title: Cough frequency and cough-receptor sensitivity are increased in man at altitude.
abstract: 1. Travellers to high altitude often complain of paroxysmal cough, which has not been previously investigated. We recorded overnight cough frequency and cough-receptor sensitivity to inhaled citric acid in a group of climbers travelling to 5300 m or higher. 2. Cough frequency, monitored in ten subjects, increased from a median of 0 coughs at sea level (range 0-1) to 5 coughs at 5000 m (range 0-13) and to over 60 coughs in subjects ascending to 7000 m. Citric acid cough threshold, measured in 42 subjects, was unchanged on arrival at 5300 m compared with sea level (geometric mean difference 1.26, 95% confidence intervals 0.84-1.89, P = 0.25), but was significantly reduced after 6 days, or more, at altitude compared with sea level (geometric mean difference 2.2, 95% confidence intervals 1.54-3.15, P = 0.0002). Cough threshold was not related to symptoms of acute mountain sickness, oxygen saturation, carbon dioxide tension or lung function. 3. These results indicate an increase in cough and cough-receptor sensitivity after some days at altitude. This may be due to respiratory tract damage from breathing cold dry air at increased ventilatory rates. Other explanations, such as sub-clinical pulmonary oedema or an effect on the cough centre of acclimatization to altitude, cannot be excluded.
authors.affiliation: Department of Child Health, University of Leicester, Leicester Royal Infirmary, U.K.
authors.forename: P W
authors.initials: PW
authors.lastname: Barry
authors.forename: N P
authors.initials: NP
authors.lastname: Mason
authors.forename: M
authors.initials: M
authors.lastname: Riordan
authors.forename: C
authors.initials: C
authors.lastname: O'Callaghan
mesh_terms: D000531:Altitude; D001985:Bronchial Provocation Tests; D019343:Citric Acid; D003371:Cough / Q000139:chemically induced / Q000209:etiology*; D006801:Humans; D009330:Nebulizers and Vaporizers; D011984:Sensory Receptor Cells / Q000503:physiopathology; D012684:Sensory Thresholds / Q000502:physiology
chemical_list: D019343:Citric Acid