>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


****************************************************************
*Etienne Beaule, ebeaule@gl*.ne*       *     ****     *
*B. Sc. Physiology                              *     ****     *
*First aid/CPR instructor                       *  **********  *
*Search and rescue consultant                   *  **********  *
*Nitrox diver                                   *     ****     *
*                                               *     ****     *
****************************************************************

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