Study objectives: The inhalation of hypoxic gas has
been reported to enhance the airway responsiveness to methacholine in
some animal models. However, the data on humans have so far been
conflicting. We attempted to examine the effect of hypoxic gas
inhalation on the airway responsiveness to methacholine.
Design: We evaluated the airway responsiveness to
methacholine by continuously measuring respiratory conductance with the
forced oscillation method under normoxia or hypoxia in a single-blind,
randomized, crossover fashion (2 days for each).
Participants: Twelve asymptomatic male volunteers
(mean ± SD age, 27 ± 4 years) with airway hyperresponsiveness to
methacholine. Two of the 12 volunteers had a history of bronchial
Setting: The participants inhaled
either normoxic or hypoxic gas with continuous inhalation of
aerosolized methacholine in incremental doses with a sustained
respiratory rate of 15 breaths/min. The arterial oxygen saturation was
kept to 90% on the hypoxic days.
There were no significant differences in any indexes of airway
responsiveness to methacholine (the cumulative dose of methacholine at
the threshold and the point of 35% decrease of the respiratory
conductance, and the slope factor of the dose-response curve) between
the hypoxic days and the normoxic days.
The inhalation of mildly hypoxic gas does not enhance the airway
responsiveness to methacholine in humans with airway