IOP PUBLISHING PHYSIOLOGICAL MEASUREMENT Physiol. Meas. 28 (2007) 465–479 doi:10.1088/0967-3334/28/5/002 Wavelet assessment of cerebrospinal compensatory reserve and cerebrovascular reactivity M Latka 1 , W Kolodziej 2 , M Turalska 1 , D Latka 2 , W Zub 3 and B J West 4 1 Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland 2 Department of Neurosurgery, Opole Regional Medical Center, Al Witosa 26, 45-401 Opole, Poland 3 Department of Neurosurgery, Medical University, 50-420 Wroclaw, ul. R. Traugutta 118, Poland 4 Mathematical and Information Science Directorate, Army Research Office, PO Box 12211, Research Triangle, NC 27709-2211, USA E-mail: Miroslaw.Latka@pwr.wroc.pl Received 3 November 2006 Published 5 April 2007 Online at stacks.iop.org/PM/28/465 Abstract We introduce a wavelet transfer model to relate spontaneous arterial blood pressure (ABP) fluctuations to intracranial pressure (ICP) fluctuations. We employ a complex continuous wavelet transform to develop a consistent mathematical framework capable of parametrizing both cerebral compensatory reserve and cerebrovascular reactivity. The frequency-dependent gain and phase of the wavelet transfer function are introduced because of the non-stationary character of the ICP and ABP time series. The gain characterizes the dampening of spontaneous ABP fluctuations and is interpreted as a novel measure of cerebrospinal compensatory reserve. For a group of 12 patients who died as a result of cerebral lesions (Glasgow Outcome Scale (GOS) = 1) the average gain in the low-frequency (0.02– 0.07 Hz) range was 0.51 ± 0.13 and significantly exceeded that of 17 patients with GOS = 2 having an average gain of 0.26 ± 0.11 with p = 1×10 −4 (Kruskal–Wallis test). A time-averaged synchronization index (which may vary from 0 to 1) defined in terms of the wavelet transfer function phase yields information about the stability of the phase difference of the ABP and ICP signals and is used as a cerebrovascular reactivity index. A low value of synchronization index reflects a normally reactive vascular bed, while a high value indicates pathological entrainment of ABP and ICP fluctuations. Such entrainment is strongly pronounced in patients with fatal outcome (for this group the low-frequency synchronization index was 0.69 ± 0.17). The gain and synchronization parameters define a cerebral hemodynamic state space (CHS) in which the patients with GOS = 1 are to large extent partitioned away 0967-3334/07/050465+15$30.00 © 2007 IOP Publishing Ltd Printed in the UK 465