Estimation of wall shear stress in bypass grafts with computational fluid dynamics method.
ABSTRACT Coronary artery bypass graft (CABG) operation for coronary artery disease with different types of grafts has a large clinical application world wide. Immediately after this operation patients are usually relieved of their chest pain and have improved cardiac function. However, after a while, these bypass grafts may fail due to for example, neointimal hyperplasia or thrombosis. One of the causes for this bypass graft failure is assumed to be the blood flow with low wall shear stress. The aim of this research is to estimate the wall shear stress in a graft and thus to locate areas were wall shear stress is low. This was done with the help of a blood flow computer model. Post-operative biplane angiograms of the graft were recorded, and from these the three-dimensional geometry of the graft was reconstructed and imported into the computational fluid dynamics (CFD) program FLUENT. The stationary diastolic flow through the grafts was calculated, and the wall shear stress distribution was estimated. This procedure was carried out for one native vessel and two different types of bypass grafts. One bypass graft was a saphenous vein and the other one was a varicose saphenous vein encased in a fine, flexible metal mesh. The mesh was attached to give the graft a defined diameter. The computational results show that each graft has distinct areas of low wall shear stress. The graft with the metal mesh has an area of low wall shear stress (< 1 Pa, stationary flow), which is four times smaller than the respective areas in the other graft and in the native vessel. This is thought to be caused by the smaller and more uniform diameter of the metal mesh-reinforced graft.
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ABSTRACT: The influence of the presence of neighboring entities on drag in blood flow where the dominating mechanisms are expected to be viscous, drag, and gravity forces is investigated in a 3-D anatomically realistic right coronary artery. A classical Eulerian multiphase model on the Fluent v6.3.26 platform is used to model pulsatile non-Newtonian blood flow. Two new drag models based on the mixture viscosity concept are developed by using the drag similarity criteria. In literature, drag models based on the mixture viscosity concept are only depended on volume fraction and show Newtonian viscosity effects on drag. However, mixture viscosity depends on the primary independent variables such as the volume fraction and the shear rate in most of the dispersed flows like blood flow. Non-Newtonian drag effects on red blood cell are so calculated by using these new volume fraction and the shear rate dependent drag models. Five different drag models including these new drag models are used to model the blood flow in this study to investigate the effectiveness of drag force model on blood flow. Keywordstwo-phase–blood–right coronary artery–drag–CFDKorea-Australia rheology journal 09/2011; 23(2):89-103. DOI:10.1007/s13367-011-0012-8 · 0.63 Impact Factor
Historian 06/2011; 73(2):398 - 399. DOI:10.1111/j.1540-6563.2011.00294_63.x
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ABSTRACT: The Coronary Artery Bypass Graft (CABG) yields excellent results and remains the modern standard of care for treatment of occlusive disease in the cardiovascular system. However, the development of anastomotic Intimal Hyperplasia (IH) and restenosis can compromise the medium-and-long term effects of the CABG. This problem can be correlated with the geometric configuration and hemodynamics of the bypass graft. A novel geometric configuration was proposed for the CABG with two symmetrically implanted grafts for the purpose of improving the hemodynamics. Physiological blood flows in two models of bypass grafts were simulated using numerical methods. One model was for the conventional bypass configuration with a single graft (1-way model); the other model was for the proposed bypass configuration with two grafts (2-way model). The temporal and spatial distributions of hemodynamics, such as flow patterns and Wall Shear Stress (WSS) in the vicinity of the distal anastomoses, were analyzed and compared. Calculation results showed that the 2-way model possessed favorable hemodynamics with uniform longitudinal flow patterns and WSS distributions, which could decrease the probability of restenosis and improve the effect of the surgical treatment. Concerning the limitations of the 2-way bypass grafts, it is necessary to perform animal experiments to verify the viability of this novel idea for the CABG.Journal of Biological Physics 05/2005; 31(2):161-82. DOI:10.1007/s10867-005-5829-2 · 1.15 Impact Factor