Second heart sound in normal subjects.

Splitting of the second heart sound in the pulmonary area into two components was first recognized by Potain (1866). In expiration, the two components fuse, while in inspiration delay of pulmonary valve closure (P2) occurs almost invariably in healthy subjects, enabling identification of aortic valve closure (A2) and P2, and hence comparison of the duration of right and left ventricular systole (Leatham and Towers, 1951). Knowledge of splitting of the second sound has proved an essential part of auscultation of the heart, and greatly facilitates the bedside diagnosis of atrial septal defect and pulmonary stenosis, physiological murmur, conduction defects, and ventricular function (Leatham, 1964). Detailed analyses of the second heart sound (S2) in normal subjects have been made by several authors, including Boyer and Chisholm (1958), Shafter (1960), Castle and Jones (1961), and Aygen and Braunwald (1962). The main emphasis has been upon an analysis of the splitting of S2 during respiration into its two components. The groups investigated have been children or young adults. Though these authors have shown that A2 becomes earlier and P2 later at the beginning of inspiration, there has been disagreement about the relative contribution of each of these events to the width of splitting of S2. In this study the second heart sound has been analysed by phonocardiography in a number of normal subjects of different age-groups, from infancy to old age. The relative intensities of A2 and P2 in the pulmonary area, and the frequency of transmission of P2 to the mitral area have received particular attention, since in heart disease these characteristics may be altered. In addition we have reinvestigated the splitting of S2 to establish normal values in different age-groups.