Circulatory Changes During Recovery from Intense Exertion

Abstract

Simultaneous measurements were made of pulse rate (continuous), systolic and diastolic blood pressures (1/2-minute intervals), pulmonary ventilation, oxygen consumption, and carbon dioxide elimination (10-20 consecutive samples) during the half hour following the fastest possible run upstairs, viz., 17 meters (5 flights) in 1/2-3/4 of a minute. The subjects were 20 young adults and 100 adolescent children—50 boys and 50 girls—and were resting supine while the measurements were made both in basal conditions before and also after the exercise. Fig. 1 shows the result of a typical experiment. At first the pulse rate and pulse pressure were high and the diastolic pressure usually more or less low. The adults showed a maximum drop of 25 mm. Hg. and the children showed a maximum drop of 65 mm. Hg. below the basal value. Twenty-two percent of the children showed a drop of more than 25 mm. Hg., which was the greatest drop shown by any adult. Low diastolic pressure with raised pulse rate and pulse pressure would appear to imply that arterial relaxation has taken place. The ensuing simultaneous decrease of pulse pressure and pulse rate indicates falling cardiac output (a phenomenon measured by Lindhard in similar circumstances), and the simultaneous rise in the diastolic pressure which we observed can only have been accomplished by a vaso-constriction decreasing the peripheral resistance faster than the cardiac output dropped. Variations in the time and intensity relations of these 2 vascular responses-relaxation followed by constriction-which appear to have been present in every case, can be held to account for all the types of diastolic pressure curves obtained on the basis of the 3 type curves shown in the diagram (Fig. 2). Although for convenience of discussion the diagram emphasizes 3 distinct types, all the intermediate varieties of curves were found between these types. All our data may be considered in one or other of these categories as far as the continuous lines are concerned.