Decompression comparison of N2 and O2 in rats.

We have previously reported that O2 in the breathing gas mixture contributed significantly to the risk of decompression sickness (DCS) in rats after rapid (less than 10 s) decompression to the surface from depth. The rate of O2 uptake was extremely fast (less than 1 min estimated for equilibrium after a pressure change) compared to much slower rates for He and N2. To further define the role that O2 plays in diving, the present investigation examined decompression outcome in unanesthetized male albino rats after 60-min N2-O2 dives (1-3 atm abs O2, depth 6.26 or 7.26 atm abs). Slower decompression profiles were used to determine the elimination rates of N2 and O2 as pressure was reduced and included "stops" of up to 20 min. The probability of DCS was modeled using the maximum likelihood technique. O2 again contributed significantly to the risk of DCS, although O2 was eliminated very rapidly during decompression; the washout of N2 was considerably longer. These findings support the view that O2 can add significantly to decompression risk. However, this phenomenon may not normally be encountered during human diving operations where relatively slower decompression and lower PO2's are used.