Figure 1. Comparison of respiratory responses.

A, mean (±s.e.m.) end-tidal partial pressures of oxygen and carbon dioxide and ventilatory responses to isocapnic (eucapnic) hypoxia are greater on day 14 (filled symbols) than on day 1 (open symbols). Variables were binned (1 min) and averaged for all volunteers. B, the ventilatory response to hypoxic iso-oxic rebreathing of a representative volunteer before (open symbols) and after (filled symbols) a single 20 min exposure to isocapnic (eucapnic) hypoxia on day 8, showing a post-hypoxic increase in threshold. C, the ventilatory response to iso-oxic (hypoxic) rebreathing of a representative volunteer before a single 20 min exposure to isocapnic (eucapnic) hypoxia on day 1 (open symbols) and day 14 (filled symbols), showing a decrease in chemoreflex threshold (V˙_E,T1) with daily hypoxic exposures.