Sinusoidal intrathecal infusion for assessment of CSF dynamics in kaolin-induced hydrocephalus

Objective. To evaluate whether changes of CSF outflow resistance and compliance in hydrocephalus can be assessed by an intrathecal infusion which is performed at a sinusoidal varying rate. Methods. Hydrocephalus was produced in 10 Sprague Dawley rats by instillation of 0.0375 g of kaolin in 0.9% saline into the cisterna magna. Measurements were performed 4 weeks later: With each animal both, three successive constant rate infusions (0-0.02 ml/min) and a sinusoidal infusion (0-0.02 ml/min, frequency 0.006 Hz) were performed. 6 normal animals served as control. The pressure recordings of both infusion techniques were used for the assessment of the CSF outflow resistance. The time constant and the pressure volume index were calculated only from the sinusoidal input testing. Results. The sinusoidal test as well as the constant rate infusion both demonstrated a severe impairment of CSF absorption. By the sinusoidal input, a decreased compliance was confirmed additionally. Thus, the sinusoidal infusion test demonstrated a high resistance and low compliance hydrocephalus in the kaolin-treated group. A simple graphical procedure is presented which allows an easy assessment of CSF dynamics by the sinusoidal infusion test.