title: Nonstationary multivariate modeling of cerebral autoregulation during hypercapnia.
abstract: We examined the time-varying characteristics of cerebral autoregulation and hemodynamics during a step hypercapnic stimulus by using recursively estimated multivariate (two-input) models which quantify the dynamic effects of mean arterial blood pressure (ABP) and end-tidal CO2 tension (PETCO2) on middle cerebral artery blood flow velocity (CBFV). Beat-to-beat values of ABP and CBFV, as well as breath-to-breath values of PETCO2 during baseline and sustained euoxic hypercapnia were obtained in 8 female subjects. The multiple-input, single-output models used were based on the Laguerre expansion technique, and their parameters were updated using recursive least squares with multiple forgetting factors. The results reveal the presence of nonstationarities that confirm previously reported effects of hypercapnia on autoregulation, i.e. a decrease in the MABP phase lead, and suggest that the incorporation of PETCO2 as an additional model input yields less time-varying estimates of dynamic pressure autoregulation obtained from single-input (ABP-CBFV) models.
authors.affiliation: Department of Electrical and Computer Engineering, University of Cyprus, Nicosia, Cyprus.
authors.forename: Kyriaki
authors.initials: K
authors.lastname: Kostoglou
authors.affiliation: Department of Physical Medicine and Rehabilitation, Faculty of Medicine, University of Calgary, AB, Canada.
authors.forename: Chantel T
authors.initials: CT
authors.lastname: Debert
authors.affiliation: Department of Physiology & Pharmacology, Faculty of Medicine, University of Calgary, AB, Canada; Department of Clinical Neurosciences, Faculty of Medicine, University of Calgary, AB, Canada; Faculty of Kinesiology, University of Calgary, AB, Canada; Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, AB, Canada; Libin Cardiovascular Institute of Alberta, Faculty of Medicine, University of Calgary, AB, Canada.
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Poulin
authors.affiliation: Department of Electrical and Computer Engineering, University of Cyprus, Nicosia, Cyprus. Electronic address: mitsis.georgios@ucy.ac.cy.
authors.forename: Georgios D
authors.initials: GD
authors.lastname: Mitsis
mesh_terms: D000328:Adult; D001794:Blood Pressure; D001921:Brain / Q000098:blood supply / Q000503:physiopathology*; D005260:Female; D006706:Homeostasis; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D020768:Middle Cerebral Artery / Q000502:physiology; D008954:Models, Biological; D015999:Multivariate Analysis
keywords: CO(2) reactivity; Cerebral hemodynamics; Laguerre functions; Multiple forgetting factors; Recursive Least Squares; Time varying systems