Squeeze flow measurements in mechanical heart valves.

High-speed squeeze flow during mechanical valve closure is often thought to cause cavitation, either between the leaflet tip and flat contact area in the valve housing, seating lip, or strut flat seat stop, depending on design. These sites have been difficult to measure within the housing, limiting earlier research to study of squeeze flow outside the housing or with computational fluid dynamics. We directly measured squeeze flow velocity with laser Doppler velocimetry at its site of occurrence within the St. Jude Medical (SJM), Omnicarbon (OC), and Medtronic Hall Standard (MHS) 29 mm valves in a mock circulation loop. Quartz glass provided an observation window to facilitate laser penetration. Our results showed increasing squeeze flow velocity at higher heart rates: 2.39-3.44 m/s for SJM, 3.07-4.33 m/s for OC, and 3.87-5.33 m/s for MHS. Strobe lighting technique captured the images of cavitation formation. Because these results were obtained in a mock circulation loop, one can assume this may occur in vivo resulting in valve damage, hemolysis, and thromboembolism. However, velocities of this magnitude alone cannot produce the pressure drop required for cavitation, and the applicability of the Bernoulli equation under these circumstances requires further investigation.