Effect of Shear on Hemolysis in a Centrifugal Blood Pump

为了减少离心血泵的溶血，有必要了解泵内部流动的机制，同时了解红细胞的机械损伤机制。本研究采用锥形和平板流变镜，在稳定剪切流条件下研究溶血，得到剪切速率与溶血的关系。观察了红细胞在锥形和平板的稳定剪切流动和平行平板的非稳定剪切流动中的变形。研究了稳态剪切和非稳态剪切对红细胞变形的影响。结果表明，当剪切速率高于100Pa时，细胞的表面积增加，这对应于一个屈服点。我们进行了高达600Hz的非定常流动实验，得到了与定常流动相同的结果。我们的1毫秒量级的时间尺度比以往研究者报道的10毫秒要短。采用条纹线法和路径线法对泵的内部流动进行了可视化。在泵内观察到径向反转流动。采用循环条件采样法和冲洗式热膜探头测量了泵壳盖上的剪切应力分布。剪切应力随泵转速的增加而增大，当转速不变时，叶轮通道处的剪切应力比叶轮中心处的剪切应力大。这种高剪切区域仅限于非常薄的边界层。然而，当红细胞穿过这个边界层时，细胞会发生很大的变形，从而产生溶血。使高剪切层变窄的泵设计对减少溶血很重要。

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.