It has been reported that the normally functional bileaflet valve ATS with open-pivot design does not exhibit a full opening motion either in the mitral or in the aortic position in patients. An in vitro experiment was conducted to investigate the mechanism of the ATS leaflet movement. ATS 29 mm for the mitral position was chosen in our experiment and SJM 29 mm was chosen as a control. Two pulsatile simulators were employed to investigate the factors affecting leaflet movement. Two different conduits to be incorporated downstream (in simulator I) and three different inlet coverings to alter the local flow field around the open pivot (in simulator II) were used. A high-speed video camera was employed to observe leaflet movement. The ATS valve could exhibit a fully open movement in straight conduit but could not fully open when an enlarging shape was incorporated downstream of the ATS valve. The covering of the ATS open pivot could make the leaflets fully open or increase the opening angle with the existence of the enlarging downstream shape. The enlargement downstream of the ATS valve, which induces a divergent transvalvular flow, is the main reason that the leaflets do not fully open. The local flow field around the open pivot, which induces an additional moment Ma, plays an important role in the movement of the ATS leaflets.
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