Lee C S, Chandran K B, Chen L D
Departments of Biomedical and Mechanical Engineering, University of Iowa, Iowa City 52242, USA.
J Biomech Eng. 1996 Feb;118(1):97-105. doi: 10.1115/1.2795951.
The cause of cavitation in mechanical heart valves is investigated with Medtronic Hall tilting disk valves in an in vitro flow system simulating the closing event in the mitral position. Recordings of pressure wave forms and photographs in the vicinity of the inflow surface of the valve are attempted under controlled transvalvular loading rates averaged during valve closing period. The results revealed presence of a local flow field with a very high velocity around the seat stop of mechanical heart valves that could induce pressure reduction below liquid vapor pressure and a cloud of cavitation bubbles. The analysis of the results indicates that the "fluid squeezing" between the stop and occluder as the main cause of cavitation in Medtronic Hall valves. The threshold loading rate for cavitation initiation around the stop was found to be very low (300 and 400 mmHg/s; half the predicted normal human loading rate that was estimated to be 750 mmHg/s) because even a mild impact created a high speed local flow field on the occluder surface that could induce pressure reduction below vapor pressure. The present study suggests that mechanical heart valves with stops at the edge of major orifice region are more vulnerable to cavitation, and hence, have higher potential for damage on valve components and formed elements in blood.
利用美敦力霍尔倾斜盘式瓣膜，在模拟二尖瓣位置关闭过程的体外流动系统中，研究了机械心脏瓣膜中空化的成因。在可控的跨瓣膜加载速率（在瓣膜关闭期间平均）下，尝试记录瓣膜流入表面附近的压力波形并拍照。结果显示，在机械心脏瓣膜的阀座止动件周围存在局部流场，其速度非常高，这可能导致压力降低至液体蒸气压以下，从而形成空化气泡云。结果分析表明，止动件与封堵器之间的“流体挤压”是美敦力霍尔瓣膜中空化的主要原因。发现止动件周围空化起始的阈值加载速率非常低（300和400 mmHg/s；预计正常人体加载速率的一半，估计为750 mmHg/s），因为即使是轻微的冲击也会在封堵器表面产生高速局部流场，从而导致压力降低至蒸气压以下。本研究表明，在主要孔口区域边缘设有止动件的机械心脏瓣膜更容易发生空化，因此，对瓣膜组件和血液中的有形成分造成损伤的可能性更高。
