1. Field of Our Invention
Our invention relates to apparatus for testing mechanical heart valves, and in particular mechanical heart valves having a rigid annulus and one or more pivoting leaflets mounted therein.
2. Description of Related Art
Various types of heart valve prostheses have been proposed, and many give generally satisfactory operation. One popular design for a heart valve prosthesis includes an annular valve body in which a pair of opposed leaflet occluders are pivotly mounted. The occluders are moveable between a closed, mated position, blocking blood flow in an upstream direction, thereby minimizing regurgitation, and an open position, allowing blood flow in a downstream direction. One such heart valve is described, for example, in U.S. Pat. No. 5,147,390 to Campbell, which patent is assigned to CarboMedics, Inc., the assignee of our invention.
A mechanical heart valve, such as that described in the '390 patent, can be expected to open and close a great number of times during its use. It is desirable to minimize, in so far as possible, the number of failures experienced in the use of a prosthetic heart valve. Testing for function is therefore an important part of prosthetic heart valve development and manufacture. Heart valve function testers are known which open and close the mechanical heart valve in an in vitro environment, mimicking the action of the heart. Fluid is forced past the valve to open the valve. An existing back pressure is then allowed to close the valve when the pulsatile forward pressure is removed.
There is, however, another possibility for defects which can be tested. Minute cracks or other surface defects in pivots of leaflet occluders or in pivot recesses of the valve body are difficult to detect. It is known, however, from the application of fracture mechanics, that cracks below a certain maximum size will not cause failure. Cracks or other surface defects larger than the maximum allowable size can be detected by applying a proof test load to the component. The proof test load should be some multiple of the functional vivo load, to provide a factor of safety associated with the test. The primary purpose of proof testing is to detect components of heart valves with flaws larger than a specific size.