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On Mon, 12 Jan 1998, Ben Greenhouse wrote: > I am not sure about this, but it is an educated guess. For starters, an > increased PO2 will increase the pressure gradient across the alveolar > tissues. This will result in an increased rate of uptake of O2 by the > blood. The absence of Nitrogen in the breathing mixture will increase the > pressure gradient across the alveoli in the other direction. In this > manner, I imagine that breathing 100% oxygen would seem to actively "pull" > Nitrogen out of the blood stream relative to when breathing air. This > phenomenon would work in the same manner in the various tissues, but to a > lesser extent for Oxygen as it is used up, and hence the gradient drops. I > think that you might have been referring to this when you said "filler" gas, > but I wasn't positive. Yes, that's exactly what I meant, sorry, I should have been more specific. > I was thinking of all sorts of other ways that high PO2s could increase > the rate of offgassing, using pH values and Bohr effects etc until I > realized one important thing. I have a typical human oxygen equilibrium > curve infront of me, and our blood becomes saturated with oxygen at a PO2 of > around 120 mmHg (oxygen bound to hemoglobin, and dissolved in hematocrit). > Now unless my math is wrong.... 100% oxygen at sea level is at a PO2 of 1 > atm, which is equal to 760mmHg. Even a normoxic mixture has a PO2 of around > 160mmHg. This would indicate to me (again unless my math is wrong) that > breathing gases with higher PO2s will allow for no physiological or > biochemical mechanisms of increased gas exchange since no more oxygen can > physically get into our systems. Interesting about the saturation issue. I assume you mean that no more O2 can get into our systems via hemoglobin/hematocrit. There's still direct dissolution in the blood and tissues at elevated PO2, just like there's direct dissolution of N2 at elevated PN2's, though unlike N2 or He, as Rich points out, it's probably reduced somewhat by direct metabolic consumption. Hence, presumably because of the benefits of direct tissue consumption of O2, we see the rising popularity of alternative medical uses (besides unbending divers), of high PO2 therapy. Not that I'm arguing for any particular conclusion except "filler" here - just curious if there are alternative ideas floating around out there. -Will -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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