Pressure reduction limits for rats subjected to various time/pressure exposures.

The impact of the combined effects of exposure time and hydrostatic pressure on pressure reduction is explored in this study. In Phase I of the study, excursion dives were made to 10, 20, and 30 ATA for 5, 10, 20, 40, or 80 min. In Phase II, the animals were saturated at 1.3, 10, or 20 ATA for 60 min; each saturation exposure was followed by a 10-atm excursion dive of either 1, 5, 10, 20, or 40 min. The chamber gas mixture during all pressure exposures was 0.51 ATA oxygen, 0.79 ATA nitrogen, and the remainder helium. The subjects were 655 rats; during each pressure exposure 5 rats were exercised in a rotating cage. After each exposure, the rats were abruptly decompressed to a lesser pressure for observation and tabulation of the decompression sickness incidence. Results suggest that neither the starting saturation pressure nor the differential excursion pressure alters the time required for an animal to reach equilibrium with the surrounding environment. Pressure-reduction values, however, vary with both the exposure pressure and exposure time. These results will have a direct impact on the formulation of future decompression models.