title: Cerebrovascular Response to CO2 Following 10 Days of Intermittent Hypoxia in Humans.
abstract: BACKGROUND
  It has been demonstrated that the cerebrovascular response to hypoxia is blunted following 10 d of intermittent hypoxia (IH) in healthy humans. The purpose of this study was to test the hypothesis that IH reduces the cerebrovascular response to CO2.
  
  
  METHODS
  Healthy male subjects (N=8; 25±2 yr) were exposed to 10 consecutive days of IH (12% O2 for 5 min followed by 5 min of normoxia for 1 h/d). The cerebrovascular response to CO2 was assessed prior to (PRE-IH) and following (POST-IH) the IH paradigm with transcranial Doppler ultrasound.
  
  
  RESULTS
  There was no change in eupnic measures during or following the IH paradigm; however, the ventilatory response to IH increased by the last exposure (3.0±2.8 L·min(-1)). Cerebral blood flow velocity decreased and increased with hypocapnia and hypercapnia, respectively, but cerebrovascular sensitivity to CO2 remained unchanged with IH (PRE-IH: 2.58±0.50%/mmHg; POST-IH: 2.59±0.74%/mmHg).
  
  
  CONCLUSIONS
  Our data indicates that 10 d of IH in healthy humans does not alter the cerebrovascular response to CO2. Redundancy of cerebrovascular regulation mechanisms to CO2 may work to counteract IH-induced dysregulation and protect cerebral tissue.
authors.affiliation: Faculty of Medicine and the School of Kinesiology, University of British Columbia - Vancouver, Vancouver, British Columbia, Canada.
authors.forename: Jordan S
authors.initials: JS
authors.lastname: Querido
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Welch
authors.forename: Najib T
authors.initials: NT
authors.lastname: Ayas
authors.forename: A William
authors.initials: AW
authors.lastname: Sheel
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000008:administration & dosage*; D002560:Cerebrovascular Circulation / Q000187:drug effects* / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide