Ge Liang, Dasi Lakshmi P, Sotiropoulos Fotis, Yoganathan Ajit P
St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, Minneapolis, MN 55414, USA.
Ann Biomed Eng. 2008 Feb;36(2):276-97. doi: 10.1007/s10439-007-9411-x. Epub 2007 Nov 30.
Bileaflet mechanical heart valves (BMHV) are widely used to replace diseased heart valves. Implantation of BMHV, however, has been linked with major complications, which are generally considered to be caused by mechanically induced damage of blood cells resulting from the non-physiological hemodynamics environment induced by BMHV, including regions of recirculating flow and elevated Reynolds (turbulence) shear stress levels. In this article, we analyze the results of 2D high-resolution velocity measurements and full 3D numerical simulation for pulsatile flow through a BMHV mounted in a model axisymmetric aorta to investigate the mechanical environment experienced by blood elements under physiologic conditions. We show that the so-called Reynolds shear stresses neither directly contribute to the mechanical load on blood cells nor is a proper measurement of the mechanical load experienced by blood cells. We also show that the overall levels of the viscous stresses, which comprise the actual flow environment experienced by cells, are apparently too low to induce damage to red blood cells, but could potentially damage platelets. The maximum instantaneous viscous shear stress observed throughout a cardiac cycle is <15 N/m(2). Our analysis is restricted to the flow downstream of the valve leaflets and thus does not address other areas within the BMHV where potentially hemodynamically hazardous levels of viscous stresses could still occur (such as in the hinge gaps and leakage jets).
双叶机械心脏瓣膜（BMHV）被广泛用于替换病变的心脏瓣膜。然而，植入BMHV与一些主要并发症相关，这些并发症通常被认为是由BMHV所诱导的非生理血流动力学环境（包括再循环流区域和升高的雷诺兹（湍流）剪切应力水平）导致的血细胞机械性损伤引起的。在本文中，我们分析了通过安装在轴对称主动脉模型中的BMHV的脉动流的二维高分辨率速度测量结果和全三维数值模拟结果，以研究生理条件下血液成分所经历的力学环境。我们表明，所谓的雷诺兹剪切应力既不直接导致血细胞上的机械负荷，也不是对血细胞所经历的机械负荷的恰当度量。我们还表明，构成细胞实际经历的流动环境的粘性应力的总体水平明显过低，不足以对红细胞造成损伤，但可能会损伤血小板。在整个心动周期中观察到的最大瞬时粘性剪切应力<15 N/m²。我们的分析仅限于瓣膜小叶下游的流动，因此未涉及BMHV内其他可能仍会出现具有血流动力学危害水平的粘性应力的区域（如铰链间隙和泄漏射流处）。
