ABSTRACT
Alternative respiratory gases to compressed air have been sought because of the restriction to effective diving at depths greater than 40-60 metres of seawater due to nitrogen narcosis (see Chapter 15). Projection of knowledge concerning inert gas narcosis, especially lipid solubilities, suggested that substituting helium for nitrogen would prevent severe narcosis until over 40 ATA. However, in the 1960s difficulties were encountered beyond a depth of 200 metres (pressure of 20 ATA), using a helium/oxygen breathing mixture. This syndrome, which is also characterized by a disturbance to the nervous system, is quite different to the effects of nitrogen (i.e. inert gas narcosis). As the most prominent feature noted was tremors the condition was initially referred to as helium tremors,1 although it is now realized that helium itself is not the cause.2
