Fluid Mechanical Study on the Effect of Endothelial Surface Glycocalyx on the Cell Function

血管内皮细胞的管腔表面覆盖着一层称为糖萼的大分子。最近的实验证据表明，糖萼影响血管功能的几个方面。在本研究中，我们从流体力学的角度研究了内皮表面糖萼的生理作用。我们首先考虑了溶质在微血管壁上的运输。基于最近对表面糖萼超微结构的详细测量，我们建立了糖萼的数学模型，并估计了传输系数作为溶质大小的函数。我们的扩散渗透性和反射系数预测值与实验结果吻合较好，也符合内皮表面糖萼对溶质在微血管渗透性中形成主要大小选择结构的假设。其次，我们考虑了流体在微血管壁上的细胞旁运输，并通过分析内皮表面糖萼和内皮间隙的一系列通道来估计水的水力传导率。结果表明，与溶质转运相反，水转运主要是由裂缝的结构决定的，而不是由表面糖萼决定的。关于施加在内皮表面的流体剪切应力，我们发现，由于表面糖萼的存在，管腔表面的大小显著降低，而在细胞间隙中，无论是否存在间隙分子，它们都可能非常高。

The luminal surface of vascular endothelial cells is covered by a layer of macromolecules referred to as the glycocalyx. Recent experimental evidence showed that the glycocalyx influences several aspects of vascular function. In the present study, we have studied physiological roles of the endothelial surface glycocalyx from a stand-point of fluid mechanics. We first considered the transport of solutes across microvessel walls. Based on recent detailed measurements of the ultrastructure of the surface glycocalyx, we developed a mathematical model for the glycocalyx, and estimated the transport coefficients as a function of the solute size. Our predicted values of diffusive permeability and the reflection coefficient showed a reasonable agreement with experimental observations, and conformed to the hypothesis that the endothelial surface glycocalyx forms the primary size selective structure to solutes in microvascular permeability. Second, we considered the paracellular transport of fluid across the microvessel wall, and estimated the hydraulic conductivity to water, by analyzing the flow through a serial pathway of the endothelial surface glycocalyx and the interendothelial cleft. It was suggested that, in contrast to the solute transport, the water transport is mainly determined by the structure of the cleft, rather than the surface glycocalyx. With respect to the fluid shear stresses exerted on the endothelial surface, we have found that the magnitudes on the luminal surface are remarkably reduced due to the presence of the surface glycocalyx, whereas they could be extremely high in the intercellular cleft, irrespective of presence or absence of the cleft-spanning molecules.