Changes of ventilation and ventilatory response to hypoxia during the menstrual cycle.

The relationship between change in hypoxic sensitivity in respiration, defined as increment in ventilation per drop of arterial O2 saturation (delta VE/delta SaO2), with the phase change from follicular to luteal and those in resting pulmonary ventilation (VE), mean inspiratory flow (VT/TI), alveolar partial pressures of CO2 and O2 (PACO2 and PAO2, respectively) and body temperature was studied in 10 women. There was a significant relationship between % increase in hypoxic sensitivity and decrement of resting PACO2 that occurred in the luteal phase. However, no significant relationships were observed between change in hypoxic sensitivity and those in the remaining parameters studied. The intersubject variation in % increase in resting VE during the luteal phase was not associated with that in % increase in hypoxic sensitivity. The results indicate that the contribution of increased hypoxic sensitivity to increasing VE during the luteal phase is variable among subjects. Reasons for the increase in hypoxic sensitivity with hypocapnia are discussed.