Regulation of local oxygen tension and blood flow in the inner retina during hyperoxia

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Abstract
A study has been undertaken to determine whether local changes in PO2 could be a factor in the regulation of retinal blood flow during 100% O2 breathing. For this purpose we have measured simultaneously in eyes of anesthetized and artificially ventilated miniature pigs the change in local preretinal PO2 and retinal blood flow using O2-sensitive microelectrodes and laser Doppler velocimetry. Although preretinal intervascular PO2 changed little, periarteriolar PO2 increased markedly during 100% O2 breathing. When measured less than 50 microns from the arteriolar wall, the time course of this increase preceded that of the decrease in retinal blood flow. The results indicate that O2 diffusing through the wall of the large retinal arterioles represents the most important component of periarteriolar PO2. This diffusion coupled with the decrease in retinal blood flow could play a major role in the regulation of inner retinal PO2. The data also suggest that diffusional shunting of O2 between retinal arterioles and veins could explain the unexpected increase in venous O2 saturation during 100% O2 breathing that has been previously reported by others. The finding that retinal periarteriolar PO2 is always higher than the PO2 in the outer retina does not support the previously formulated hypothesis that O2 from the choroid is responsible for the constriction of the arterioles during hyperoxia.