Eichler M J, Reul H M
Helmholtz-Institute for Biomedical Engineering, RWTH Aachen, Aachen-Germany.
Int J Artif Organs. 2004 Oct;27(10):855-67. doi: 10.1177/039139880402701007.
Several aspects of mechanical heart valve cavitation, in particular of "severe" vapor cavitation, have been investigated in order to describe the phenomenon of cavitation itself and to classify various mechanical heart valves with respect to their tendency to cavitation. Furthermore, following the results of the measurements, a model for determination of time-dependent physical properties and dynamics of cavitation bubbles, such as size, pressure and temperature was developed. In order to classify the cavitation tendency of mechanical valves, a pulsatile hydraulic-driven circularly mock loop was used. Besides measurements of the relevant hemodynamic parameters, the leaflet velocities of the valves were also determined. In addition, numerous high-resolution pressure measurements, in particular the pressure drops necessary for the initiation of cavitation (local atrial pressure drop), were performed. For the investigation of bubble dynamics, a second pulsatile electro-magnetically-driven tester was used. The influence of density, viscosity and temperature of the fluid on the onset of cavitation was investigated. Cavitation events were recorded with a digital high-speed video camera (up to 40,500 frames/sec) for all investigated heart valves and under different conditions. A critical local upstream pressure drop (located within the model atrium after valve closure) of 450 mmHg was found for all valves as well as a valve specific correlation between left ventricular pressure gradient and local upstream pressure drop. Also, a valve dependent correlation between left ventricular pressure gradient and the local upstream pressure drop was provided. Finally, valve specific parameters were found to predict the cavitation tendency for a specific heart valve. The implementation of a suitable theoretical model allowed conclusions on bubble physics. High pressures (up to 800 bar) and temperatures (up to 1,300 degrees C) at bubble collapse have been determined. The influence of fluid parameters such as density, viscosity and temperature on the onset of cavitation is negligible within physiological range. Critical regions for cavitation for all mechanical heart valves were detected. All mechanical heart valves investigated show cavitation under different conditions (dp/dt) associated with high pressures and temperatures at bubble collapse. Cavitation bubble occurrence depends on valve design and location.
为了描述空化现象本身，并根据各种机械心脏瓣膜产生空化的倾向对其进行分类，研究了机械心脏瓣膜空化的几个方面，特别是“严重”蒸汽空化。此外，根据测量结果，开发了一个用于确定空化气泡随时间变化的物理特性和动力学（如尺寸、压力和温度）的模型。为了对机械瓣膜的空化倾向进行分类，使用了一个脉动液压驱动的圆形模拟回路。除了测量相关的血液动力学参数外，还测定了瓣膜的瓣叶速度。此外，还进行了大量高分辨率压力测量，特别是空化起始所需的压力降（局部心房压力降）。为了研究气泡动力学，使用了第二个脉动电磁驱动测试仪。研究了流体的密度、粘度和温度对空化起始的影响。使用数字高速摄像机（高达40500帧/秒）记录了所有研究的心脏瓣膜在不同条件下的空化事件。发现所有瓣膜的临界局部上游压力降（位于瓣膜关闭后模型心房内）为450 mmHg，以及左心室压力梯度与局部上游压力降之间的瓣膜特异性相关性。此外，还提供了左心室压力梯度与局部上游压力降之间的瓣膜依赖性相关性。最后，发现瓣膜特异性参数可预测特定心脏瓣膜的空化倾向。合适理论模型的实施得出了关于气泡物理的结论。已确定气泡崩溃时的高压（高达800 bar）和高温（高达1300摄氏度）。在生理范围内，流体参数如密度、粘度和温度对空化起始的影响可忽略不计。检测到所有机械心脏瓣膜的空化临界区域。所有研究的机械心脏瓣膜在不同条件下（dp/dt）均显示空化，且气泡崩溃时伴有高压和高温。空化气泡的出现取决于瓣膜设计和位置。
