A Quantitative, Comparative Study of Sound Produced in vitro by Pulsatile Flow in and Around Prosthetic, Aortic Heart-Valves

Citation

Suobank, David Walter (1983) A Quantitative, Comparative Study of Sound Produced in vitro by Pulsatile Flow in and Around Prosthetic, Aortic Heart-Valves. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/q5r7-a318. https://resolver.caltech.edu/CaltechETD:etd-12142006-094228

Abstract

A quantitative, comparative study was made of sound produced in vitro by pulsatile flow in and around three designs of prosthetic aortic heart-valves. Designs studied were 25mm Bjork-Shiley, 24mm Smeloff and Starr-Edwards model 2400 valves. A digital method for the analysis of the sounds using the fast Fourier transform is presented and applied. Results are examined in both the time domain and a variety of formats in the frequency domain. Formats include original time vs. amplitude plots, power-density spectra, power-distribution functions, a 3-D (three-dimensional) surface of power-frequency-time, auxiliary views of these 3-D surfaces, and a 3-D, power-distribution surface showing the difference between two 3-D, power-distribution surfaces. Enhanced distinguishability of sound was clearly shown by the 3-D, power-difference surface which provided a very convenient means for the overall comparison of two sounds.

Attention was given to understanding effects of valvar and pulsatile conditions upon the frequency characteristics of the opening, systolic, and closing sounds. Failure modes were simulated and resulting changes of the sounds were examined. Simulated overgrowth was placed on the inner apical surface of the Starr-Edwards model 2400 valve and on the upstream struts of the Smeloff valve. Results showed that the sounds produced provided information pertinent to the simulated malfunction.

Effects of pulse rate, mean flow-rate, and mean aortic pressure associated with the normal valvar sounds were investigated. Results were interpreted in terms of the known physical changes of the valve and known changes of the pulsatile state. Under alternate pulsatile states, the total power of the opening and closing sounds were influenced primarily by the rate of change of the ventricular pressure prior to these events. The difference between systolic sounds was much greater than between opening and closing sounds for cases involving changes of the stroke volume for each normal valve design. An increase in systolic flow rate produced a corresponding increase in the power of peaks in the spectra of the systolic sound for each design. The location of peaks within the power density spectra of opening, systolic and closing sounds were more similar during the studies of alternate, non-normal, pulsatile states of normal valves than they were during the studies of normal/abnormal valves under normal pulsatile states.

Visualization of the valve and particle trajectories and simultaneous recording of sound, flow rate, and upstream and downstream pressure, provided direct evidence of the cause of many of the acoustical events. Strouhal numbers were estimated from center-frequencies of resonance peaks associated with sounds that were related to periodic vortex shedding in flows past the struts, annular gaps and phonocatheter.

The overall results indicate that the method used could distinguish changes of valvar and pulsatile states for each of the valvar designs that were studied.

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