Physiological functions of the endothelial cells in relation to the to the mass transport at carotid bifurcation

本研究的目的是探讨血管内皮细胞的生理功能与颈动脉分叉处物质传递机制的关系。首先，我们研究了人颈动脉分叉处的氧质量传递，着重研究了血管壁顺应性和流场对氧流量的时间变化和空间分布的影响。详细的不稳定的对流扩散氧气运输进行了研究，使用一个符合人体颈动脉分叉和现实的血流波形模型数值。结果表明，在外颈总动脉-颈内动脉壁的轴向流分离可以显着改变流场，氧张力场，和氧壁流量分布。在窦的外壁处，舍伍德数Sh（无量纲氧壁通量）由于远离壁的对流使运输速率衰减而呈现出比其他部位显著更低的值。更具体地说，Sh的最低值为Sh ≥ 6（窦部），远低于无量纲耗氧率值（Damkohler数，Da）（Da=29-39）。接下来，为了阐明一氧化氮及其下游机制在动脉粥样硬化定位中的作用，研究了质量传递和血流动力学对内皮细胞功能的影响。一个体外实验模型，模拟在体内的空间模式的流动分离，再循环，和再附着已被开发来检查释放的一氧化氮（NO）从内皮细胞层响应剪切应力与复杂的空间变化。细胞直接暴露于20 dyne/cm 2的剪切应力后，开始流诱导的一氧化氮释放在第一个十分钟内迅速升高，其次是一个不太迅速的生产。

The purpose of the present research project was to investigate physiological functions of vascular endothelial cells in relation to the mechanism of mass transport at the carotid bifurcation.Firstly, we studied oxygen mass transfer in the human carotid bifurcation, focusing on the effects of the wall compliance and flow field on the temporal variation and spatial distribution of the oxygen wall flux. Details of unsteady convective-diffusive oxygen transport were examined numerically using a compliant model of the human carotid bifurcation and realistic blood flow waveforms. Results reveal that axial flow separation at the outer common-internal carotid wall can significantly alter the flow field, oxygen tension field, and oxygen wall flux distribution. At the outer wall of the sinus, the Sherwood number, Sh (non-dimensional oxygen wall flux), takes on significantly lower values than at other sites due to the attenuation of transport rates by convective flow away from wall. More specifically, the lowest value of Sh was Sh〜6 (in the sinus), which is much lower than the value of the non- dimensional oxygen consumption rate (Damkohler number, Da) in the reactive wall tissue (Da=29-39).Next, in order to address the role of nitric oxide and its downstream mechanism in the localization of atherosclerosis, the effects of mass transport and hemodynamics on endothelial cells functions were investigated. An in vitro experiment model that simulates in vivo spatial patterns of flow separation, recirculation, and reattachment have been developed to examine the release of nitric oxide (NO) from the endothelial cell layer in response to the shear stress with a complex spatial variation. Direct exposure of cells to 20dyne/cm2 shear stress after the onset of flow induced a rapid elevation in the nitric oxide release in the first ten minutes followed by a less rapid production.