Effect of acute alterations in inspired oxygen tension on methacholine induced bronchoconstriction in patients with asthma

BACKGROUND: Recent in vitro and in vivo studies in animals have suggested that ambient oxygen tension may influence airway responsiveness to bronchoconstrictor stimuli. These observations may have relevance to the management of acute exacerbations of asthma. The present studies were designed to exam...

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Bibliographic Details
Published in:Thorax 1997-05, Vol.52 (5), p.453-457
Main Authors: Dagg, K D, Thomson, L J, Clayton, R A, Ramsay, S G, Thomson, N C
Format: Article
Language:English
Subjects:
Administration, Inhalation
Adult
Asthma - blood
Asthma - physiopathology
Biological and medical sciences
Bronchial Provocation Tests
Bronchoconstrictor Agents
Chronic obstructive pulmonary disease, asthma
Double-Blind Method
Female
Forced Expiratory Volume
Heart Rate - drug effects
Humans
Male
Medical sciences
Methacholine Chloride
Oxygen - administration & dosage
Oxygen - blood
Pneumology
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Summary:BACKGROUND: Recent in vitro and in vivo studies in animals have suggested that ambient oxygen tension may influence airway responsiveness to bronchoconstrictor stimuli. These observations may have relevance to the management of acute exacerbations of asthma. The present studies were designed to examine the influence of inspired oxygen tension (Fio2 1.0, 0.21, 0.15) on methacholine-induced broncho-constriction in patients with asthma. METHODS: In a dual study two groups of asthmatic patients performed methacholine inhalation challenges breathing either air (Fio2 0.21) or a hypoxic gas mixture (Fio2 0.15) in study 1 and air (Fio2 0.21) or hyperoxia (Fio2 1.0) in study 2. The gases were administered through a closed breathing circuit in a randomised double blind fashion. The PC20 values (dose of methacholine causing a 20% fall in forced expiratory volume in one second (FEV1) were calculated after each methacholine challenge by linear interpolation from the logarithmic dose response curve. Plasma catecholamine levels were measured before and after methacholine challenges as well as heart rate, oxygen saturation, and percentage end tidal carbon dioxide levels. RESULTS: The geometric mean PC20 value for methacholine was significantly lower on the hypoxic study day than on the normoxic day in study 1 (mean difference in PC20 values 2.88 mg/ml (95% CI 1.4 to 5.3); p < 0.05), but there was no significant difference in the geometric mean PC20 value for methacholine between the hyperoxic and normoxic study days in study 2 (mean difference in PC20 values 1.45 mg/ ml (95% CI 0.83 to 2.51)). CONCLUSIONS: Acute hypoxia potentiates methacholine induced bronchoconstriction and acute hyperoxia has no effect in mild to moderate patients with stable asthma.
ISSN:0040-6376
1468-3296
DOI:10.1136/thx.52.5.453