Design of a function test apparatus for prosthetic heart valves. Initial results in the mitral position

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Abstract
A test rig has been developed to investigate the function of prosthetic heart valves under pulsatile flow conditions. The rig uses a servo-controlled pump to produce a physiological flow waveform through the valve. The pressure difference across the valve and flow through the valves are measured to assess the valve function. The mean pressure difference, root mean square (RMS) forward flow and regurgitant volumes are calculated on a computer. In the initial study, seven popular mechanical prostheses (Sizes 29 and 27 mm) were evaluated in the mitral position under five different flow conditions. The mean pressure difference was dependent on the position of the downstream pressure tapping, the orientation of the valve and the time interval used to average the signals. The orientation of some valves also affected the regurgitant volumes. These variations (10-25%) were similar in size to the differences measured between individual valves. Test conditions have to be specified very carefully for accurate comparison of valve function to be made.