Circadian rhythm of cerebral perfusion pressure and intracranial pressure in head injury.

The aim of the study was to determine if Cerebral Perfusion Pressure (CPP) and Intracranial Pressure (ICP), in patients with head injury, has a circadian rhythm. CPP and ICP data of 13 patients were analysed using the Regressive and Iterative Cosinor methods. The Regressive Cosinor method did not detect a strong 24-hour rhythm. Therefore, the Iterative Cosinor method was used to seek rhythms with period not necessarily equal to 24 hours. Studying consecutive patient days by the Iterative cosinor method showed that rhythm is present but the rhythm period was often not 24 hours. A significant rhythm in the range of 20-30 hours was detected in eight patients for CPP (62%) and in six patients for ICP (46%). To validate the results real and surrogate time series were compared. The clinical implications of rhythmic data analysis are discussed.