ICP dependent changes of CSF outflow resistance.

CSF outflow resistance was studied in cats using the lumbar infusion tests. Different infusion rates were applied from 0.012 to 1.8 ml/min. ICP level obtained during infusions varied from 8.9 +/- 3.0 to 144.0 +/- 25.7 mmHg. The calculated resistance (R) values were within 75.2 +/- 14.4 to 255.6 +/- 71.2. mm Hg/ml/min. The relation between ICP and R are characterized by a curve which can be divided into three parts. First R rises until an ICP level of about 20 mmHg is reached, then R decreases fast until the ICP value is about 50 mmHg, a further drop is much slower and the ICP/R curve becomes almost parallel to the ICP axis. The possible reasons for the ICP dependent changes of R as well as the clinical importance of the results obtained are discussed.