title: A decrease in spatially resolved near-infrared spectroscopy-determined frontal lobe tissue oxygenation by phenylephrine reflects reduced skin blood flow.
abstract: BACKGROUND
  Spatially resolved near-infrared spectroscopy-determined frontal lobe tissue oxygenation (ScO2) is reduced with administration of phenylephrine, while cerebral blood flow may remain unaffected. We hypothesized that extracranial vasoconstriction explains the effect of phenylephrine on ScO2.
  
  
  METHODS
  We measured ScO2 and internal and external carotid as well as vertebral artery blood flow in 7 volunteers (25 [SD 4] years) by duplex ultrasonography during IV infusion of phenylephrine, together with middle cerebral artery mean blood velocity, forehead skin blood flow, and mean arterial blood pressure.
  
  
  RESULTS
  During phenylephrine infusion, mean arterial blood pressure increased, while ScO2 decreased by -19% ± 3% (mean ± SE; P = 0.0005). External carotid artery (-27.5% ± 3.0%) and skin blood flow (-25.4% ± 7.8%) decreased in response to phenylephrine administration, and there was a relationship between ScO2 and forehead skin blood flow (Pearson r = 0.55, P = 0.042, 95% confidence interval [CI], = 0.025-0.84; Spearman r = 0.81, P < 0.001, 95% CI, 0.49-0.94) and external carotid artery conductance (Pearson r = 0.62, P = 0.019, 95% CI, 0.13 to 0.86; Spearman r = 0.64, P = 0.012, 95% CI, 0.17-0.88).
  
  
  CONCLUSIONS
  These findings suggest that a phenylephrine-induced decrease in ScO2, as determined by INVOS-4100 near-infrared spectroscopy, reflects vasoconstriction in the extracranial vasculature rather than a decrease in cerebral oxygenation.
authors.affiliation: From the *Department of Biomedical Engineering, Toyo University, Kawagoe-Shi, Saitama; †Research Institute of Physical Fitness, Japan Women's College of Physical Education, Tokyo; ‡Department of Environmental Physiology for Exercise, Osaka City University Graduate School of Medicine; §Faculty of Health Sciences, Morinomiya University of Medical Sciences, Osaka, Japan; ‖Department of Anesthesia, The Copenhagen Muscle Research Center, University of Copenhagen, Copenhagen, Denmark; and ¶Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
authors.forename: Shigehiko
authors.initials: S
authors.lastname: Ogoh
authors.forename: Kohei
authors.initials: K
authors.lastname: Sato
authors.forename: Kazunobu
authors.initials: K
authors.lastname: Okazaki
authors.forename: Tadayoshi
authors.initials: T
authors.lastname: Miyamoto
authors.forename: Frederik
authors.initials: F
authors.lastname: Secher
authors.forename: Henrik
authors.initials: H
authors.lastname: Sørensen
authors.forename: Peter
authors.initials: P
authors.lastname: Rasmussen
authors.forename: Niels H
authors.initials: NH
authors.lastname: Secher
mesh_terms: D000465:Algorithms; D001794:Blood Pressure / Q000187:drug effects; D002342:Carotid Artery, External / Q000187:drug effects / Q000502:physiology; D005625:Frontal Lobe / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D016014:Linear Models; D008297:Male; D020768:Middle Cerebral Artery / Q000187:drug effects / Q000502:physiology; D010101:Oxygen Consumption / Q000187:drug effects*; D010656:Phenylephrine / Q000494:pharmacology*; D012039:Regional Blood Flow / Q000187:drug effects; D012867:Skin / Q000098:blood supply* / Q000187:drug effects; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D014655:Vascular Resistance / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014711:Vertebral Artery / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
chemical_list: D014662:Vasoconstrictor Agents; D010656:Phenylephrine