AUTHOR=Zhao Jinfeng , Ding Yanfeng , Kline Geoffrey P. , Zhou Zhengyang , Mallet Robert T. , Shi Xiangrong 

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

JOURNAL=Frontiers in Physiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.989635

DOI=10.3389/fphys.2022.989635

ISSN=1664-042X

ABSTRACT=<p><bold>Background:</bold> 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.</p><p><bold>Methods</bold>: Seven elderly men (70.3 ± 6.0 years old) and nine women (69.4 ± 5.5 years old) breathed 10% O<sub>2</sub> for 5 min while arterial (SaO<sub>2</sub>; transcutaneous photoplethysmography) and cerebral tissue O<sub>2</sub> saturation (ScO<sub>2</sub>; near-infrared spectroscopy), ventilatory frequency, tidal volume, minute-ventilation, and partial pressures of end-tidal O<sub>2</sub> (P<sub>ET</sub>O<sub>2</sub>) and CO<sub>2</sub> (mass spectrometry) were continuously monitored. Cerebral tissue oxygen extraction fraction (OEF) equaled (SaO<sub>2</sub>–ScO<sub>2</sub>)/SaO<sub>2</sub>.</p><p><bold>Results:</bold> During 5 min hypoxia SaO<sub>2</sub> 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 ΔSaO<sub>2</sub>/min was steeper in the women than the men (−4.71 ± 0.96 vs. −3.24 ± 0.76%/min; <italic>p</italic> = 0.005). Although SaO<sub>2</sub> fell twice as sharply per unit decrease in P<sub>ET</sub>O<sub>2</sub> in the women than the men (−1.13 ± 0.11 vs. −0.54 ± 0.06%/mmHg; <italic>p</italic> = 0.003), minute-ventilation per unit hypoxemia increased less appreciably in the women (−0.092 ± 0.014 vs. −0.160 ± 0.021 L/min/%; <italic>p</italic> = 0.023). OEF fell with hypoxia duration in the women, but remained stable in the men.</p><p><bold>Conclusion:</bold> 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<sub>2</sub> dissociation from hemoglobin during hypoxia. These sex-related differences merit attention when implementing brief hypoxic exposures for therapeutic purposes.</p>