Effect of tapered grafts on hemodynamics and flow rate in dialysis access grafts

Aside from the high incidence of venous stenosis, high-output failure and peripheral steal syndromes remain serious problems of vascular access. Meanwhile commercial tapered grafts are available to address this topic, but little is known about its effect neither on graft flow nor on hemodynamics.

Anastomotic models were constructed using a clear silicon elastomer. The arterial anastomosis was shaped in two ways: 1) like a direct connection of artery and 7-mm graft and 2) with a 4-mm diameter segment between artery and graft. Hemodynamic measurements were performed in a pulsatile flow circuit to simulate blood flow at physiological conditions. Flow patterns were obtained by direct dye injection. Additionally, the correlation between the length of narrow segment and mean arterial pressure was investigated.

In all models using a 4-mm segment, the oscillating anastomotic vortex was disappeared. This vortex was shifted to the area behind the well-rounded expansions of the graft demonstrating a new separation region, but the flow direction was constant during the whole simulated cycle. At identical pressure rates and waveforms the length of narrow segment determined the graft flow rate directly (e.g., at mean pressure 100 mmHg, flow reduction up to 28% in 4-mm segments, and up to 55% in 3-mm segments).

These findings indicate that taper is an important consideration in the design of vascular access grafts.