Use of H2 as an inert gas during diving: pulmonary function during H2-O2 breathing at 7.06 ATA.

A review of the characteristics of hydrogen as an inert gas for use in diving is presented, with special emphasis on the extension of the respiratory limitation in diving by use of this least dense of all gases. Forced vital capacity, FEV1, FEV2, PEFR, PIFR, and MVV were measured on groups of subjects using the following gas mixtures, all at 7.06 ATA: four subjects breathing 97% H2-3% O2, two subjects breathing 97% He-3% O2, and two subjects using 97% N2-3% O2. The MVV while breathing H2-O2 at 7.06 ATA was 14% higher than with air at the surface, and was improved 40% compared with He-O2 and 171% when compared with N2-O2 at 7.06 ATA. Similar findings were obtained for FEV1, FEV2, PEFR, and PIFR. The values in this study for the relationship of relative gas density (rho) to flow are rho-0.41 for MVV, rho-0.44 for PEFR, and rho-0.45 for PIFR (method of Wood and Bryan).