[Hyperbaria and stress]

Causes of the appearance of stress-reaction at action of hyperbaira on the organism were studied on rats. It has been established that at the 5-h action of gas mixtures (oxygen-nitrogen and oxygen-argon) under pressure 0.35 and 0.5 MPa and partial pressure of oxygen 0.02-0.03 MPa in the chamber of the volume of 300 1 there is obviously manifested stress confirmed by the corresponding markers. The appearance of stress was connected with the gas mixture density that amounts to 6 g/l, which interferes with respiration mechanically. Use of helium at the same pressure of the gas mixture did not cause stress, as its pressure did not exceed the normal air density. On the other hand, use for respiratory mixtures of elegas (SF6) with density of 6 g/l at the normal pressure produced obvious stress. No difference was revealed in action of nitrogen, argon or elegas at equal density. Thus, use of high pressures needs light gases (helium, hydrogen, neon) that have low density.