MECHANICAL HEART VALVE CAVITATION FLUID MECHANICS

Abstract

In vitro high speed videography (HSV) studies of mechanical heart valve IMHV) closure and rebound have revealed the development of bubble and vortex cavitation, which contributes to valve and blood element damage. The local fluid mechanics during closure play an essential role with MHV cavitation, thus necessitating the fundamental understanding for cavitation development and promoting efforts to minimize the impact in vivo. A Bjork-Shiley Monostrut (BSM) MHV was modified to investigate flow structures using HSV and laser Doppler velocimetry (LDV). LDV studies were conducted 1 mm upstream of the valve around the major orifice. Subsequently, the valve housing was modified by removing a rectangular window of titanium from pivot joint to pivot joint along the major orifice while retaining part of the valve housing. Consequently, a modified single shot chamber that included filling the window with acrylic was constructed to retain valve geometry and most of the structural integrity. LDV studies confirmed minimal flow changes due to the modification. The HSV and LDV studies demonstrated the development of vertical structures during closure, which continued through the initial rebound. The structure began 'it the onset of valve closure and decreased in size until it became a tight vortex at valve impact. It briefly enlarged during rebound before finally dispersing clue to the regurgitant jet, In addition, flow velocities up to 18 m/s were measured in the clearance gap suggesting a potential hemolytic cause. The flow measurements determined from within the MHV housing suggest a mechanism for cavitation.