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. 2014 May 15;10(5):517-22.
doi: 10.5664/jcsm.3700.

Hypercapnia is a key correlate of EEG activation and daytime sleepiness in hypercapnic sleep disordered breathing patients

David Wang  1 , Amanda J Piper  1 , Brendon J Yee  2 , Keith K Wong  2 , Jong-Won Kim  3 , Angela D'Rozario  4 , Luke Rowsell  5 , Derk-Jan Dijk  6 , Ronald R Grunstein  2
Affiliations

Hypercapnia is a key correlate of EEG activation and daytime sleepiness in hypercapnic sleep disordered breathing patients

David Wang et al. J Clin Sleep Med. .

Abstract

Background: The key determinants of daytime drowsiness in sleep disordered breathing (SDB) are unclear. Hypercapnia has not been examined as a potential contributor due to the lack of reliable measurement during sleep. To overcome this limitation, we studied predominantly hypercapnic SDB patients to investigate the role of hypercapnia on EEG activation and daytime sleepiness.

Methods: We measured overnight polysomnography (PSG), arterial blood gases, and Epworth Sleepiness Scale in 55 severe SDB patients with obesity hypoventilation syndrome or overlap syndrome (COPD+ obstructive sleep apnea) before and ∼3 months after positive airway pressure (PAP) treatment. Quantitative EEG analyses were performed, and the Delta/ Alpha ratio was used as an indicator of EEG activation.

Results: After the PAP treatment, these patients showed a significant decrease in their waking pCO(2), daytime sleepiness, as well as all key breathing/oxygenation parameters during sleep. Overnight Delta/Alpha ratio of EEG was significantly reduced. There is a significant cross-correlation between a reduced wake pCO(2), a faster (more activated) sleep EEG (reduced Delta/Alpha ratio) and reduced daytime sleepiness (all p < 0.05) with PAP treatment. Multiple regression analyses showed the degree of change in hypercapnia to be the only significant predictor for both ESS and Delta/ Alpha ratio.

Conclusions: Hypercapnia is a key correlate of EEG activation and daytime sleepiness in hypercapnic SDB patients. The relationship between hypercapnia and sleepiness may be mediated by reduced neuro-electrical brain activity.

Keywords: CO2; EEG Spectra; O2; cortical depression.; daytime drowsiness; hypersomnolence; hypoxia.

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Figures

Figure 1
Figure 1. Inter-correlations between the changes of pCO2, EEG Delta/Alpha ratio and ESS before and after PAP treatment.
The 3 panels show consistent pattern of relationships between OHS and overlap subtypes. Panel C shows that even though the overall correlation between the changes of ESS and D/A ratio is relevantly loose (p = 0.049), the OHS and overlap subgroups show a similar pattern of relationship.
See this image and copyright information in PMC

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