Comparison of platelet activation through hinge vs bulk flow in bileaflet mechanical heart valves.

Bileaflet mechanical heart valves (BMHVs) are prone to thromboembolic complications which are believed to be initiated by platelet activation. Platelets are activated by non-physiologic shear stresses in the bulk flow or the leakage/hinge flow, whose contributions has yet to be quantified. Here, the contribution of bulk and hinge flows to the activation of platelets in BMHVs is quantified for the first time by performing simulations of the flow through a BMHV and resolving the hinge by overset grids (one grid for the bulk flow and two for the hinge regions coupled together using one-way and two-way interpolation). It was found that two-way coupling is essential to obtain correct hinge flow features. The platelet activation through the hinge for two gap sizes (250 and 150 μm) is compared to the activation in the bulk flow using two platelet activation models to ensure the consistency of the observed trends. The larger gap has a higher total activation, but a better washout ability due to higher velocities. The maximum shear stress observed in the bulk flow (∼320dyne/cm2) is much smaller than the hinge (∼1000dyne/cm2). However, the total activation by the bulk flow is found to be several folds higher than by the hinge/leakage flow. This is mainly due to the higher flow rate of the bulk flow which exposes much more platelets to shear stress than the leakage flow.