Mechanisms of mechanical heart valve cavitation: Investigation using a tilting disk valve model

Background and aim of the study: The induction of mechanical heart valve (M HV) cavitation was investigated using a 27 mm Medtronic Hall (MH27) tilting disk valve. Methods: The MH27 valve was mounted in the mitral position of a simulating pulse flow system, and stroboscopic lighting used to visualize cavitation b ubbles on the occluder inflow surface at the instant of valve closure. MHV cavitation was monitored using a digital camera with 0.04 mm/pixel resoluti on sufficient to render the tiny bubbles clearly visible on the computer mo nitor screen. Results: Cavitation on MH27 valve was classified as five types according to the time, site and shape of the cavitation bubbles. Valve cavitation occur red at the instant of occluder impact with the valve seat at closing. The i mpact motion was subdivided into three temporal phases: W squeezing flow, ( ii) elastic collision, and (iii) leaflet rebound. MHV cavitation caused by vortices was found to be initiated by the squeezing jet and/or by the trans valvular leakage jets. By using a tension wave which swept across the occlu der surface immediately upon elastic impact, nuclei in the vortex core were expanded to form cavitation bubbles. Conclusion: Analysis of the shape and location of the cavitation bubbles pe rmitted a better understanding of MHV cavitation mechanisms, based on the f luid dynamics of jet vortex and tension wave propagations.