Retinal and Choroidal Blood Flow in Unstressed Fetal and Neonatal Lambs

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Abstract
Summary: The relationship between retinal blood flow (RBF) and choroidal blood flow (ChBF) and the oxygen content of arterial blood was investigated in 12 fetal lambs. The postnatal changes in these flows were studied in twelve newborn lambs. RBF and ChBF were determined by means of radioactive microspheres 3 to 10 days after implantation of the injection and sampling catheters. Fetal blood flows were measured at different levels of oxygenation. The postnatal flows were measured while the lamb breathed room air. The fetal data suggest an inverse relationship between RBF and arterial oxygen content. Concomitant changes in fetal ChBF were unrelated to arterial oxygen content. Because of the inverse relationship between RBF and arterial oxygen content, the product of RBF and arterial oxygen content was independent of the state of fetal oxygenation. RBF did not change with birth, whereas ChBF increased. There was no change in RBF with postnatal age whereas ChBF decreased significantly with increasing age. Speculation: A reduced vascular resistance in the immature choroid might be an important predisposing factor in the development of retrolental fibroplasia in preterm babies treated with high environmental oxygen.

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