Mechanisms of Mechanical Heart Valve Cavitation: Investigation Using a Tilting Disk Valve Model
Zhaoming He PhD, Baoshu Xi PhD, Keqin Zhu PhD, Ned H. C. Hwang PhD

The induction of mechanical heart valve (MHV) cavitation was investigated using a 27 mm Medtronic Hall (MH27) tilting disk valve. The MH27 was mounted in the mitral position of a simulating pulse flow system and stroboscopic lighting used to visualize cavitation bubbles on the occluder inflow surface at the instant of valve closure. MHV cavitation was monitored using a digital camera with 0.04 mm/pixel resolution that rendered very tiny bubbles clearly visible on the computer monitor screen. Cavitation on the MH27 valve may be classified according to the time, site and shape of the cavitation bubbles. Valve cavitation occurred at the instant of occluder impact with the valve seat at closing. The impact motion was subdivided into three temporal phases: (i) squeezing flow; (ii) elastic collision; and (iii) leaflet rebound. MHV cavitation was caused by vortices initiated by the squeezing jet and/or by the transvalvular leakage jets. By using a tension wave that swept across the occluder surface immediately upon elastic impact, nuclei in the vortex core expand to form cavitation bubbles. The bubble shape and location may be analyzed to better understand MHV cavitation mechanisms, based on the fluid dynamics of jet vortex and tension wave propagations.