In my post on this subject on 20/9/98 I was inappropriately critical of
Etienne Beaule.  In particular, I mistakenly attributed to Etienne a
reference to the role of the autonomic nervous system (ANS) in control
of respiration. (Slaps self on forehead.  Glares at John Walker.)

I apologise to Etienne and retract the offensive "little comments",
while standing by the substance of the post.  In particular, I re-assert
the relevance of research on classical anaesthetic substances to hyperbaric
N2 effects on respiratory control.

Gerard Stainsby (obviously working too many hours)

Sod's Law: the net result of the interaction between the Universe and
you is that you'll be dead (and the Universe will hardly have noticed...)

------------------------------

Etienne Beaule wrote:
> 
> >1. The ANS? Respiratory control is a function of the brainstem but _not_ the
> >ANS.  Read any physiology book.
> 
> The original post (the one to which I replied) was suggesting that
> narcosis could affect the ability of chemoreceptors to sense correctly
> CO2 levels. It is the peripheral chemoreceptors that are involved with
> sensing PCO2 (along with PO2 and [H+] while the central chemoreceptors
> are mainly involved in sensing [H+] in CFS). This is why I expressed my
> doubts regarding this "theory". FYI, respiratory control involves *much*
> more than the brainstem alone. The following CNS areas are also involved
> to some extent: cortex, amygdala, hypothalamus & limbic areas,
> mesencephalic regions, pons & medulla.
> 
> And don't worry, I do read a lot of physiology books.
> 
> >2. You're curious, but not curious enough to go to the effort to find out
> >for yourself.  Oh well, here goes:
> 
> I do not really know if hyperbaric N2 could affect the peripheral
> chemoreceptors and I would have been quite interested to read a paper
> suggesting/proving such a thing. I was curious to see if the sender of
> the original message would be able to prove this theory.
> 
> >The pCO2/ventilation response curve is flattened and shifted to the right
> >by anaesthetic agents and most CNS depressant drugs.  Presumably nitrogen
> >narcosis (to which I presume you're referring, although I seem to have missed
> >pH's original submission) would have such an effect.  Narcotic effects due to
> >hypercarbia itself don't depress respiration until pCO2 gets well over
> >100-150 mmHg - unlikely to be a 'primary' factor, but potentially part of
> >a terminal death spiral initiated by some other process.
> 
> Agreed. But this is not related to the the original subject.
> 
> >The pCO2/ventilation response is largely due to central chemoreceptors,
> >not peripheral ones (which are oxygen sensitive).  The peripheral chemo-
> >receptors _are_ exquisitely sensitive to anaesthetics (incl hyperbaric N2?)
> >which causes loss of ventilatory response to hypoxia.  There can be little
> >doubt that central chemoreceptors are also depressed by 'narcotics'.
> 
> Again, I agree with you.
> In essence, you are asking the same question I was asking when you write
> "(incl hyperbaric N2?)". This is what I would like to know and this is
> why I asked if any research was done on that particular subject. I don't
> care about the other anesthetics. I already know about these.
> 
> >Since you asked for research, try:
> >[...]
> 
> >Obviously these refer to more formal 'anaesthetic substances' than hyperbaric
> >nitrogen: the principles (if not the specifics) are likely to be applicable
> >to respiratory control while diving.
> 
> Thanks for the references but if you understand my "curiosity" now, you
> should be able to understand that these references have nothing to do
> with what I was asking. Besides, I have plenty of references of that kind
> here. The only one I don't have is one suggesting an effect of hyperbaric
> N2 on the peripheral chemoreceptors. You have not been very helpful here.
> 
> >Additional factors contributing to hypercarbia during diving will be well
> >known to most readers; I will not enumerate them here.
> 
> Indeed, it will... And, BTW, you e-mail would have been much more
> appreciated if you had omitted all the little comments in the beginning...
> 
> Etienne

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