Two-Dimensional Simulation of Flow and Platelet Dynamics in the Hinge Region of a Mechanical Heart Valve

(a) Photograph of a bileaflet valve. (b) Three-dimensional model of 1∕4 of a bileaflet valve with a cutting plane from which the two-dimensional model was extracted. (c) Zoomed in view of the hinge region. (d) Resultant two-dimensional model that was used in this study.

(a) Schematic of the hinge geometry used in the analysis with dimensions and the leaflet ear position at 32deg and the fully closed position at 63.8deg. Also indicated are the applied boundary conditions. (b) Angular velocity of the leaflet starting at 32deg moving toward closure. (c) Time varying pressure drop at the vicinity of the hinge region specified as pressure boundary condition. (d) Plot of the Cartesian grid with local mesh refinement on the hinge geometry. The mesh is adapted according to the gradients of flow for efficiency and accuracy. (e) Comparison of velocity profiles at an instant in the lower gap width with the base mesh and the finer mesh density.

(a) Velocity, (b) shear stress, (c) vorticity contour plots in the hinge region based on the static analysis with the leaflet ear in the fully closed position, and (d) platelet activation parameter calculated during static analysis. Jetlike flow and high bulk shear stresses through the gap width, as well as the development of strong vortices that are advected away from the leaflet edge, can be observed.

Plots of (a) velocity (m/s), (b) fluid shear stress (Pa), (c) concentration, and (d) simulated platelet activation (Pa s) at various stages of the closing phase in the dynamic analysis of flow in the hinge region

The velocity, fluid shear stress (FSS), and platelet concentration distribution at cross sections 1–3 within the gap width with the rectangular geometry of the leaflet ear. The horizontal axis indicates the distance from the valve housing (lower) edge to the leaflet ear (top) edge in reference to the figure within the gap width (GW) in the schematic of the geometry (top panel).

Flow field with contours of existing geometry and the ellipsoidal geometry: (a) velocity contour showing the leakage jet from the hinge region, (b) shear stress contour during the late stage of valve closure where the shear stress reaches the maximum value, (c) particle concentration, and (d) activation parameter at the time of closure.

Activation parameter during various stages of valve closure of the two geometries. The thick line shows the activation parameter of the existing geometry and the dashed line shows that of the ellipsoidal geometry.

The product of activation parameter and the concentration of platelets at the end stage of closure for (a) existing geometry and (b) elliptical geometry. It can be inferred that the number of platelets getting trapped in the region of high activation is less in the elliptical geometry than in the existing geometry.