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

本研究的目的是研究血管内皮细胞的生理功能与颈动脉分叉处的质量传输机制有关。首先，我们研究了人颈动脉分叉处的氧气质量传输，重点研究了管壁顺应性和流场对氧壁流量的时间变化和空间分布的影响。使用人体颈动脉分叉的顺应性模型和真实的血流波形，对非稳定对流-扩散氧传输的细节进行了数值研究。结果表明，颈总动脉-颈内动脉外壁的轴向流动分离会显著改变流场、氧压场和氧壁流量分布。在鼻窦外壁，舍伍德数Sh(无因次氧气壁通量)明显低于其他位置，这是由于远离壁面的对流对输运速率的衰减。更具体地说，Sh的最低值是Sh~6(在鼻窦)，远低于反应壁组织中无因次耗氧率(Damkohler数值，Da=29~39)的值。其次，为了探讨一氧化氮在动脉粥样硬化定位中的作用及其下游机制，我们研究了物质传输和血流动力学对内皮细胞功能的影响。建立了一种模拟体内血流分离、再循环和再附着的空间模式的体外实验模型，以研究具有复杂空间变化的剪应力对内皮细胞层一氧化氮(NO)释放的影响。在血流开始后，直接将细胞暴露在20dyne/cm2的剪应力下，在最初的10分钟内，一氧化氮的释放迅速增加，随后产生的速度变慢。

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.