Quinlan Nathan J, Dooley Patrick N
National Centre for Biomedical Engineering Science and Department of Mechanical and Biomedical Engineering, National University of Ireland, Galway, Ireland.
Ann Biomed Eng. 2007 Aug;35(8):1347-56. doi: 10.1007/s10439-007-9308-8. Epub 2007 Apr 13.
Viscous shear stress and Reynolds stress are often used to predict hemolysis and thrombosis due to flow-induced stress on blood elements in cardiovascular devices. These macroscopic stresses are distinct from the true stress on an individual cell, which is determined by the local microscale flow field. In this paper the flow-induced stress on blood cells is calculated for laminar and turbulent flow, using simplified models for cells and for turbulent eddies. The model is applied to estimate shear stress on red blood cells in flow through a prosthetic heart valve, using the energy spectral density measured by Liu et al. [J. Biomech. Eng. 122:118-124, 2000]. Results show that in laminar flow, the maximum stress on a cell is approximately equal to the macroscopic viscous shear stress. In turbulent flow through a prosthetic heart valve, the estimated root mean square of flow-induced stress on a cell is at least an order of magnitude less than the Reynolds stress. The results support the hypothesis that smaller turbulent eddies cause higher stress on cells. However, the stress due to an eddy depends on the velocity scale of the eddy as well as its length scale. For the heart valve flow investigated, turbulence contributes to flow-induced stress on cells almost equally across a broad range of the frequency spectrum. The model suggests that Reynolds stress alone is not an adequate predictor of cell damage in turbulent flow, and highlights the importance of the energy spectral density.
粘性剪切应力和雷诺应力常被用于预测心血管装置中血流诱导应力对血液成分造成的溶血和血栓形成。这些宏观应力与单个细胞上的真实应力不同，后者由局部微观尺度流场决定。本文使用细胞和湍流涡旋的简化模型，计算了层流和湍流中血流对血细胞的诱导应力。该模型应用于通过人工心脏瓣膜的血流中红细胞上的剪切应力估计，使用了Liu等人[《生物力学工程杂志》122:118 - 124, 2000]测量的能量谱密度。结果表明，在层流中，细胞上的最大应力大约等于宏观粘性剪切应力。在通过人工心脏瓣膜的湍流中，估计的细胞上血流诱导应力的均方根比雷诺应力至少小一个数量级。这些结果支持了较小的湍流涡旋会对细胞造成更高应力的假设。然而，涡旋引起的应力取决于涡旋的速度尺度及其长度尺度。对于所研究的心脏瓣膜血流，在广泛的频谱范围内，湍流对细胞上血流诱导应力的贡献几乎相同。该模型表明，仅雷诺应力不足以预测湍流中细胞的损伤，并突出了能量谱密度的重要性。
