title: Heart rate variability during sleep at high altitude: effect of periodic breathing.
abstract: BACKGROUND
  Heart rate variability (HRV) during sleep in normal subjects at high altitude shows a decrease in parasympathetic tone associated with an increase in the sympathetic one, which tends to be reversed with acclimatization. However, periodic breathing (PB) during sleep may influence this effect detected by HRV spectral analysis.
  
  
  OBJECTIVE
  The aim of our study was to investigate HRV during sleep periodic breathing (PB) at high altitude in normal subjects at two different times of acclimatization, i.e., two different levels of hypoxemia.
  
  
  METHODS
  Recordings of six healthy climbers (aged between 33 and 40 years), at sea level (SL) and at Everest North Base Camp (5180 m), during the first (BC1) and the tenth (BC2) overnight unattended polygraphy, were analyzed. PB was commonplace in all subjects at high altitude to a variable extent. At SL and at BC1 and BC2, HRV was evaluated overnight and separately during clear regular breathing (RB) and PB.
  
  
  RESULTS
  A mean overnight beat-by-beat series interval (RR) reduction at acute environmental hypoxic exposure that resumed to SL values after 10-day sojourn was observed. This reduction was mostly due to RR during RB, while during PB, RR values were not different from SL. Higher peaks of tidal volume were associated with higher HRV.
  
  
  CONCLUSIONS
  The present study shows that in healthy subjects, PB with central apneas increases the amplitude of RR oscillations, and these oscillations are tightly related to respiratory amplitude. Oxygenation does not influence this phenomenon. Therefore, oscillations in ventilation itself should be taken into account when investigating HRV.
authors.affiliation: Institute of Biomedicine and Molecular Immunology, "A. Monroy", Sleep Laboratory, National Research Council of Italy, Via Ugo La Malfa, 153, 90146, Palermo, Italy. insalaco@ibim.cnr.it.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Insalaco
authors.affiliation: Institute of Biomedicine and Molecular Immunology, "A. Monroy", Sleep Laboratory, National Research Council of Italy, Via Ugo La Malfa, 153, 90146, Palermo, Italy.
authors.forename: Adriana
authors.initials: A
authors.lastname: Salvaggio
authors.affiliation: Biomedical Sport Studies Center, University of Ferrara, Ferrara, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Pomidori
authors.affiliation: Biomedical Sport Studies Center, University of Ferrara, Ferrara, Italy.
authors.forename: Annalisa
authors.initials: A
authors.lastname: Cogo
authors.affiliation: Institute of Biomedicine and Molecular Immunology, "A. Monroy", Sleep Laboratory, National Research Council of Italy, Via Ugo La Malfa, 153, 90146, Palermo, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Romano
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000531:Altitude; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D008297:Male; D009051:Mountaineering; D010275:Parasympathetic Nervous System / Q000503:physiopathology; D017286:Polysomnography; D012119:Respiration; D012815:Signal Processing, Computer-Assisted; D012891:Sleep Apnea Syndromes / Q000175:diagnosis* / Q000503:physiopathology*; D012984:Software; D013564:Sympathetic Nervous System / Q000503:physiopathology; D013990:Tidal Volume / Q000502:physiology
keywords: Arterial oxygen saturation; Heart rate variability; High altitude; Periodic breathing; Sleep