Gerard,

Thanks for the excellent post with your thoughts on the possible role O2 may
play in narcosis symptoms.  I'd like to add a couple comments.

First of all, I'm not "Dr." Pyle yet - although this looks like it will be
the year (finally). O.K., maybe early next year...

Next, whenever I've seen or participated in discussions on the topic of
oxygen's role in narcosis, I am often struck by two issues:

1) People rarely define how they are using the word "narcosis", and it seems
different people apply different definitions without realizing it (i.e., a
semantics problem).

2) As is the case with most diving physiolgy issues, the amount of stuff we
really don't know vastly exceeds the amount of stuff we really do know.

> Has anyone got a physiological basis for the phenomenon (widely
> reported, and therefore not to be easily discounted) of O2 narc?

To my knowledge: no.  In fact, to my knowledge, we don't really have a good
grip exactly how nitrogen induces narcosis either (as an anaesthesia
specialist, you're in a much better position to understand this sort of
thing than I am).  However, from what I do know, I fully agree with you that
oxygen's role in narcosis is almost certainly NOT (from a biochemical
perspective) the same as that of nitrogen.

> Important anti-flaming note: I'm NOT saying that O2 narc doesn't
> happen, nor that O2 isn't equipotent with N2 in its subjective
> narcotic potential in diving (But: see quote from Richard Pyle,
> below.)  I AM saying that if this is so it is not due to a simple
> "inert gas" effect, but is instead more likely to involve cerebral
> vasoconstriction, hypercarbia, free radicals (or some combination
> of these) and is therefore more alike in mechanism to (sub)acute
> ox tox than N2 narc.

Those are all interesting ideas, and I'd like to see further discussion
along those lines.  However, the evidence is growing (in my mind, at least),
that the body of manifestations we collectively refer to as "CNS [acute] O2
toxicity", are likely based on several different (and perhaps even
unrelated) processes.  Thus, it seems likely to me that the role O2 may or
may not play in narcosis symptoms perhaps is founded upon yet another
biochemical process (or suite of processes). Whether we lump those processes
and their manifestations under the umbrella term "CNS O2 toxicity" or
"narcosis" is perhaps more an argument of semantics than an argument of
mechanism.

This relates to my point 1 above: the definition of "narcosis".  Some people
think of it as a term that represents the specific biochemical mechanism
associated with nitrogen and how it impairs our neurology.  Others think of
it as a more generic term representing some form of mental incapacitation.
Naturally, the first group tend be the ones who say O2 does not cause
"narcosis", whereas the latter gorup tend to be more inclusive about it.

In the context of my diving experienced, I am quite convinced of two things
related to this topic: 1) Without doubt, oxygen DOES play a role in the
severity of "narcosis" symptoms ("narcosis as definied in the more general
sense); and 2) that role is a lot more complex than what most people who
dicuss the topic seem to appreciate.

Several times on these lists I have subjectively described my own personal
interpretation of subtle and not-so-subtle differences between classical
(and apparently primarily nitogen-induced) narcosis v.s. narcosis that
appears to involve oxygen in some way, so I won't go over it again here.
However, one thing I haven't previous mentioned is that, whereas
Nitrogen-type narcosis is most definitly affected by exertion levels
(hinting strongly towards a direct or indirect role for CO2), I have not, in
my somewhat limited and highly subjective experience, noticed the same
exertion correlation with the more oxygen-type narcosis (again I emphasize
the limited and subjective nature of this observation, since I have seldom
exerted substantially while in a position to experience oxygen-type
narcosis).

> It would be interesting to test this hypothesis with a hyperbaric
> chamber, variable inhaled gases, a really good test for narcosis (ie.
> involve a person expert in neuropsychiatric evaluation) and (preferably)
> a jugular bulb venous sampling catheter.  Does anyone know of this
> experiment being done?  Any volunteers?  Can someone lend me a chamber?

I'd LOVE to give it a try!

I read the rest of your post, but I'm afraid it's nearly 1 am and I've had a
LONG day of diving, so I'm going to wait until I can read it again with a
fresh mind and bust out my trusty copy of B&E to follow the references.

As I said in the beginning, thanks for the great post.

Aloha,
Rich

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