Origin and Conduction of the Mitral Sound in the Heart

Abstract

Mitral heart sounds were recorded by small microphones inserted in the heart muscles of dogs. Recordings showed that components having frequencies between 20 and 40 cycles/ sec originate at the base of the heart and travel from there to the apex. The velocity of conduction is in the order of 4 m/sec, so that the wavelengths can be calculated to be about 20 to 10 cm. At these frequencies the ventricle seems to vibrate as a whole. Components having frequencies higher than 40 cycles/sec could not be followed during their progression over the heart. In the range from 20 to 160 cycles/sec, the mitral sounds recorded above and below the mitral valve were of opposite phase so that the mitral valve is the main elastic element responsible for the mitral sound. The combined masses of the heart and the blood in it constitute the inertia of the cardiohemic system. In this range of frequencies oscillations in transmural pressure and circumferential tension of the heart were synchronous and of the same phase. The low velocity of conduction, the structural similarity between the heart and arteries, and the synchronism in the oscillations of transmural pressure and circumferential tension allow the conclusion that the mitral sound is conducted through the ventricle in the form of a transverse vibration, strictly analogous to the way pulse waves are conducted in arteries.