ASSESSMENT OF CEREBRAL HEMODYNAMICS IN TRAUMATIC BRAIN INJURY

We employ complex continuous wavelet transforms to develop a consistent mathematical framework capable of quantifying both cerebrospinal compensatory reserve and cerebrovascular pressure–reactivity. The wavelet gain ()ICPABP fη, defined as the frequency dependent ratio of time averaged wavelet coefficients of intracranial pressure (ICP) and arterial blood pressure (ABP) fluctuations, characterizes the dampening of spontaneous ABP oscilla-tions. This gain is introduced as a novel measure of cere-brospinal compensatory reserve. For a group of 12 pa-tients who died as a result of cerebral lesions (Glasgow Outcome Scale GOS =1) the average gain calculated at f=0.05 Hz significantly exceeds that of 17 patients with GOS=2: with 0.45ICPABPη = 0.24ICPABPη = 54 10p − = × (Kruskal-Wallis test). We also study the dynamics of in-stantaneous phase difference ()fφΔ between the fluctua-tions of ABP and ICP. The time-averaged synchronization index 2 ( ) sin cosICPABP f 1 2γ φ = Δ + Δφ, which depends upon frequency, yields information about the stability of the phase difference φΔ and is used as a cerebrovascular pressure–reactivity index. For both groups of patients the synchronization is strong. We hypothesize that in patients who died the impairment of cerebral autoregulation is followed by the breakdown of residual pressure reactivity. For example at f=0.05 Hz (GOS=1) and (GOS=2). While these two synchronization levels are not statistically different (p=0.15) the corre-sponding average phase difference for GOS=1 is equal to 10 degrees in sharp contrast to the mean value of 44 de-grees for patients with GOS=2 ()