Recirculatory spinal subarachnoid perfusions in dogs: A method for determining CSF dynamics under non-steady state conditions

Open-ended ventriculocisternal perfusion techniques for determining cerebrospinal fluid production and absorption rates are severely restricted by the absolute requirement that steady state conditions be present. A new closed recirculatory spinal perfusion technique is described. Because steady state equilibrium is not necessary, numerous determinations at multiple intracranial pressures or under varied experimental conditions are possible within relatively brief perfusion periods. Cerebrospinal fluid (CSF) and nondiffusible albumin tracer are rapidly recirculated through the spinal subarachnoid space in a cephalad direction. The concentration of fluorescein-tagged albumin is continuously monitored as the CSF is circulated through a fluorometric flow cell. Measured continuously, intracranial pressure (ICP) is regulated by changing the volume of the external perfusion circuit with a syringe pump connected in series to the recirculatory spinal perfusion. CSF formation and absorption rates are calculated from measurements of albumin concentration, concentration changes with time, ICP, syringe pump infusion rate, and the external perfusion circuit volume. In dogs, data can be collected after only 45 minutes for mixing; perfusions at four or five intracranial pressures in addition to normal resting pressure can be completed within 2 to 3 hours. The data from 15 perfusions in 14 dogs are presented. The method provides normal resting pressure values of CSF production and absorption consistent with those values in the literature determined by traditional ventriculocisternal perfusion techniques. Determinations at multiple intracranial pressures suggest a proportional relationship between absorption and ICP. No consistent acute change in CSF formation with pressures to 50 mm Hg can be inferred from these data.