Time Course of Mental and Psychomotor Effects of 30 Per Cent Nitrous Oxide during Inhalation and Recovery

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Abstract
Two experiments were conducted testing the duration of action of N2O on human performance. In the 1st experiment, 11 subjects inhaled 30% N2O for 2 periods of 40 min each, 45 min apart. Their mental and psychomotor skills were measured using free recall, tapping board, arithmetic and flicker fusion tests before and 2, 12, 22 and 32 min after establishing an end-tidal concentration of N2O of 30%. Recovery was tested using the same tests 2, 12, 22 and 32 min after discontinuation of N2O. Eleven additional subjects inhaled O2 only and served as a control group. In the 2nd experiment, 8 subjects received both 30% N2O and O2 in crossover fashion and their flicker fusion threshold was measured. When compared to baseline or O2 administration, N2O significantly impaired tapping rate, number of words recalled, and performance in arithmetic tests. The effects of N2O were maximal at 2 min and remained similar throughout the entire administration. In flicker fusion tests, the effects of N2O were similar to those of stimulant drugs; N2O improved the subjects'' ability to discriminate the fusion of flickering light. Recovery was complete in 22 min. The effects of, and recovery from the 2nd administration of N2O were similar to those of the 1st experiment. There was no evidence of development of tolerance to mental and psychomotor effects of the drug.