Study on Spectral Phonocardiogram in Mitral Stenosis : with Special Reference to Frequency Analysis of the First Heart Sound

Abstract

Spectral phonocardiograms (SPCG) were studied in 66 cases of pure mitral stenosis, 49 with normal sinus rhythm and 17 with atrial fibrillation. Method SPCG were recorded by use of Soundspectrograph (Rion Co.) specially designed for analysis of cardiovascular sounds. Quantitative analyses of the frequency-intensity characteristics were made by section pattern display of the apparatus. In this study, a dynamic microphone and a preamplifier with ear-like characteristics were used for recording SPCG. Results 1) The fundamental tone of the first heart sound in mitral stenosis was about 100cps, which is slightly higher than normal (70cps). The high frequency attenuation was about -10dB/oct. In normal cases, this attenuation was about -25dB/oct. In severe cases, shift of the fundamental tone to higher frequency and the decreased high frequency attenuation was more marked. 2) The fundamental tone of the second heart sound was also about 70∼100cps but, approximately equal level of the overtones from 100 to 250cps, fused with the fundamental tone, gave a definitely different configuration-a plateau type pattern-from that of the first heart sound in the section display. The attenuation of the second heart sound was about -12dB/oct. In cases with the elevated pulmonary arterial pressure, the attenuation tended to be decreased. 3) The frequency-intensity characteristics of the opening snap showed a marked attenuation of lower frequency under 100cps. The section pattern of the opening snap in higher frequency range was resembled to that of the first heart sound. 4) Frequency distribution of diastolic murmur was ranged from 50 to 300cps and the attenuation of high frequency was ranged from -30 to -45dB/oct. 5) Although slight changes of the fundamental tone and of the high frequency attenuation observed, the basic configuration of the frequency-intensity characteristics of the first heart sound remained unchanged in atrial fibrillation, after commissurotomy, inhalation of amyl nitrite and exercise test. However, it changed completely after the artificial mitral. valve replacement. Discussion and Conclusion 1 ) Spectral phonocardiography was proved to be a best procedure for frequency analysis of heart sounds and murmurs in mitral stenosis. For precise assessment of the results, several limitations of the method, such as, frequency, intensity and time dissolving capacity should be considered. 2) Irrespective of underlying diseases, the frequency-intensity characteristics of the first heart sound as observed in section pattern dis-play showed a similar contour and differed from that of the second heart sound. From this result, it is possible to assume two different sound-sources for production of the first and second heart sounds. 3) Spectral phonocardiographic changes of the first heart sound after hemodynamic changes and artificial mitral valve replacement will strongly support the conception that the mitral valve is a main sound-source of the first heart sound. This idea was also theoretically proved applying an electrical analog simulation of the left heart construction and hemodynamics. 4) Conversely, the change of the physical property (organic change) of mitral valve can be estimated, to some extent, from the spectral phonocardiographic findings of the first heart sound.