Sound Pressure Correlates of the Second Heart Sound

The sound pressure correlates of the second heart sound were studied in 22 patients during diagnostic cardiac catheterization. Simultaneous right ventricular and pulmonary artery pressures were recorded with equisensitive catheter-tip micromanometers together with the external phonocardiogram and ECG. In 12 patients having normal pulmonary vascular resistance (group 1), pulmonic closure sound was coincident with the incisura of the pulmonary artery pressure curve which in turn was separated from the right ventricular pressure trace by an interval denoted hangout. The duration of this interval varied (33-89 msec), was independent of pulmonary artery pressure or resistance and was felt to be primarily a reflection of the capacitance of the pulmonary vascular tree. The absolute value of this interval during inspiration was very similar to the splitting interval and, when subtracted from the Q-P2 interval, the remaining interval (QRV) was almost identical to the Q-A2 interval, indicating that the actual duration of right and left ventricular systole is nearly equal. Awareness of the existence of the hangout interval and its hemodynamic determinants offers a reasonable mechanism to explain the audible expiratory splitting of the second heart sound found in patients with idiopathic dilatation of the pulmonary artery following atrial septal defect repair and in one additional patient studied with mild valvular pulmonic stenosis.. In nine patients with elevated pulmonary vascular resistance approaching systemic levels (group 2), the absolute value of the hangout interval was markedly reduced (15-28 msec) consistent with the decrease in capacitance of the pulmonary vascular bed and the increased pulmonary vascular resistance known to occur in pulmonary hypertension. In those patients where the duration of right and left ventricular systole were nearly equal, narrow splitting of the second heart sound was present. In those patients where selective prolongation of right ventricular systole occurred, the narrow hangout interval persisted, but the splitting interval was prolonged proportionate to the increased duration of right ventricular systole.