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More Co2 = less brains?

Jaimie Polson jaimiep at cortex.physiol.su.oz.au
Tue Feb 11 08:41:26 EST 1997

In <01bc17cd$42cb8560$b049bacd at dnawten.ix.netcom.com> "Nate" <dnawten at ix.netcom.com> writes:

>Hope I'm not unwelcome in chiming in on this but regarding the displacement
>of O2 by CO2 on hemoglobin, this is physically impossible.  CO2 binds to
>the "globin" part of Hb (23% of all CO2 is carried this way, about 70% is
>carried in the plasma) while O2 is carried by the "heme" portion (98% of
>all O2 binds to Fe++ ions).  So theoretically both CO2 and O2 can can be
>carried on the same Hb meaning that an increase of CO2 by itself probably
>will not cause drowziness.  It probably has to do moreso with an inadequate
>supply of O2 than anything else.  

>A good example of this would be if someone suffocated in a plastic bag. 
>Drowziness, unconsciousness and eventual death wouldn't be a result of the
>increased CO2 per se, but due to the lack of oxygen.

>Hope this answers your question.


According to Smith & Kampine, "Circulatory Physiology" text...
A decrease in pH or an increase in CO2 will shift the oxygen dissociation
curve to the right - ie a greater PO2 is then required for haemoglobin to
bind the same amount of O2.  If I recollect correctly, this is part of the
way in which O2 is released from haemaglobin in the tissues. The higher
level of CO2 caused by metabolic activity increases the release of oxygen

So presumably, this means that with a higher PCO2 in the blood, less O2
would bind for a given PO2 - but I don't know how significant this would
be at any imaginable increase in CO2 levels.
(And also, this does not account for the body's homeostatic responses to
reduce the high CO2 - that were kindly explained to me earlier.)

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