Acute hypoxia and related symptoms on mild exertion at simulated altitudes below 3048 m

Helicopter aircrew have reported features of hypoxia below 3048 m (10,000 ft). The aim of this study was to examine the effect of physical activity below 3048 m on the development of hypoxia.

Six subjects exercised at 30 W and 60 W for 4 min at sea level, 610 m, 2134 m, and 2743 m (2000 ft, 7000 ft, and 9000 ft).

There was an abrupt decrease in Spo2 once physical activity was commenced. This was small at sea level (1%) and 610 m (2.2%), however, the Spo2 fell by 4.3% at 2134 m and 5.5% at 2743 m (to Spo2 88.1% and 85.7%, respectively). Spo2 returned to near-resting values within 3 min of stopping exercise. Symptoms of hypoxia were reported significantly more frequently during activity than rest at each of the altitudes.

Helicopter aircrew should be aware that physical activity as low as 2134 m can produce hypoxemia and symptoms of hypoxia similar to that which would normally be expected in a person resting at approximately 3658-4572 m (12,000-15,000 ft).