Repeated exercise-induced arterial hypoxemia in a healthy untrained woman

A healthy 36-year-old untrained (maximal oxygen consumption ((V) over dot(O2) (max)): 39 mL/kg/min) woman completed multiple graded exercise tests on a treadmill. Temperature-corrected arterial blood samples were obtained in addition to esophageal pressure. Significant hypoxemia (-13 mmHg arterial oxygen tension decrease) and arterial oxyhemoglobin desaturation (-6% decrease) was absented relative to rest and occurred during submaximal exercise and worsened at maximal intensities. Expiratory flow limitation (28-40% intersection of tidal volume) was present at near-maximal intensities. Relieving mechanical ventilatory constraints with a helium inspirate (79% He:21% O-2) partially reversed the hypoxemia. Conversely, increasing chemical ventilatory stimuli, with hypercapnia (3.5% CO2), failed to increase ventilation. Maintaining oxyhemoglobin saturation, via a mildly hyperoxic (26% O-2) inspirate, increased exercise duration (+45 s) and (V) over dot(O2 max) (+5 mL/kg/min). We attribute the hypoxemia to an excessive A-aO(2) resulting from ventilation-perfusion mismatch and secondarily to mechanical ventilatory constraints. We conclude that a healthy untrained woman can develop EIAH and this remains stable over a period of 6 months. (C) 2012 Elsevier By. All rights reserved.