Mr. Banks:

The reply you got was actually a very good explanation.  I think, based on your
question,  you may be missing some basic physiology knowledge.  Hemoglobin is
carried in your red blood cells, the heme portion combines with oxygen in your
pulmonary capillaries to form oxyhemoglobin.  A small percentage of oxygen
dissolves
directly in the fluid portion of the blood, approx. 3%.    The presence of
hemoglobin allows your blood to carry 30-100 times the amount of oxygen as
could be
transported in the form of dissolved oxygen in the plasma under normal
conditions.
The hemoglobin binds with oxygen during periods of high PO2 and releases the
oxygen
when PO2 is low.  This is the basis for picking up oxygen in the lungs and
releasing
it in the tissues where it is consumed.  The inspired oxygen concentration has
little effect on the amount carried by the hemoglobin, it is already nearly
saturated at normal atmospheric pressure.  However, at high PO2's the amount
transported in the dissolved state goes up dramatically.  This is where the
oxygen
toxicity comes into play.  There is a very good explanation of oxygen transport
both
at normal ambient pressure and during high pressure in "Textbook of Medical
Physiology" by Arthur C. Guyton (WB Saunders).  Hope this helped and didn't
further
'muddy' the waters.

Maureen

Cam Banks wrote:

> Here is a response I received privately, so I'll leave it anonymous.
> Basically, I still don't get how your blood can magically absorb  more
> oxyhemoglobin than it needs.  Any further comments anyone?  Thanks.
>
> Cam
>
> > Date: Wed, 19 Sep 2001 07:08:00 -0500 To: "Cam Banks" <cam@ca*.co*>
> > Subject: Re: weekly dumb question
> >
> > In the pulmonary capillary beds, O2 binds to hemoglobin to make
oxyhemoglobin.
> > More O2 diffuses directly into solution in the bloodstream. Out in the
> > peripheries, the cellular life processes take the oxyhemoglobin in, extract
> > the O2, and release hemoglobin.  The hemoglobin then rebinds with dissolved
> > O2, and the process repeats itself.
> >
> > Observe that there is FAR more oxyhemoglobin circulating than is needed by
the
> > body from instant to instant, so that when it gets out to the farthest point
> > from the capillary beds, even though every cell on the way has extracted its
> > cut of the take, there is still plenty of oxyhemoglobin to keep your right
> > little piggy happy.
> >
> > Now, oxygen is a gas, just like nitrogen and helium, and is subject to the
gas
> > laws and physics, just like nitrogen and helium.  It dissolves in the
tissues,
> > just like them.  It is also consumed by the tissues, as needed, unlike them.
> > This is just another transport phenomenon.  Oxygen diffuses freely across
the
> > capillary walls in the pulmonary beds, in both directions, just like
nitrogen
> > and helium.  (The miracle of hemoglobin oxygenation depends on free
diffusion
> > one way.  The miracle of deco depends on it going the other way as well.)
> > When the excess oxygen returns to the pulmonary capillary beds, if the
partial
> > pressure of oxygen in the blood is sufficiently higher than the partial
> > pressure of oxygen in the airspace, the excess oxygen will diffuse out.
> >
> > Now, if you have a heavy oxygen load in the slow tissues, caused by e.g. a
> > long deco on hot mixes, and you spike the ascent rate sufficiently, just as
> > with nitrogen and helium, you can trigger the aggregation of microbubbles
into
> > macrobubbles, and develop DCS.  This is "oxygen bends".  The key difference
is
> > that the cells in the immediate vicinity of the oxygen macrobubble all
scream
> > "ICE CREAM!  We're gonna have ICE CREAM!" and consume the oxygen macrobubble
> > in situ.
> >
> > I remember reading somewhere that oxygen bends has been demonstrated on
goats,
> > and the goats cleared the symptoms almost immediately, as cellular biology
> > eliminated the bubbles.
> >
> >
> > ----- Original Message ----- From: Cam Banks <cam@ca*.co*> To: Techdiver
> > Mailing List <techdiver@aquanaut.com> Sent: Tuesday, September 18, 2001
11:50
> > PM Subject: weekly dumb question
> >
> >
> >> Okay, time for a weekly dumb one: can someone explain to me the
physiological
> >> mechanism by which nitrox works?
> >>
> >> On the face of it, it would seem like once your body had used all the
oxygen
> >> it needed from a lungful of gas (any mix), the rest of it would diffuse
into
> >> your blood, regardless of gas type.
> >>
> >> How is it that we are able to magically dispose of the excess oxygen? What
> >> are "oxygen bends" that I've heard alluded to?  Thanks.
> >>
> >> Cam
> >>
> >> -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
> >> Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
> >>
> >
>
>
> --
> Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
> Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.

--
Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]