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I believe that the paper refered to by Richard which was partially written by Hamilton is as follows:- ----------- In EUBS '90 DOES OXYGEN CONTRIBUTE TO THE NARCOTIC ACTION OF HYPERBARIC AIR? D. Linnarsson, A. Ostlund, A. Sporrong, F. Lind and R. W. Hamilton Environmental Physiology Laboratory Department of Physiology, Karolinska Institutet Stockholm, Sweden, and Hamilton Research, Tarrytown, NY, USA ABSTRACT Although not a biochemically inert gas, oxygen has a lipid solubility which is almost twice that of N2, and O2 may therefore exert an narcotic action apart from its biochemical effects. We determined the psychomotor and mental performance impairments during exposures to air to normoxic N2-O2 mixtures at 6, 8.5 and 11 bar ambient pressure in 10 subjects. In this pilot study 3, 3, and 4 subjects were studied at 6, 8.5, and 11 bar respectively, and N2-O2 and air exposures were not randomized. Overall mental and psychomotor performance was im-paired by up to 40% at the highest ambient pressure as compared to control at 1.3 bar breathing air. Despite a substantially lower N2 partial pressure in the hyperbaric air experiments, performance was impaired to the same degree as in the corresponding N2-O2 experiments. It thus seems that substituting O2 fro some of the N2 does not ameliorate the mild narcosis. Within the limitations of the experimental design our results suggest that O2 contributes to the narcosis of hyperbaric air. INTRODUCTION Exposure to hyperbaric air causes narcosis which limits the usefulness of air as a diving gas. This well known phenomenon can be observed already at depth of 30 m and becomes more serious with increasing depth (2,5). Adolfson (1) reported that some subjects became totally incapacitated at an air pressure corresponding to 120-130 m sea water (13-14 bar absolute pressure) and that 11 bar air caused considerable decrements in psychomotor performance. Usually this narcosis has been considered as an effect of the N2 component of hyperbaric air. In this pilot study we have addressed the question whether O2 present in the hyperbaric air contributes to the narcosis together with N2. This may be so, since the narcotic potency of gases is related to their lipid solubility (4) and since the lipid solubility of O2 is almost twice that of N2. METHODS Ten healthy subjects were studied. All experiments were performed in a hyperbaric chamber. Respired gases were supplied with a low-resistance demand regulator (InterSpiro, Sweden). Psychomotor and mental performance was assessed with a computerized test battery (6). Each subject performed repeated training sessions at 1 bar air before the hyperbaric experiments in order to minimize learning effects of repeated tests. The test battery consisted of three 2-minute tests of reaction time, perceptive ability and cognitive ability. Each hyperbaric session started and ended with base-line control measurements with air at 1.3 bar. After a first control, subjects were compressed to 6 bar (n=3), 8.5 bar (n=3) or 11 bar (n=4). At these ambient pressures each subject performed the test battery twice, first breathing a normoxic N2-O2 and then breathing air. Each test was preceded by a 5-10 min resting period to permit wash-in/wash-out of gases. The order of the test was randomized among the subjects but was constant for each subject. Results were computed as the total number of correct responses per two-minute test in per cent of the arithmetic mean of the two control runs. An overall performance index was computed as an average per cent number of correct responses for all three test types. RESULTS There was a gradually increasing degree of performance impairment as the ambient pressure was increased (Fig. 1). In 6 subjects the impairment of overall performance at a given ambient pressure was less marked with air than with normoxic N2-O2. and in 4 subjects the reverse was true. No significant intra-individual differences (Student's t-test) were observed when applying Student's t-test. DISCUSSION Study design and statistics The design of this pilot study was dictated by that of a parallel study with a differing scientific objective, whey the present design has not been optimized to address the issue whether oxygen contributes to the narcotic action of hyperbaric air or not. Thus the air and normoxic N2-O2 experiments were not randomized and all 10 subjects were not observed at the same ambient pressure. With these limitations in mind, a cautious interpretation of data is warranted. Contribution of oxygen to the narcotic action of hyperbaric air
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