title: The cumulative influence of hyperoxia and hypercapnia on blood oxygenation and R*₂.
abstract: Cerebrovascular reactivity (CVR)-weighted blood-oxygenation-level-dependent magnetic resonance imaging (BOLD-MRI) experiments are frequently used in conjunction with hyperoxia. Owing to complex interactions between hyperoxia and hypercapnia, quantitative effects of these gas mixtures on BOLD responses, blood and tissue R2*, and blood oxygenation are incompletely understood. Here we performed BOLD imaging (3 T; TE/TR=35/2,000 ms; spatial resolution=3 × 3 × 3.5 mm(3)) in healthy volunteers (n=12; age=29±4.1 years) breathing (i) room air (RA), (ii) normocapnic-hyperoxia (95% O2/5% N2, HO), (iii) hypercapnic-normoxia (5% CO2/21% O2/74% N2, HC-NO), and (iv) hypercapnic-hyperoxia (5% CO2/95% O2, HC-HO). For HC-HO, experiments were performed with separate RA and HO baselines to control for changes in O2. T2-relaxation-under-spin-tagging MRI was used to calculate basal venous oxygenation. Signal changes were quantified and established hemodynamic models were applied to quantify vasoactive blood oxygenation, blood-water R2*, and tissue-water R2*. In the cortex, fractional BOLD changes (stimulus/baseline) were HO/RA=0.011±0.007; HC-NO/RA=0.014±0.004; HC-HO/HO=0.020±0.008; and HC-HO/RA=0.035±0.010; for the measured basal venous oxygenation level of 0.632, this led to venous blood oxygenation levels of 0.660 (HO), 0.665 (HC-NO), and 0.712 (HC-HO). Interleaving a HC-HO stimulus with HO baseline provided a smaller but significantly elevated BOLD response compared with a HC-NO stimulus. Results provide an outline for how blood oxygenation differs for several gas stimuli and provides quantitative information on how hypercapnic BOLD CVR and R2* are altered during hyperoxia.
authors.affiliation: Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Carlos C
authors.initials: CC
authors.lastname: Faraco
authors.affiliation: Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Megan K
authors.initials: MK
authors.lastname: Strother
authors.affiliation: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Jeroen C W
authors.initials: JC
authors.lastname: Siero
authors.affiliation: Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Arteaga
authors.affiliation: Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Allison O
authors.initials: AO
authors.lastname: Scott
authors.affiliation: Department of Pediatric Neurology, Vanderbilt Children's Hospital, Nashville, Tennessee, USA.|Department of Neurology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Lori C
authors.initials: LC
authors.lastname: Jordan
authors.affiliation: Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA.|Department of Neurology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.|Department of Psychiatry, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Manus J
authors.initials: MJ
authors.lastname: Donahue
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000378:metabolism; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000378:metabolism*; D018496:Hyperoxia / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D008297:Male; D010100:Oxygen / Q000097:blood*; D015203:Reproducibility of Results; D055815:Young Adult
chemical_list: D010100:Oxygen