CHANGES OF HEART RATE DURING DIVING AND BREATH-HOLD AFTER EXERCISE

The influence of diving and breath-hold following different levels of exercise on the changes of heart rate was investigated in male humans. The subjects had to swim against variable forces, until their heart rate had reached mean values of 80, 100, 120, and 140 beats min-1. 5-10 sec, after diving had started, the heart rate began to decrease and reached values of 50-60 min-1 which were independent from the starting level. The corresponding values recorded during breath-hold in water without diving were found to be about 20% higher. About 20 sec after the end of diving or breath-hold the heart rate was 10-20% lower than its starting level. It is discussed that the effect is due to an isolated augmentation of vagal tone on the heart which is elicited from stretch receptors of the right heart and the pulmonary trunk. The threshold of these receptors seems to be exceeded by the combined pressure effects of immersion and inspiration on the central blood volume. The diving reflex" in man generally seems to be an effect of a general augmentation of sympathetic tonus caused by the preliminary exercise or oxygen lack combined with an isolated increase in the heart vagal tonus. © 1969 Springer-Verlag."