Red Blood Cell Hemolysis in Laminar and Turbulent Flow

• Main Authors: Jen-Hong Yen, 嚴仁鴻
• Other Authors: 盧博堅
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/79881488073467668689

博士 === 淡江大學 === 水資源及環境工程學系博士班 === 103 === Artificial prostheses such as left ventricular assist devices, artificial heart valves, and oxygenators can create non-physiologic flow conditions within the cardiovascular system. The stress forces generated in these flow fields can induce blood cell damage, particularly red blood cell damage or hemolysis. The Index of Hemolysis (IH; %) is affected by the magnitude of shear stress and exposure time. Giersiepen et al. (1990), based on experiments by Wurzinger et al. (1986), determined that the Index of Hemolysis can be calculated by IH(%) . This model has been widely used in computational fluid dynamics (CFD) for the evaluation of new artificial prosthesis designs. However, the IH calculated via CFD are often inconsistent with actual measured values from experiments done on prototypes. The stress value in the equation is based on the shear stress generated from a simple Couette viscometer; however, actual flow field forces include both shear stress and extensional stress. As such, the shear stress alone cannot accurately determine IH. We applied laminar and turbulent flow that was utilized to hemolysis porcine RBCs, in order to compare the IH derived. In laminar flow, we created a strong extensional stress flow field with the sharp contraction of short capillary and small channels. The flow field generated at the entrance of the capillary was calculated with CFD to determine the stress values, which was followed by hemolysis experiments with porcine red blood cells to determine the effects of extensional stress on hemolysis. Our results were consistent with prior studies in that the extensional stress was the primary mechanical force involved in hemolysis with a threshold value of 800-1000 Pa. In turbulent flow, We applied two-dimensional laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) to measure the flow field of a free submerged axi-symmetric jet that was utilized to hemolysis the porcine red blood cells in selected locations. However, the resolution of current instrumentation is insufficient to measure the smallest eddy sizes. Assuming a dynamic equilibrium between the resolved and sub-grid scale (SGS) energy flux, the SGS energy flux was calculated from the strain rate tensor computed from the resolved velocity fields and the SGS stress was determined by the Smagorinsky model, from which the turbulence dissipation rate and then the viscous dissipative stresses were estimated. Our results showed that the hemolytic threshold of major principal Reynolds stresses is up to 500 Pa and the viscous dissipative stresses is 40-60 Pa, it’s at least an order of magnitude less than the Reynolds stresses. The viscous dissipative stresses for hemolysis also tend to be an order of magnitude lower than the laminar shear thresholds. In addition, the time scales are three orders of magnitude smaller than the laminar shear. Because of these differences, a reliable damage quantification model needs to fully understand about the varying mechanisms of blood cell damage by different shear stress conditions.