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Venturi pressure cannot cause cavitation in mechanical heart valve prostheses.
J M Gross1, G X Guo, N H Hwang
1Department of Biomedical Engineering, Memphis State University, Tennessee 38152.
ASAIO Transactions
|July 1, 1991
Summary
Surface pitting in mechanical heart valves (MHVs) is not caused by cavitation. Leakage flow velocities in MHVs are insufficient to induce cavitation at typical operating pressures.
Area of Science:
- Biomedical Engineering
- Fluid Dynamics
- Cardiovascular Devices
Background:
- Surface pitting observed in explanted mechanical heart valves (MHVs) suggests potential damage mechanisms during operation.
- Cavitation, a phenomenon involving bubble formation and collapse, is a suspected cause of such surface degradation.
Purpose of the Study:
- To investigate whether cavitation occurs in mechanical heart valves due to leakage flow.
- To determine the relationship between transvalvular pressure, leakage flow, and the potential for cavitation.
Main Methods:
- Mechanical heart valve leaflets were fixed with varying B-datum (BD) gaps (0.0089, 0.0174, 0.0219 cm).
- Leakage flow was established in a steady flow chamber across a range of transvalvular pressures (20–200 mmHg).
- Laser Doppler Velocimetry (LDV) measured flow velocities distal to the BD gap; these were compared to theoretical calculations.
Main Results:
- Flow velocities measured by LDV were similar across different BD gap settings at identical pressures, indicating geometric independence.
- Calculated velocities were compared to the threshold velocity required to cavitate liquid blood (approx. 13 m/sec at atmospheric pressure).
- The measured and calculated leakage velocities were found to be insufficient to cause cavitation.
Conclusions:
- The leakage flow velocity in mechanical heart valves is not high enough to induce cavitation.
- Surface pitting in MHVs may result from mechanisms other than cavitation, such as Venturi effects requiring higher pressure differentials.