title: Effects of hyperoxia and hypocapnia on regional venous oxygen saturation in the primary visual cortex in conscious humans.
abstract: Hyperoxia can improve oxygen delivery in patients exposed to hypocapnia for neurosurgical procedures but this effect may be modified by regional differences in the degree of hypocapnic vasoconstriction. Using functional magnet resonance imaging (fMRI), we have investigated the influence of hyperoxia on blood flow and blood oxygenation in the primary visual cortex in hypocapnic volunteers. Consecutive fMRI measurements were performed in 10 awake, male volunteers during hypocapnia (mean PE'CO2 3.3 (SD 0.1) kPa) and normocapnia (PE'CO2 5.3 (0.1) kPa) at FIO2 values of 0.21 and 1.0, respectively. Hypocapnia significantly reduced the pixel count in the primary visual cortex (median 169 (quartiles 34-246) vs 21 (0-40) pixels at an FIO2 of 0.21). Additional hyperoxia had no influence on this reduction in pixel count (16 (0-28) pixels at FIO2 1.0 vs 21 (0-40) pixels at FIO2 0.21). Hyperoxia did not influence hypocapnic vasoconstriction in the primary visual cortex. These data suggest that in the primary visual cortex, administration of oxygen alone may not be sufficient to improve oxygen delivery under hypocapnic conditions.
authors.affiliation: Department of Anaesthesia and Intensive Care Medicine, University of Innsbruck, Austria.
authors.forename: C
authors.initials: C
authors.lastname: Kolbitsch
authors.forename: M
authors.initials: M
authors.lastname: Schocke
authors.forename: C
authors.initials: C
authors.lastname: Hörmann
authors.forename: I H
authors.initials: IH
authors.lastname: Lorenz
authors.forename: C
authors.initials: C
authors.lastname: Kremser
authors.forename: R
authors.initials: R
authors.lastname: Ellinger
authors.forename: F
authors.initials: F
authors.lastname: Zschiegner
authors.forename: S
authors.initials: S
authors.lastname: Felber
authors.forename: F
authors.initials: F
authors.lastname: Aichner
authors.forename: A
authors.initials: A
authors.lastname: Benzer
mesh_terms: D000328:Adult; D001794:Blood Pressure; D006339:Heart Rate; D006801:Humans; D018496:Hyperoxia / Q000097:blood / Q000503:physiopathology*; D016857:Hypocapnia / Q000097:blood / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D010100:Oxygen / Q000097:blood*; D011446:Prospective Studies; D012039:Regional Blood Flow; D014793:Visual Cortex / Q000502:physiology*
chemical_list: D010100:Oxygen