Ventilatory response to CO₂ at rest and during positive and negative work in normoxia and hyperoxia

Summary

Ventilation versus alveolar$P_{CO_2 }$ relationships were determined by the steady-state method in 6 normal male subjects at rest and during positive and negative work at one load in both normoxic and hyperoxic condition. In 5 subjects the slopes of the$\dot V_E - P_{A_{CO_2 } }$ lines during positive and negative work increased in normoxia as compared with rest. This effect was less evident in hyperoxia. It was also found that the slopes of the$\dot V_E - P_{A_{CO_2 } }$ lines in positive and in negative work were about the same in both normoxic and hyperoxic conditions. Oxygen uptake and CO₂ production during positive work is higher than during negative work.

These results suggest that: 1) the disagreement between various authors on the change of the slope of the$\dot V_E - P_{A_{CO_2 } }$ line may be due to the differences in the method of calculation of the slope or the method of the determination of$\dot V_E - P_{A_{CO_2 } }$ lines; 2) the stimuli from the muscle spindles in the working muscle during exercise probably do not contribute to the increase in ventilatory response to CO₂; 3) the increased slope of the normoxic$\dot V_E - P_{A_{CO_2 } }$ line during exercise may be due to the interaction of several factors such as impulses from working muscles, chemosensitivity of central or peripheral chemoreceptors, adrenal-sympathetic pathways or temperature; 4) respiratory oscillations of$P_{A_{O_2 } }$ or$P_{A_{CO_2 } }$ do not seem to influence the respiratory response to CO₂.