The influence of carbon dioxide on brain activity and metabolism in conscious humans.
A better understanding of carbon dioxide (CO(2)) effect on brain activity may have a profound impact on clinical studies using CO(2) manipulation to assess cerebrovascular reserve and on the use of hypercapnia as a means to calibrate functional magnetic resonance imaging (fMRI) signal. This study investigates how an increase in blood CO(2), via inhalation of 5% CO(2), may alter brain activity in humans. Dynamic measurement of brain metabolism revealed that mild hypercapnia resulted in a suppression of cerebral metabolic rate of oxygen (CMRO(2)) by 13.4% ± 2.3% (N=14) and, furthermore, the CMRO(2) change was proportional to the subject's end-tidal CO(2) (Et-CO(2)) change. When using functional connectivity MRI (fcMRI) to assess the changes in resting-state neural activity, it was found that hypercapnia resulted in a reduction in all fcMRI indices assessed including cluster volume, cross-correlation coefficient, and amplitude of the fcMRI signal in the default-mode network (DMN). The extent of the reduction was more pronounced than similar indices obtained in visual-evoked fMRI, suggesting a selective suppression effect on resting-state neural activity. Scalp electroencephalogram (EEG) studies comparing hypercapnia with normocapnia conditions showed a relative increase in low frequency power in the EEG spectra, suggesting that the brain is entering a low arousal state on CO(2) inhalation.
Xu
Feng
F
Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Uh
Jinsoo
J
Brier
Matthew R
MR
Hart
John
J
Yezhuvath
Uma S
US
Gu
Hong
H
Yang
Yihong
Y
Lu
Hanzhang
H
D000328:Adult; D001921:Brain / Q000187:drug effects*; D001923:Brain Chemistry / Q000187:drug effects*; D002245:Carbon Dioxide / Q000494:pharmacology*; D002560:Cerebrovascular Circulation / Q000187:drug effects; D003243:Consciousness; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects; D055724:Electrophysiological Phenomena; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006935:Hypercapnia / Q000378:metabolism; D008279:Magnetic Resonance Imaging; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D056152:Respiratory Rate / Q000187:drug effects; D055815:Young Adult
D002245:Carbon Dioxide