title: Asthma in medium altitude--exercise-induced bronchoconstriction in hypobaric environment in subjects with asthma.
abstract: BACKGROUND
  Hypoxic gas inhalation has been reported to enhance airway responsiveness and results in bronchoconstriction in animal models and in humans with asthma. However, the data have so far been conflicting. The aim of the present study was to examine the effect of reduced barometric pressure on exercise-induced bronchoconstriction (EIB) in subjects with asthma.
  
  
  METHODS
  Twenty subjects (10-45 years old, male symbol/female symbol = 13/7) with asthma (at least 10% reduction in forced expiratory volume in 1-second postexercise) participated in exercise testing in barometric pressure corresponding to altitudes of 200 (normobaric) and 2500 (hypobaric) m above sea level in random order on separate days. Lung function was measured before and after exercise, as well as after inhalation of salbutamol. Heart rate, oxygen uptake (), arterial oxygen saturation (S(p)O(2)), respiratory gas exchange ratio (RER) and minute ventilation () were measured during exercise.
  
  
  RESULTS
  There was no difference in lung function after exercise. The and HR(peak) during exercise did not differ. The RER(peak) was higher (P = 0.04) in hypobaric environment. The decreased 10.1% (7.2-13.0) [mean (95% confidence intervals)] (P < 0.001) from normobaric to hypobaric environment. At the same time, S(p)O(2) at decreased from 94.4 (92.2-96.6) to 85.6% (82.8-88.4) (P < 0.001).
  
  
  CONCLUSIONS
  A barometric pressure corresponding to altitude of 2500 m did not increase EIB in subjects with asthma. The reduction in is most probably due to the lower S(p)O(2) in hypobaric environment.
authors.affiliation: Norwegian School of Sport Sciences, Oslo, Norway.
authors.forename: S
authors.initials: S
authors.lastname: Berntsen
authors.forename: T
authors.initials: T
authors.lastname: Stensrud
authors.forename: F
authors.initials: F
authors.lastname: Ingjer
authors.forename: A
authors.initials: A
authors.lastname: Vilberg
authors.forename: K-H
authors.initials: KH
authors.lastname: Carlsen
mesh_terms: D000293:Adolescent; D000328:Adult; D000531:Altitude; D001250:Asthma, Exercise-Induced / Q000503:physiopathology*; D016084:Bronchoconstriction / Q000502:physiology*; D002648:Child; D018592:Cross-Over Studies; D015444:Exercise / Q000502:physiology*; D005541:Forced Expiratory Volume; D006339:Heart Rate; D006801:Humans; D008450:Maximal Midexpiratory Flow Rate; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D012123:Pulmonary Ventilation
chemical_list: D010100:Oxygen