title: Persistence of baroreceptor control of cerebral blood flow velocity at a simulated altitude of 5000 m.
abstract: OBJECTIVE
  To assess the effects of acute exposure to simulated high altitude on baroreflex control of mean cerebral blood flow velocity (MCFV).
  
  
  METHODS
  We compared beat-to-beat changes in RR interval, arterial blood pressure, mean MCFV (by transcranial Doppler velocimetry in the middle cerebral artery), end-tidal CO2, oxygen saturation and respiration in 19 healthy subjects at baseline (Albuquerque, 1779 m), after acute exposure to simulated high altitude in a hypobaric chamber (barometric pressure as at 5000 m) and during oxygen administration (to achieve 100% oxygen saturation) at the same barometric pressure (HOX). Baroreflex control on each signal was assessed by univariate and bivariate power spectral analysis performed on time series obtained during controlled (15 breaths/min) breathing, before and during baroreflex modulation induced by 0.1-Hz sinusoidal neck suction.
  
  
  RESULTS
  At baseline, neck suction was able to induce a clear increase in low-frequency power in MCFV (P<0.001) as well as in RR and blood pressure. At high altitude, MCFV, as well as RR and blood pressure, was still able to respond to neck suction (all P<0.001), compared to controlled breathing alone, despite marked decreases in end-tidal CO2 and oxygen saturation at high altitude. A similar response was obtained at HOX. Phase delay analysis excluded a passive transmission of low-frequency oscillations from arterial pressure to cerebral circulation.
  
  
  CONCLUSIONS
  During acute exposure to high altitude, cerebral blood flow is still modulated by the autonomic nervous system through the baroreflex, whose sensitivity is not affected by changes in CO2 and oxygen saturation levels.
authors.affiliation: Department of Internal Medicine, University of Pavia and IRCCS S. Matteo, Pavia, and Department of Internal Medicine, Unita' Ospedaliera S. Maria Nuova, Firenze, Italy. passino@ifc.cnr.it
authors.forename: Claudio
authors.initials: C
authors.lastname: Passino
authors.forename: Simone
authors.initials: S
authors.lastname: Cencetti
authors.forename: Giammario
authors.initials: G
authors.lastname: Spadacini
authors.forename: Robert
authors.initials: R
authors.lastname: Quintana
authors.forename: Daryl
authors.initials: D
authors.lastname: Parker
authors.forename: Robert
authors.initials: R
authors.lastname: Robergs
authors.forename: Otto
authors.initials: O
authors.lastname: Appenzeller
authors.forename: Luciano
authors.initials: L
authors.lastname: Bernardi
mesh_terms: D000328:Adult; D000531:Altitude; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D008297:Male; D010102:Oxygen Inhalation Therapy; D011311:Pressoreceptors / Q000502:physiology*