Hydrodynamics of St. Jude Medical, Carbomedics, Advancing The Standard, and On-X bileaflet valves with an annular diameter of 25 mm were obtained using an in-vitro test system. Steady flow studies demonstrated different pressure drops due to differences in valve design, particularly the geometric orifice diameter and the opening angle. The On-X valve produced the least pressure drop, whereas the Carbomedics valve had the greatest pressure drop. In pulsatile flow experiments, the On-X and St. Jude Medical valves consistently produced the lowest mean positive pressure gradients, while the Carbomedics valve had the highest gradients. In spite of its parallel leaflets design, the On-X valve showed a closing volume as small as that of Carbomedics valve. The results indicate that a larger orifice diameter and greater opening angle can significantly reduce transvalvular pressure loss. This study also demonstrated that attempts to improve the hydrodynamic efficacy of the On-X valve were successful in reducing the pressure gradient as well as maintaining a low closing volume.
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