ABSTRACT
Alternative respiratory gases to compressed air have been sought because of the restriction to eective diving at depths greater than 40 to 60 metres of sea water (msw) as a result of nitrogen narcosis and the high density of air (see Chapter 15). Projection of knowledge concerning inert gas narcosis, especially lipid solubilities, suggested that substituting helium for nitrogen would prevent severe narcosis until pressures were greater than 40 ATA. However, in the 1960s, diculties were encountered beyond
a depth of 200 metres (pressure of 20 ATA) when using a helium-oxygen breathing mixture. is syndrome, which is also characterized by a disturbance of the nervous system, is quite dierent from the eects of nitrogen (i.e. inert gas narcosis). Because the most prominent feature noted was tremors, the condition was initially referred to as helium tremors1, although it is now realized that the use of helium is merely an association and that helium itself is not the cause2.
