Effect of Hyperoxia on the Cerebral Ciculation of the Newborn Puppy

Abstract

Extract: Local cerebral blood flow (CBF) in the 2-day-old puppy ranged between 0.58 (superior olive) and 0.07 ml/g/min (centrum ovale), with average values in gray matter of the cerebral cortex, deep cerebral structures, and brain stem equal to 0.34, 0.38, and 0.45 ml/g/min, respectively. Animals of the same age, after being placed in oxygen for 1 hr, had a mean arterial oxygen tension (Pao2) of 349 mm Hg; arterial carbon dioxide tension (Paco2) did not change from the level seen in animals kept in air. The CBF of nearly all structures was 20-30% lower in the hyperoxic newborns than in control animals. In 3-week-old puppies, CBF ranged between 1.41 (inferior colliculus) and 0.20 ml/g/min (centrum ovale), with average values for gray matter in the cerebral cortex, deep cerebral structures, and brain stem equal to 0.61, 0.72, and 0.93 ml/g/min, respectively. Puppies at this age breathing oxygen attained a mean Pao2 of 357 mm Hg; again, PaCo2 values were not different from those in air. The oxygen effect on CBF in the 3-week-old animals was less than had been found at 2 days, there being far fewer structures in which the difference was significant. The smallest differences were in white matter ( – 11%). Continuous exposure to oxygen for 1 week, followed by removal of the puppies to air for 2–3 days, resulted in values for CBF which were comparable with those found in control animals.Speculation: Fligh concentrations of oxygen at ambient pressure alter a number of growth processes of the cell. The vasoconstrictive action of oxygen on cerebral vessels, which is exaggerated in early postnatal life, may be part of a homeostatic mechanism to limit oxygen concentration in the brain when the arterial Po., is elevated.