Women candidates for diving with oxygen-enriched gas mixtures have a lower end tidal CO2 than men during moderate exercise

We have previously determined the thresholds for CO2 detection (conscious recognition of elevated CO2) and retention in male divers, beyond which a diving candidate should not continue his diving activity due to an increased risk of CNS oxygen toxicity. The purpose of the present study was to establish whether there is a difference in end tidal PCO2 between male and female divers who use oxygen-enriched gas mixtures. Ventilatory and perceptual responses to variations in inspired CO2 (range 0-42 mmHg) were assessed during moderate exercise in 18 males and 18 females. End tidal PCO2 was lower in the female divers when breathing oxygen with 42 mmHg CO2 (58.2 ± 3.0 mmHg vs. 61.5 ± 4.5 mmHg, P < 0.03). These results suggest that female divers have a lower end tidal CO2 than males when breathing a hyperoxic gas mixture during exercise, which might imply that women are less susceptible to CNS oxygen toxicity than men.