Dynamic ventilatory responses of females and males to acute isocapnic and poikilocapnic hypoxia

The human ventilatory response during acute hypoxia appears to be biphasic (growth and decay), but the effect of sex on the size and timing of this response is not known. We studied the effects of 15 min of poikilocapnic and isocapnic hypoxia (FiO2 ≈ 0.10) on ventilation (V˙i) in 14 healthy female and 13 healthy male subjects. Parameters (amplitudes, time delays, time constants) describing individual V˙i responses were estimated using a biexponential function. There were no significant effects of sex on any of these parameters. CO2 regulation significantly altered the amplitudes of growth and decay phases and the onset of the latter phase in females and males. These human data suggest that sex does not affect the biphasic response of ventilation during hypoxia. However, additional evidence in this study suggests that sex influences the breathing frequency response during hypoxia and that this effect depends on the control of CO2.