Hypoxic breathing produces more intense hypoxemia in elderly women than in elderly men

Background: Brief hypoxic exposures are increasingly applied as interventions for aging-related conditions. To optimize the therapeutic impact of hypoxia, knowledge of the sex-related differences in physiological responses to hypoxia is essential. This study compared hypoxia-induced hypoxemic responses in elderly men and women. Methods: Seven elderly men (70.3 +/- 6.0 years old) and nine women (69.4 +/- 5.5 years old) breathed 10% O-2 for 5 min while arterial (SaO(2); transcutaneous photoplethysmography) and cerebral tissue O-2 saturation (ScO2; near-infrared spectroscopy), ventilatory frequency, tidal volume, minute-ventilation, and partial pressures of end-tidal O-2 (PETO2) and CO2 (mass spectrometry) were continuously monitored. Cerebral tissue oxygen extraction fraction (OEF) equaled (SaO(2)-ScO2)/SaO(2). Results: During 5 min hypoxia SaO(2) fell from 97.0 +/- 0.8% to 80.6 +/- 4.6% in the men and from 96.3 +/- 1.4% to 72.6 +/- 4.0% in the women. The slope delta SaO(2)/min was steeper in the women than the men (-4.71 +/- 0.96 vs. -3.24 +/- 0.76%/min; p = 0.005). Although SaO(2) fell twice as sharply per unit decrease in PETO2 in the women than the men (-1.13 +/- 0.11 vs. -0.54 +/- 0.06%/mmHg; p = 0.003), minute-ventilation per unit hypoxemia increased less appreciably in the women (-0.092 +/- 0.014 vs. -0.160 +/- 0.021 L/min/%; p = 0.023). OEF fell with hypoxia duration in the women, but remained stable in the men. Conclusion: During 5 min hypoxic breathing, elderly women experience more intense hypoxemia and reduced chemoreflex sensitivity vs. their male counterparts, which may lower OEF stability in women despite augmented O-2 dissociation from hemoglobin during hypoxia. These sex-related differences merit attention when implementing brief hypoxic exposures for therapeutic purposes.