Cavitation Dynamics of Medtronic Hall Mechanical Heart Valve Prosthesis: Fluid Squeezing Effect

Author:

Lee C. S.1,Chandran K. B.2,Chen L. D.3

Affiliation:

1. University of Iowa, Iowa City, IZ 52242

2. Departments of Biomedical and Mechanical Engineering, University of Iowa, Iowa City, IA 52242

3. University of Iowa, Iowa City, IA 52242

Abstract

The cause of cavitation in mechanical heart valves is investigated with Medtronic Hall tilting disk valves in an in vitro flow system simulating the closing event in the mitral position. Recordings of pressure wave forms and photographs in the vicinity of the inflow surface of the valve are attempted under controlled transvalvular loading rates averaged during valve closing period. The results revealed presence of a local flow field with a very high velocity around the seat stop of mechanical heart valves that could induce pressure reduction below liquid vapor pressure and a cloud of cavitation bubbles. The analysis of the results indicates that the “fluid squeezing” between the stop and occluder as the main cause of cavitation in Medtronic Hall valves. The threshold loading rate for cavitation initiation around the stop was found to be very low (300 and 400 mmHg/s; half the predicted normal human loading rate that was estimated to be 750 mmHg/s) because even a mild impact created a high speed local flow field on the occluder surface that could induce pressure reduction below vapor pressure. The present study suggests that mechanical heart valves with stops at the edge of major orifice region are more vulnerable to cavitation, and hence, have higher potential for damage on valve components and formed elements in blood.

Publisher

ASME International

Subject

Physiology (medical),Biomedical Engineering

Reference35 articles.

1. Bluestein D. , EinavS., and HwangN. H. C., 1994, “A Squeeze Flow Phenomenon at the Closing of a Bileaflet Mechanical Heart Valve Prosthesis,” J. Biomechanics, Vol. 27, pp. 1369–1378.

2. Chandran, K. B., 1988, “Heart Valve Prostheses: in vitro flow dynamics,” in Encyclopedia of Medical Devices and Instrumentation John G., Webster, ed., Wiley, New York, 3rd ed., pp. 1475–1483.

3. Chandran K. B. , SchoephoersterR., and DellspergerK. C., 1989, “Effect of prosthetic mitral valve geometry and orientation on flow dynamics in a model human left ventricle,” J. Biomechanics, Vol. 22, pp. 51–65.

4. Chandran K. B. , LeeC. S., and ChenL. D., 1994, “Pressure field in the vicinity of mechanical valve occluders at the instant of valve closure: Correlation with cavitation initiation,” J. Heart Valve Disease, Vol. 3 (Suppl. 1), pp. S65–S76S65–S76.

5. Cheon, G. J., and Chandran, K. B., 1994, “Transient behavior analysis of a mechanical monoleaflet heart valve prosthesis in the closing phase,” ASME JOURNAL OF BIOMECHANICAL ENGINEERING (in press).

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