Time course of mental and psychomotor effects of 30 per cent nitrous oxide during inhalation and recovery

Two experiments were conducted testing the duration of action of nitrous oxide on human performance. In the first experiment, 11 subjects inhaled 30 per cent nitrous oxide for two 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 per cent. Recovery was tested using the same tests 2, 12, 22 and 32 min after discontinuation of N₂O. Eleven additional subjects inhaled oxygen only and served as a control group. In the second experiment, 8 subjects received both 30 per cent N₂O and oxygen in crossover fashion, and their flicker fusion threshold was measured. When compared to baseline or oxygen 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 second administration of N₂O were similar to those of the first experiment. There was no evidence of development of tolerance to mental and psychomotor effects of the drug.