title: Precise control of end-tidal carbon dioxide and oxygen improves BOLD and ASL cerebrovascular reactivity measures.
abstract: In-depth investigation of cerebrovascular blood flow and MR mechanisms underlying the blood oxygenation level dependent signal requires precise manipulation of the arterial partial pressure of carbon dioxide and oxygen, measured by their noninvasive surrogates, the end-tidal values. The traditional methodology consists of administering a fixed fractional concentration of inspired CO(2), but this causes a variable ventilatory response across subjects, resulting in different values of end-tidal partial pressures of CO(2) and O(2). In this study, we investigated whether fine control of these end-tidal partial pressures would improve stability and predictability of blood oxygenation level dependent and arterial spin labeling signals for studying cerebrovascular reactivity. In 11 healthy volunteers, we compared the MR signals generated by the traditional fixed fractional concentration of inspired CO(2) method to those of an automated feed-forward system, a simpler, safer, and more compact alternative to dynamic end-tidal forcing systems, designed to target constant end-tidal partial pressures of CO(2) and O(2). We found that near square-wave changes in end-tidal partial pressure of CO(2) of 5, 7.5, and 10 mm Hg (+/-1.01 mm Hg within two to three breaths) and constrained changes in the end-tidal partial pressure of O(2) (<10 mm Hg) induced cerebral vascular reactivity measurements with faster transitions, together with improved stability and gradation, than those achieved with the traditional fixed fractional concentration of inspired CO(2) method.
authors.affiliation: McConnell Brain Imaging Center, Montreal Neurological Institute, Montreal, Quebec, Canada. clarisse.mark@mail.mcgill.ca
authors.forename: Clarisse I
authors.initials: CI
authors.lastname: Mark
authors.forename: Marat
authors.initials: M
authors.lastname: Slessarev
authors.forename: Shoji
authors.initials: S
authors.lastname: Ito
authors.forename: Jay
authors.initials: J
authors.lastname: Han
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fisher
authors.forename: G Bruce
authors.initials: GB
authors.lastname: Pike
mesh_terms: D002245:Carbon Dioxide / Q000097:blood*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D018810:Magnetic Resonance Angiography / Q000295:instrumentation* / Q000379:methods; D008297:Male; D010100:Oxygen / Q000097:blood*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012121:Respiration, Artificial / Q000295:instrumentation*; D013990:Tidal Volume / Q000502:physiology; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen