The long term success of bypass grafts is frequently compromised by the devel- opment of intimal hyperplasia at the downstream anastomosis, leading eventually to occlusion of the graft lumen. It has been suggested that hemodynamic factors play a role in such graft failure. To test the role of vessel wall distensibility in determining anastomotic flow patterns, a computer code, based upon the penalty method com- bined with a Crouzeix-Raviart finite element, has been developed to simulate flow in rigid and distensible walled 2D geometries. Using parameters appropriate for the distal circulation, studies in a 2D rigid end-to-side anastomosis model with a 45° graft angle and an equal graft/host area ratio indicate the presence of elevated wall shear stresses at sites known to be susceptible to the development of intimal hyper- plasia. At these same sites, large temporal variations and spatial gradients of wall shear stress were also noted.

To simulate flow in physiologically distensible-walled geometries, a novel numerical approach has been developed in which the wall velocities are solved implicitly in conjunction with the fluid and pressure fields, while the wall displacements are treated in an explicit iterative update. This method results in a less than twofold increase in computational effort as compared to similar rigid-walled studies. Assuming a purely elastic artery wall, results from the distensible simulations reveal the same overall wall shear stress and flow features as for the rigid model. These results also hold true for the case of an impedance mismatch due to a rigid graft section, as well as for the case of unphysiologically short wavelengths. It is concluded that the effects of wall distensibility on wall shear stress patterns in the distal circulation are minimal.