title: Assessing cerebrovascular reactivity by the pattern of response to progressive hypercapnia.
abstract: Cerebral blood flow responds to a carbon dioxide challenge, and is often assessed as cerebrovascular reactivity, assuming a linear response over a limited stimulus range or a sigmoidal response over a wider range. However, these assumed response patterns may not necessarily apply to regions with pathophysiology. Deviations from sigmoidal responses are hypothesised to result from upstream flow limitations causing competition for blood flow between downstream regions, particularly with vasodilatory stimulation; flow is preferentially distributed to regions with more reactive vessels. Under these conditions, linear or sigmoidal fitting may not fairly describe the relationship between stimulus and flow. To assess the range of response patterns and their prevalence a survey of healthy control subjects and patients with cerebrovascular disease was conducted. We used a ramp carbon dioxide challenge from hypo- to hypercapnia as the stimulus, and magnetic resonance imaging to measure the flow responses. We categorized BOLD response patterns into four types based on the signs of their linear slopes in the hypo- and hypercapnic ranges, color coded and mapped them onto their respective anatomical scans. We suggest that these type maps complement maps of linear cerebrovascular reactivity by providing a better indication of the actual response patterns. Hum Brain Mapp 38:3415-3427, 2017. © 2017 Wiley Periodicals, Inc.
authors.affiliation: Department of Physiology, University of Toronto, Toronto, Canada.|Institute of Medical Science, University of Toronto, Toronto, Canada.|Department of Anaesthesia and Pain Management, University Health Network, University of Toronto, Toronto, Canada.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fisher
authors.affiliation: Institute of Medical Science, University of Toronto, Toronto, Canada.
authors.forename: Olivia
authors.initials: O
authors.lastname: Sobczyk
authors.affiliation: Joint Department of Medical Imaging and the Functional Neuroimaging Laboratory, University Health Network, Toronto, Canada.
authors.forename: Adrian
authors.initials: A
authors.lastname: Crawley
authors.affiliation: Joint Department of Medical Imaging and the Functional Neuroimaging Laboratory, University Health Network, Toronto, Canada.
authors.forename: Julien
authors.initials: J
authors.lastname: Poublanc
authors.affiliation: Joint Department of Medical Imaging and the Functional Neuroimaging Laboratory, University Health Network, Toronto, Canada.
authors.forename: Paul
authors.initials: P
authors.lastname: Dufort
authors.affiliation: Department of Anaesthesia and Pain Management, University Health Network, University of Toronto, Toronto, Canada.
authors.forename: Lashmi
authors.initials: L
authors.lastname: Venkatraghavan
authors.affiliation: Joint Department of Medical Imaging and the Functional Neuroimaging Laboratory, University Health Network, Toronto, Canada.
authors.forename: Kevin
authors.initials: K
authors.lastname: Sam
authors.affiliation: Institute of Medical Science, University of Toronto, Toronto, Canada.|Joint Department of Medical Imaging and the Functional Neuroimaging Laboratory, University Health Network, Toronto, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Mikulis
authors.affiliation: Department of Physiology, University of Toronto, Toronto, Canada.|Department of Anaesthesia and Pain Management, University Health Network, University of Toronto, Toronto, Canada.
authors.forename: James
authors.identifier: http://orcid.org/0000-0003-2270-7392
authors.initials: J
authors.lastname: Duffin
keywords: carbon dioxide; cerebral blood flow; cerebrovascular reactivity