title: Measuring cerebrovascular reactivity: the dynamic response to a step hypercapnic stimulus.
abstract: We define cerebral vascular reactivity (CVR) as the ratio of the change in blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) signal (S) to an increase in blood partial pressure of CO2 (PCO2): % Δ S/Δ PCO2 mm Hg. Our aim was to further characterize CVR into dynamic and static components and then study 46 healthy subjects collated into a reference atlas and 20 patients with unilateral carotid artery stenosis. We applied an abrupt boxcar change in PCO2 and monitored S. We convolved the PCO2 with a set of first-order exponential functions whose time constant τ was increased in 2-second intervals between 2 and 100 seconds. The τ corresponding to the best fit between S and the convolved PCO2 was used to score the speed of response. Additionally, the slope of the regression between S and the convolved PCO2 represents the steady-state CVR (ssCVR). We found that both prolongations of τ and reductions in ssCVR (compared with the reference atlas) were associated with the reductions in CVR on the side of the lesion. τ and ssCVR are respectively the dynamic and static components of measured CVR.
authors.affiliation: Joint Department of Medical Imaging, University Health Network, Toronto, Ontario, Canada.
authors.forename: Julien
authors.initials: J
authors.lastname: Poublanc
authors.affiliation: Joint Department of Medical Imaging, University Health Network, Toronto, Ontario, Canada.
authors.forename: Adrian P
authors.initials: AP
authors.lastname: Crawley
authors.affiliation: Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Olivia
authors.initials: O
authors.lastname: Sobczyk
authors.affiliation: Joint Department of Medical Imaging, University Health Network, Toronto, Ontario, Canada.
authors.forename: Gaspard
authors.initials: G
authors.lastname: Montandon
authors.affiliation: Department of Physiology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Kevin
authors.initials: K
authors.lastname: Sam
authors.affiliation: Joint Department of Medical Imaging, University Health Network, Toronto, Ontario, Canada.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Mandell
authors.affiliation: Joint Department of Medical Imaging, University Health Network, Toronto, Ontario, Canada.
authors.forename: Paul
authors.initials: P
authors.lastname: Dufort
authors.affiliation: Department of Anaesthesia and Pain Management, University Health Network, Toronto, Ontario, Canada.
authors.forename: Lashmikumar
authors.initials: L
authors.lastname: Venkatraghavan
authors.affiliation: Department of Physiology, University of Toronto, Toronto, Ontario, Canada.|Department of Anaesthesia and Pain Management, University Health Network, Toronto, Ontario, Canada.
authors.forename: James
authors.initials: J
authors.lastname: Duffin
authors.affiliation: Joint Department of Medical Imaging, University Health Network, Toronto, Ontario, Canada.|Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada.
authors.forename: David J
authors.initials: DJ
authors.lastname: Mikulis
authors.affiliation: Joint Department of Medical Imaging, University Health Network, Toronto, Ontario, Canada.|Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada.|Department of Physiology, University of Toronto, Toronto, Ontario, Canada.|Department of Anaesthesia and Pain Management, University Health Network, Toronto, Ontario, Canada.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fisher
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001931:Brain Mapping; D002245:Carbon Dioxide / Q000097:blood; D016893:Carotid Stenosis / Q000097:blood / Q000503:physiopathology; D002560:Cerebrovascular Circulation; D002561:Cerebrovascular Disorders / Q000097:blood / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen