title: Effects of oxygen and carbon dioxide on human retinal circulation.
abstract: OBJECTIVE
  Carbogen, a gas mixture of 95% O2 and 5% CO2, is given to patients with retinal artery obstruction in an attempt to improve retinal oxygenation. The purpose of this study was to compare the effects of carbogen and 100% O2 breathing on retinal blood flow.
  
  
  METHODS
  On two separate occasions, 12 normal, healthy volunteers breathed air and then either 100% O2 or carbogen while laser Doppler velocimetry measurements and monochromatic fundus photographs were taken. Retinal vessel diameter, maximum velocity of red blood cells, and volumetric blood flow rate were determined in a main temporal vein.
  
  
  RESULTS
  Both 100% O2 and carbogen caused significant average reductions in vessel diameter (14.1% and 10.6%, respectively), maximum red blood cell velocity (42.1% and 27.3%, respectively), and blood flow (56.4% and 42.2%, respectively). The average vasoconstriction of the large retinal veins caused by carbogen was not significantly smaller than that caused by 100% O2. The average reductions in maximum red blood cell velocity and blood flow caused by carbogen were significantly smaller than those caused by 100% O2 (P < .001 and P < .01, respectively).
  
  
  CONCLUSIONS
  In normal subjects, inhalation of carbogen leads to less reduction in blood flow than inhalation of 100% O2, presumably by reducing the vasoconstriction of small arterioles induced by elevated oxygen levels.
authors.affiliation: Scheie Eye Institute, Department of Ophthalmology, University of Pennsylvania School of Medicine, Philadelphia.
authors.forename: S J
authors.initials: SJ
authors.lastname: Pakola
authors.forename: J E
authors.initials: JE
authors.lastname: Grunwald
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D002245:Carbon Dioxide / Q000494:pharmacology*; D006439:Hemodynamics; D006801:Humans; D017078:Laser-Doppler Flowmetry; D010100:Oxygen / Q000494:pharmacology*; D012039:Regional Blood Flow / Q000187:drug effects; D012171:Retinal Vessels / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D002245:Carbon Dioxide; C011700:carbogen; D010100:Oxygen