Oxygen therapy [was Migraine question]
Richard L. Hall
rhall at webmail.uvi.edu
Sat Feb 17 09:26:25 EST 2001
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"
>"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
rhall at uvi.edu
"Live life on the edge...the view is always better" rlh
More information about the Neur-sci