Effects of positive and negative exercise on ventilatory CO2 sensitivity

Investigations in our laboratory have shown an increased slope of the ventilatory response curve to CO₂ (CO₂ sensitivity) during positive and negative exercise as compared with the resting condition. CO₂ sensitivity during positive and negative exercise did not differ in spite of differences in metabolism ( \(\dot V\) O₂, \(\dot V\) CO₂) and type of muscle contraction (concentric or eccentric). Various aspects of positive and negative exercise were examined in order to find out whether they can explain the identical CO₂ sensitivity. Cardiac output, oxygen consumption, rectal temperature and venous catecholamine concentration appeared to be higher in positive exercise than in negative exercise, and higher in negative exercise than at rest. However, these differences between the two types of exercise contrast with the identical CO₂ sensitivity and thus cannot be of major importance in determining CO₂ sensitivity. It is hypothesized that one or more of these variables might be responsible for increased CO₂ sensitivity during exercise as compared with rest. The CO₂ sensitivity, once increased, seems to be unaffected by further increases in these variables.