Effects of blood cells on the resistance to flow in microvessels

为了对微血管内的血流阻力进行流体动力学估计，重点考虑血细胞的影响，我们对微血管的管腔几何形状进行了统计分析，并对微血管内的血流进行了数值模拟。微血管几何形状数据分析：体内微血管腔内几何形状数据显示，小血管的横截面形状不是圆形的，这是在评估血管阻力时通常假设的，并且形状沿着血管轴不是均匀的。在某些情况下，在细胞核附近可观察到内皮细胞进入管腔的准周期性突起。血管流动的数值模拟：采用有限元法分析血浆或血浆伴血细胞通过内皮核突出的血管进入血管腔的流动。研究发现，非均匀血管的血管阻力不断大于均匀管的血管阻力，并且由于非均匀几何形状与血细胞之间的流体动力学相互作用，这种趋势在血细胞存在时得到增强。血细胞的影响：数值分析了红细胞在小血管中不同流动模式下的运动，并评估了血管阻力作为红细胞结构的函数。通过数值模拟研究了白细胞在毛细血管上游形成红细胞列的影响。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学相互作用在微血管血流阻力的升高中起重要作用。

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.