Continuous estimates of index of intracranial compliance derived from intracranial pressure recordings

The purpose of this study is to explore the development of a method to derive continuous estimates of an index of intracranial compliance from recordings of intracranial pressure (ICP). The proposed index, percent change of compliance per mmHg of ICP (%CC/mmHg), is based on two assumptions: (1) the pressure-volume characteristic of the craniospinal sac can be linearized for small perturbations about an equilibrium; and (2) during a brief interval in which these perturbations occur the pathophysiologic state of the craniospinal sac does not significantly change. Values of %CC/mmHg were derived from laboratory recordings of ICP obtained from four bovine preparations and found to be strongly inversely correlated with ICP with all r-values greater than 0.97. To date three clinical cases also demonstrate the same inverse relationship between %CC/mmHg and ICP. This index may be of value as an independent check on the D.C. drift of the transducer and in patient management during long term monitoring