shear

In-Vitro Wall Shear Stress Measurements for Microfluid Flows by Using Second-Order SPE Micro-PIV

2007 ◽  
Author(s):  
Han-Sheng Chuang ◽  
Steven T. Wereley
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Measurement Errors ◽  
Pearson Correlation ◽  
Second Order ◽  
Bias Error ◽  
Central Difference ◽  
Micro Piv ◽  
Wall Shear

Conventional single pixel evaluation (SPE) significantly improves the spatial resolution of PIV measurements to the physical limit of a CCD camera based on the forward difference interrogation (FDI). This paper further enhances the computational algorithm to second-order accuracy by simply modifying the numerical scheme with the central difference interrogation (CDI). The proposed central difference scheme basically superposes the forward-time and the backward-time correlation domains, thus resulting in reduced bias error as well as rapid background noise elimination. An assessment of the CDI SPE algorithm regarding the measurement errors was achieved via numerous synthetic images subject to a four-roll mill flow. In addition, preliminary wall shear stress (WSS) measurements regarding different algorithms are also evaluated with an analytical turbulent boundary flow. CDI scheme showed a 0.32% error deviated from the analytical solution and improved the same error in FFT-based correlation correlation (FFT-CC) by 32.35%. To demonstrate the performance in practice, in-vitro measurements were implemented in a serpentine microchannel made of polydimethyl siloxane (PDMS) for both CDI SPE and spatial cross-correlation. A series of steady-state flow images at five specified regions of interest were acquired using micro-PIV system. Final comparisons of the WSS regarding the Pearson correlation coefficient, R2, between the numerical schemes and the simulations showed that an overall result was improved by CDI SPE due to the fine resolution and the enhanced accuracy.

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