Aim Interval hypoxic training was proposed as a technique for adapting hypoxia of various origins. Its effects on the hypoxic ventilatory response and on cardiovascular autonomic control are unknown.

Methods and Results We recorded ventilation, end-tidal oxygen (PETO₂) and carbon dioxide partial pressures, RR interval and blood pressure during progressive isocapnic hypoxia, before and after 14 days of: (a) interval hypoxic training (three to four periods of 7min progressive hypoxia in 1h, each day) in 12 healthy men (training group); (b) breathing into a spirometer by six age-matched male controls. The hypoxic ventilatory response was estimated by the hyperbolic relationship between PETO₂and ventilation (shape factor A). Spectral analysis was used to characterize low- (mainly sympathetic) and high-frequency (vagal) cardiovascular fluctuations. Shape factor A was increased in the interval hypoxic training group from 268±59 to 984±196 l.mmHg⁻¹(P<0·003), but not in the control group (from 525±180 to 808±245 l.mmHg⁻¹,P =ns). Before interval hypoxic training, progressive hypoxia decreased, to a similar extent in both groups, mean RR, RR variability and high-frequency power. After interval hypoxic training, RR still decreased significantly, but the decrease in RR variability and high-frequency power was no longer significant in the training group. No significant changes were observed in blood pressure fluctuations. No changes were observed in the control group.

Conclusions Two weeks of interval hypoxic training increased the hypoxic ventilatory response, in association with reduced vagal withdrawal during progressive hypoxia.