Relation of breathing oxygen-argon gas mixtures to altitude decompression sickness

A 95% oxygen-5% argon breathing mixture produced by a molecular sieve generator was shown to be similar to a 95% O2-5% N2 mixture for breathing during 1-h exposures at 7,620 m (25,000 ft) or 10,972 m (35,000 ft), as determined by the detection of proportionate numbers of intravascular bubbles in the pulmonary artery of dogs. Comparable results were obtained with 95% O2-5% He or 100% O2. The partial pressures of a 5% mixture at 7,620 and 10,972 m were 14.1 and 8.6 torr, respectively, and were apparently low enough so that the nonmetabolizable gases did not result in differences in the incidence of intravascular bubble formation or decompression sickness. Argon at the 10% level showed a nonsignificant trend to produce more bubbles. Individual susceptibility or resistance to form bubbles was observed with the different gases. Denitrogenation with either 5 or 10% mixtures of the inert gases was quite effective, as shown by a reduction in the number of intravascular bubbles detected.