Fraser Katharine H, Zhang Tao, Taskin M Ertan, Griffith Bartley P, Wu Zhongjun J
Artificial Organs Laboratory, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
J Biomech Eng. 2012 Aug;134(8):081002. doi: 10.1115/1.4007092.
Ventricular assist devices (VADs) have already helped many patients with heart failure but have the potential to assist more patients if current problems with blood damage (hemolysis, platelet activation, thrombosis and emboli, and destruction of the von Willebrand factor (vWf)) can be eliminated. A step towards this goal is better understanding of the relationships between shear stress, exposure time, and blood damage and, from there, the development of numerical models for the different types of blood damage to enable the design of improved VADs. In this study, computational fluid dynamics (CFD) was used to calculate the hemodynamics in three clinical VADs and two investigational VADs and the shear stress, residence time, and hemolysis were investigated. A new scalar transport model for hemolysis was developed. The results were compared with in vitro measurements of the pressure head in each VAD and the hemolysis index in two VADs. A comparative analysis of the blood damage related fluid dynamic parameters and hemolysis index was performed among the VADs. Compared to the centrifugal VADs, the axial VADs had: higher mean scalar shear stress (sss); a wider range of sss, with larger maxima and larger percentage volumes at both low and high sss; and longer residence times at very high sss. The hemolysis predictions were in agreement with the experiments and showed that the axial VADs had a higher hemolysis index. The increased hemolysis in axial VADs compared to centrifugal VADs is a direct result of their higher shear stresses and longer residence times. Since platelet activation and destruction of the vWf also require high shear stresses, the flow conditions inside axial VADs are likely to result in more of these types of blood damage compared with centrifugal VADs.
心室辅助装置（VADs）已经帮助了许多心力衰竭患者，但如果目前血液损伤（溶血、血小板活化、血栓形成和栓塞以及血管性血友病因子（vWf）破坏）的问题能够得到解决，就有可能帮助更多患者。朝着这个目标迈出的一步是更好地理解剪切应力、暴露时间和血液损伤之间的关系，并在此基础上开发针对不同类型血液损伤的数值模型，以设计出改进的VADs。在本研究中，采用计算流体动力学（CFD）来计算三种临床VAD和两种研究性VAD中的血流动力学，并研究剪切应力、停留时间和溶血情况。开发了一种新的溶血标量传输模型。将结果与每个VAD中压头的体外测量值以及两个VAD中的溶血指数进行比较。对VAD之间与血液损伤相关的流体动力学参数和溶血指数进行了对比分析。与离心式VAD相比，轴流式VAD具有：更高的平均标量剪切应力（sss）；更宽的sss范围，在低sss和高sss时都有更大的最大值和更大的体积百分比；以及在非常高的sss下更长的停留时间。溶血预测结果与实验一致，表明轴流式VAD具有更高的溶血指数。与离心式VAD相比，轴流式VAD中溶血增加是其更高的剪切应力和更长的停留时间的直接结果。由于血小板活化和vWf的破坏也需要高剪切应力，与离心式VAD相比，轴流式VAD内部的流动条件可能会导致更多此类血液损伤。
