Flexible Prosthetic Vein Valve

[+] Author and Article Information
Rahul D. Sathe

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405rdsathe@gmail.com

David N. Ku1

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405david.ku@me.gatech.edu


Corresponding author.

J. Med. Devices 1(2), 105-112 (Nov 12, 2006) (8 pages) doi:10.1115/1.2736393 History: Received April 06, 2006; Revised November 12, 2006

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 300mmHg with less than 1.0mLmin of leakage; (2) open with distal pressure gradients less than 5mmHg; and (3) meet criteria 1 and 2 after 500,000cycles 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 2.6mmHg±0.7mmHg, which matches physiologic vein valve function. The valve also withstood 300mmHg of backpressure with less than 0.5mLmin of leakage, and maintained this performance even after 508,000cycles of opening and closing in simulated physiologic conditions. The valve’s burst pressure was a minimum of 530mmHg±10mmHg, 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 500,000cycles. Finally, the valve can be manufactured easily with low cost.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Test setup for Tests A and C: opening pressure tests

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Figure 2

Test setup for Test B: reflux leak-rate testing

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Figure 3

Test setup for Test D: cyclic life functionality

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Figure 4

Good competency results: leak-rate is less than 1.0mL∕min (test specimen B3-8-T9)

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Figure 5

Excellent competency results: leak rate is less than 0.5mL∕min (test specimen B2-8-T9)

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Figure 6

Valve competency, assessed by measured leak rate, was categorized as excellent during an operation span from 0 to over 500,000cycles of opening and closing. Leak rate was less than 0.5mL∕min. This graph depicts the leak rate of the valve from 0mmHgto300mmHg prior to cyclic testing and after 500,000cycles of testing.

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Figure 7

Valve opening pressures before reflux testing met design criteria throughout cyclic life testing. High reflux pressure (300mmHg) sustained for 30s increased the valve’s opening pressure when measured after reflux testing.

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Figure 8

Synthetic vein-like tube for testing valves displayed similar compliance and diameter distention behavior to natural human leg veins. Distension was limited to about 1.5 times the original diameter by a restrictive plastic tube placed around test specimens. This graph was recreated in part using data from Stooker (28) and Wesley (29). Error data was not available for Wesley

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Figure 9

Prosthetic vein valve prevents leakage when exposed to back pressure (R‐L): 0mmHg, 90mmHg, 170mmHg. The sinus expands proximal to the valve site, mimicking natural valve behavior.



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