High frequency phonocardiography

Abstract

A systematic study of the high frequency components of the heart sounds and murmurs was made by means of a new standardized and calibrated phonocardiograph provided with a variable band pass filter. The frequency bands 500–1000 c.p.s. and higher were particularly studied but comparison was also made with the vibrations found in lower bands. This study was made in forty-seven subjects including five subjects without evidence of heart disease. The study revealed that the groups of high frequency vibrations were normally shorter than the equivalent group of lower bands; they often (but not always) appeared at the beginning of equivalent vibrations; they often presented a relative increase of amplitude. Several clinical phenomena were better revealed by the study of high frequency bands including the physiologic or pathologic splitting of the first and second sounds, the opening snap, and certain murmurs. The high frequency bands often revealed more clearly the “shape” of a murmur. In some cases, splitting of the heart sounds or the existence of a murmur was revealed only by these bands. The high frequency bands revealed that in about 25 per cent of the cases the first sound was composed of two simple vibrations (or groups of vibrations). These were identified through their time of occurrence as coinciding with mitral closure and aortic opening. One of the two may disappear in the highest band. The high frequency bands revealed that in more than one-third of the cases the second sound was composed of two simple vibrations (or groups of vibrations). These were identified as coinciding with aortic closure and pulmonic closure. The latter usually disappeared in the highest band except in cases of pulmonary hypertension. The optimum and maximum frequency bands in both normal subjects and clinical cases were studied for the first and second sounds, as well as for the third and fourth. A similar study was made in regard to the “ejection sound” and the opening snap of the mitral valve. Murmurs recorded in the high frequency range either disappeared, were still present, or became more clearly visible. The murmurs of mitral and aortic insufficiency were usually in the last group and were sometimes recorded only in the high frequency range. Detailed observations were made in the various valvular defects. It is concluded that the study of the high frequency vibrations of the phonocardiogram presents great interest both in normal subjects and in clinical cases. In the latter, it may be of diagnostic importance. Problems of cardiovascular physiology and pathology may at times be clarified by this study.