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University Laboratory of Physiology, University of Oxford, Oxford OX1 3PT, United Kingdom
Ventilatory acclimatization to
hypoxia is associated with an increase in ventilation under conditions
of acute hyperoxia
(
Ehyperoxia) and an increase in acute hypoxic ventilatory response (AHVR). This
study compares 48-h exposures to isocapnic hypoxia
( protocol I) with 48-h
exposures to poikilocapnic hypoxia ( protocol
P) in 10 subjects to assess the importance of
hypocapnic alkalosis in generating the changes observed in ventilatory
acclimatization to hypoxia. During both hypoxic exposures,
end-tidal PO2 was maintained at
60 Torr, with end-tidal PCO2 held at the subject's prehypoxic level
( protocol I) or uncontrolled
( protocol P).
Ehyperoxia
and AHVR were assessed regularly throughout the exposures.
Ehyperoxia
(P < 0.001, ANOVA) and AHVR
(P < 0.001) increased during the
hypoxic exposures, with no significant differences between
protocols I and
P. The increase in
Ehyperoxia
was associated with an increase in slope of the
ventilation-end-tidal PCO2 response
(P < 0.001) with no significant
change in intercept. These results suggest that changes in respiratory
control early in ventilatory acclimatization to hypoxia
result from the effects of hypoxia per se and not the alkalosis
normally accompanying hypoxia.
ventilation; acclimatization; alkalosis
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