A Trimix saturation dive to 660 m Studies of cognitive performance, mood and sleep quality

Abstract

This paper reports psychological observations on men during a simulated (pressure chamber) dive to 660 m of sea-water (msw) using a gas mixture known as Trimix (He-O₂-N₂). Recent studies by Bennett (1981) have suggested that this mixture allows for faster compression with less impairment in performance than the mixture traditionally used (He-O₂). Data were obtained from two divers on tests of cognitive performance, namely arithmetic ability, grammatical reasoning, perceptual speed, visuo-spatial manipulation and semantic processing. At maximum depth there was a severe blanket impairment of ability to perform any of the tests. However, at shallower depths the impairments were not as marked, with performance at 300 msw close to that measured at surface pressure. Subjects were also required to fill in two questionnaires, one concerned with the quality of their previous night's sleep, the other with their mood at the time. Sleep quality was disrupted throughout the dive, with one subject affected rather more than the other. Mood patterns varied less systematically, with large individual differences. Low correlations between sleep quality and performance indicate that performance decrements were due almost entirely to breathing Trimix at high pressure.