Observation and quantification of gas bubble formation on a mechanical heart valve

Clinical studies using transcranial Doppler ultrasonography in patients wit h mechanical heart valves (MHV) have detected gaseous emboli. The relations hip of gaseous emboli release and cavitation an MHV has been a subject of d ebate in the literature. To study the influence of cavitation and gas conte nt on the formulation and growth of stable gas bubbles, a mock circulatory loop, which employed ct Medtronic-Hall pyrolytic carbon disk valve in the m itral position, was used. A high-speed video camera allowed observation of cavitation and gas bubble release on the inflow valve surfaces as a functio n of cavitation intensity and carbon dioxide (CO2) concentration, while an ultrasonic monitoring system scanned the aortic outflow tract to quantify g as bubble production by calculating the gray scale levels of the images. In the absence of cavitation, no stable gas bubbles were formed. When gas bub bles were formed, they were first seen a few milliseconds after and in the vicinity of cavitation collapse. The volume of the gees bubbles detected bl the aortic track increased with both increased CO2 and increased cavitatio n intensity. No correlation was observed between O-2 concentration and bubb le volume. We conclude that cavitation is an essential precursor to stable gas bubble formation, and CO2, the most soluble blood gas, is the major com ponent of stable gas bubbles. [S0148-0731(00)00204-1].