McCormick Susan M, Seil Justin T, Smith David S, Tan Francis, Loth Francis
Section of Vascular Surgery and Endovascular Therapy, Department of Surgery, University of Chicago, MC 5028, 5841 S. Maryland Ave., Chicago, IL 60637 USA.
Cardiovasc Eng Technol. 2012 Dec;3(4):439-449. doi: 10.1007/s13239-012-0107-5. Epub 2012 Sep 11.
Fluid shear stress is an important regulator of vascular and endothelial cell (EC) functions. Its effect is dependent not only on magnitude but also on flow type. Although laminar flow predominates in the vasculature, transitional flow can occur and is thought to play a role in vascular diseases. While a great deal is known about the mechanisms and signaling cascades through which laminar shear stress regulates cells, little is known on how transitional shear stress regulates cells. To better understand the response of endothelial cells to transitional shear stress, a novel cylindrical flow chamber was designed to expose endothelial cells to a transitional flow environment similar to that found in vivo. The velocity profiles within the transitional flow chamber at Reynolds numbers 2200 and 3000 were measured using laser Doppler anemometry (LDA). At both Reynolds numbers, the velocity profiles are blunt (non-parabolic) with fluctuations larger than 5% of the velocity at the center of the pipe indicating the flows are transitional. Based on near wall velocity measurements and well established data for flow at these Reynolds numbers, the wall shear stress was estimated to be 3-4 and 5-6 dynes/cm(2) for Reynolds number 2200 and 3000, respectively. In contrast to laminar shear stress, no cell alignment was observed under transitional shear stress at both Reynolds numbers. However, transitional shear stress at the higher Reynolds number caused cell elongation similar to that of laminar shear stress at 3 dynes/cm(2). The fluctuating component of the wall shear stress may be responsible for these differences. The transitional flow chamber will facilitate cellular studies to identify the mechanisms through which transitional shear stress alters EC biology, which will assist in the development of vascular therapeutic treatments.
流体剪切应力是血管和内皮细胞（EC）功能的重要调节因子。其作用不仅取决于大小，还取决于流动类型。尽管层流在脉管系统中占主导地位，但过渡流也可能发生，并且被认为在血管疾病中起作用。虽然人们对层流剪切应力调节细胞的机制和信号级联了解很多，但对于过渡剪切应力如何调节细胞却知之甚少。为了更好地理解内皮细胞对过渡剪切应力的反应，设计了一种新型圆柱形流动腔室，以使内皮细胞暴露于类似于体内发现的过渡流动环境中。使用激光多普勒测速仪（LDA）测量了雷诺数为2200和3000时过渡流动腔内的速度分布。在这两个雷诺数下，速度分布都是钝的（非抛物线形），波动大于管道中心速度的5%，表明流动是过渡性的。根据近壁速度测量结果以及这些雷诺数下流动的既定数据，估计雷诺数2200和3000时的壁面剪切应力分别为3-4和5-6达因/平方厘米。与层流剪切应力不同，在这两个雷诺数下的过渡剪切应力下均未观察到细胞排列。然而，较高雷诺数下的过渡剪切应力导致细胞伸长，类似于3达因/平方厘米的层流剪切应力下的情况。壁面剪切应力的波动分量可能是造成这些差异的原因。过渡流动腔室将有助于细胞研究，以确定过渡剪切应力改变内皮细胞生物学的机制，这将有助于血管治疗方法的开发。
