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Richard,
>
>Could you please describe the possible relationship between N2 narcosis and  
>HPNS .
>

I presume that R.P. was refering to the inverse relationship between N2 
narcosis and HPNS.  HPNS is an excitation of the central nervous system 
(CNS) as a direct result of elevated pressure, and inert gas narcosis (IGN) 
is a depression of the CNS that is the result of incipient anaesthesia as 
the narcotic gas partial pressure approaches the minimal alveolar 
concentration required to produce anaesthesia (MAC).  It is well known that 
increased ambient pressure can reverse the effects of gaseous anaesthetics 
(raise the MAC); likewise, it is well known that adding a narcotic gas such 
as N2 or H2 to heliox can reduce the symptoms of HPNS.  While HPNS and IGN 
clearly have opposing actions, it is unlikely that HPNS and IGN are actually 
opposite ends of the same phenomena, they just appear to be so.  The 
mechanism of either phenomena is not well understood.

regards,

David Doolette
ddoolett@me*.ad*.ed*.au*

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