Clinical studies of cranial and spinal compliance and the craniospinal flow of cerebrospinal fluid.

The cranial compartment contributed 37% and the spinal compartment 63% to the total compliance of the craniospinal space in the horizontal body position. In the erect position the values were almost reversed, the cranial compartment contributing 66% and the spinal compartment 34%. The total compliance was almost unaffected by body position. The pulsatile volume of cerebrospinal fluid (CSF) moving between the cranial and spinal compartments was about 1 ml in the horizontal position. The corresponding pulsatile change in cerebral blood volume was calculated to be 1.6 ml. A craniospinal block increased the intracranial pressure amplitude by 110% in the horizontal position. The volume of CSF moving between the cranial and spinal compartments when sitting up and lying down, was about 3 ml. The pulsatile and postural flow rate of CSF may reach about 200 ml/min. High CSF flow velocity may impair the protective coating of CSF around the brain and thus contribute to herniation.