More Co2 = less brains?

Jesus M. NAVARRO jmnav at gustavo.mizar.csic.es
Fri Feb 14 10:45:38 EST 1997


Jaimie Polson wrote:
> 
> 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.
: 
: >Nate
: 
: 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.)
: Jaimie

True enough: this is called Bohr effect.  And about the need of air and
unconsciousness and even death are lately caused, of course, as a result
of the lack of oxigen, *but* the trigger is CO2.  Indeed we are almost
unsensible to PO2 in blood, the sensors detect PCO2 (some of the most
importants are at carotidean arteria, in the neck) and this is the
origin of anguish sensation of no air after an apnea (no breathing)
lapse.  The "closed-room" effect then is multiple: an undefinable
sensation of uncomfortability due to high CO2 concentration *plus*
disturbed brain metabolism due to lower PO2, both because Bohr effect
and lower O2 pressure in the air *and* increased blood pH, again because
CO2, that difficults taking away brain cells catabolites.

SALUD,
Jesus
-- 
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