title: Circadian and Sex Differences After Acute High-Altitude Exposure: Are Early Acclimation Responses Improved by Blue Light?
abstract: OBJECTIVE
  The possible effects of blue light during acute hypoxia and the circadian rhythm on several physiological and cognitive parameters were studied.
  
  
  METHODS
  Fifty-seven volunteers were randomly assigned to 2 groups: nocturnal (2200-0230 hours) or diurnal (0900-1330 hours) and exposed to acute hypoxia (4000 m simulated altitude) in a hypobaric chamber. The participants were illuminated by blue LEDs or common artificial light on 2 different days. During each session, arterial oxygen saturation (Spo2), blood pressure, heart rate variability, and cognitive parameters were measured at sea level, after reaching the simulated altitude of 4000 m, and after 3 hours at this altitude.
  
  
  RESULTS
  The circadian rhythm caused significant differences in blood pressure and heart rate variability. A 4% to 9% decrease in waking nocturnal Spo2 under acute hypoxia was observed. Acute hypoxia also induced a significant reduction (4%-8%) in systolic pressure, slightly more marked (up to 13%) under blue lighting. Women had significantly increased systolic (4%) and diastolic (12%) pressures under acute hypoxia at night compared with daytime pressure; this was not observed in men. Some tendencies toward better cognitive performance (d2 attention test) were seen under blue illumination, although when considered together with physiological parameters and reaction time, there was no conclusive favorable effect of blue light on cognitive fatigue suppression after 3 hours of acute hypobaric hypoxia.
  
  
  CONCLUSIONS
  It remains to be seen whether longer exposure to blue light under hypobaric hypoxic conditions would induce favorable effects against fatigue.
authors.affiliation: Departamento Biomédico, Universidad de Antofagasta, Antofagasta, Chile.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Silva-Urra
authors.affiliation: Departament de Fisiologia i Immunologia.
authors.forename: Cristian A
authors.initials: CA
authors.lastname: Núñez-Espinosa
authors.affiliation: Departament de Ciències Fisiològiques II, Universitat de Barcelona, Barcelona, Spain.
authors.forename: Oscar A
authors.initials: OA
authors.lastname: Niño-Mendez
authors.affiliation: Departament de Fisiologia i Immunologia.
authors.forename: Héctor
authors.initials: H
authors.lastname: Gaitán-Peñas
authors.affiliation: Departament de Fisiologia i Immunologia.
authors.forename: Cesare
authors.initials: C
authors.lastname: Altavilla
authors.affiliation: Departament de Fisiologia i Immunologia.
authors.forename: Andrés
authors.initials: A
authors.lastname: Toro-Salinas
authors.affiliation: Departament de Fisiologia i Immunologia.
authors.forename: Joan R
authors.initials: JR
authors.lastname: Torrella
authors.affiliation: Departament de Fisiologia i Immunologia.
authors.forename: Teresa
authors.initials: T
authors.lastname: Pagès
authors.affiliation: Departament de Ciències Fisiològiques II, Universitat de Barcelona, Barcelona, Spain.
authors.forename: Casimiro F
authors.initials: CF
authors.lastname: Javierre
authors.affiliation: Laboratorio de Ambientes Extremos (ICBM), Universidad de Chile, Santiago de Chile, Chile.
authors.forename: Claus
authors.initials: C
authors.lastname: Behn
authors.affiliation: Departament de Fisiologia i Immunologia. Electronic address: gviscor@ub.edu.
authors.forename: Ginés
authors.initials: G
authors.lastname: Viscor
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000531:Altitude; D000532:Altitude Sickness / Q000503:physiopathology* / Q000523:psychology; D001288:Attention / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D008027:Light; D008297:Male
keywords: altitude acclimatization; altitude shift work; attentional blink; blue light illumination; heart rate variability; intermittent hypoxia