The influence of N2-O2 and He-O2 saturation diving on electroencephalogram of human bodies.

This paper reports the changes of the EEG of human bodies during saturation exposure at different depths to different mixed gases. The results of the research show that the most obvious on EEG was the appearance of diffused slow waves, usually theta waves of 4-7 times/s, and delta waves of 2-3 times/s within individual subjects. The EEG changes at 50 m were more obvious than those at 36.5 m. With the prolonging of time under high pressure, the EEG had some improvements, for instance, the slow waves decreased and the alpha waves increased. There was a certain relationship between these changes and the symptoms which appeared in the human body. The chief factor of the EEG changes is due to the effect of nitrogen narcosis during the oxygen-nitrogen diving experiment. In addition, carbon dioxide retention under the high pressure is also a factor of the EEG changes, because repeated inhaling of CO2-dense mixtures could aggravate the EEG changes and the reduction of carbon dioxide in humans by hyperventilation could improve abnormal EEGs. The main changes of the EEG during the helium-oxygen exposure at 302 m were the increase of theta waves, and even of delta waves, the decrease in alpha rhythm and the decline of amplitude of alpha waves. Increased theta index and decreased alpha index could be seen at the depth of 302 m. Under any of the above-mentioned pressure conditions when slow waves characteristic of abnormal changes appeared in the EEGs, the EEGs could be temporarily improved by photic stimulation, i.e. slow waves disappeared and alpha waves reappeared. When photic stimulation was over, alpha waves disappeared and slow waves reappeared. It was indicated that abnormal changes of the EEG under high pressure were a kind of temporary and reversible changes of the brain function.