The effect of gap width on viscous stresses within the leakage across a bileaflet valve pivot

Stresses of leakage flow may contribute to the increased tendency for thromboembolic complications in patients with mechanical valves. In bileaflet valves, leakage occurs primarily in the pivots, and the width of the pivot gap influences viscous stress magnitudes. The present study was conducted to investigate the effects of gap width on viscous stresses within the pivots of a bileaflet mitral valve during the leakage phase.

A computational model of a bileaflet valve was created and inserted between models of the left atrium and ventricle. Three simulations were performed, varying gap width between the leaflet and housing in the pivot region. To validate these calculations, steady leakage across a scaled in-vitro model of a single pivot was initiated, and velocity measurements at specific locations within flow the pivot were obtained using one-component laser Doppler velocimetry.

The average viscous stresses on the housing surface of the pivot increased from 198 to 299 Pa, and on the leaflet surface from 242 to 271 Pa, as gap width was increased from 100 to 300 microm. These stresses were similar in magnitude to the maximum turbulent stresses reported within the pivots in previous studies. Velocities measured experimentally were even larger than those estimated computationally.

These experiments suggest that viscous stresses in leakage flow across a bileaflet mitral valve increase with gap width, and may contribute more to blood damage and increased risk of thromboembolic complications in patients with such valves than would turbulence.