DAMAGE ACCUMULATION MODEL, FSI, AND MULTISCALE SIMULATIONS FOR STUDYING THE THROMBOGENIC POTENTIAL OF PROSTHETIC HEART VALVES

摘要

3D physiologic geometry of St. Jude Medical (SJM) valve after implantation was simulated with non-Newtonian two-phase blood model. The simulation used the unsteady Reynolds averaged Navier-Stokes (URANS) approach and the Wilcox k-ω turbulent model. Platelet stress accumulation and the resulting platelet damage were calculated from the results. Thrombogenic potential of two bileaflet MHV geometries was conducted using fluid-structure interaction (FSI) computation. Two commercially available valve geometries, SJM and ATS, which differ mostly in their hinge design, were simulated in a straight geometry with sudden expansion downstream of the valve. The thrombogenic potential of the two valves was based on computed wall shear stresses on the leaflets and cumulative shear stress on multiple particles released during forward and reverse flow phases. Platelet stress accumulation along pertinent trajectories from the FSI studies indicated that the SJM valve has a higher thrombogenic potential then the ATS valve. Flow patterns generated by the valve are conducive to platelet activation provide optimal conditions for activated platelets to interact with each other and form aggregates are hypothesized to be the source of thromboemboli formation, increasing the risk for cardioembolic stroke. The new damage model developed was utilized to estimate the effects of repeated passages and platelet senescence on this thrombogenic potential. Flow and pressure effects on a cell like a platelet can be well represented by a continuum mechanics model down to the order of the μm level. However, the molecular effects of adhesion/aggregation bonds are on the order of nm. Thus we also adopt a discrete particles dynamics (DPD) approach in which the macroscopic model provides information about the flow induced stresses that may activate blood cellular constituents. This multiscale modeling approach concentrates on flow regions in prosthetic devices like MHVs and cardiovascular pathologies that have a high propensity to activate platelets and form aggregates. Preliminary simulations of blood flow in simple geometries using this approach, which widely departs from the traditional continuum approach, is successful in generating viscous blood flow velocity distributions in these geometries.