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Ryan McNabb schrieb:
> pO2 levels) is that our respiratory drive is two pronged in
> nature. Our first impulse to inspire air is triggered by a
> dropping pH (or increasing acidity) of our cerebrospinal fluid.
> When we don't breathe enough O2, the ph drops and we get a
> trigger to breathe. It happens very quickly.
Ryan,
think about that twice. You are right with 2 happens very quickly. But
the trigger is ppCo2, not ventilated oxygen. Consumed oxygen, yes,
because it is metabolized into CO2.
But, triggerwise,you could very well breathe nitrogen, be happy with it
until you pass out.
You are very much right on the asthmatics trigger scenario.
it has also been proved, that experienced divers build up a certain
tolerance to CO2 (10 times more than with beginners).
Well, I did not find any relations till now with the dangers you
implied. Might be worthwhile to have a look.
Matthias
Barring that
> stimulus, our backup respiratory drive trigger is actually the
> hypoxic drive, or our low O2 emergency situation. The chronic
> smoker/emphysema ("chronic lunger") patient will have long since
> altered his/her body chemistry into a chronic acidic state where
> their brain doesn't care anymore what the spinal fluid pH is
> (I'm exaggerating only a little). And in this patient the risk
> is giving them too much O2 or you will satisfy their hypoxic
> drive (a bad thing in this instance) and bingo, their
> respiratory drive slows to a crawl. They get a faraway look in
> their eyes as CO2 builds up, and then it's the beginning of the
> end. Thus patients come into the ER pale and gasping and we put
> them on a measley 2 liters a minute so as not to shut them down.
> Usually this patient will get paralyzed and intubated, and
> placed on a ventilator.
>
> Why did I say all that? I wonder if continually high inspired
> O2 percentages by physically fatigued/stressed divers cannot
> reproduce this chemical situation, basically shutting down the
> hypoxic respiratory drive causing a (probably not unpleasant)
> buildup of CO2 and unconsciousness. I wonder if a lot of the
> "we found him hanging at his deco stop unconcscious" type
> stories don't show this exact scenario, as opposed to the more
> generally assumed seizure activity from an oxygen
> toxicity/neurological syndrome. I am certainly not advocating
> 80/20 as a "safer, lower O2" deco gas because the vast majority
> of divers are young and healthy and the object of deco is to
> offgas toxic nitrogen first and foremost, not necessarily to get
> out of the water as quickly as possible.
>
> I am not a decompression diver yet...I'm here to STFD and STFU
> and listen to experts, but I thought that the above might be
> something to consider.
>
> Cheers
> Ryan McNabb
>
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