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: Local wall shear stress (WSS) has an impact on local remodelling of the vessel wall. WSS in turn strongly depends on local geometry. Our aim was to characterize patterns of local wall shear stress associated with distinct types of remodelling in coronary arteries. Vessel size and flow rates are different between patients, however. To compare distribution patterns of WSS in analogy to fluid-dynamic modelling, non-dimensional WSS/area functions are calculated. Right coronary arteries from seven controls, five patients with coronary artery disease (CAD) and five patients with aneurysmatic CAD (AnCAD) were analyzed. Flow simulations were performed in three-dimensionally reconstructed coronary vessels from biplane angiographic projections. Local WSS was normalized as percentage of maximum value in a histogram (100 classes) and corresponding area was expressed as percentage of total area. The normalized WSS distribution was characterized by a single peak with a large lower tie in controls, a loss of the single peak and a stochastic distribution in AnCAD and a narrowing of the lower tie in CAD. Correct classification of 16/17 coronary arteries was feasible by Fisher's discriminant functions based on median WSS, mean diameter, percentage of area with WSS <or=0.4 Pa and with WSS >or=15 Pa. Normalized WSS distribution might be an efficient tool in comparing wall shear stress between different patient groups. Whether normalized WSS distribution curves are apt to grade severity of disease remains to be investigated.Atherosclerosis 07/2008; 202(2):483-90. · 3.71 Impact Factor
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ABSTRACT: Computational fluid dynamics (CFD) methods based on three-dimensional (3D) vessel reconstructions have recently been shown to provide prognostically relevant hemodynamic data. However, the geometry reconstruction and the assessment of clinically relevant hemodynamic parameters may depend on the used imaging modality. In this study, the silicon model of the left coronary artery (LCA) was acquired with a biplane angiography. The geometry reconstruction was done using commercial CAAS 5.2 QCA 3D software and compared with an original geometry. The original model is an optically digitized post-mortem vessel cast. The biplane angiography reconstruction achieved a Hausdorff surface distance of 0.236 mm to the original geometry that is comparable with results obtained in our earlier study for computed tomography (CT) and magnetic resonance imaging (MRI) reconstructions. Steady flow simulations were performed with a commercial CFD program FLUENT. A comparison of the calculated wall shear stress (WSS) shows good correlation for histograms (r=0.97) and good agreement among the four modalities with a mean WSS of 0.65 Pa in the original model, of 0.68 Pa in the CT-based model, of 0.67 Pa in the MRI based model, and of 0.69 Pa in the biplane angiography-based model. We can conclude that the biplane angiography-based reconstructions can be used for the WSS profiling of the coronary arteries.Annals of biomedical engineering 03/2009; 37(4):682-91. · 2.41 Impact Factor
- Lecture Notes in Engineering and Computer Science. 01/2010;