ABSTRACT
Exposure to pressures of air higher than 4 atmospheres absolute (ATA) induced in man dangerous signs and symptoms of euphoria, intoxication and narcosis. Compressed air or nitrogen-oxygen mixture produces from 4 ATA, disturbances at the level of the nervous system called nitrogen narcosis. On the base of lipid solubility, the narcotic effect of helium would occur around 40 bars. However the pressure reversal effect counteract this weak narcotic potency and the symptoms that occur are different from those observed in narcosis; they are called the High Pressure Nervous Symptoms. The high density of neon relative to helium will cause respiratory embarrassment at much lower pressure. On the basis of animal experiments, Marshall predicted that this gas would be three times less narcotic than nitrogen which is in good correlation with the lipid solubility theory. Hydrogen is another inert gas which has been considered and used for deep diving.
