title: Circadian rhythm of peripheral perfusion during 10-day hypoxic confinement and bed rest.
abstract: BACKGROUND
  Future planetary habitats will be hypobaric and hypoxic to reduce the risk of decompression sickness during preparation for extra-vehicular activities. This study was part of a research programme investigating the combined effects of hypoxia and microgravity on physiological systems.
  
  
  OBJECTIVE
  We tested the hypothesis that hypoxia-induced peripheral vasoconstriction persists at night and is aggravated by bed rest. Since sleep onset has been causally linked to nocturnal vasodilatation, we reasoned that hypoxia-induced vasoconstriction at night may explain sleep disturbances at altitude. Peripheral perfusion alterations as a consequence of bed rest may explain poor sleep quality reported during sojourns on the International Space Station.
  
  
  METHODS
  Eleven males underwent three 10-day interventions in a randomised order: (1) hypoxic ambulatory confinement; (2) hypoxic bed rest; (3) normoxic bed rest. During each intervention we conducted 22-h monitoring of peripheral perfusion, as reflected by the skin temperature gradient. Measurements were conducted on the first (D 1) and last day (D 10) of each intervention.
  
  
  RESULTS
  All interventions resulted in a decrease in daytime toe perfusion from D 1 to D 10. There was no difference in the magnitude of the daytime reduction in toe perfusion between the three interventions. There was a significant vasodilatation of the toes in all interventions by 11 pm. The fingertips remained well perfused throughout.
  
  
  CONCLUSIONS
  Daytime vasoconstriction induced by hypoxia and/or bed rest is abolished at night, lending further support to the theory that changes in peripheral skin temperature may be functionally linked to sleep onset.
authors.affiliation: Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia, adam.mcdonnell@ijs.si.
authors.forename: Adam C
authors.initials: AC
authors.lastname: McDonnell
authors.forename: Ola
authors.initials: O
authors.lastname: Eiken
authors.forename: Polona Jaki
authors.initials: PJ
authors.lastname: Mekjavic
authors.forename: Igor B
authors.initials: IB
authors.lastname: Mekjavic
mesh_terms: D000328:Adult; D001510:Bed Rest / Q000009:adverse effects*; D002940:Circadian Rhythm; D005385:Fingers / Q000098:blood supply; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D012039:Regional Blood Flow; D014034:Toes / Q000098:blood supply; D014661:Vasoconstriction; D014893:Weightlessness