Semi-automatic analysis of electroencephalogram in sleep apnea syndromes

The present study was undertaken to validate a system of condensed display of the sleep EEG spectral analysis with a view to simplifying sleep studies in patients affected by sleep apnea syndromes (SAS).

All subjects underwent polysomnography on two consecutive nights using a Respisomnograph. The 8-h EEG, electro-oculogram, and electromyogram were digitalized. A fast Fourier transform was done and successive spectrums were computed resulting in one spectrum for each 20-s period. Then the EEG spectrum was plotted as a Lofard color diagram.

To validate this system we compared a visual analysis of EEG recordings by a trained neurophysiologist with 10-s epochs and a visual analysis of the Lofard diagram by a practitioner with no previous understanding in EEG after only 2 h of instruction. The 8-h recording was divided into 10-min blocks. Each block was staged in function of the amplitude and prevailing frequency of EEG as indicated by the color (wakefulness, light slow wave sleep, deep slow wave sleep, rapid eye movement sleep). The stage of each block was compared with the predominant stage found in this block by the neurophysiologist.

Eight normal adults and 24 patients suffering from SAS were recruited.

When all the blocks of all patients were pooled (1,438 blocks), agreement was total in 81 percent, partial in 11 percent, and discordant in 8 percent.

This system of spectral analysis representation allows a fast evaluation of quality of sleep and of EEG.