Assessment of cerebrovascular autoregulation: Changes of highest modal frequency of cerebrovascular pressure transmission with cerebral perfusion pressure

Background and Purpose - Development of a method to continuously assess cerebrovascular autoregulation of patients with traumatic brain injury would facilitate therapeutic intervention and thus reduce secondary complications. Methods - Changes in arterial blood pressure (ABP), intracranial pressure (ICP), cerebral blood flow velocity (CBFV), and pial arteriolar diameter (PAD) induced by acute pressor challenge (norepinephrine; 1 μg/[kg · min]) were evaluated in both uninjured and fluid percussion injured piglets equipped with cranial windows. The linear correlation coefficient and corresponding slope of the regression line of the relationship between highest modal frequency (HMF) of cerebrovascular pressure transmission of ABP to ICP and cerebral perfusion pressure (CPP) were determined for each challenge. Results - For all uninjured piglets, pressor challenge resulted in an inverse relationship between HMF and CPP characterized by significant negative correlation values and negative corresponding regression line slopes with respective group mean values (±SD) of -0.50 (±0.14) and -0.6 (±0.44) Hz/mm Hg, respectively. Consistent with functional autoregulation of the uninjured preparations, pressor challenge resulted in a decrease of PAD, and CBFV remained relatively constant. For all injured piglets, pressor challenge resulted in direct relationship between HMF and CPP, characterized by positive correlation values and corresponding regression line slopes with group mean values of 0.48 (±0.21) and 1.13 (±2.08) Hz/mm Hg, respectively. Consistent with impaired autoregulation, PAD and CBFV increased during pressor challenge after brain injury. Conclusions - Evaluation of changes of the HMF of cerebrovascular pressure transmission with respect to CPP changes permits continuous monitoring of cerebral autoregulation.