CO2 Chemoreflex Drive of Ventilation in Man: Effects of Hyperoxia and Sex Differences

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Abstract
CO2 single breaths have been performed in 7 men and 7 women in conditions of normoxia (FICO2≈0.13; FIO2≈0.21; FIN2 6≈ 0.66) and of hyperoxia (FICO2≈0.13; FIO2≈0.87). Ventilatory responses of the subjects and modifications of breathing pattern in the course of the CO2 tests were also explored in the two conditions. The results (mean ± SEM) show that, whatever the oxygenation, men and women exhibit the same ventilatory response during a CO2 test from a qualitative point of view but with a smaller intensity in women (men: 0.37 ± 0.088 Lbtps min-1 Torr-1;women: 0.15 ± 0.025 LBTPS•min-1•Torr-1; p < 0.05). Considering men and women together, CO2 tests induced an increase of minute volume VE (p < 0.001), VT (p < 0.01) and rate of breathing (NS) but this response is decreased in hyperoxic conditions (p < 0.05) mainly in men (men: 0.19 ± 0.043 LBTPS•min-1•Torr1; women: 0.11 ± 0.023 LBTPS•min-1•Torr-1). These results show that sensitivity to transient hypercapnia and its interaction with hyperoxia are weaker in women than in men