RETINAL AND CHOROIDAL BLOOD-FLOW RESPONSE TO HYPEROXEMIA AFTER SEVEREHYPOXEMIA IN THE NEWBORN PIGLET

To investigate the effect of hyperoxemia on the ocular circulation aft er a severe hypoxemic insult (8% O-2 until base excess reached -20 mmo l/l), we randomly reoxygenated newborn piglets with 100% (study group, n = 8) or 21% O-2 (control group, n = 10). Retinal (RBF) and choroida l blood flow (ChBF) were measured with radioactive microspheres. The h ypoxemic insult did not change RBF, while ChBF significantly decreased . However, a marked reduction in both retinal (RDO(2)) and choroidal o xygen delivery (ChDO(2)) was observed, probably resulting in hypoxia b oth in the inner and outer retina. At 5 and 20 min of reoxygenation a similar hyperemic response in the retina was seen in both groups. RDO( 2) also increased significantly and no significant differences between the 2 groups could be demonstrated. We found no indication of retinal vasoconstriction during hyperoxemia. We speculate that the vasodilati ng effect of the preceding hypoxemia overrules the vasoconstrictive ef fect of the retinal vessels normally found during hyperoxemia.