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Exercise-induced arterial hypoxemia in healthy young women; role of mechanical constraints to ventilation Dominelli, Paolo Biagio


Many young adult male athletes with a high maximal O₂ consumption (VO₂Max) show exercise-induced arterial hypoxemia (EIAH). In women, EIAH may occur at submaximal exercise intensities and at lower fitness levels, but this is controversial. Greater EIAH in women may be attributed to their increased mechanical constraints to ventilation owing to smaller airway diameters. Accordingly, the purpose of this study was to characterize EIAH, gas exchange and respiratory mechanics during exercise in young healthy women. Subjects (n=31, VO₂Max =48±1, range 28-62 mL/kg/min) completed a step-wise maximal test on a treadmill. A 3-stage constant load exercise test was also completed where the inspired gas was switched between room air and heliox (21% O₂: 79% He). Arterial blood gases (PaO₂, PaCO₂, pH), corrected for esophageal temperature, and oxyhemoglobin saturation (SaO₂) were measured at rest and during the last 30 s of each exercise stage. The work of breathing (WOB) was obtained using an esophageal balloon-tipped catheter. Expiratory flow limitation (EFL) was determined by superimposing tidal flow-volume loops on the maximum expiratory flow-volume curve. Twenty of the 31 women developed some degree of EIAH with a nadir PaO₂ and SaO₂ ranging from 58-103 mmHg and 87-98%; respectively. Subjects with EIAH were fitter (VO₂Max 51±1 vs. 42±2 mL/kg/min), had a greater VEMax (91±3 vs. 77±4 L/min) and had an increased resistive WOB (30±2 vs. 19±1 cmH₂O/breath); for the EIAH and non-EIAH groups respectively (P<0.05). Six untrained subjects (VO₂Max <50 mL/kg/min) developed EIAH and 18/20 of the EIAH group were hypoxemia at submaximal intensities. Six distinct patterns of hypoxemia were observed indicating multiple mechanisms are responsible for EIAH in women. Fourteen subjects developed EFL and 12/14 who showed flow limitation also displayed EIAH. Inspiring heliox gas decreased the WOB by ~32% and partially reversed any EIAH. In conclusion, the pulmonary system response to progressive treadmill exercise in healthy young women is variable and distinct patterns of EIAH exist. EIAH appears to start at submaximal intensities and untrained women can develop hypoxemia. Mechanical ventilatory constraints can lead to or exacerbate EIAH in women, while inspiring heliox gas can partially reverse EIAH.

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