Bluestein D, Einav S
Department of Mechanical Engineering, Florida International University, Miami 33199, USA.
J Biomech. 1995 Aug;28(8):915-24. doi: 10.1016/0021-9290(94)00154-v.
Many problems and complications associated with heart valves are related to the dynamic behavior of the valve and the resultant unsteady flow patterns. An accurate depiction of the spatial and temporal velocity and rms distributions imparts better understanding of flow related valve complications, and may be used as a guideline in valve design. While the generalized correlation between increased turbulence level and the severity of the stenosis is well established, few studies addressed the issue of the intermittent nature of turbulence and its timing in the cardiac cycle, and almost none assessed the effect of a progressive stenosis on the flow characteristics through heart valves. In this experimental work we simulated the type of flow which is present in normal and stenosed valves and conducted a comprehensive investigation of valve hemodynamics, valvular turbulence and morphology under varying degrees of stenosis. The characteristics of valves and stenoses were simulated closely, to achieve the flow conditions that initiate turbulent flow conditions. Laser Doppler anemometry (LDA) measurements were carried out in a pulse duplicator system distal to trileaflet polyurethane prosthetic heart valves, installed at mitral and aortic positions. The effect of the degree of the stenosis was comparatively studied through the structure of the turbulent jets emerging from normal and stenotic heart valves. Maximum turbulence level was achieved during the decelerating phase and correlated to the severity of the stenosis, followed by relaminarization of the flow during the acceleration phase. The intermittent nature of the turbulence emphasized the importance of realizing the timing of the turbulence production and its spatial location for optimizing current valve designs. The plug flow through the normal aortic valve prosthesis was replaced by jet like behavior for a 65% stenosis, with the jet becoming narrower and stronger for a 90% stenosis. The morphology of the velocity and turbulence waveforms was found to be governed by the stenosis geometry and the valve position (aortic, mitral).
许多与心脏瓣膜相关的问题和并发症都与瓣膜的动态行为以及由此产生的非定常流动模式有关。对空间和时间速度以及均方根分布的准确描述有助于更好地理解与流动相关的瓣膜并发症，并且可作为瓣膜设计的指导原则。虽然湍流水平增加与狭窄严重程度之间的普遍相关性已得到充分确立，但很少有研究探讨湍流的间歇性及其在心动周期中的时间问题，几乎没有研究评估渐进性狭窄对通过心脏瓣膜的流动特性的影响。在这项实验工作中，我们模拟了正常和狭窄瓣膜中存在的流动类型，并对不同程度狭窄下的瓣膜血流动力学、瓣膜湍流和形态进行了全面研究。紧密模拟瓣膜和狭窄的特征，以实现引发湍流条件的流动状况。在安装于二尖瓣和主动脉位置的三叶聚氨酯人工心脏瓣膜远端的脉搏复制系统中，进行了激光多普勒测速（LDA）测量。通过正常和狭窄心脏瓣膜产生的湍流射流结构，对狭窄程度的影响进行了比较研究。在减速阶段达到最大湍流水平，且与狭窄严重程度相关，随后在加速阶段流动重新层流化。湍流的间歇性强调了了解湍流产生时间及其空间位置对于优化当前瓣膜设计的重要性。对于65%的狭窄，通过正常主动脉瓣膜假体的塞流被类似射流的行为所取代，对于90%的狭窄，射流变窄且更强。发现速度和湍流波形的形态受狭窄几何形状和瓣膜位置（主动脉、二尖瓣）的控制。
