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

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.