CAVITATION BEHAVIOR OF THREE MONOLEAFLET VALVES UNDER ACCELERATED TESTING

Abstract

Cavitation with mechanical valve closure has been observed both in vitro and in vivo when local pressure drops below vapor pressure. Under physiological conditions, adequate data on random cavitation formation is difficult to obtain. We used accelerated testing to 600 bpm, a transvalvular pressure of 120 mmHg, synchronized high-speed videography, and high-frequency pressure measurements to study cavitation intensity and behavior. The Medtronic Hall Standard 29mm (MHS), Medtronic Hall D-16 29mm (MHD), and Omni Carbon 29mm (OC) were studied with a Millar micro-tip transducer catheter, a PCB high-fidelity piezoelectric pressure transducer, and a CCD high-speed video camera to indicate downstream pressure changes with valve closure and cavitation intensity and distribution. MHS creates a cloud of bubbles near the seat stop due to squeeze flow, followed by peripheral cavitation between the housing ring and leaflet edge due to occluder rebound and Venturi effect; cavitation lasts for 400 μs. MDH, without a seat stop and squeeze flow, has a water hammer effect causing more distributed bubbles on the occluder surface followed by similar rebound and Venturi effects, lasting 350 μs. The OC valve also has the water hammer, but a cloud of localized bubbles does not appear until 50 μs after rebound. The tension wave and Venturi effect both contribute to cavitation lasting 350 μs. The underlying major contributor to cavitation varies based on valve design. However, all three valves tested here show significant rebound effect intensifying cavitation, implying future designs must account for this phenomenon.