Preferential blood flow increase to the brain stem in moderate neonatal hypoxia: reversal by naloxone
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Previous studies have shown that severe neonatal asphyxia and hypoxia lead to a redistribution of cerebral blood flow (CBF) with a preferential perfusion of the brain stem.
The present study shows that this mechanism is operative also in moderately hypoxic newborn lambs (oxygen saturation 32.7–65.2) with a threshold of about 25% reduction in oxygen saturation. In hypoxia, the mean increase in total CBF, brain stem and telencephalic blood flow was 44%, 68% and 43%, respectively (five lambs).
We found that naloxone reverses this redistribution, and that the effects of naloxone on telencephalic perfusion and cerebral metabolic rate of oxygen (CMRO2) were proportional. In hypoxia + naloxone (1 mg/kg), a further increase in total CBF, brain stem, and telencephalic blood flow of 30%, 7% and 31% was noted.
We therefore suggest that the redistribution of CBF is an important opioid-mediated homeostatic mechaism, which diminishes the metabolic requirements of the newer part of the brain in hypoxia and allows a preferential perfusion of the vital structures of the brain stem.
Key wordsNewborn Hypoxia CBF Brain stem Naloxone Opioids
cerebral blood flow
cerebral metabolic rate of oxygen
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