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: Carlos C Faraco, Megan K Strother, Jeroen C W Siero, Daniel F Arteaga, Allison O Scott, Lori C Jordan, Manus J Donahue
• Journal: Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism (J Cereb Blood Flow Metab) Vol. 35 Issue 12 Pg. 2032-42 (Dec 2015) ISSN: 1559-7016 [Electronic] United States
• PMID: 26174329 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Oxygen

Topics

• Adult
• Brain Mapping
• Cerebral Cortex (metabolism)
• Female
• Humans
• Hypercapnia (metabolism)
• Hyperoxia (metabolism)
• Magnetic Resonance Imaging
• Male
• Oxygen (blood)
• Reproducibility of Results
• Young Adult