Hemodynamics in a compliant hydraulic in vitro model of straight versus tapered PTFE arteriovenous graft.

BACKGROUND Hemodialysis patients require a vascular access to deliver sufficient blood flow to the artificial kidney. Of these vascular accesses, 30% are prosthetic (mainly polytetrafluorethylene [PTFE]) graft implants. These grafts are prone to the development of stenosis in the vein due to intimal hyperplasia, subsequently leading to thrombosis and graft failure. AIM We investigated the hemodynamics in a straight and a tapered PTFE-graft and compare the hydrodynamical behavior of both grafts. MATERIALS AND METHODS Two different vascular access geometry models were examined: a 6-mm diameter straight graft and a 4- to 7-mm tapered graft. The grafts were sutured to a compliant silicon model of an artery and vein in a loop configuration. Flow rate varied between 500 and 1500 mL/min. Two conditions were tested: 1). control: mean pressure is 100 mm Hg at the arterial inlet; and 2). low resistance condition: pressure is 20 mm Hg at the venous outlet. Pulse pressure is 60 mm Hg at the arterial inlet for both conditions. Pressure and flow velocity are measured continuously, while flow rate is measured volumetrically. RESULTS The pressure drop at the arterial anastomosis of the tapered graft is three times higher compared to the straight graft model. Intragraft pressure drops are similar in both graft types. Mean pressure and pulse pressure in the graft and vein are decreased in the low resistance condition. Also, the difference between maximum and minimum velocity is smaller in this. CONCLUSIONS No significant differences are noted between the graft geometries: pressure drop over the graft is almost equal. The major difference is the higher pressure drop at the arterial anastomosis of the tapered graft.