Hypoxemia in healthy subjects at moderate altitude

Healthy individuals are known to have significantly reduced oxygen saturations at rest when acutely exposed to moderate altitudes, such as during commercial flight. There is a paucity of data on the response of healthy individuals to exercise at these altitudes. The aim of this study was to establish the normal response to exercise during acute, moderate altitude exposure with regard to oxygen saturations. Secondary aims were to establish if this response can be predicted from pulmonary function measurements at sea level.

At sea level, 20 subjects performed pulmonary function tests, including submaximal steady state exercise, followed by replication of submaximal steady state exercise during acute altitude exposure at 6844 ft (2086 m).

Mean resting oxygen saturation at 6844 ft (2086 m) was 96%, a significant reduction from the sea level value of 99%. Mean nadir oxygen saturation during steady state exercise at moderate altitude was 89%. There was a weak negative correlation between aerobic capacity and end exercise oxygen saturation at altitude. Modified BORG dyspnea scores were unchanged at rest at 6844 ft (2086 m) and higher post-exercise at 6844 ft (2086 m) when compared to sea level, although absolute values were low.

Healthy individuals desaturate at rest and upon exercise during acute altitude exposure at 6844 ft (2086 m). A quarter of participants experienced SpO2 < or = 85% upon exercise at altitude, although this had no correlation with dyspnea scores or baseline pulmonary function measurements. The weak negative correlation between aerobic capacity and end exercise oxygen saturation is unexplained and merits further research.