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.
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, 2 min), during 7% CO₂/air mixture inhalation (hypercapnia, 90 s) and post-CO₂ (ambient air, 2 min) 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 (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), beta 2 (20-30 Hz) and gamma (30-40 Hz) 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.


CONCLUSIONS
In amnesic MCI patients, global EEG functional coupling is basically low in amplitude and does not react to hypercapnia.
Department of Physiology and Pharmacology, University of Rome "La Sapienza", Rome, Italy; IRCCS San Raffaele Pisana, Rome, Italy. Electronic address: claudio.babiloni@uniroma1.it.
Claudio
C
Babiloni
IRCCS San Raffaele Pisana, Rome, Italy; A.Fa.R. Dip. Neurosci, Ospedale 'San Giovanni Calibita' Fatebenefratelli, Isola Tiberina, Rome, Italy.
Fabrizio
F
Vecchio
Unità di Neurologia, Università Campus Bio-Medico di Roma, Rome, Italy.
Riccardo
R
Altavilla
A.Fa.R. Dip. Neurosci, Ospedale 'San Giovanni Calibita' Fatebenefratelli, Isola Tiberina, Rome, Italy.
Francesco
F
Tibuzzi
IRCCS San Raffaele Pisana, Rome, Italy.
Roberta
R
Lizio
Unità di Neurologia, Università Campus Bio-Medico di Roma, Rome, Italy.
Claudia
C
Altamura
Unità di Neurologia, Università Campus Bio-Medico di Roma, Rome, Italy.
Paola
P
Palazzo
Unità di Neurologia, Università Campus Bio-Medico di Roma, Rome, Italy.
Paola
P
Maggio
Unità di Neurologia, Università Campus Bio-Medico di Roma, Rome, Italy.
Francesca
F
Ursini
A.Fa.R. Dip. Neurosci, Ospedale 'San Giovanni Calibita' Fatebenefratelli, Isola Tiberina, Rome, Italy.
Matilde
M
Ercolani
IRCCS SDN, Napoli, Italy; Department of Studies of Institutions and Territorial Systems, University of Naples Parthenope, Naples, Italy.
Andrea
A
Soricelli
IRCCS SDN, Napoli, Italy.
Giuseppe
G
Noce
IRCCS San Raffaele Pisana, Rome, Italy; Department of Geriatrics, Neuroscience & Orthopedics, Institute of Neurology Catholic University "Sacro Cuore", Rome, Italy.
Paolo Maria
PM
Rossini
Unità di Neurologia, Università Campus Bio-Medico di Roma, Rome, Italy.
Fabrizio
F
Vernieri
D000368:Aged; D000375:Aging / Q000502:physiology; D000647:Amnesia / Q000150:complications / Q000503:physiopathology*; D001921:Brain / Q000503:physiopathology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D060825:Cognitive Dysfunction / Q000150:complications / Q000503:physiopathology*; D004569:Electroencephalography / Q000379:methods; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D006935:Hypercapnia / Q000150:complications / Q000503:physiopathology*; D008297:Male
Amnesic mild cognitive impairment (MCI); Electroencephalography (EEG); Hypercapnia (CO(2)); Near-infrared spectroscopy (NIRS); Resting state