Effect of hypertension on the closing dynamics and Lagrangian blood damage index measure of the b-datum regurgitant jet in a bileaflet mechanical heart valve.

We hypothesize that the formation of the closing vortex and subsequent b-datum regurgitation jet in bileaflet mechanical heart valves is governed by the magnitude of the driving mean aortic pressure (MAP), and that this sensitivity does impact the blood damage index (BDI) corresponding to platelet activation and lysis. High spatial resolution time resolved (1 kHz) as well as phase locked particle image velocimetry techniques captured the dynamic leaflet closure and regurgitation jet of a model 25 mm St. Jude Medical BMHV. Cell trajectories were estimated using Lagrangian particle tracking analysis while the leaflet kinematics was quantified by tracking the leaflet tip-position throughout closure. The non-principal as well as principal shear stress loading histories along each cell trajectory revealed BDI for platelet activation and lysis as a function of cell initial position, release time-point, and blood pressure. Results show that the leaflet closing time reduces by roughly 10 ms, in response to an increase in MAP by 40 mmHg. We report that higher MAP leads to a stronger b-datum vortex and jet formation. Platelet activation BDI lowers with a higher MAP due to reduction in exposure times despite an increase in principal shear stress experienced. Platelet lysis BDI however increases with higher MAP. Maximum BDI may occur for cells initially in the b-datum zone during the onset of leaflet closure. Our results provide a better understanding of BDI of the regurgitant b-datum jet and sheds light on the potential importance of blood damage testing under hypertensive conditions.