Exercise-induced arterial hypoxaemia in healthy young women

1. We questioned whether exercise-induced arterial hypoxaemia (EIAH) occurs in healthy active women, who have smaller lungs, reduced lung diffusion, and lower maximal O-2, consumption rate (V(over dot)(O?2,max)) than age-and height-matched men. 2. Twenty-nine healthy young women with widely varying fitness levels (V(over dot)(O?2,max), 57 +/- 6 ml kg(-1) min(-1); range, 35-70 ml kg(-1) min(-1); or 148 +/- 5%; range, 93-188% predicted) and normal resting lung function underwent an incremental treadmill test to V(over dot)(O?2,max) during the follicular phase of their menstrual cycle. Arterial blood samples were taken at rest and near the end of each workload. 3. Arterial P-O?2 (P-a,P-O?2) decreased > 10 mmHg below rest in twenty-two of twenty-nine subjects at V(over dot)(O?2,max) (P-a,P-O?2 77.5 +/- 0.9 mmHg; range, 67-84mmHg; arterial O-2 saturation (S-a,S-O?2)) 92.3 +/- 0.2%; range, 87-94%). The remaining seven subjects maintained P-a,P-O?2 within 10 mmHg of rest P-a,P-O?2 at V(over dot)(O?2,max) was inversely related to the alveolar to arterial O-2, difference (A-aDO(2)) (r = -0.93; 35-52 mmHg) and to arterial P-CO?2 (P-a,P-CO?2) (r = 0.62; 26-39 mmHg). 4. EIAH was inversely related to V(over dot )(O?2,max) (r = 0.49); however, there were many exceptions. Almost half of the women with significant EIAH had V(over dot)(O?2,max) within 15% of predicted normal values (V(over dot)(O?2,max) 40-55 ml kg(-1)min(-1)); among subjects with very high V(over dot)(O?2,max), (55-70 ml kg(-1)min(-1)), the degree of excessive A-aDO(2) and EIAH varied markedly (e.g. A-aDO(2), 30-50 mmHg; P-a,P-O?2 68-91 mmHg). 5. In the women with EIAH at V(over dot)(O?2,max) many began to experience an excessive widening of of their A-aDO(2), during moderate intensity exercise, which when combined with a weak ventilatory response, led to a progressive hypoxaemia. Inactive, less fit subjects had no EIAH and narrower A-aDO(2) when compared with active, fitter subjects at the same V(over dot)(O?2) (40-50 ml kg(-1) min(-1)). 6. These data demonstrate that many active healthy young women experience significant EIAH, and at a V(over dot)(O?2,max), that is substantially less than those in their active male contemporaries. The onset of EIAH during submaximal exercise, and/or its occurrence at a relatively low V(over dot)(O?2,max), implies that lung structure/function subserving alveolar to arterial O-2 transport is abnormally compromised in many of these habitually active subjects.