Comparison of effects of sustained isocapnic hypoxia on ventilation in men and women

Sleep-related respiratory disturbances are more common in men than in premenopausal women. This might, in part, be due to different susceptibilities to the respiratory depressant effects of hypoxia. Therefore, we compared ventilation during 10 min of baseline room-air breathing and 20- min sustained isocapnic hypoxia (fractional inspired O₂ = 11%, arterial saturation of O₂ ≃ 80%) followed by 10 min of breathing 100% O₂ in 10 normal men and in 10 women in the follicular phase of the menstrual cycle. Control measurements were made during two transitions from room air (10 min) to 100% O₂ (10 min) and averaged. Inspired minute ventilation (VI) after 2 min of hypoxia was the same in men and women [131 ± 6.1% baseline for men, 136 ± 7.7% baseline for women; not significant (NS)] and declined to the same level after 20 min (115 ± 5.0% baseline for men, 116 ± 6.6% baseline for women; NS) associated with a similar decline in inspiratory time and tidal volume. Breathing frequency did not change. V(I) decreased transiently during subsequent 100% O₂ breathing in both men and women, associated with reduced frequency and duty cycle and increased expiratory time. The fall in V(I) was significantly greater than that observed during control hyperoxia experiments in men but not in women. We conclude that ventilatory responses to sustained isocapnic hypoxia do not differ between awake healthy men and women in the follicular phase of their menstrual cycle. However, after termination of isocapnic hypoxia, men appear to depress their ventilation to a greater degree than women.