Flexible Prosthetic Vein Valve

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Over 7 million Americans suffer from chronic venous insufficiency (CVI), a disease that affects the venous system of the lower extremities. Problems associated with CVI include ulcerations, bleeding, swelling, and varicose veins, as well as deep vein thrombosis and pulmonary embolism. The presence of CVI is the result of incompetent, or malfunctioning, one-way vein valves in leg veins. There are few effective clinical therapies for treating CVI and there are currently no prosthetic vein valves commercially available. The purpose of this study was to define clinically relevant design requirements, develop functional tests for assessing a prosthetic vein valve, and design and fabricate a functional prosthetic vein valve for eventual clinical use. Engineering design methods were used to develop the valve, building a product based on well-defined consumer needs and design specifications. Emphasis was placed on creating a valve with potential clinical functionality. This clinical functionality was distilled into three major design criteria: that the valve (1) withstand backpressure of 300  mmHg with less than 1.0  mL/min of leakage; (2) open with distal pressure gradients less than 5  mmHg; and (3) meet criteria 1 and 2 after 500,000  cycles of opening and closing. Hydrostatic testing was conducted to measure the opening pressure and reflux leak rate of the valve. Cyclic life functionality was assessed using a cyclic flow loop simulating physiologic conditions of cyclic flow and pressure found in leg veins. The valve opened with a pressure of 2.6  mmHg±0.7  mmHg, which matches physiologic vein valve function. The valve also withstood 300  mmHg of backpressure with less than 0.5  mL/min of leakage, and maintained this performance even after 508,000  cycles of opening and closing in simulated physiologic conditions. The valve's burst pressure was a minimum of 530  mmHg±10  mmHg, six times greater than physiologic pressure natural vein valves experience. The valve continued to function well in an environment of vein-like tube expansion. The newly designed bi-leaflet prosthetic valve is comprised of a flexible, biocompatible material. Bench test results have shown that the valve is hydrodynamically functional and meets the mechanical design criteria for backpressure competency and opening pressure after 500,000  cycles. Finally, the valve can be manufactured easily with low cost.

©2007 American Society of Mechanical Engineers