Computational design of a bypass graft that minimizes wall shear stress gradients in the region of the distal anastomosis

Abstract

This study demonstrates that it is possible to design a terminal graft geometry for an end-to-side anastomosis that significantly reduces wall shear stress gradients. If the wall shear stress gradient is confirmed to be a major hemodynamic determinant of intimal hyperplasia and restenosis, these results may point to the design of optimal bypass graft geometries.

Shape optimization for viscous flows by reduced basis methods and free‐form deformation

“…A remarkable observation is that -even if the optimal shape are quite similar -the magnitude of the vorticity on the anastomosis highly depends on the presence of a residual patency in the obstructed host coronary artery; in particular, in the down field region vorticity magnitude is higher whether a residual flow is present. In both cases, the iteratively optimized geometry has a much smoother toe and heel than the initial shape; optimal shapes also show smoother curvatures at the heel with a gradual transition in the toe region, as already pointed out in the work by Lei et al [25]. The localization of maximum values of vorticity at the heel and toe is expected, because this is the region where disturbed flows occur, even with a Stokes model; the same conclusion can be drawn for wall shear stress gradient and Navier-Stokes flows [25].…”

“…In both cases, the iteratively optimized geometry has a much smoother toe and heel than the initial shape; optimal shapes also show smoother curvatures at the heel with a gradual transition in the toe region, as already pointed out in the work by Lei et al [25]. The localization of maximum values of vorticity at the heel and toe is expected, because this is the region where disturbed flows occur, even with a Stokes model; the same conclusion can be drawn for wall shear stress gradient and Navier-Stokes flows [25]. Moreover, higher values in the heel region are not as clinically significant as the high vorticity values near the toe region and in the down-field region, which is a well-known location where restenosis might reform.…”

“…This can have useful clinical applications especially in surgical procedures. Moreover, computational studies have highlighted the correlation between geometrical features (such as anastomotic angle and graft-artery diameter ratio) and vorticity, shear stress, shear stress gradient [25,45] and oscillatory shear index [34], as effect of recirculation, flow separation and moving stagnation zones [11,14]. For the problem at hand, we are interested in the minimization of the blood vorticity in the downfield region of the bypass by changing the shape of the anastomosis.…”

Fluid dynamic characterization of a novel branching anastomosis design

“…Although this design restores blood flow, the double thickness of the vessel wall at the lumen of the anastomosis may increase WSS and WSSG within the connection. WSSG is known to play a role in modifying endothelial cell response, and high WSSGs may cause intimal hyperplasia (Lei et al 1997;El Zahab et al 2010). The goal of this study was to design a new anastomosis with a recessed central obstruction in order to minimize local WSS and WSSG.…”

“…Disturbed flow patterns caused by geometric transitions at the anastomosis site (as well as altered biomechanical properties of the blood vessel walls themselves) may lead to intimal hyperplasia, atherosclerosis, and/or platelet thrombosis (Ojha 1993;Archie et al 2001;Cunningham & Gotlieb 2005;Loth et al 2008). High wall shear stress (WSS) and wall shear stress gradient (WSSG) are two factors proposed to underlie such outcomes (Ku 1997;Lei et al 1997). Therefore, it is essential to design anastomoses that restore normal circulation without effecting high WSS or WSSG.…”