Intracranial pressure dynamics: changes of bandwidth as an indicator of cerebrovascular tension

The transmission bandwidth (BW) of arterial blood pressure (ABP) to intracranial pressure (ICP) was examined as a means of bedside monitoring of the state of cerebrovascular tension. Changes of BW of a black box identification model, relative arteriolar resistance and intracranial compliance were obtained from a piglet model equipped with a cranial window during induction of asphyxia, hypercapnia, and hypoxia. Changes of black box BW values and simulated changes of BW produced by a physiologically based lump parameter model of ICP dynamics are used to evaluate the hypothesis that during active cerebrovascular tension, changes of BW are inversely related to cerebral perfusion pressure (CPP), and during passive cerebrovascular tension, changes of BW are not inversely related to changes of CPP. Induction of asphyxia (n = 3) produced BW changes of the black box model that were simulated as an active cerebrovascular tension phase during decreasing CPP followed by a passive tension phase. Reventilation after prolonged asphyxia produced significant increases of BW that were simulated by a passive tension. Hypercapnic (n = 6) and hypoxic (n = 6) challenges produced: (1) significant changes of BW that were matched with simulations of the lumped parameter model for active tension; and (2) relationships between values of BW and relative average cerebral arteriolar resistance and intracranial compliance were inverse and correlated to a regression function of approximately x(-1). Changes of BW of the black box model and the simulations of the lumped parameter model support the feasibility of the stated hypothesis. As such, the evaluation of changes of BW of the black box model with respect to changes of CPP may be a useful method for monitoring the state of cerebrovascular tension.