Alveolar to arterial gas exchange during constant-load exercise in healthy active men and women

ABSTRACT

Inadequate hyperventilation and inefficient alveolar to arterial gas exchange are gas exchange challenges that can limit capacity and cause exercise-induced arterial hypoxaemia (EIAH). This work evaluated if the prevalence of gas exchange inefficiencies, defined as AaDO₂>25 mmHg, PaCO₂>38 mmHg, and/or ΔPaO₂>-10 mmHg at any point during constant-load exercise in healthy, active, but not highly trained, individuals suggested an innate sex difference that would make females more susceptible to EIAH. Sixty-four healthy, active males and females completed 18-min of cycling exercise (moderate and vigorous intensity, 9 min/stage). Arterial blood gases were measured at rest and every 3-min during exercise, while constantly assessing gas exchange. Both sexes demonstrated similar levels of AaDO₂ widening until the final 3 min of vigorous exercise, where females demonstrated a trend for greater widening than males (16.3±6.2 mmHg vs. 19.1±6.0 mmHg, p=0.07). Males demonstrated a blunted ventilatory response to moderate exercise with higher PaCO₂ (38.5±2.6 vs. 36.5±2.4, p=0.002) and a lower ventilation when corrected for workload (0.42±0.1 vs. 0.48±0.1, p=0.002). No significant arterial hypoxaemia occurred, but in 6 M and 5 F SaO₂ dropped by ≥2%. There was no difference in prevalence of pulmonary gas exchange inefficiencies between sexes, but the type of inefficiency was influenced by sex.

Abbreviations: AaDO₂: alveolar-arterial oxygen difference; BP: blood pressure; EIAH: exercise-induced arterial hypoxaemia; F: females; HR: heart rate; M: males; Q: cardiac output; PaCO₂: arterial partial pressure of carbon dioxide; PaO₂: arterial partial pressure of oxygen; ΔPaO₂: change in arterial partial pressure of oxygen; PAO₂: alveolar partial pressure of oxygen; RPE: rating of perceived exertion; SaO₂: arterial oxygen saturation; V_E: ventilation; V_E/VCO₂: ventilatory equivalent for carbon dioxide; VO_2PEAK: peak oxygen consumption; W_MAX: workload maximum

KEYWORDS:

• Sex
• exercise-induce arterial hypoxaemia
• PaO₂
• AaDO₂
• submaximal exercise
• cycling

Acknowledgments

We would like to thank Kathy O’Malley, Chris Johnson, and Shelly Roberts for their assistance with data collection. We also thank the participants for their effort. This work was supported by grant numbers HL71478 (BDJ) and 1KL2RR024151 (TPO) from the National Institutes of Health (NIH) and grant number 56051Z (EMS) from the American Heart Association. We also thank the staff of the Clinical Research Unit (CRU) for their assistance throughout this study. The Mayo Clinic CRU is supported by grant number 1UL1RR024150 from the National Center for Research Resources (NCRR). EMS, TPO, and BDJ were responsible for study design and data collection. JCS, CMW, and BDJ were responsible for analysis and manuscript writing. All authors read and approved the final manuscript.

Disclosure statement

JCS, CMW, EMS, and BDJ declare they have no conflict of interests.

Additional information

Funding

This work was supported by the American Heart Association [56051Z]; National Center for Research Resources [1UL1RR024150]; National Institutes of Health [HL71478]; National Institutes of Health [1KL2RR024151].