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

Exercise-induced arterial hypoxemia (EIAH) has been reported in male athlet es, particularly during fast-increment treadmill exercise protocols. Recent reports suggest a higher incidence in women. We hypothesized that 1-min in cremental (fast) running (R) protocols would result in a lower arterial Po- 2 (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 O-2 uptake ((V) over dot o(2max)) = 51 ml . k g(-1) . min(-1)]. They were studied in random order (C or R), with a fast ( V) over dot o(2max) protocol. After recovery, the women performed 5 min of exercise at 30, 60, and 90% of (V) over dot o(2max) (slow). One week later, the other exercise mode (R or C) was similarly studied. There were no sign ificant differences in (V) over dot o(2max) between R and C. Pulmonary gas exchange was similar at rest, 30%, and 60% of (V) over dot o(2max). At 90% of (V) over dot o(2max), Pa-o2 was lower during R (mean +/- SE = 94 +/- 2 T orr) 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 Pco(2) (32.0 +/- 0.5 vs. 30. 0 +/- 0.6 Torr, P < 0.001) and alveolar-arterial O-2 difference (A-aDo(2); 22 +/- 2 vs. 16 +/- 2 Torr, P < 0.0001) were greater during R. Pao(2) and A -aDo(2) were similar between slow and fast. Nadir Pa-o2 was less than or eq ual to 80 Torr in four women (24%) but only during fast-R. In all subjects, Pa-O2 at (V) over dot o(2max) was greater than the lower 95% prediction li mit calculated from available data in men (n = 72 C and 38 R) for both R an d 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 Pa-O2 responses to R and C exercise in our 17 subjects do not differ si gnificantly from those previously observed in men.