title: Cerebral water and ion balance remains stable when humans are exposed to acute hypoxic exercise.
abstract: BACKGROUND
  Intense physical activity increases the prevalence of acute mountain sickness (AMS) that can occur within 10 h after ascent to altitudes above 1500 m and is likely related to development of cerebral edema. This study evaluated whether disturbed cerebral water and ion homeostasis can be detected when intense exercise is carried out in hypoxia and monitored the influence of muscle metabolism for changes in arterial variables.
  
  
  METHODS
  On two separate days, in random order, 30 min cycling exercise was performed in either hypoxia (10% O2) or normoxia at an intensity that was exhaustive in the hypoxic trial (∼120 W; n=9).
  
  
  RESULTS
  Exercise in hypoxia affected muscle metabolism, as evidenced by higher (p<0.05) leg lactate release at 7.5 min and a continuous decline in arterial pH (p<0.001) that was not observed in normoxia. Middle cerebral artery flow velocity increased (p<0.01) with exercise under both circumstances. No cerebral net exchange of Na(+) or K(+) was evident. Likewise, no significant net-exchange of water over the brain was demonstrated and the arterial and jugular venous hemoglobin concentrations were similar.
  
  
  CONCLUSIONS
  Challenging exercise in hypoxia for 30 min affected muscle metabolism and increased an index of cerebral blood flow, but cerebral net water and ion homeostasis remained stable. Thus, although AMS develops within hours and may be related to exercise-induced disturbance of cerebral ion and water balance, such changes are not detectable when subjects are exposed to acute 30 min maximal exercise in hypoxia.
authors.affiliation: 1 Department of Anesthesia, The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen , Copenhagen, Denmark .
authors.forename: Magnus B
authors.initials: MB
authors.lastname: Avnstorp
authors.forename: Peter
authors.initials: P
authors.lastname: Rasmussen
authors.forename: Patrice
authors.initials: P
authors.lastname: Brassard
authors.forename: Thomas
authors.initials: T
authors.lastname: Seifert
authors.forename: Morten
authors.initials: M
authors.lastname: Overgaard
authors.forename: Peter
authors.initials: P
authors.lastname: Krustrup
authors.forename: Niels H
authors.initials: NH
authors.lastname: Secher
authors.forename: Nikolai B
authors.initials: NB
authors.lastname: Nordsborg
mesh_terms: D000136:Acid-Base Equilibrium; D000328:Adult; D000532:Altitude Sickness / Q000378:metabolism*; D001834:Body Water / Q000378:metabolism*; D001921:Brain / Q000098:blood supply / Q000378:metabolism*; D001923:Brain Chemistry / Q000502:physiology; D001929:Brain Edema / Q000209:etiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D019344:Lactic Acid / Q000096:biosynthesis; D007866:Leg / Q000502:physiology; D008297:Male; D020768:Middle Cerebral Artery / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism; D011897:Random Allocation
chemical_list: D019344:Lactic Acid
keywords: K+; Na+; brain; cerebral; cycling; edema; exercise; hypoxia; ion balance; lactate; water balance