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Fig. 1.
Example of raw EEG (normal subject). Time marks, 1 second.
2.2 Recording and Visual Analysis of the EEG
EEG recordings were obtained before the beginning of the hemodialysis session
in psycho-physical rest for 20 minutes, alternating eyes open and closed and ac-
tivation is performed with 3 minutes of hyperventilation and intermittent light
stimulation at 8, 10, 15 and 20 Hz. An example of normal EEG is shown in
figure 1. To record the signal, a video-EEG equipment (Neuroworks Xltek ver-
sion 5.4.0) of 32 channels was used. The EEG signal was recorded using surface
electrodes,
AgCl
, once an impedance of less than 10
KΩ
was reached. Using
the 10
/
20 International System for electrode placement, scalp electrodes were
placed at Fp1, F3, C3, P3, O1, F7, T3, T5, Fz, Cz, Pz, Fp2, F4, C4, P4, O2,
F8, T4, T6 and A1 as reference. Recording was performed with a longitudinal
mounting: Fp1-F3, F3-C3, C3-P3, P3-O1, Fp2-F4, F4-C4, C4-P4, P4-O2, Fp1-
F7, F7-T3, T3-T5, T5 -O1, Fp2-F8, F8-T4, T4-T6, T6-O2, Fz-Cz, Cz-Pz, and
other reference (each against a common reference electrode used: A1). The sam-
pling frequency was 500 Hz, high pass filters set at 0.5 Hz and low pass at 100
Hz, with AC filter (notch filter) at 50 Hz. Records were stored on computer disk
for off-line analysis. The initial visual inspection was performed with a scanning
screen of 15 seconds (30 mm
/
second) and with the scale extended to 10
μ
V/mm.
2.3 Quantitative Analysis of the EEG
Signals were exported to MATLAB environment. After semiautomatic elimi-
nation of artifacts, with visual confirmation, quantitative analysis of EEG was
performed in each of the derivations using different numerical techniques. Power
spectrum was calculated using Welch averaged periodogram, with a window of
4 seconds, 50% overlap and a Hanning window. Blocks containing artifacts were
skipped when averaging the periodograms. Relative power was evaluated in the
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