Total and regional cerebral blood flow measurement with 7-10-, 15-, 25-, and 50-mum microspheres

Cerebral arteriovenous shunting of 7–10-, 15-, 25-, and 50-mum labeled microspheres was studied in 12 anesthetized dogs. Approximately 8% of the 7–10-mum spheres were shunted to cerebral venous blood, whereas less than 2% of the 15-, 25-, and 50-mum spheres were shunted. Cerebral vascular dilatation induced by hypoxia or hypercapnia did not alter the shunting. The calculated total cerebral flow was 10–15% lower with 7–10-mum microspheres as compared with simultaneous flows measured with the larger microspheres which also suggests that 7–10-mu spheres were shunted through the brain. The calculated distribution of cerebral flow was similar with 7–10- and 15-mum spheres but markedly altered when 50-mum spheres were used. Repeated injections of 15-mum spheres were used. Repeated injections of 15-mum microspheres given under stable conditions yielded total cerebral blood flows which averaged +/- 6% of their respective mean and the regional distribution of flow was highly reproducible. These data suggest that, in dogs, 15-mum spheres are an appropriate size to use to measure cerebral blood flows, since shunting is minimal, the distribution is not artifactually distorted, and the measurements are reproducible.