Lee C S, Chandran K B
Department of Biomedical Engineering, University of Iowa, Iowa City 52242.
Ann Biomed Eng. 1994 Jul-Aug;22(4):371-80. doi: 10.1007/BF02368243.
An investigation of the flow dynamics through the peripheral clearance (the gap formed between the occluder tip and the metal housing in the closed position) of a tilting disc heart valve at the moment of valve closure is presented. A Medtronic Hall valve in the mitral position of an in vitro experimental set up is employed to measure the transient pressure pulses near the entrance (ventricular side) and exit (atrial side) of the peripheral clearance at valve closure. Flow within the peripheral clearance is analyzed employing a two-dimensional quasisteady computational fluid dynamics model with the measured peak pressures specified as the boundary conditions inducing the flow. The valve is visualized from its inflow (atrial) side using a stroboscopic lighting technique to investigate the presence of cavitation bubbles within the clearance. The pressure measurements showed that a relatively large pressure drop exists between the entrance and the exit to the clearance for about 0.5 msec at the moment of valve closure. The numerical simulation resulted in relatively large magnitudes of wall shear stress and pressure reduction within the clearance due to the flow established by the large pressure drop between the entrance and the exit. Cavitation bubbles visualized within the peripheral clearance at higher loading rates for valve closure correlated with the presence of large pressure reduction within the clearance. Analysis of the results of this study indicates that the back flow through the clearance at the instant of valve closure may contribute toward injury to formed elements in blood in spite of the short duration of the flow.
本文介绍了对倾斜盘式心脏瓣膜在关闭瞬间通过外周间隙（瓣膜关闭时封堵器尖端与金属外壳之间形成的间隙）的流动动力学进行的研究。在体外实验装置的二尖瓣位置使用美敦力霍尔瓣膜，以测量瓣膜关闭时外周间隙入口（心室侧）和出口（心房侧）附近的瞬态压力脉冲。采用二维准稳态计算流体动力学模型分析外周间隙内的流动，将测量得到的峰值压力指定为诱导流动的边界条件。使用频闪照明技术从瓣膜的流入（心房）侧观察瓣膜，以研究间隙内是否存在空化气泡。压力测量结果表明，在瓣膜关闭瞬间，间隙入口和出口之间存在约0.5毫秒的较大压降。数值模拟结果显示，由于入口和出口之间的大压降建立的流动，间隙内的壁面剪应力和压力降低幅度相对较大。在较高的瓣膜关闭加载速率下，在外周间隙内观察到的空化气泡与间隙内较大的压力降低有关。对本研究结果的分析表明，尽管瓣膜关闭瞬间通过间隙的回流持续时间较短，但可能会对血液中的有形成分造成损伤。
