The Calibration of Heart Sound Intensity

There is no standardized method for the calibration of total energy conducted to the surface of the chest caused by the cardiac sounds. Loudness is a subjective term which is dependent upon total energy, frequency of the main components and the specific sensitivity of the human hearing mechanism. A method is described in which the amplitude of the chief component of the heart sounds is compared to that produced by a standard sound signal at 80 decibels at 500 cycles per second and an intensity ratio calculated. The method has been applied to normal individuals of different ages and to those with mitral valve disease and those with pulmonary hypertension. The findings confirm the clinical observation that mitral stenosis with persisting mobility of the valve leaflets is associated with a loud first heart sound. However, the measurement of intensity of the second heart sound did not show so reliable a correlation between the loudness of the sound and the pulmonary blood pressure. The relationship is somewhat obscured by the wide range of normal values in the intensity of the second heart sound.