Oxygen therapy [was Migraine question]

Richard L. Hall rhall at webmail.uvi.edu
Sat Feb 17 09:26:25 EST 2001

Hi Richard,

I am just waking up after a splendid night partying about St. Thomas 
so this may wander.

One possible factor is the relationships between filtration 
pressures, gas diffusion coefficients,  and solubilities of oxygen 
and carbon dioxide.  At body temperatures and high salt conditions of 
the ECF, dissolved oxygen is very low compared with carbon dioxide. 
The oxygen cascade predicts that at the tissue level pO2 is far less 
than 94-98% saturation but super saturated plasma oxygen may be 
elevated in concentration.  The movement of dissolved oxygen from red 
cells in blood into the interstitium is driven by filtration 
pressures and simple diffusion.  The filtration pressure is the 
larger component since it drives bulk flow.  However, the filtration 
pressure is inversely related to the precapillary diameter which is 
sensitive to autoregulation by carbon dioxide.  If flow through the 
capillary bed increases due to vasodilation, the filtration pressure 
may be decreasing which effectively increases the diffusional 
distance for all gases.   The effect is to reduce oxygen delivery 
into the tissues.  Carbon dioxide has a forty fold greater solubility 
and diffusion coefficient so as long as capillary flow is high, 
carbon dioxide removal is  less impaired.  If the interstitial 
compartment was supersaturated with dissolve oxygen that might 
mitigate the effects of reduced bulk flow.

My reasoning, however tenuous, is based on observations from my work 
with the isolated stomatogastric  nerve preparations from lobsters. 
I continuously superfuse my nerve preparations with supersaturated 
lobster saline.  At high temperatures, oxygen solubility declines but 
the solution contains thousands of small oxygen bubbles that adhere 
to the nerves, ganglia, and cell bodies.  As long as the bubbles 
persist, the preparation keeps functioning since the diffusional 
distance remains very small.  I suspect a similar circumstance occurs 
in tissues receiving oxygen supersaturated plasma filtrates.  Air 
bubbles are 79% N2, but in pure oxygen atmospheres they are mostly 
O2, so the 94-98% difference in oxygen saturation in blood may not be 
the critical factor.  Tiny bubbles from dissolved oxgyen...  hmmm.

Then again this could be a legacy from last night.  ;-).


>I still don't get the mechanism.   That is, the mechanism between
>breathing O2 and blood pCO2.  I do understand the relation between
>pCO2 and circulatory response.
>Certainly hyperventilating lowers blood pCO2.  But considering air
>has such a low pCO2 already, breathing pure O2 shouldn't really
>make a difference.  Or is it that breathing anything "different"
>produces hyperventilation?
>"Andrew T. Austin" <slightlynervous at NOSPAMbtinternet.com> wrote in message
>news:96k4pt$rv11 at eccws12.dearborn.ford.com...
>  > The effect (vaso-dilation/constriction) is not in response to the oxygen
>  > percentage, but in fact related to the relative levels of carbon dioxide.
>  >
>  > Breathing in extra levels of oxygen or hyperventilating will lower the
>  > relative levels of CO2 and result in vaso-constriction.
>  >
>  > Regards,
>  > Andrew "remember to breathe" Austin.
>  >
>  > Richard Norman <rsnorman at mediaone.net> wrote in message
>  > news:4daj6.2595$AP1.282851 at typhoon.mw.mediaone.net...
>  > > <et_al at my-deja.com> wrote in message
>  > >
>  > > Given that arterial blood is normally saturated with oxygen, could
>  > > someone please explain a mechanism by which breathing more
>  > > oxygen could possibly make a difference? Is there really a
>  > > difference between 94% saturated and 98% saturated?
>  > >
>  > > I am not saying it doesn't work -- I'd just like to know why.
>  > news:3a8c9cc4 at duster.adelaide.on.net...
>  > > > On Mon, 12 Feb 2001 16:10:06 +0100, "Klein" <chklein at gmx.de> wrote:
>  > > >
>  > > > >High flow oxygen is the treatment of choice for so-called cluster
>  > > headaches,
>  > > > >a condition of very intense, unilateral pain acoompanied by runny
>  > eye(s)
>  > > and
>  > > > >a runny nose. Rather rare form of headache. The mechanism of action
>  > > this
>  > > > >treatment is unknown, but it works.
>  > > > >Greetings
>  > > > >C.
>  > > >
>  > > > Oxygen is also an effective hangover "cure," IME
>  > > > Ian
>  > > >

Richard L. Hall, Ph.D.
Comparative Animal Physiologist

University of the Virgin Islands
2 John Brewers Bay
St. Thomas, U.S.V.I. 00802

340-693-1385 FAX

rhall at uvi.edu

"Live life on the edge...the view is always better"  rlh


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