Electroencephalographic and other changes induced by high partial pressures of nitrogen

Abstract

Men have been subjected to compressed air in a pressure chamber and their electroencephalograms recorded while they solved arithmetical problems. At atmospheric pressure these problems elicited a blocking of the alpha rhythm, but after a variable time at increased pressures no such alpha blocking occurred. The time from the beginning of their exposure to high pressures, until abolition of the alpha blocking response, was found to be inversely proportional to the square of the pressure, i.e. P√ T is a constant. If after blocking abolition, an oxy-helium mixture was substituted for the compressed air, blocking reappeared, implicating nitrogen as the agent responsible. A diminution in the amplitude of the alpha activity was observed at 7 atm absolute which was severe at 10 atm absolute. At these pressures, when the time to abolition of blocking was very short signs and symptoms of narcosis were present. Correlations between the EEG findings and the mental state are discussed, together with their possible connection with the ascending reticular formation of the brain stem.