The equilibration of labeled water (H215O) with the exchangeable water pool of brain was examined during a single capillary transit. The labeled water did not equilibrate freely when cerebral blood flow (CBF) exceeded 20 (ml/100 gm)/min in the rhesus monkey. At normal CBF [.. 50 (ml/100 gm)/min] only 90% of the injected bolus freely equilibrated with brain. This value progressively declined as CBF increased.
Raichle ME, Eichling JO, Grubb RL. Brain Permeability of Water. Arch Neurol. 1974;30(4):319–321. doi:10.1001/archneur.1974.00490340047010