Effects of oxygen and carbon dioxide on human retinal circulation.
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.
Pakola
S J
SJ
Scheie Eye Institute, Department of Ophthalmology, University of Pennsylvania School of Medicine, Philadelphia.
Grunwald
J E
JE
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
D002245:Carbon Dioxide; C011700:carbogen; D010100:Oxygen