Flow dynamics across end-to-end vascular bypass graft anastomoses

In this article, a numerical simulation of steady flow across an end-to-end vascular bypass graft anastomosis is presented. In vitro experiments were performed to determine the variations in the conduit cross section at the anastomosis. Penrose surgical drainage tubing was used to simulate an artery and was anastomosed with Polytetrafluoroethylene (PTFE) vascular grafts using a continuous suturing technique. Artery to artery anastomosis was simulated by suturing two Penrose tubing segments. The anastomotic specimens were subject to static transmural pressure in the physiologic range to determine the instantaneous diameter and compliance as a function of the distance from the anastomotic site. The experimentally determined geometries were used to simulate steady flow through an end-to-end anastomosis using the finite analytic (FA) numerical solution technique. The results demonstrated a region of flow separation 2 mm distal to the Penrose tubing-Penrose tubing anastomosis (simulating an artery-artery anastomosis) at higher transmural pressures. Moreover, wall shear stresses increased proximal to the anastomosis in flow from the Penrose tubing to the graft. In flow from the graft to the Penrose tubing, low wall shear stresses were observed distal to the anastomosis. Flow separation was observed distal to the anastomosis at higher transmural pressures with uniform inlet velocity condition. The region of low shear stress in flow from PTFE graft to the Penrose tubing was located nearer to the anastomosis with thin wall grafts than that with standard wall thickness grafts. Our steady flow model studies suggest a correlation between regions of low wall shear stress and the development of anastomotic neointimal fibrous hyperplasia in end-to-end anastomoses.