Figure 2. Chemoreflex threshold changes.

The variation of mean ±s.e.m. chemoreflex threshold (V˙_E,T1), determined from the ventilatory responses to hypoxic (iso-oxic) rebreathing tests for all volunteers, with day of exposure, before (□) and after (□) daily 20 min exposures to isocapnic (eucapnic) hypoxia. A strong negative correlation was found between threshold and days of exposure before the exposures but not after. The post-hypoxia thresholds were significantly higher than the pre-hypoxia thresholds from day 8 onwards.