Flow Characteristics in Tapered Vascular Grafts

Synthetic vascular grafts are widely used to replace the damaged blood vessel. However, the patency rate of small size vascular graft (smaller than 6 mm diameter) are poor because of the occulusions of vascular grafts, which are initiated by anastomotic intimal hyperplasia. Various factors, such as thrombogenic nature of synthetic material, size, mechanical properties, surgical technique, and hemodynamic characteristics, influence the development of anastomotic intimal hyperplasia. Among the fluid mechanical factors, turbulence, flow separation, recirculation, and shear stress are suspected to be the important hemodynamic factors (Nerem, 1992). Since matching the diameter and compliance of a graft to those of a host artery is difficult, convergent and divergent shape near the anastomotic sites are frequently observed. Sudden diameter increase generates the flow disturbances, separated, recirculated, low shear region. In order to avoid sudden diameter changes near anastomotic sites, taper vascular grafts are suggested in this study. Tapered arterial grafts are suggested by Black and How (1989) in order to reduce the disturbance intensity using stabilizing chracteristics of the convergent channels. If convergent grafts are used, sudden expansions are found near the distal side of the anastomosis, which causes unfaborable hemodynamic effects. We want to remove the sudden expansion generated by diameter mismatch using gradually divergent vascular grafts.