Longitudinal study of performance after deep compressions with heliox and He-N2-O2

This study concerns three hyperbaric experiments. During SAGITTAIRE iv, compression to 610 msw was accomplished in 11 days with an atmosphere of helium-oxygen. For the two CORAZ experiments, compression to 300 msw was done in 4 hours with He-N2-O2 trimix, varying nitrogen concentration from CORAZI (2.8 ATA N2 =9%) to CORAZ II (1.4 ATA N2=4.5%). Oxygen partial pressure was always maintained at 0.4 ATA except during decompression. The same two subjects participated in all three experiments and underwent the following psychometric tests: manual dexterity, visual choice-reaction time, and number ordination. Results show a large decrement in performance at 610 msw after slow compression (-50% and -47% on the number ordination test, -34% and -24% on the visual choice-reaction time). Test performance was less affected after the rapid compressions to 300 msw, and recuperation to control values occurred within 1 day at 300 msw. Our data show that 1.4 ATA N2 is less detrimental to performance than 2.8 ATA N2 for trimix compressions to 300 msw in 4 hours.