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Current methods of cerebral blood flow (CBF) determination provide only discrete, episodic data and are limited in assessing dynamic changes in cerebral circulation. We adapted a venous outflow technique employing cannulation of the superior sagittal sinus in newborn puppies to measure changes in CBF rapidly and sequentially during ventilatory maneuvers. CBF velocity (CBFV) was measured simultaneously with Doppler ultrasound of the anterior cerebral artery. Relationships between flow and velocity were determined during hypocarbia, hypercarbia, hypoxia and asphyxia. During hyperventilation, CBF decreased by a mean of 14%, and CBFV by 13%, whereas maximal CO2 inhalation increased CBF by 59% and CBFV by 110%. Although CBFV exhibited the same directional changes as shown by the area under the velocity curve, the magnitude of change was not proportional to flow. CBFV indicated trends in the direction of changes in flow in individual animals, but did not correlate with flow between animals. A fluctuating unstable pattern of CBFV, previously associated with neonatal intracranial hemorrhage, was demonstrated with hyperventilation and hypocarbia. During asphyxia, CBFV ceased 2-5 min prior to CBF, presumably reflecting continued brain perfusion from vessels other than anterior cerebral artery.