In vitro squeeze-flow phenomena at the instant of mechanical valve closure

Abstract

Cavitation bubble formation associated with mechanical valve closure has been investigated in vitro, and the region of bubble formation has been correlated with large negative pressure transients. The region of cavitation bubbles forms in valve designs where leaflets interact with seat stops. It has been postulated that the fluid is squeezed between the leaflet and the seat stop and radially propelled at high velocities, resulting in further pressure reduction below the vapor pressure of fluid and initiating cavitation bubble formation. We conducted in vitro experiments to visualize and detect the presence of squeeze-flow phenomena associated with valve closure of mechanical heart valves. The closing dynamics were studied by simulating a single closing event of the leaflet with the valve mounted at the mitral position. Squeeze flow was detected at the instant of valve closure, when the valve leaflet interacts with the valve seat stop. The use of a high-speed video camera at 1000 frames per second with strobe light at 16000 pulses per second enabled the visualization of cavitation bubbles and its radial motion from the valve's seat stop due to the squeeze-flow effect. Vapor cavitation bubbles were observed to collapse within 0.5ms after inception. In mechanical valves without seat stops in the major orifice region, bubbles of duration longer than that of the cavitation bubbles were observed. These microbubbles were present for 4s before collapsing and are believed to be air bubbles whose presence in vivo has been detected with ultrasound imaging.