title: Concentration-dependent vasoconstrictive effect of hyperoxia on hypercarbia-dilated retinal arterioles.
abstract: OBJECTIVE
  The relative effects of simultaneously administered oxygen and carbon dioxide on vascular resistance are unknown. The purpose of the study was to investigate the independent effect of oxygen partial pressure on hypercarbia-induced vasodilation in the retinal arterioles.
  
  
  METHODS
  Twelve young healthy volunteers participated in the study. End-tidal partial pressure of carbon dioxide was raised 23% from the baseline (i.e. air) at normoxia and then maintained constant while end-tidal partial pressure of oxygen (PETO(2)) was raised in a stepwise incremental fashion. Retinal vessel diameter and blood velocity were measured in the superior-temporal arteriole using the Canon Laser Blood Flowmeter.
  
  
  RESULTS
  Hypercarbia resulted in a 16% increase in blood velocity and a 22% increase in blood flow (p<0.05). At maximal hyperoxia (group mean PETO(2) of 556 mm Hg) vessel diameter, blood velocity and flow were reduced by 9%, 22% and 36%, respectively, relative to baseline (p<0.001).
  
  
  CONCLUSIONS
  The concentration-dependent vasoconstrictive effect of oxygen in retinal arterioles was quantified for the first time by implementing precise control of end-tidal concentrations of CO(2) and O(2). Oxygen-induced vasoconstriction is sufficiently potent to offset and reverse hypercarbia-induced vasodilation.
authors.affiliation: Department of Ophthalmology and Vision Science, University of Toronto, Toronto, ON, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Kisilevsky
authors.forename: C
authors.initials: C
authors.lastname: Hudson
authors.forename: A
authors.initials: A
authors.lastname: Mardimae
authors.forename: T
authors.initials: T
authors.lastname: Wong
authors.forename: J
authors.initials: J
authors.lastname: Fisher
mesh_terms: D000280:Administration, Inhalation; D000328:Adult; D001160:Arterioles / Q000187:drug effects / Q000503:physiopathology; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D018496:Hyperoxia / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000008:administration & dosage*; D012039:Regional Blood Flow / Q000187:drug effects; D012161:Retinal Artery / Q000187:drug effects* / Q000503:physiopathology; D014661:Vasoconstriction / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen