Effects of Exercise on Changes in Arterial Oxygen Saturation and Psychomotor Performance during Mild Hypoxia
Matthew Greenfield
Introduction: Pilots of light aircraft, microlights and helicopters are increasingly flying above 13,000 feet without supplemental oxygen. Recently, commercial pulse oximeters have been marketed to aviation pilots to self-monitor arterial oxygen saturation as a surrogate method of determining mental impairment due to hypoxia. During hypoxia, arterial oxygen saturation alone is an unreliable guide to specific tissue oxygenation. Additionally, it is well documented that pilots when flying are not at rest and have a workload equivalent to light exercise. Most of the effects of hypoxia have been evaluated with subjects at rest. This study investigated the effect of light exercise on the changes seen in hypoxia induced by breathing air at a simulated altitude of 15,000 feet.
Methods: 7 healthy unacclimatized volunteers individually completed a psychomotor performance task (NASA Multi-Attribute Task (MAT) Battery) at ground level and on exposure to a simulated altitude of 15,000 feet in a hypobaric chamber. During both the ground and altitude sessions, subjects completed the psychomotor performance task whilst at rest and whilst performing exercise at 30 watts on an electromagnetically braked ergometer.
Results: No significant change in psychomotor performance was observed between ground and altitude either at rest or during light exercise. Arterial oxygen saturation decreased at altitude from a mean value at rest of 74.19% (±6.53) to 71.24% (±6.87) during exercise, but this decrease was not significant. A significant increase in the number and severity of hypoxia related symptoms was noted during exercise at altitude compared to rest (P<0.05). Likewise, a significant increase in subjective perceived effort was also noted (P<0.05).
Discussion: The study failed to show any significant effect of breathing ambient air at a simulated altitude of 15,000 feet on psychometric performance as measured by the MAT Battery compared to ground level. Light exercise also had no significant effect on psychomotor performance at either ground level or 15,000 feet. However, the observed physiological changes and increase in severity of symptoms with exercise suggests further investigation is required before important conclusions are made about the effect of light exercise on the hypoxia that occurs at this altitude. Correspondingly, the use of pulse oximeters for pilot self-assessment of hypoxia should be restricted.
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