Simultaneous cerebral blood flow measured by direct and indirect methods

By diversion of the sagittal sinus blood flow of the dog, obliteration of the extracerebral veins communicating with the sinus, and determination of the amount of brain drained by the sagittal sinus, direct cerebral flow was measured and compared to indirect measurements determined by the modified Kety-Schmidt method using krypton-85 ( 85Kr) as the tracer gas. Twenty-two comparisons were made in 7 dogs at flows ranging from 25 to 98 ml. per 100 gm. per minute. In individual dogs small systematic differences in the values for cerebral blood flow generally were observed; the discrepancies could not be accounted for entirely by the method of converting direct flow (milliliters per minute) to flow per unit weight (ml./100 gm./min.). For the group no systematic difference was apparent and the results are considered confirmative evidence of the validity of the modified Kety-Schmidt method. When the calculations of indirect flows were made from a 10-minute saturation period with 85Kr and without extrapolation of the arteriovenous difference of 85Kr to infinity, a systematic error was introduced, resulting in a 5 to 10% overestimation at normal and low flow levels. The method for direct measurement of sagittal sinus flow offers promise for further laboratory studies of cerebral blood flow and metabolism.