Repeated exercise-induced arterial hypoxemia in a healthy untrained woman

Abstract

A healthy 36-year-old untrained (maximal oxygen consumption (V˙O2max): 39mL/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 (−13mmHg arterial oxygen tension decrease) and arterial oxyhemoglobin desaturation (−6% decrease) was observed 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% O2) 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% O2) inspirate, increased exercise duration (+45s) and V˙O2max (+5mL/kg/min). We attribute the hypoxemia to an excessive A–aO2 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.