The effect of tip angle on cavitation potential during closure of a bileaflet prosthesis model.

BACKGROUND AND AIM OF THE STUDY: Mechanical heart valve (MHV) cavitation has been widely investigated by negative pressure transient (NPT) measurements. Whilst NPT is believed to be the cause of cavitation as the valve occluder approaches its fully closed position, some valves are also more prone to cavitation initiation. The study aim was to determine the effect of tip angle on the occluder trailing edge for the MHV closure flow field and cavitation potential.

METHODS: Three pairs of 1:1 transparent bileaflet models, with different tip angles (30 degrees, 60 degrees and 90 degrees), were used in a pulsatile mock loop. Particle image velocimetry (PIV) and micro-tip pressure catheters were applied respectively for the closure flow and transient pressure investigations. A mechanism was designed to enable triggering when the valve occluder approached its closing position.

RESULTS: The transient pressure showed two maximum pressure drops, the magnitudes of which differed with various angle designs. A series of flow fields with continuously narrowing gap channels was captured. Different flow features were demonstrated for the three valve models.

CONCLUSION: The tip angle design on the occluder trailing edge affected both the NPT magnitude and MHV closure flow field. The 60 degrees and 30 degrees valves had higher vorticity and fluid deceleration rate within the squeeze flow and occluder sudden stop respectively, which correlated with their larger pressure drops for the first and second NPT peaks.