In vitro testing of a newly developed arteriovenous double-outflow graft.

INTRODUCTION: The long-term prognosis of arteriovenous polytetrafluoroethylene (PTFE) hemodialysis grafts remains poor, causing significant morbidity and costs. The high failure rate is due to a stenosis development of the graft-vein anastomosis, consisting of two pathophysiologically separate and characteristic lesions emerging from two main mechanisms: development of intimal hyperplasia in the vein and pseudointima in the graft. We developed a new venous anastomotic graft design that combines a flow diffuser and flow division, thereby creating a double-channel graft (Bi-Flow graft) and tested it in vitro. METHODS: In vitro experiments have been performed using silastic models of six different anastomotic configurations (straight end-to-side, cuffed Venaflo-type, large and small diffuser, and large and small Bi-Flow) inserted into a pulsatile-flow circuit. The silastic models were created using a computerized numerical control design approach, varying only the venous anastomoses. Velocity fields and shear stresses were obtained using particle image velocimetry, and volumetric flow rates through the models were measured using an ultrasound flowmeter. RESULTS: The hooded graft configurations showed significantly lower shear forces than did the end-to-side anastomosis. The shear stresses in the straight end-to-side graft were as high as arterial wall stresses. Large separation areas were present in the hooded grafts, except for the small Bi-Flow graft, which showed only isolated separation zones near the baffle used to divide the flow. The double-channel grafts exhibited a parabolic flow profile consisting of laminar flow in the double-outflow portion of the model's laminar flow pattern through the venous anastomosis. A marked flow separation was present in the large Bi-Flow model. Volumetric flow measurements revealed an average flow increase of 21% through the small Bi-Flow graft, which was attributed to the optimization of flow dynamics and pattern within the venous anastomosis of the double-channel graft. CONCLUSION: The new arteriovenous Bi-Flow graft design addresses two major problems responsible for the development of venous stenosis of prosthetic hemodialysis grafts in vitro. The new graft design should be further investigated in animal studies.