Compartmental analysis of compliance and outflow resistance of the cerebrospinal fluid system.

The distribution of compliance and outflow resistance between cerebral and spinal compartments was measured in anesthetized, ventilated cats by analysis of the cerebrospinal fluid (CSF) pressure response to changes in CSF volume. Cerebral and spinal compartments were isolated by inflating a balloon positioned epidurally at the level of C-6. The change of CSF volume per unit change in pressure (compliance) and change of CSF volume per unit of time (absorption) were evaluated by inserting pressure data from the experimental responses into a series of equations developed from a mathematical model. It was found that 68% of total compliance is contributed by the cerebral compartment while the remaining 32% is contained within the spinal axis. The cerebral compartment accounted for 84% of total CSF absorption. The mechanism for spinal absorption appears to be similar in that no differences were obvious on the basis of pressure dynamics.