Oxygen therapy [was Migraine question]
rsnorman at mediaone.net
Sat Feb 17 11:38:58 EST 2001
The argument is interesting, but I fear that reasoning from crustacean
physiology might be a bit misleading. Crustacean blood with
hemocyanin carries such a limited amount of bound oxygen that
oxygen in solution can be an important factor. I don't remember
the HCy content exactly, but I believe that is only perhaps 5 ml O2
per 100 ml of blood. Saline saturated with O2 at 760 mm Hg will
hold about half of that. Vertebrate (and mammalian) blood carries
about 20 ml O2/100 ml so that dissolved O2 is much less
But your argument about coating crustacean nervous systems
with lots of small oxygen bubbles explains why my own
stomatogastric ganglion preps always used to die so quickly!
I would hesitate to allow small gas bubbles to accumulate in
my personal circulatory system, though.
""Richard L. Hall"" <rhall at webmail.uvi.edu> wrote in message
> 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.
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