In vitro studies of gas bubble formation by mechanical heart valves

Area of Science:

• Biomedical Engineering
• Cardiovascular Research
• Fluid Dynamics

Background:

• Clinical studies report emboli in mechanical heart valve (MHV) patients, suspected to be gas bubbles.
• Echocardiography shows bright particles near MHV, also considered gas bubbles.

Purpose of the Study:

• Investigate the relationship between dissolved gas concentration and bubble formation after MHV closure.
• Determine the origin and characteristics of bubbles associated with MHV function.

Main Methods:

• In vitro study using a mock circulatory loop with a Medtronic Hall tilting disc valve.
• Experiments conducted in saline and porcine blood with varying dissolved CO2 levels.
• Utilized Doppler ultrasound, high-speed video, and pressure transducers for bubble detection and cavitation measurement.

Main Results:

• Stable gas bubbles were observed forming and detaching from the valve post-closure.
• Bubble formation increased with higher dissolved CO2 concentrations.
• Cavitation and bubble formation were identified as distinct events during valve closure.
• Experiments in blood confirmed bubble presence near the valve, especially at high CO2 and valve loading.

Conclusions:

• Stable gas bubbles can form during mechanical heart valve operation.
• Bubble formation is influenced by cavitation, regurgitant flow low-pressure regions, and dissolved CO2.
• Findings provide insight into the mechanisms of bubble generation in MHV patients.