Numerical simulation of the haemodynamics in end‐to‐side anastomoses

Abstract

SUMMARYIn this paper, the commercial CFD package Ansys workbench 11 was used to analyse the three-dimensional haemodynamics of a typical stenotic Coronary Artery Bypass Grafting (CABG). Two end-to-side CABG configurations with anastomosis angle of 20 • and 40 • and graft-artery diameter ratios of 1/0.6, 1/1 and 1/1.6 were examined. The flow measurements from in vitro Doppler guide wire technique acquired in left interior mammary artery (LIMA) and grafted to the left anterior descending artery (LAD) were used to impose the physiologically flow conditions at proximal and distal CABG inlet and outlet, respectively. The blood flow was considered to be incompressible, pulsatile, Newtonian, and laminar rheology. The main objective was to determine the effect of anastomosis angle and graft-artery diameter ratio on the flow patterns and the long-term functionality of the graft. In analysing the results, the distributions of temporal and spatial wall shear stress (WSS) gradient and oscillating shear index (OSI) in the critical regions of CABG such as heel, toe and the centre of the junction were presented and the vortex motions and the occurrence of recirculation zones were examined. The findings showed asymmetrically disturbed flows in the localized regions of the proximal and distal host artery for all models considered and the movement of the recirculation zones from heel to toe was found to depend on the time at the cardiac cycle. These regions are known as susceptible sites to thrombosis and re-stenosis due to their association with low values of WSS.

Boundary control and shape optimization for the robust design of bypass anastomoses under uncertainty

“…Three dimensional effects were found not to have a large impact on the total downstream vorticity for moderate Reynolds numbers. Differences up to [10][11][12][13][14][15][16][17][18][19][20] • in the optimal angle predictions were found between different cost functionals and flow split values used. In all cases studied the optimal angle increased as the severity of the occlusion in the host artery increased, which indicates that underestimating the level of occlusion in the host artery may lead to bypass designs with too small angles.…”

“…On the other hand, theoretical methods of optimal control and shape optimization enable a suitable formulation of the optimal design problem for bypass grafts. Many works [1,2,16,17,21,35,38,43,49,51,56,58] have focused in the last decade on the optimal shape design of end-to-side anastomoses, typically by acting on the wall shape near the anastomosis by local shape variations. The three most significant design variables in end-to-side anastomoses are [39]: the anastomosis angle, the graft-to-host diameter ratio [32], and the toe shape (see Fig.…”

“…It seems clear that in order to design a bypass graft in a robust way, one must be prepared to take into account all the various sources of uncertainty that can effect the final optimized design. Concerning previous works on optimization of bypass anatomoses, the effect of the anastomosis angle was studied in [16,17,37,58], the effect of the toe shape in [1,2,18,37,38,43,56], and the graft-to-host ratio in [16]. For a more complete review of bypass graft design results, we refer to [45,47].…”

Graft–Artery Junctions: Design Optimization and CAD Development

“…With this method, the pressure and fluid flow characteristics as well as the wall shear stress (WSS) during a cardiac cycle could be accurately simulated. In addition, it is widely accepted that using CFD is a better alternative to invasive or noninvasive flow measurements of blood flow by in vitro and/or ex vivo experimental flow setups, which can be very expensive and time consuming (10). The mathematical description of the flows to be solved for this type of problem is based on 3D Navier-Stokes equations.…”

“…This is because the layer of endothelial cells (ECs) on the wall of the artery has the ability to act as a wall-shear biosensor which maintains a more uniform shear stress level in the range 10-20 dyne/cm 2 . Conversely, low shear stress over time can cause the arteries to remodel by intimal thickening (9)(10)(11).…”