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Tracey (tab@pa*.co*) wrote:

> jheimann@sc*.gt*.co* wrote:
> > In his nitrox FAQ posting, Alan mentioned a friend who insists that he
> > uses less air when diving nitrox due to the higher O2 content.  I don't
> > see how this is physiologically possible, [...]
> 
> It is entirely possible to use less air when diving nitrox.  However,
> the higher O2 content _probably_ has nothing to do with it -- a much
> more likely scenario is that the diver is simply more relaxed 
> [... relaxation detail cut ...]
> Diving nitrox has on occasion been a significant part of
> that comfort factor, so it has resulted in me using less air.

I will add a comment to this effect to the nitrox text but in terms of
nitrox diving in general it is still fair to say that your gas comsumption
will not change automatically for physiological reasons.

> There are some individuals whose breathing is regulated by oxygen levels
> rather than CO2, although most of these individuals probably shouldn't
> be diving anyway.  This is known as "hypoxic drive", and often occurs
> in COPD (chronic obstructive pulmonary disease -- emphysema, etc.)
> patients.  The body adjusts to chronic elevated CO2 levels by ignoring
> that as a breathing stimulus (it has been theorized that this CO2
> tolerance occurs in divers to some extent as well), at which point the
> body's normal "backup" stimulus -- lowered O2 levels -- takes over as
> the primary means of regulating respiration.  This, in itself, is not
> really a problem, although some of these people may stop breathing if
> exposed to high concentrations of oxygen.
> 
> --tab

In experiments carried out in the 1940's in the UK (Donald) and the 1950's
in the US (Lanphier), the researchers failed to find a reliable means of
identifying CO2 retainers or to link CO2 to hyperbaric acute O2 toxicity
in hyperoxic mixes. Also, in tests to find out if "divers are really
different" the results were inconclusive. At the time divers were taught
to skip breath because this was thought to improve consumption. Thus,
during diving they appeared to have slightly higher CO2 levels in expired
gas. However, when comparing divers with non-divers and ex-divers the
only conclusion was that non-divers feel less comfortable breathing
through a regulator. As far as I'm aware this has not yet been resloved
 - maybe this is an opening for someone to do some research :-)

Alan

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