title: Hyperventilation-induced asthma: evidence for two mechanisms.
abstract: The mechanism by which airway cooling induces airflow obstruction in asthmatic subjects has not yet been established. Using a pair of isocapnic hyperventilation challenges, with a 40-minute interval, we looked for the presence of a refractory period in 19 asthmatic patients (aged 9-18 years). The subjects fell into two groups. The eight in the "non-refractory" group showed less than a 25% reduction in response to the second challenge, but the 11 in the "refractory" group showed at least a 35% reduction. Twelve subjects also performed a hyperventilation challenge after cholinergic blockade with inhaled ipratropium bromide. In five, in whom no refractoriness after hyperventilation was seen, there was a significant protection from cholinergic blockade (p less than 0.05). In these a vagal (cholinergic) reflex seems likely. The remaining seven, who had a refractory period, received no significant protection from cholinergic blockade and therefore no evidence for the presence of any cholinergic mechanism. We conclude that two mechanisms are responsible for hyperventilation-induced asthma, one of which is a vagal reflex while mediator release may be the other.
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000503:physiopathology*; D001250:Asthma, Exercise-Induced / Q000503:physiopathology*; D001286:Atropine Derivatives / Q000494:pharmacology*; D002648:Child; D006801:Humans; D009241:Ipratropium / Q000494:pharmacology*; D008688:Methacholine Compounds / Q000494:pharmacology; D010366:Peak Expiratory Flow Rate; D012018:Reflex / Q000187:drug effects; D012119:Respiration; D014630:Vagus Nerve / Q000503:physiopathology
chemical_list: D001286:Atropine Derivatives; D008688:Methacholine Compounds; D009241:Ipratropium