title: Acute mountain sickness is not repeatable across two 12-hour normobaric hypoxia exposures.
abstract: OBJECTIVE
  The purposes of this experiment were to determine the repeatability of acute mountain sickness (AMS), AMS symptoms, and physiological responses across 2 identical hypoxic exposures.
  
  
  METHODS
  Subjects (n = 25) spent 3 nights at simulated altitude in a normobaric hypoxia chamber: twice at a partial pressure of inspired oxygen (PIO2) of 90mmHg (4000 m equivalent; "hypoxia") and once at a PIO2 of 132 mmHg (1000 m equivalent; "sham") with 14 or more days between exposures. The following variables were measured at hours 0 and 12 of each exposure: AMS severity (ie, Lake Louise score [LLS]), AMS incidence (LLS ≥3), heart rate, oxygen saturation, blood pressure, and the fraction of exhaled nitric oxide. Oxygen saturation and heart rate were also measured while subjects slept.
  
  
  RESULTS
  The incidence of AMS was not statistically different between the 2 exposures (84% vs 56%, P > .05), but the severity of AMS (ie, LLS) was significantly lower on the second hypoxic exposure (mean [SD], 3.1 [1.8]) relative to the first hypoxic exposure (4.8 [2.3]; P < .001). Headache was the only AMS symptom to have a significantly greater severity on both hypoxic exposures (relative to the sham exposure, P < .05). Physiological variables were moderately to strongly repeatable (intraclass correlation range 0.39 to 0.86) but were not associated with AMS susceptibility (P > .05).
  
  
  CONCLUSIONS
  The LLS was not repeatable across 2 identical hypoxic exposures. Increased familiarity with the environment (not acclimation) could explain the reduced AMS severity on the second hypoxic exposure. Headache was the most reliable AMS symptom.
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada. Electronic address: martin@alumni.ubc.ca.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: MacInnis
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Sarah
authors.initials: S
authors.lastname: Koch
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Kristin E
authors.initials: KE
authors.lastname: MacLeod
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Carter
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Radha
authors.initials: R
authors.lastname: Jain
authors.affiliation: Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada; School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Koehle
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Jim L
authors.initials: JL
authors.lastname: Rupert
mesh_terms: D000064:Acclimatization; D000293:Adolescent; D000532:Altitude Sickness / Q000503:physiopathology*; D001794:Blood Pressure; D016022:Case-Control Studies; D005260:Female; D006339:Heart Rate; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D055815:Young Adult
chemical_list: D009569:Nitric Oxide; D010100:Oxygen
keywords: acclimation; acclimatization; high altitude; previous history; reproducibility