Cerebral Doppler and misrepresentation of flow changes

To determine whether cerebral blood flow velocity (CBFV) measurements were representative of cerebral blood flow (CBF) changes in pathological flow situations five newborn piglets were investigated. They underwent measurements of CBF by electromagnetic flowmetry on a modified common carotid artery where extracerebral branches were tied off simultaneously with Doppler recording either from the same precerebral or an intracerebral artery. The two methods agreed well within moderate carbon dioxide and blood pressure changes. During severe hypotension and hypertension Doppler overestimated CBF by 25-100%. During transfusion of infected or incompatible blood the two methods differed in opposite directions with Doppler reading from 30-200% of CBF. Transfusion of chilled blood caused CBFV to overestimate 15% and heated blood caused 20% underestimation. These results could be explained by diameter changes in response to variation in myogenic tone or vasoactive substances. CBFV measurements could be seriously misleading in severe clinical derangements where neonatal brain damage might occur.