Bulk flow in the cerebrospinal fluid system of the dog

Ventriculo-cisternal, intracranial subarachnoid-to-subarachnoid space and spinal subarachnoid space perfusions were carried out on dogs. The perfusate contained inulin as a tracer and the design of these experiments was based upon the concept that inulin leaves cerebrospinal fluid (CSF) compartments only by means of bulk absorption, and that actual diffusion and active transport of inulin is negligibly small. Inulin was removed from different CSF spaces by bulk absorption at rates which varied linearly with hydrostatic pressure. The rate of formation of CSF is equal to inulin clearance plus the difference between outflow and inflow rates. The total CSF formation in dogs weighing 12 to 17 kg was measured as 0.065 ml/min, and 58.5 per cent of this amount was found to come from extraventricular CSF space. The rates are independent of hydrostatic pressure in the range studied.