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Regarding the several questions about CO2 and hemoglobin:
> Is CO2 removed only as dissloved molecules in the blood?
> Haemoglobin does not bind CO2, only O2 and CO.
> CO2 is dissolved in the blood liquid as H2CO3 (Carbonic acid)
Hemoglobin removes CO2 to a small extent (15 to 25% of total CO2) in
the form carbaminohemoglobin (CO2HHb). Most CO2 remains
dissolved in blood, reacting with water to form first carbonic acid,
but then rapidly dissociating into bicarbonate.
> you might just have a tendency to saturate hemoglobin with O2,
> inhbiting (to a limited extent) its ability to carry CO2 out of the
> tissues.
Hemoglobin contains an iron group called heme, and a protein called
globulin. It has four iron atoms that each loosely bind one oxygen
molecule, therefore each hemoglobin molecule has room for four
atoms of oxygen. CO2 bonds with the protein subunit unlike oxygen
so they do not ordinarily compete for sites and can be carried
simultaneously. Note the qualifier 'ordinarily '. There are particular
instances, but I do not believe they relate here.
> I've tried to get a handle on the effects of elevated inspired
> PPO2 on satuaration of hemoglobin.
At one atmosphere, about 97% of oxygen is carried in combined form
with hemoglobin called oxyhemoglobin (Hb-O2), the rest dissolved in
blood. That means that at sea level with no increased pressure
exposure at all, your hemoglobin has almost all the O2 it can hold
(almost totally saturated already).
> is it possible that the O2 is causing and acidic "rush" in our
> system...?
I'm not acquainted with your term 'acidic rush'. O2 is a main
remover of hydrogen ions (H-) that build up 'acidity'. This occurs in
the electron transport chain of respiration. That's why, without
enough 'aerobic' metabolism during intense exercise lactic acid builds
up, but that is another story...
Regarding conjecture that pCO2 increases merely with depth:
There are several parts to understanding this. First, it is not true that
diving deeper, by itself, increases pCO2 in a diver's body. You do not
produce any more CO2 merely for being underwater. It's not like
nitrogen that you are breathing in increased density with increased
depth. You ordinarily, and again - note the qualifier 'ordinarily',
produce the same amount of CO2, so pCO2 does not change with
change in ambient pressure as does pN2 and pO2. It is also not true
that the exercise of ordinary diving causes CO2 to build up in a
diver's body in ordinary conditions. Your breathing speeds up
during exercise to breathe off the excess and your blood has
powerful buffers to control CO2 level. Increased CO2 with skip
breathing and equipment dead space in helmets, full face masks,
and rebreathers is another story, as is increased work of breathing at
depth and increased gas density. These things may increase CO2
retention - another story for another time.
> It would be ethically "difficult" to expose people to a possibly
> harmful dose of whatever this phenonemon is.
Been done. Read Kenneth Donald's 'Oxygen and the Diver'. Plus, with
tek divers doing such marvelous things, we have a built-in ongoing
and growing database. Keep up all your good work.
Jolie Bookspan, Ph.D.
Research physiologist in environmental physiology (exercise in heat,
cold, altitude, and at depth).
--------
It ain't so much what we don't know that gets us into trouble, it's
what we know that ain't so.
-Will Rogers
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