Über die numerische Bestimmung der Blutschädigung in Rotationsblutpumpen
Groß-Hardt, Sascha; Steinseifer, Ulrich (Thesis advisor); Karagiannidis, Christian (Thesis advisor)
Dissertation / PhD Thesis
Despite decades of research related to blood damage and numerical blood damage estimation, the accuracy of prediction algorithms for complex flows could not be improved significantly. Nonphysiologically high shear stresses are associated with blood trauma and many of the complications in mechanical circulatory support devices, but direct blood damage predictions (e.g. hemolysis or thrombosis) with Computational Fluid Dynamics (CFD) tend to be inaccurate. An important, but often underestimated factor for the accuracy of the entire simulation is mesh generation, describing the subdivision of a continuous geometric space into discrete geometric and topologic cells. The first publication details the strong dependency of mesh resolution on shear stress prediction within a generic rotary centrifugal blood pump. To avoid under prediction and to maintain a consistent quantification of the actual shear stress, much finer mesh resolutions were required, compared to the current state of the art. Accordingly, the mesh-induced error in subsequent hemolysis prediction was minimized. The second publication highlights crucial aspects for improved numerical accuracy with respect to result validation, choice of turbulence model and setup verification. Simulation results of a benchmark centrifugal blood pump from the FDA Critical Path Initiative were compared with experimental data, demonstrating that the simulation accuracy depends highly on the validation of both pump pressure head and internal velocity field. Furthermore, shear stress quantification demanded particularly high near-wall mesh resolutions, which were not required for the validation of pressure heads or velocity. Using the findings from the previous two publications, the third publication demonstrates the high risk of increased bleeding or clotting complications of currently used rotary blood pumps when operated at blood flow rates below 2 L/min, as in recent clinical use for ECCO2R systems or neonatal and pediatric ECMO applications. Using high resolution CFD analysis, it was observed that the pump internal flow recirculation rate increases 6-12-fold in these flow ranges, potentially increasing adverse effects due to multiple exposures to high shear stress. This dissertation discusses the importance of systematic model verification and result validation as decisive prerequisites for improved simulation accuracy. The findings will support the development of more advanced and more credible blood damage models in the future. Furthermore, CFD could contribute to the understanding of the deleterious consequences that present with the low-flow operation of current rotary blood pump systems, stressing the urgent need to design blood pumps dedicated for low flow applications.