A study of the period of isovolumic relaxation in normal subjects and in patients with heart disease

1. 1. Measurements of isovolumic relaxation time from simultaneous recording of the apex cardiogram, carotid tracing and phonocardiogram were obtained in 64 normal subjects and in 60 patients with compensated heart disease. This time interval was measured from the second heart sound of the phonocardiogram to the O point of the apex cardiogram. The range for normal values was 50 to 140 milliseconds, with a mean of 103 ± 22 milliseconds. In the patients with compensated heart disease this interval ranged from 58 to 175, with a mean of 102 ± 26 milliseconds. The standard error of the measurement was 4 per cent of the mean. 2. 2. Age itself did not influence the duration of isovolumic relaxation time. Heart rate, exercise and the administration of isoproterenol significantly decreased the isovolumic relaxation time. 3. 3. Digitalis significantly increased the duration of the isovolumic relaxation time, which may prove to be the basis for a useful and simple method of evaluating digitalization in man. 4. 4. Since this period of the cardiac cycle may be altered by pharmacologic means and by disease states, it may be a useful avenue to the study of the condition of ventricular function in man.