Engineering analysis of the effect of atrial contraction on mitral prosthetic valve closing

In order to clarify the effect of atrial contraction on the closing motion of mitral prosthetic valves, a mechanical circulatory model has been developed. It consists of a sphere-shaped left atrium (volume: 120 ml, thickness: 0.3 mm) and a cone-shaped left ventricle (volume: 120 ml, thickness: 0.2 mm). They were made of silicone and driven by compressed air. Under the condition of 60 BPM and diastolic period of 720 ms, Bjork-Shiley Monostrut valve (annulus diameter 29 mm) has been tested. The motion was measured with a high speed video camera. After the contraction of the atrium (100 ms), there was a delay of 75 ms before the ventricular contraction started. Mitral flow similar to physiological conditions have been produced. The closing period was measured for 10 cycles, then mean value as well as standard deviation were calculated. Three comparative results were obtained under the condition of atrial contraction and non-contraction. By the atrial contraction, 1). The valve closure started earlier, 2) The closing period was increased from 22.4±3.4 ms to 63±3.2 ms, 3) The maximum back flow at valve closure was decreased from 0.69±0.01 m/s to 0.23±0.02 m/s. From the evaluation of the results compared with the animal experiments in the literature, we concluded 1) Our mechanical circulatory model could simulate the end-diastolic inflow characteristics, 2) A closing duration' was prolonged by the atrial contraction and softer closure of the valve could be achieved. This phenomenon was observed in natural mitral valve.