Respiratory and cardiovascular adaptations to progressive hypoxia - Effectof interval hypoxic training

Aim Interval hypoxic training was proposed as a technique for adapting hypo xia 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 c arbon dioxide partial pressures, RR interval and blood pressure during prog ressive isocapnic hypoxia, before and after 14 days of: (a) interval hypoxi c 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 b y six age-matched male controls. The hypoxic ventilatory response was estim ated by the hyperbolic relationship between PETO2 and ventilation (shape fa ctor A). Spectral analysis was used to characterize low- (mainly sympatheti c) and high-frequency (vagal) cardiovascular fluctuations. Shape factor A w as increased in the interval hypoxic training group from 268+/-59 to 984 +/ - 196 1.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, progres sive hypoxia decreased, to a similar extent in both groups, mean RR, RR var iability and high-frequency power. After interval hypoxic training, RR stil l decreased significantly, but the decrease in RR variability and high-freq uency power was no longer significant in the training group. No significant changes were observed in blood pressure fluctuations. No changes were obse rved in the control group. Conclusions Two weeks of interval hypoxic training increased the hypoxic ve ntilatory response, in association with reduced vagal withdrawal during pro gressive hypoxia. (Eur Heart J 2001; 22: 879-886, doi:10.1053/euhj.2000.246 6) (C) 2001 The European Society of Cardiology.