Semi-closed underwater breathing apparatus has commonly been used among military and commercial divers, but never available for recreational divers because of complicated operations, difficulties of maintenance, and expensiveness. Nippon Sanso K. K. has newly deployed a semi-closed circuit underwater breathing apparatus called the "eOBA". It is especially designed for divers to enjoy shallow (max. 5 m) and short (10 min.) dives. This eOBA was evaluated from manned testing based on physiological requirements for the apparatus. Four male and four female subjects partlcipated in the three test trials. Subjects maintained their position at the depths of 2 m and 4 m for 10 min. and exercised on the underwater ergometer at the depth of 2.4 m. The pressure at the mouthpiece, tidal volume, breathing rate, the inspired 02 level, CO₂ level were monitored on breath-by-breath basis. The inspired 02 level ranged from 45% (at exercise) to 60% (at rest) and the inspired CO₂ level were kept less than 1.0% in the most cases. The P-V loop indicated relatively little extemal work of breathing (<0, lkg.m/l) and allowable peak pressures (<25cmH₂0). Results show that the eOBA meets the standards sufficiently under the test conditions and is a safe apparatus for recreational divers if it is properly used.

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