Effects of dexamethasone on blood flow and volume of perfused microvessels in traumatic brain edema.

We have hypothesized that dexamethasone acts, in part, to reduce the formation and spread of edema fluid by altering CBF and VPM and have tested this proposition by measuring CBF and VPM in treated and untreated rats at several times after cold injury of the cerebral cortex. Both CBF and VPM were markedly decreased within the lesioned cortex. This suggests that the major cause of the fall in CBF was a decrease in the number of perfused microvessels. In untreated rats after cold injury, CBF was not appreciably changed in cortical tissue adjacent to the primary lesion and in contralateral cortex. Dexamethasone may, however, have lowered CBF in these two "normal" brain areas after cold injury. In the ipsilateral corpus callosum adjacent to the lesion, CBF was significantly lowered after cold injury. In the corpus callosum on both sides. CBF tended to be lower in dexamethasone-treated than in untreated rats. Because arterial pressure was similar in treated and untreated rats but CBF was consistently lower in treated rats, dexamethasone may increase the resistance to flow of the blood vessels proximal to the leaky microvessels and reduce the hydrostatic pressure that drives the formation of edema fluid.