Journal of Applied Physiology, Vol 70, Issue 4 1770-1774, Copyright © 1991 by American Physiological Society
Exercise endurance and arterial desaturation in normobaric hypoxia with increased chemosensitivity
G. G. Giesbrecht, A. Puddy, M. Ahmed, M. Younes and N. R. Anthonisen
Respiratory Investigation Unit, University of Manitoba, Winnipeg, Canada.
We studied whether exercise endurance under normobaric hypoxia can be
enhanced by increasing hypoxic ventilatory sensitivity with almitrine
bismesylate (ALM). On both ALM and placebo (PL) days, resting subjects
breathed a hypoxic gas mixture (an inspired O2 fraction of 10.4-13.2%),
which lowered resting arterial O2 saturation (SaO2) to 80%. After 15 min of
rest there was a 3-min warm-up period of exercise at 50 W (light) on a
cycle ergometer, followed by a step increase in load to 60% of the
previously determined maximum power output with room-air breathing
(moderate), which was maintained until exhaustion. With PL, SaO2 decreased
rapidly with the onset of exercise and continued to fall slowly during
moderate exercise, averaging 71.0 +/- 1.8% (SE) at exhaustion. With ALM,
saturation did not differ from PL during air breathing but significantly
exceeded SaO2 with PL, by 3.4% during resting hypoxia, by 4.0% at the start
of exercise, and by 5.9% at exhaustion. Ventilation was not affected by ALM
during air breathing and was slightly, although not significantly,
increased during hypoxic rest and exercise. ALM was associated with an
increased heart rate during room air breathing but not during hypoxia.
Endurance time was 20.6 +/- 1.6 min with ALM and 21.3 +/- 0.9 min with PL.
During hypoxic exercise, the potential benefit of greater saturation with
ALM is apparently offset by other unidentified factors.
