EEG changes measured by spectrum analysis under hyperbaric conditions

The subject of experimental, saturated dividing to 20 m depth was alertness level measured by means of spectral analysis of EEG records. Air was served as breathing mixture compressed to a given depth in closed circulating system. Altogether 49 EEG records made during compression, plateau and decompression, were analysed. Two methods of analysis were applied. "Normality ratio" combined the information from 20 different EEG values and "EEG alertness indicator" showed in three cases pathological slowing and fluctuations of the alertness. According to index of alertness, the most prominent changes were seen during the compression and decompression phase. During the plateau phase sleepiness was recorded. The applied method could provide information when slowing is due to metabolic impairment of brain activity from that of sleepiness.