The Influence of Carbon Dioxide on Brain Activity and Metabolism in Conscious Humans

• Published in: Journal of cerebral blood flow and metabolism Vol. 31; no. 1; pp. 58 - 67
• Main Authors: Xu, Feng, Uh, Jinsoo, Brier, Matthew R, Hart, John, Yezhuvath, Uma S, Gu, Hong, Yang, Yihong, Lu, Hanzhang
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01.01.2011; Nature Publishing Group; Sage Publications Ltd
• Subjects: Adult; Biological and medical sciences; Brain - drug effects; Brain Chemistry - drug effects; Carbon Dioxide - pharmacology; Cerebrovascular Circulation - drug effects; Consciousness; Dose-Response Relationship, Drug; Electroencephalography - drug effects; Electrophysiological Phenomena; Female; Heart Rate - physiology; Humans; Hypercapnia - metabolism; Investigative techniques, diagnostic techniques (general aspects); Magnetic Resonance Imaging; Male; Medical sciences; Nervous system; Neurology; Original; Oxygen Consumption - drug effects; Respiratory Rate - drug effects; Ultrasonic investigative techniques; Vascular diseases and vascular malformations of the nervous system; Young Adult; carbon dioxide; functional connectivity MRI; cerebral metabolic rate of oxygen; electroencephalogram; hypercapnia; Human; Oxygen; Nervous system diseases; Respiratory disease; Carbon dioxide; Electroencephalography; Metabolism; Nuclear magnetic resonance imaging; Cerebral disorder; Encephalon; Hypercapnia; Central nervous system disease; Cerebrovascular disease
• ISSN: 0271-678X; 1559-7016; 1559-7016
• DOI: 10.1038/jcbfm.2010.153

A better understanding of carbon dioxide (CO2) effect on brain activity may have a profound impact on clinical studies using CO2 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 CO2, via inhalation of 5% CO2, 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 (CMRO2) by 13.4%±2.3% (N=14) and, furthermore, the CMRO2 change was proportional to the subject's end-tidal CO2 (Et-CO2) 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 CO2 inhalation.