A validated computational fluid dynamics model to estimate hemolysis in a rotary blood pump.

A major part of developing rotary blood pumps requires the optimization of hemolytic properties of the entire pump. Application of a suited computational fluid dynamics (CFD)-based hemolysis model allows approximation of blood damage in an early phase of the design process. Thus, a drastic reduction of time- and cost- intensive hemolysis experiments can be achieved. For the MicroDiagonal Pump (MDP), still under development at Helmholtz-Institute in Aachen, Germany, different pump configurations have been analyzed, both numerically and experimentally. The CFD model of the pump has been successfully validated based on the comparison of the pressure head curves (H-Q curves), as discussed in a prior publication. In the present study, the authors focus on the development of a semiempiric blood damage model using the CFD and in vitro hemolysis data. On the one hand, mean key characteristics (shear stress and exposure time) and other characteristics affecting blood damage have been calculated based on numerical data. On the other hand, in vitro hemolysis tests have been accomplished in order to determine the hemolytic curves of two different pump configurations (with the same impeller but different tip clearances). Finally, a new function based on a general power law has been defined by means of the mean key characteristics. The unknown constants of the function have been determined by multidimensional regression analysis using the hemolytic curves. For the final validation of this new blood damage model, the calculated and the in vitro obtained hemolysis indices at the specific VAD operating point have been compared for all pump configurations. The comparison showed an excellent agreement, both qualitatively and quantitatively.

Comparison of hydraulic and hemolytic properties of different impeller designs of an implantable rotary blood pump by computational fluid dynamics.

A mixed-flow blood pump for long-term applications has been developed at the Helmholtz-Institute in Aachen, Germany. Central features of this implantable pump are a centrally integrated motor, a blood-immersed mechanical bearing, magnetic coupling of the impeller, and a shrouded impeller, which allows a relatively wide clearance. The aim of the study was a numerical analysis of hydraulic and hemolytic properties of different impeller design configurations. In vitro testing and numerical simulation techniques (computational fluid dynamics [CFD]) were applied to achieve a comprehensive overview. Pressure-flow charts were experimentally measured in a mock loop in order to validate the CFD data. In vitro hemolysis tests were performed at the main operating point of each impeller design. General flow patterns, pressure-flow charts, secondary flow rates, torque, and axial forces on the impeller were calculated by means of CFD. Furthermore, based on streak line techniques, shear stress (stress loading), exposure times, and volume percentage with critical stress loading have been determined. Comparison of CFD data with pressure head measurements showed excel-lent agreement. Also, impressive trend conformity was observed between in-vitro hemolysis results and numerical data. Comparison of design variations yielded clear trends and results. Design C revealed the best hydraulic and hemolytic properties and was chosen as the final design for the mixed-flow rotary blood pump.