Respiratory and cardiovascular adaptations to progressive hypoxia

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 7 min progressive hypoxia in 1 h, 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 PETO2 and 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