Studies on circulatory, respiratory and thermal adaptation during heavy exercise.

Abstract

The behaviour of ventilation, rectal temperature, pulse rate, systolic blood pressure and peripheral circulation in man was examined during heavy exercise, taking special notice of the changes in the region of “dead point” (“toter Punkt”, DP). It was observed that the ventilation volume — both the tidal volume and the frequency — and the oxygen consumption reached their maximum values in DP, but the rise in ventilation was relatively greater than in oxygen consumption, and thus the ventilation equivalent for O2, rose in DP (hyperventilation). The pulse rate and also the skin blood flow as measured in the hand reached their highest values in DP in the same manner. The rectal temperature rose nearly equally until DP, but not any more in the “second wind”. The blood flow in resting muscles as measured in the forearm changed in the same way. The systolic blood pressure rose clearly at the beginning of exercise, hut changed only a little later in the first “steady state” and DP. ‘I’hen, in the “second wind” an obvious decrease occurred. A hypothesis is presented according to which the essential point in the origin of DP is a slight collapse due to the adaptation of the circulatory system to new conditions of heat loss, when the body temperature during work stabilizes at its final level.