Pulmonary gas exchange during exercise in women: Effects of exercise type and work increment

Exercise-induced arterial hypoxemia (EIAH) has been reported in male athletes, particularly during fast-increment treadmill exercise protocols. Recent reports suggest a higher incidence in women. We hypothesized that 1-min incremental (fast) running (R) protocols would result in a lower arterial P(O₂) (Pa(O₂)) than 5-min increment protocols (slow) or cycling exercise (C) and that women would experience greater EIAH than previously reported for men. Arterial blood gases, cardiac output, and metabolic data were obtained in 17 active women [mean maximal O₂ uptake (VO(2 max)) = 51 ml · kg^-1 · min^-1]. They were studied in random order (C or R), with a fast VO(2 max)) protocol. After recovery, the women performed 5 min of exercise at 30, 60, and 90% of VO(2 max) (slow). One week later, the other exercise mode (R or C) was similarly studied. There were no significant differences in VO(2 max) between R and C. Pulmonary gas exchange was similar at rest, 30%, and 60% of VO(2 max). At 90% of VO(2 max), PaO₂ was lower during R (mean ± SE = 94 ± 2 Torr) than during C (105 ± 2 Torr, P < 0.0001), as was ventilation (85.2 ± 3.8 vs. 98.2 ± 4.4 l/min BTPS, P < 0.0001) and cardiac output (19.1 ± 0.6 vs. 21.1 ± 1.0 l/min, P < 0.001). Arterial PCO₂ (32.0 ± 0.5 vs. 30.0 ± 0.6 Torr, P < 0.001) and alveolar-arterial O₂ difference (A-aDO₂; 22 ± 2 vs. 16 ± 2 Torr, P < 0.0001) were greater during R. PaO₂ and A-aDO₂ were similar between slow and fast. Nadir PaO₂ was ≤80 Torr in four women (24%) but only during fast-R. In all subjects, PaO₂ at VO(2 max) was greater than the lower 95% prediction limit calculated from available data in men (n = 72 C and 38 R) for both R and C. These data suggest intrinsic differences in gas exchange between R and C, due to differences in ventilation and also efficiency of gas exchange. The PaO₂ responses to R and C exercise in our 17 subjects do not differ significantly from those previously observed in men.