A study of the wall shear rate distribution near the end-to-end anastomosis of a rigid graft and a compliant artery

Abstract

The development of intimal hyperplasia in the anastomotic region of a vascular graft which does not match the compliance of the parent artery may be related to altered wall shear rates near the anastomosis. The purpose of this study is to determine the effect of radial wall motion and the phase angle between pressure and flow waves (impedance phase angle) on the wall shear rate distribution near an end-to-end vascular graft anastomosis model incorporating a rigid graft and a compliant artery. The wall shear rate is determined from near-wall velocity profiles obtained by a flow visualization method using a photochromic dye for different locations near the anastomosis. The results show that the mean wall shear rate under pulsatile flow conditions is 15–30% lower than under steady flow conditions at the same mean flow rate. The effect of the impedance phase angle on the mean wall shear rate is shown to be small, but its effect on the amplitude of the wall shear rate is not negligible. For our anastomosis model which has well-matched diameters at the mean pressure, the mean shear rates at the distal sites are lower than at the proximal sites by 15–23%. We suppose that the differences in the mean wall shear rate between the proximal and distal sites are related to the convergent/divergent geometry caused by the mismatch of the compliance. Since the distal side of the anastomosis is more prone to intimal hyperplasia, lower shear rates near the distal anastomosis favor the hypothesis that low/oscillatory wall shear rates lead to intimal hyperplasia.