Khoo Dominica Py, Cookson Andrew N, Gill Harinderjit S, Fraser Katharine H
Department of Mechanical Engineering, University of Bath, Bath, UK.
Int J Artif Organs. 2018 Nov;41(11):738-751. doi: 10.1177/0391398818792757. Epub 2018 Aug 24.
Despite the evolution of ventricular assist devices, ventricular assist device patients still suffer from complications due to the damage to blood by fluid dynamic stress. Since rotary ventricular assist devices are assumed to exert mainly shear stress, studies of blood damage are based on shear flow experiments. However, measurements and simulations of cell and protein deformation show normal and shear stresses deform, and potentially damage, cells and proteins differently. The aim was to use computational fluid dynamics to assess the prevalence of normal stress, in comparison with shear stress, in rotary ventricular assist devices. Our calculations showed normal stresses do occur in rotary ventricular assist devices: the fluid volumes experiencing normal stress above 10 Pa were 0.011 mL (0.092%) and 0.027 mL (0.39%) for the HeartWare HVAD and HeartMate II (HMII), and normal stresses over 100 Pa were present. However, the shear stress volumes were up to two orders of magnitude larger than the normal stress volumes. Considering thresholds for red blood cell and von Willebrand factor deformation by normal and shear stresses, the fluid volumes causing deformation by normal stress were between 2.5 and 5 times the size of those causing deformation by shear stress. The exposure times to the individual normal stress deformation regions were around 1 ms. The results clearly show, for the first time, that while blood within rotary ventricular assist devices experiences more shear stress at much higher magnitudes as compared with normal stress, there is sufficient normal stress exposure present to cause deformation of, and potentially damage to, the blood components. This study is the first to quantify the fluid stress components in real blood contacting devices.
尽管心室辅助装置不断发展，但心室辅助装置患者仍会因流体动力应力对血液造成的损伤而出现并发症。由于旋转式心室辅助装置被认为主要施加剪切应力，因此血液损伤的研究基于剪切流实验。然而，对细胞和蛋白质变形的测量与模拟表明，法向应力和剪切应力对细胞和蛋白质的变形及潜在损伤作用不同。本研究旨在运用计算流体动力学，评估旋转式心室辅助装置中法向应力与剪切应力相比的普遍程度。我们的计算表明，旋转式心室辅助装置中确实存在法向应力：对于HeartWare HVAD和HeartMate II（HMII），法向应力高于10 Pa的流体体积分别为0.011 mL（0.092%）和0.027 mL（0.39%），且存在超过100 Pa的法向应力。然而，剪切应力的体积比法向应力的体积大两个数量级。考虑到红细胞和血管性血友病因子因法向应力和剪切应力而变形的阈值，由法向应力导致变形的流体体积是由剪切应力导致变形的流体体积的2.5至5倍。单个法向应力变形区域的暴露时间约为1毫秒。结果首次清楚地表明，虽然旋转式心室辅助装置内的血液与法向应力相比，承受的剪切应力更大、量级更高，但仍有足够的法向应力暴露会导致血液成分变形并可能造成损伤。本研究首次对实际血液接触装置中的流体应力成分进行了量化。
