title: Physiological risk factors for severe high-altitude illness: a prospective cohort study.
abstract: BACKGROUND
  An increasing number of persons, exposed to high altitude for leisure, sport, or work, may suffer from severe high-altitude illness.
  
  
  OBJECTIVE
  To assess, in a large cohort of subjects, the association between physiological parameters and the risk of altitude illness and their discrimination ability in a risk prediction model.
  
  
  METHODS
  A total of 1,326 persons went through a hypoxic exercise test before a sojourn above 4,000 m. They were then monitored up at high altitude and classified as suffering from severe high-altitude illness (SHAI) or not. Analysis was stratified according to acetazolamide use.
  
  
  RESULTS
  Severe acute mountain sickness occurred in 314 (23.7%), high-altitude pulmonary edema in 22 (1.7%), and high-altitude cerebral edema in 13 (0.98%) patients. Among nonacetazolamide users (n = 917), main factors independently associated with SHAI were previous history of SHAI (adjusted odds ratios [aOR], 12.82; 95% confidence interval [CI], 6.95-23.66; P < 0.001), ascent greater than 400 m/day (aOR, 5.89; 95% CI, 3.78-9.16; P < 0.001), history of migraine (aOR, 2.28; 95% CI, 1.28-4.07; P = 0.005), ventilatory response to hypoxia at exercise less than 0.78 L/minute/kg (aOR, 6.68; 95% CI, 3.83-11.63; P < 0.001), and desaturation at exercise in hypoxia equal to or greater than 22% (aOR, 2.50; 95% CI, 1.52-4.11; P < 0.001). The last two parameters improved substantially the discrimination ability of the multivariate prediction model (C-statistic rose from 0.81 to 0.88; P < 0.001). Preventive use of acetazolamide reduced the relative risk of SHAI by 44%.
  
  
  CONCLUSIONS
  In a large population of altitude visitors, chemosensitivity parameters (high desaturation and low ventilatory response to hypoxia at exercise) were independent predictors of severe high-altitude illness. They improved the discrimination ability of a risk prediction model.
authors.affiliation: Université Paris, Association pour la Recherche en Physiologie de l’Environnement, Unité de Formation et de Recherche Santé Médecine Biologie Humaine, Bobigny, France. richalet@smbh.univ-paris13.fr
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Richalet
authors.forename: Philippe
authors.initials: P
authors.lastname: Larmignat
authors.forename: Eric
authors.initials: E
authors.lastname: Poitrine
authors.forename: Murielle
authors.initials: M
authors.lastname: Letournel
authors.forename: Florence
authors.initials: F
authors.lastname: Canouï-Poitrine
mesh_terms: D000086:Acetazolamide / Q000008:administration & dosage; D000208:Acute Disease; D000328:Adult; D000532:Altitude Sickness / Q000150:complications / Q000453:epidemiology / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control*; D001929:Brain Edema / Q000453:epidemiology / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control*; D015331:Cohort Studies; D016001:Confidence Intervals; D004232:Diuretics / Q000008:administration & dosage; D005080:Exercise Test; D005260:Female; D005602:France / Q000453:epidemiology; D006261:Headache / Q000209:etiology; D006801:Humans; D006976:Hypertension, Pulmonary / Q000453:epidemiology / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012720:Severity of Illness Index
chemical_list: D004232:Diuretics; D000086:Acetazolamide