Effects of addition of nitrogen during rapid compression of baboons

Abstract

A series of dives was carried out to depths of 600 and 800 m seawater (msw) using baboons (Papio papio). Experiments were designed to study the effects of compression and the use of a He-N2-O2 gas mixture on high-pressure nervous syndrome (HPNS). When N2 was added to the He-O2 mixture at the beginning of a linear compression (200 msw/h), the symptoms associated with HPNS were still seen; in addition, the electroencephalogram (EEG) changes were more severe than those seen without N2. By use of an identical mixture, a 2-h exponential compression to 600 msw produced less severe signs of HPNS than the nonexponential profile. By use of a 2-h exponential compression to 600 msw and with addition of N2 at the end of compression, the HPNS that had been started under the He-O2 mixture decreased. Progressive addition of N2 during compression reduced the behavioral signs of HPNS without further EEG changes. These results show that the action of N2 is more complex than can be explained by a simple narcotic pressure antagonism and that the HPNS differed according to the gas mixture used.

EEG and sleep disturbances during dives at 450 msw in helium-nitrogen-oxygen mixture

“…Several human deep dives, animal experiments, and neuropharmacological studies have been conducted in an attempt to elucidate the origins and mechanisms of this syndrome, and some methods to counteract it have been used. The methods to prevent HPNS include selection of divers, slow exponential compression in stages, and the use of narcotic gases to antagonize the effects of pressure (2,4,18,21,23,24,26). The latter method has been extensively tested in humans by using increased partial pressure of N 2 (2,3,15,21,23).…”