title: Adaptation to Life in the High Andes: Nocturnal Oxyhemoglobin Saturation in Early Development.
abstract: OBJECTIVE
  Physiological adaptation to high altitude hypoxia may be impaired in Andeans with significant European ancestry. The respiratory 'burden' of sleep may challenge adaptation, leading to relative nocturnal hypoxia. Developmental aspects of sleep-related breathing in high-altitude native children have not previously been reported. We aimed to determine the influence of development on diurnal-nocturnal oxyhemoglobin differences in children living at high altitude.
  
  
  METHODS
  This was a cross-sectional, observational study. Seventy-five healthy Bolivian children aged 6 mo to 17 y, native to low altitude (500 m), moderate high altitude (2,500 m), and high altitude (3,700 m) were recruited. Daytime resting pulse oximetry was compared to overnight recordings using Masimo radical oximeters. Genetic ancestry was determined from DNA samples.
  
  
  RESULTS
  Children had mixed European/Amerindian ancestry, with no significant differences between altitudes. Sixty-two participants had ≥ 5 h of nocturnal, artifact-free data. As predicted, diurnal mean oxyhemoglobin saturation decreased across altitudes (infants and children, both P < 0.001), with lowest diurnal values at high altitude in infants. At high altitude, there was a greater drop in nocturnal mean oxyhemoglobin saturation (infants, P < 0.001; children, P = 0.039) and an increase in variability (all P ≤ 0.001) compared to low altitude. Importantly, diurnal to nocturnal altitude differences diminished (P = 0.036), from infancy to childhood, with no further change during adolescence.
  
  
  CONCLUSIONS
  Physiological adaptation to high-altitude living in native Andeans is unlikely to compensate for the significant differences we observed between diurnal and nocturnal oxyhemoglobin saturation, most marked in infancy. This vulnerability to sleep-related hypoxia in early childhood has potential lifespan implications. Future studies should characterize the sleep- related respiratory physiology underpinning our observations.
authors.affiliation: Division of Clinical Experimental Sciences, Faculty of Medicine, University of Southampton, UK.|Southampton Children's Hospital, Southampton, UK.
authors.forename: Catherine Mary
authors.initials: CM
authors.lastname: Hill
authors.affiliation: Department of Psychology, Universidad Privada de Santa Cruz de la Sierra, Santa Cruz - Bolivia.
authors.forename: Ana
authors.initials: A
authors.lastname: Baya
authors.affiliation: Southampton Children's Hospital, Southampton, UK.|Neurosciences Unit, UCL Institute of Child Health, UK.
authors.forename: Johanna
authors.initials: J
authors.lastname: Gavlak
authors.affiliation: Sleep Disorders Unit, Canberra Hospital, Australia.
authors.forename: Annette
authors.initials: A
authors.lastname: Carroll
authors.affiliation: Department of Otolaryngology, Poole General Hospital, UK.
authors.forename: Kate
authors.initials: K
authors.lastname: Heathcote
authors.affiliation: University College London, Institute of Education, UK.
authors.forename: Dagmara
authors.initials: D
authors.lastname: Dimitriou
authors.affiliation: Department of Primary Care and Population Health, Kings College London, UK.
authors.forename: Veline
authors.initials: V
authors.lastname: L'Esperance
authors.affiliation: Laboratory for Cancer Medicine, Harry Perkins Institute of Medical Research and University of Western Australia Centre for Medical Research, Perth, Australia.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Webster
authors.affiliation: Division of Human Development and Health. Faculty of Medicine, University of Southampton, UK.
authors.forename: John
authors.initials: J
authors.lastname: Holloway
authors.affiliation: School of Psychology, Faculty of Science, The University of Auckland, New Zealand.
authors.forename: Javier
authors.initials: J
authors.lastname: Virues-Ortega
authors.affiliation: Division of Clinical Experimental Sciences, Faculty of Medicine, University of Southampton, UK.|Southampton Children's Hospital, Southampton, UK.|Neurosciences Unit, UCL Institute of Child Health, UK.
authors.forename: Fenella Jane
authors.initials: FJ
authors.lastname: Kirkham
authors.affiliation: School of Psychology, University of Western Australia, Perth, Australia.
authors.forename: Romola Starr
authors.initials: RS
authors.lastname: Bucks
authors.affiliation: Cognitive Neuroscience & Psychiatry, UCL Institute of Child Health, UK.|North Central London School of Anaesthesia, London, UK.
authors.forename: Alexandra Marie
authors.initials: AM
authors.lastname: Hogan
mesh_terms: D000064:Acclimatization / Q000235:genetics / Q000502:physiology*; D000293:Adolescent; D041923:Adolescent Development; D000531:Altitude; D000532:Altitude Sickness; D001838:Bolivia; D002648:Child; D002657:Child Development; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005060:Europe / Q000208:ethnology; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000235:genetics / Q000378:metabolism*; D007223:Infant; D008297:Male; D010092:Oximetry; D010108:Oxyhemoglobins / Q000378:metabolism*; D012119:Respiration; D012890:Sleep / Q000235:genetics / Q000502:physiology*
chemical_list: D010108:Oxyhemoglobins
keywords: altitude; central apnea; intermittent hypoxia; respiratory control; sleep disordered breathing