Mode changes of cerebrovascular pressure transmission induced by cerebral vasodilation.

Changes in the modes of cerebrovascular pressure transmission during cerebral vasodilation induced by hypercapnic challenge were examined as a means for developing the basis for a bedside method to evaluate regulation of cerebral blood flow. Recordings of arterial blood pressure (ABP) and intracranial pressure (ICP) obtained from a piglet preparation equipped with a cranial window were used to determine serial changes of the highest modal frequency (HMF) and dampening factor (DF) of a numerical system identification model of cerebrovascular pressure transmission. Resistance and compliance elements of a Windkessel model of ICP dynamics selected to provide the mathematical structure for the system identification modeling approach were also manipulated to obtain a match with HMF, DF, and the experimental and simulated recordings of ICP. During hypercapnic challenge, significant increases of ICP, pial arterial diameter (PAD) and partial pressure of arterial blood carbon dioxide increases, and a decrease of arterial pH were observed. Vasodilation changed the modes of the system identification model of cerebrovascular pressure transmission from a dominantly over-damped process to an under-damped one with a significant increase in HMF and decrease in DF. Simulations of the Windkessel circuit model required a decrease in the relative resistance and an increase in relative compliance of the arterial-arteriolar vascular bed consistent with the observed increases in PAD induced by vasodilation. Evaluation of changes in the modes of cerebrovascular pressure transmission may provide means of assessing the state of cerebrovascular vasodilation and autoregulation of cerebral blood flow in the clinical setting.