Shear Stress Distribution and Hemolysis Measurements in a Centrifugal Blood Pump

The use of computational fluid dynamics (CFO) to predict red blood cell trauma (hemolysis) in blood pumps based on their exposure to turbulent stresses has increased in recent years. The U.S. Food and Drug Administration (FDA) has initiated a project to determine the fidelity with which modern CFO can accurately predict hemolysis in such devices. The project involves the collection of experimental data against which externally-conducted CFO simulations may be compared. Because the data will be used to judge the ability of CFO to predict hemolysis, the pump was designed to cause more turbulence and blood damage than would be typical of an approved clinical device. In support of this effort, a shaft-driven centrifugal blood pump was constructed for use in both quantitative flow visualization analysis and in blood-damage experiments. The hydraulic performance of the pump was measured to determine the degree to which it represented a typical blood pump. Particle image velocimetry (PIV) was used to measure planar velocity fields in three different regions of the pump including the blade passage, impeller rear-gap, and cutwater region. For all PIV experiments, the pump delivered volumetric flow rates of 0.6, 3.0, and 6.0 liters per minute (LPM), each at a constant shaft speed of 2800 RPM. Statistical analysis was performed on each PIV data set in order to determine the time-averaged velocity fields as well as to resolve turbulent quantities of interest to the prediction of hemolysis (namely the Reynolds shear stresses). Additionally, the pump was operated using bovine blood as the working fluid in order to measure the hemolysis caused at the same operating points measured during PIV experiments. Further experiments were conducted to determine the contribution of the pump\u27s shaft-seal interface to the total measured hemolysis. The pump\u27s hydrodynamic performance was measured to be a close match to that of a typical clinical blood pump. PIV analysis revealed that the velocity and shear stress fields within the pump were dependent on its operating point, and can thus serve as benchmarking data against which to compare CFO analyses. Finally, the pump was confirmed to produce measurable hemolysis. The contribution of a polyurethane shaft seal to the measured hemolysis was significant (39%-62% of the total VAD hemolysis), but this contribution was small (7%-9% of the total VAD hemolysis) when a Teflon seal was used