Three-dimensional fluid-structure interaction simulation of bileaflet mechanical heart valve flow dynamics.

The wall shear stress induced by the leaflet motion during the valve-closing phase has been implicated with thrombus initiation with prosthetic valves. Detailed flow dynamic analysis in the vicinity of the leaflets and the housing during the valve-closure phase is of interest in understanding this relationship. A three-dimensional unsteady flow analysis past bileaflet valve prosthesis in the mitral position is presented incorporating a fluid-structure interaction algorithm for leaflet motion during the valve-closing phase. Arbitrary Lagrangian-Eulerian method is employed for incorporating the leaflet motion. The forces exerted by the fluid on the leaflets are computed and applied to the leaflet equation of motion to predict the leaflet position. Relatively large velocities are computed in the valve clearance region between the valve housing and the leaflet edge with the resulting relatively large wall shear stresses at the leaflet edge during the impact-rebound duration. Negative pressure transients are computed on the surface of the leaflets on the atrial side of the valve, with larger magnitudes at the leaflet edge during the closing and rebound as well. Vortical flow development is observed on the inflow (atrial) side during the valve impact-rebound phase in a location central to the leaflet and away from the clearance region where cavitation bubbles have been visualized in previously reported experimental studies.

A numerical simulation of mechanical heart valve closure fluid dynamics.

A computational fluid dynamics model for the analysis of the bileaflet mechanical heart valve closure process is presented. The objective of the study is to demonstrate the ability of the numerical model to simulate the leaflet motion during the closing phase in order to investigate the closure fluid dynamics and to evaluate the effect of alterations in the leaflet tip geometry. The model has been applied to six different combinations of the leaflet tip geometry and the gap width between the leaflet tip and the housing. The results show that the negative pressure quickly develops on the atrial side of the leaflet tip. The pressure becomes more negative as the leaflet closure progresses and the lowest pressure is reached before the leaflet comes to a stop in the closed position. The flow dynamics at the instant of valve closure is strongly dependent on the leaflet velocity during the closing phase. Decrease of the tip velocity by a factor of three in the last four degrees of leaflet motion leads to a 50% reduction in the negative pressure magnitude.