Hemodynamic correlates of the first heart sound

The temporal relationship between the "crossing" of equisensitive atrial and ventricular pressure tracings and the initial components of the first heart sound of the homolateral intracardiac phonocardiogram was analyzed in 35 dog experiments. These studies showed that the first component of the first heart sound followed the atrioventricular valve closure (AV crossing) in all instances by an average time interval of 23 msec and that, at the time of its occurrence, there was a ventricular-atrial pressure gradient of 5 mm Hg in the right side and of 14 mm Hg in the left side of the heart. It is concluded that valvular closure, per se, does not cause the first component of the first heart sound. Actually the first heart sound occurs later during the period of isometric ventricular contraction, suggesting that the rise of ventricular pressure is responsible for its vibrations. Comparative analyses of right and left intracardiac and external phonocardiograms showed that the right side component of the first heart sound follows the left in about three-fourths of the cases and is coincident with it in the remainder and that these events are reflected in the same order in the external phonocardiogram.