Effects of blood cells on the resistance to flow in microvessels

为了对微血管中的血管阻力进行流体动力学估计，着重考虑血细胞的影响，我们对微血管的管腔几何形状进行了统计分析，并对微血管的流动进行了数值模拟。1.微血管几何形状的数据分析：活体微血管的管腔几何形状数据表明，小血管的横截面形状并不像传统的血管阻力评估中所假设的那样是圆形的，而且其形状沿血管轴线并不均匀。血管流动的数值模拟：用有限元方法分析了单纯血浆或含有血细胞的血浆通过内皮细胞核突出进入管腔的血管的流动情况。研究发现，非均匀血管的血管阻力始终大于均匀管的阻力，并且由于非均匀几何结构与血细胞之间的流体动力学相互作用，在血细胞的存在下，这一趋势增强。3.血液细胞的影响：数值分析了小血管中红细胞在各种流型中的运动，并评估了血管阻力作为红细胞构型的函数。通过数值模拟研究了毛细血管中白血球上游红细胞系的形成效应。研究发现，红细胞、红细胞-白细胞或血细胞-内皮细胞之间的流体动力相互作用在微血管中血流阻力的增加中起着重要作用。

In order to make a fluid dynamical estimate of the vascular resistance to flow in microvessels, with an emphasis on the effect of blood cells, we conducted a statistical analysis of the luminal geometry of microvessels, and numerical simulation of flow through microvessels.1.Data analysis of the geometry of microvessels : In vivo data of the luminal geometry of microvessels showed that the cross-sectional shapes of small vessels are not circular, as assumed conventionally in the evaluation of vascular resistance, and that the shape is not uniform along the vessel axis. Quasi-periodic protrusions of endothelial cells into the lumen were observed near the nuclei, at some conditions.2.Numerical simulation of vascular flow : A finite element method was used to analyze the flow of plasma only or plasma with blood cells, through vessels with protrusions of endothelial nuclei into the vessel lumen. It was found that the vascular resistance of non-uniform vessels is constantly larger than that of uniform tubes, and this tendency is enhanced in the presence of blood cells, due to fluid dynamical interaction between the non-uniform geometry and the blood cells.3.Effects of blood cells : The motion of red cells in various flow patterns in small vessels was numerically analyzed, and the vascular resistance was evaluated as a function of the red cell configuration. The effect of the formation of red cell trains upstream of a white cell in capillaries was also investigated by a numerical simulation. It was found that fluid-dynamical interactions between red cells, red cells-white cells or blood cells-endothelial cells play an important role in elevation of the vascular resistance to flow in microvessels.