A New Near-wall Residence Time Model Applied to Three Arterio-venous Graft End-to-side Anastomoses

Abstract

As a representative example of an end-to-side anastomosis, the distal portion of an arterio-venous hemodialysis graft with three graft-end designs and two outflow conditions has been considered. Arterio-venous graft failure for hemodialysis patients can be frequently related to stenotic developments, especially in the toe region. With critical blood particles such as LDL, platelets, and monocytes, being considered as a first-order approximation of; blood elements pathlines, near-wall residence times and wall stagnation points have been simulated to identify, in conjunction with the wall shear stress gradient, susceptible sites of stenotic developments. Assuming transient laminar three-dimensional non-Newtonian fluid flow, the transport equations were solved with validated finite-volume based CFD software and user-Fortran programs for the computation of fluid element pathlines and hemodynamic parameters. We conclude from this study that for the application of looped arterio-venous grafts, the graft-end geometry and the presence of retrograde outflow significantly influence the magnitude and location of the hemodynamic wall parameters considered. The new concept of near-wall blood “particle” behaviour, in conjunction with a wall shear stress based hemodynamic parameter, can be compared to similar histopathologic studies of intimal hyperplasia formation to understand better the role of hemodynamic factors in the biogenesis of the disease.