Retinal and choroidal blood flows in hypoxic and hypercarbic newborn lambs

Abstract

We studied the effect of changes in the arterial tensions of oxygen and carbon dioxide on blood flow to the retinal (RBF) and choroidal (ChBF) capillary beds in 20 lambs.One to three days after placement of catheters in the left ventricle abdominal aorta andbrachiocephalic artery different gas mixtures were delivered to a bag enclosing the lamb's head. One group of lambs was studied at normal and low oxygen tensions while normocarbic and another group was studied at normal and high carbon dioxide tensions whilenormoxic. RBF and ChBF were measured using the radioactive microsphere technique. RBF increased as PaO2 and thus arterial oxygen content ([O2]a) fell in contrast ChBFwas not related to [O2]a. Oxygen delivery to the capillary bed of the retinal artery (i.e., RBF [O2]a) was independent of arterial oxygen content because the change in [O2]a was balanced by a reciprocal change in RBF. Oxygen delivery to the choroidal capillary bed however rose with [O2]a becausethere was no reciprocal decrease in ChBF. Both RBF and ChBF increase as arterial carbon dioxide tension rose. Although an increase in arterial carbon dioxide tension produced anincrease in RBF with no change in [O2]a oxygen delivery to the retinal capillaries rose. Similarly oxygen delivery to the capillaries of the choroid rose with carbondioxide tension. Oxygenation of retinal tissue which depends on oxygen diffusion from boththeretinal and choroidal capillary beds may change with variations in arterial oxygenconten(increase in oxygen delivered to the choroidal capillary bed) or arterial carbon dioxide tension(increase in oxygen delivered to both the retinal and choroidal capillary beds). © 1984 International Pediatrics Research Foundation, Inc.