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

Sajkov, Dimitar, Alister Neill, Nicholas A. Saunders, and R. Douglas McEvoy. Comparison of the effects of sustained isocapnichypoxia on ventilation in men and women. J. Appl.Physiol. 83(2): 599-607, 1997.Sleep-relatedrespiratory disturbances are more common in men than in premenopausalwomen. This might, in part, be due to different susceptibilities to therespiratory depressant effects of hypoxia. Therefore, we comparedventilation during 10 min of baseline room-air breathing and 20-minsustained isocapnic hypoxia (fractional inspiredO₂ = 11%, arterial saturation ofO₂  80%) followed by 10 min ofbreathing 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) andaveraged. Inspired minute ventilation(I) after2 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.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 inI wassignificantly greater than that observed during control hyperoxiaexperiments in men but not in women. We conclude that ventilatoryresponses to sustained isocapnic hypoxia do not differ between awakehealthy 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.