Use of oxygen for optimizing decompression.

For over 70 years, decompression has been facilitated by the use of elevated oxygen partial pressures. Oxygen has been administered even though little is known about the proper dosage or the way in which this benefit is derived. The historical literature indicates that there is an envelope or narrow range of oxygen partial pressures that can be used. If the oxygen is too low, the incidence of decompression sickness increases; if the oxygen is too high, oxygen poisoning becomes a problem. The present study was designed to explore this oxygen envelope and to define the relationships between oxygen partial pressure, exposure time, and pressure, and to delineate their effects on pressure-reduction limits. To define the ED50 (the effective dose that produced signs of decompression sickness in 50% of the animals), we exposed 820 female albino rats to 42 experimental conditions. Results suggest that the optimum oxygen level and the size of the oxygen envelope both depend on the ambient hydrostatic pressure and the exposure time. For short "shallow" exposures, the optimum oxygen level is high and the oxygen envelope is large; for long "deep" exposures, the optimum oxygen level is reduced and the envelope is restricted.