Effect of Shear on Hemolysis in a Centrifugal Blood Pump

为了减少离心式血泵中的溶血现象，有必要了解泵内部流动的机理，同时了解红细胞的机械损伤机理。采用锥板流变仪对稳态剪切流场中的溶血现象进行了研究，得到了剪切速率与溶血的关系。观察了红细胞在锥板定常剪切流和平行板非定常剪切流中的变形。研究了稳态和非稳态剪切对红细胞变形的影响。结果表明，当剪切速率大于100Pa时，细胞表面积增大，这是细胞的屈服点。进行了频率高达600Hz的非定常流实验，得到了与定常流相同的结果。本文采用条纹线法和路径线法对泵内流场进行了可视化，时间尺度为1ms量级，比前人报道的10ms量级的时间尺度要短。在泵内观察到径向反向流动。采用循环条件取样法和嵌入式热膜探针测量了泵壳盖上的剪应力分布。剪切应力随着泵转速的增加而增加，并且对于恒定转速，在叶轮通道处而不是叶轮之间的中心处测量到更高的剪切应力。这种高剪切区域仅限于非常薄的边界层。然而，当红细胞穿过该边界层时，细胞遭受非常高的变形，这将产生溶血。使该高剪切层更窄的泵设计对于减少溶血是重要的。

In order to reduce hemolysis in centrifugal blood pumps, it is necessary to understand the mechanism of pump internal flow and at the same time the mechanism of mechanical damage of red blood cells. In this study, using a cone and a plate rheoscope, hemolysis was investigated in a steady shear flow, and the relationship between shear rate and hemolysis was obtained. Deformation of red blood cells was observed in a cone and a plate steady shear flow and in parallel plates unsteady shear flow. Influence of steady and unsteady shear on the deformation of red blood cells was investigated. The results indicated that the cells showed an increase in their surface area for the shear rate higher than 100Pa, which was corresponding a yield point. We carried out unsteady flow experiment up to 600Hz, and obtained the same results as the steady flow. Our time scale of 1 ms order is shorter than 10 ms reported by the past researcher.We visualized the pump internal flow by a streak line method and a path line method. The radial reversal flow was observed in the pump. The shear stress distribution on the pump casing cover was measured by means of a cyclic conditional sampling method and a flush-mounted hot-film probe. The shear stress increased with pump rotational speed, and for the constant rotational speed the higher shear stress was measured at the impeller passage rather than the center between the impellers. This high shear region is limited to very thin boundary layer. However, when red blood cells pass through this boundary layer, the cells suffer very high deformation, which would produce hemolysis. Pump design that makes this high shear layer are narrower is important to reduce hemolysis.