Hypercapnia affects the functional coupling of resting state electroencephalographic rhythms and cerebral haemodynamics in healthy elderly subjects and in patients with amnestic mild cognitive impairment

Claudio Babiloni, Fabrizio Vecchio, Riccardo Altavilla, Francesco Tibuzzi, Roberta Lizio, Claudia Altamura, Paola Palazzo, Paola Maggio, Francesca Ursini, Matilde Ercolani, Andrea Soricelli, Giuseppe Noce, Paolo Maria Rossini, Fabrizio Vernieri

Research output: Contribution to journalArticlepeer-review

Abstract

Objective: Cerebral vasomotor reactivity (VMR) and coherence of resting state electroencephalographic (EEG) rhythms are impaired in Alzheimer's disease (AD) patients. Here we tested the hypothesis that these two variables could be related. Methods: We investigated VMR and coherence of resting state EEG rhythms in nine normal elderly (Nold) and in 10 amnesic mild cognitive impairment (MCI) subjects. Resting state eyes-closed EEG data were recorded at baseline pre-CO2 (ambient air, 2min), during 7% CO2/air mixture inhalation (hypercapnia, 90s) and post-CO2 (ambient air, 2min) conditions. Simultaneous frontal bilateral near-infrared spectroscopy (NIRS) was performed to assess VMR by cortical oxy- and deoxy-haemoglobin concentration changes. EEG coherence across all electrodes was computed at delta (2-4Hz), theta (4-8Hz), alpha 1 (8-10.5Hz), alpha 2 (10.5-13Hz), beta 1 (13-20Hz), beta 2 (20-30Hz) and gamma (30-40Hz) bands. Results: In Nold subjects, 'total coherence' of EEG across all frequency bands and electrode pairs decreased during hypercapnia, with full recovery during post-CO2. Total coherence resulted lower in pre-CO2 and post-CO2 and presented poor reactivity during CO2 inhalation in MCI patients compared with Nold subjects. Hypercapnia increased oxy-haemoglobin and decreased deoxy-haemoglobin concentrations in both groups. Furthermore, the extent of changes in these variables during CO2 challenge was correlated with the EEG coherence, as a reflection of neurovascular coupling. Conclusions: Hypercapnia induced normal frontal VMR that was detected by NIRS in both Nold and amnesic MCI groups, while it produced a reactivity of global functional coupling of resting state EEG rhythms only in the Nold group. Significance: In amnesic MCI patients, global EEG functional coupling is basically low in amplitude and does not react to hypercapnia.

Original languageEnglish
Pages (from-to)685-693
Number of pages9
JournalClinical Neurophysiology
Volume125
Issue number4
DOIs
Publication statusPublished - Apr 2014

Keywords

  • Amnesic mild cognitive impairment (MCI)
  • Electroencephalography (EEG)
  • Hypercapnia (CO)
  • Near-infrared spectroscopy (NIRS)
  • Resting state

ASJC Scopus subject areas

  • Clinical Neurology
  • Neurology
  • Physiology (medical)
  • Sensory Systems
  • Medicine(all)

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