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Pulmonary hypertension is a fundamental problem in the study of diseases of the heart and lungs. Because of its importance with regard to patho- METHODThe determination of systolic pulmonary arterial pressure (SPAP) by external graphic recordings is based on the measurement of the phase of isometric relaxation of the right ventricle, which begins with the closure of the pulmonary valve and ends with the opening of the tricuspid (IIp-T interval). To measure this interval several points of reference on the graphic recordings are used (Fig. 1). The closure of the pulmonary valve is represented by the pulmonary component of the second sound of the phonocardiogram (HIp), which is easily identifiable following the aortic component (IIa), especially when there is pulmonary hypertension or the second sound is split. With paradoxical splitting of the second sound, the vertex of the incisura of the carotid pulse is useful in identifying IIa, and, therefore, by exclusion, IIp. When it is difficult to distinguish IIp, the recording ofthe external cardiogram ofthe pulmonary artery (Fishleder and Friedland, 1957) frequently demonstrates a notch that signals the closure of the pulmonary valve (Fig. 2). The opening of the tricuspid

The duration of the systolic phases of the cardiac cycle in 390 normal children was determined from high-speed simultaneous recordings of the electrocardiogram, phonocardiogram, apexcardiogram, and carotid pulse. Data were obtained on children 1 mo to 13 years of age and analyzed to define the independent effects of aging and heart rate on the systolic intervals. Electromechanical systole (Q-II) was found to prolong with increasing age in children with the same heart rate. Pre-ejection period was also prolonged in older children and occupied an increased percentage of total systole. The interval from onset of contraction to first sound varied inversely with heart rate and was independent of age. Electromechanical delay and isometric contraction time were directly related to age and independent of rate. Ejection time varied directly with age and inversely with heart rate but occupied a smaller percentage of systole in older children. Alterations in systolic phase duration occurring with maturation reflect the normal functional adaptation of the developing heart. Measurement of these phases can provide useful information relative to cardiac function in children.

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