Effects of exponential compression curves with nitrogen injection in humans

Two series of experiments were carried out on humans to study the effects of fast and slow exponential compression curves with N2 additions. Eight subjects in the first series and 13 subjects in the second series were analyzed up to the depths of 400-450 m of seawater (msw). The data indicated that injections of N2 in He-O2 mixture reduced or suppressed the hyperbaric tremor in the two series. Electroencephalographic (EEG) changes were recorded with the two types of compression, but these changes (increase in slow waves, decrease in alpha-activity, appearance of microsleep EEG traces) were more important with the fast exponential compression curves between 200 and 300 msw than with the slow exponential curves. The effects of the fast rates of compression on EEG activities were not compensated by addition of 4-5% N2. Consequently, the fast exponential compression curves, even with N2 injections, cannot be used without risk and must be avoided; the slow exponential compression curve with N2 injection allowed a human subject to reach 450 msw in satisfactory condition, i.e., without tremor and with light EEG changes.