title: The citric acid cough threshold and the ventilatory response to carbon dioxide on ascent to high altitude.
abstract: Ventilatory control undergoes profound changes on ascent to high altitude. We hypothesized that the fall in citric acid cough threshold seen on ascent to altitude is mediated by changes in the central control of cough and would parallel changes in central ventilatory control assessed by the hypercapnic ventilatory response (HCVR). Twenty-five healthy volunteers underwent measurements of HCVR and citric acid sensitivity at sea level and during a 9 day sojourn at 5200m. None of the subjects had any evidence of respiratory infection. Citric acid cough threshold fell significantly on ascent to 5200m. The slope, S, of the HCVR increased significantly on ascent to 5200m and during the stay at altitude. There was no correlation between citric acid sensitivity and HCVR. We conclude that the change in citric acid cough threshold seen on exposure to hypobaric hypoxia is unlikely to be mediated by changes in the central control of cough. Sensitivity to citric acid may be due to early subclinical pulmonary edema stimulating airway sensory nerve endings.
authors.affiliation: Academic Unit of Respiratory Medicine, University of Sheffield, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK. r.thompson@sheffield.ac.uk
authors.forename: A A Roger
authors.initials: AA
authors.lastname: Thompson
authors.forename: J Kenneth
authors.initials: JK
authors.lastname: Baillie
authors.forename: Matthew G D
authors.initials: MG
authors.lastname: Bates
authors.forename: Martin F
authors.initials: MF
authors.lastname: Schnopp
authors.forename: Alistair
authors.initials: A
authors.lastname: Simpson
authors.forename: Roland W
authors.initials: RW
authors.lastname: Partridge
authors.forename: Gordon B
authors.initials: GB
authors.lastname: Drummond
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Mason
mesh_terms: D000293:Adolescent; D000328:Adult; D000531:Altitude; D000532:Altitude Sickness / Q000378:metabolism / Q000503:physiopathology*; D002245:Carbon Dioxide / Q000378:metabolism* / Q000502:physiology; D019343:Citric Acid / Q000008:administration & dosage*; D003080:Cold Temperature; D003371:Cough / Q000209:etiology* / Q000503:physiopathology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D006813:Humidity; D006935:Hypercapnia / Q000378:metabolism / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D010366:Peak Expiratory Flow Rate; D012016:Reference Values; D012684:Sensory Thresholds / Q000502:physiology; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D019343:Citric Acid