Effects of various levels of hypoxia on plasma catecholamines at rest and during exercise.

The purpose of this study was to investigate the relationship between hypoxia and heart rate (HR), pulmonary ventilation, plasma epinephrine (E) and norepinephrine (NE) at rest and during exercise at 40% of maximal oxygen uptake. Six subjects were exposed to inspired gas mixtures containing 21%, 19%, 17%, 15%, and 13% O2. The duration of exposure to each mixture was 10 continuous min at rest, followed by 10 continuous min during exercise. The order of the inspired gas mixtures was randomized. During the exercise test, HR was elevated with exposure to 15% and 13% O2 (p less than 0.001). Pulmonary ventilation was higher at 13% O2 than at the higher O2 percents (p less than 0.001). There were no significant changes in plasma E or NE at rest or during exercise in response to the gas treatments. These results indicate that acute exposure to hypoxic gas mixtures at rest and during light work does not result in significant increases in sympathetic nervous system activity, as judged by the plasma E and NE response.