Mechanisms of Production of the First Heart Sound

Abstract

A series of open-chest expts. was made in order to study the mechanism of production of the first heart sound: in the empty heart; after ligation of the a-ygroove; after extensive damage of the a-v valves; after the ligation of the large arteries; and after necrosis of the ventricular walls. It is suggested that the first sound is the result of a combination of muscular and valvular factors. Sudden changes in muscular tension activate, first the a-v valves, and then the semilunar valves. This rapid succession causes a double vibration of the cardiac wall and is further transmitted to the chest wall including high-pitched (sound tracing) and low-pitched (cardiogram) components. Although simultaneous with the action of the valves, these vibrations are likely to arise in both the valvular and the muscular structures as a response to rapid changes in tension and pressure. Smaller vibrations, possibly of muscular origin, may be seen at times between the 2 main groups of vibrations of the first sound. Vascular vibrations occur only later, after the beginning of ejection, and have a lower pitch and less amplitude.