Haidekker M A, White C R, Frangos J A
University of California, San Diego, Department of Bioengineering, La Jolla 92092-0412, USA.
J Biomech Eng. 2001 Oct;123(5):455-63. doi: 10.1115/1.1389460.
Endothelial cells in blood vessels are exposed to bloodflow and thus fluid shear stress. In arterial bifurcations and stenoses, disturbed flow causes zones of recirculation and stagnation, which are associated with both spatial and temporal gradients of shear stress. Such gradients have been linked to the generation of atherosclerotic plaques. For in-vitro studies of endothelial cell responses, the sudden-expansion flow chamber has been widely used and described. A two-dimensional numerical simulation of the onset phase of flow through the chamber was performed. The wall shear stress action on the bottom plate was computed as a function of time and distance from the sudden expansion. The results showed that depending on the time for the flow to be established, significant temporal gradients occurred close to the second stagnation point of flow. Slowly ramping the flow over 15 s instead of 200 ms reduces the temporal gradients by a factor of 300, while spatial gradients are reduced by 23 percent. Thus, the effects of spatial and temporal gradients can be observed separately. In experiments on endothelial cells, disturbed flow stimulated cell proliferation only when flow onset was sudden. The spatial patterns of proliferation rate match the exposure to temporal gradients. This study provides information on the dynamics of spatial and temporal gradients to which the cells are exposed in a sudden-expansion flow chamber and relates them to changes in the onset phase of flow.
血管中的内皮细胞暴露于血流中，从而受到流体剪切应力的作用。在动脉分支和狭窄处，紊乱的血流会导致再循环和停滞区域的形成，这些区域与剪切应力的空间和时间梯度有关。这种梯度与动脉粥样硬化斑块的形成有关。对于内皮细胞反应的体外研究，突然扩张流动腔已被广泛使用和描述。对通过该腔室的流动起始阶段进行了二维数值模拟。计算了底板上壁面剪切应力随时间和距突然扩张处距离的函数。结果表明，根据流动建立的时间，在靠近第二个流动停滞点处会出现显著的时间梯度。将流动在15秒内而不是200毫秒内缓慢增加，可使时间梯度降低300倍，而空间梯度降低23%。因此，可以分别观察空间和时间梯度的影响。在内皮细胞实验中，只有当流动起始突然时，紊乱的流动才会刺激细胞增殖。增殖率的空间模式与时间梯度的暴露情况相匹配。本研究提供了关于细胞在突然扩张流动腔中所暴露的空间和时间梯度动态的信息，并将它们与流动起始阶段的变化联系起来。
