COMPLIANCE AND DIAMETER MISMATCH AFFECT THE WALL SHEAR RATE DISTRIBUTION NEAR AN END-TO-END ANASTOMOSIS

The development of intimal hyperplasia near the anastomosis of a vascu lar graft to an artery may be related to changes in the wall shear rat e distribution. Mismatches in compliance and diameter at the end-to-en d anastomosis of a compliant artery and a rigid graft cause shear rate disturbances that may induce intimal hyperplasia and ultimately graft failure. The gc,al of this study is to determine how compliance misma tch, diameter mismatch, and impedance phase angle affect the wall shea r rate distribution in end-to-end anastomosis models under sinusoidal flow conditions. Wall shear rates are obtained through flow visualizat ion using a photochromic dye. In a model with a well-matched graft dia meter (6% undersized), the compliance mismatch causes low mean wall sh ear rates near the distal anastomosis. Considering diameter mismatch, the wall shear rate distributions in 6% undersized, 16% undersized, an d 13% oversized graft models are markedly different at similar phase a ngles. In the two undersized graft models, the minimum mean shear rate occurs near the distal anastomosis, and this minimum is lower in the model with greater diameter mismatch. The oversized graft model has a minimum mean shear rate near the proximal anastomosis. Thus in all thr ee models, the minimum mean wall shear rate is observed at the site of the divergent geometry. The impedance phase angle, which can be alter ed by disease states and vasoactive drugs, has a minor effect on the w all shear rate amplitude far from the anastomosis but a more pronounce d effect closer to the anastomosis. Mean wall shear rates under sinuso idal flow conditions are significantly lower than under steady flow co nditions at the same mean flow rate, but they are fairly insensitive t o phase angle changes. In order to avoid the divergent geometry that m ay cause lower wall shear rates, we recommend that compliance mismatch be minimized whenever possible and that graft diameter be chosen to m atch the arterial diameter at the relevant physiologic pressure, not a t the reduced pressure present when the graft is implanted.