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Hey Chuck: I'm at a big disadvantage over here without any deco references, but here's my diluted memory and opinion of 5+ year old information.... Check out "Metabolism Decreases With Death" under my name in the archives. Regarding bubbles in general, they likely don't form in circulation--they form in tissues. The bubbles in circulation have busted in to the capillaries. The short answer to concerns about oxygen bubbles is that unless you are at a ppO2 of around 2.0, there is likely no significant oxygen tension in your tissues to drive O_2 bubble growth. Therefore there are no oxygen bubbles (or, the ppO2 in mix bubbles is near zero). This is attributed to "inherent tissue unsaturation," or "oxygen window." Vann and Thalmann give a great picture of what the O_2 window is in their chapter in "4th ed. The Physiology and Medicine of Diving." Brian Hills gives a nice analysis in "Decompression Sickness" too. As I recollect it goes like this: You breath in gas delivered at ppMix ~ Pambient. Because of the ppCO2 and ppH2O in your lungs, the ppMix is reduced slightly in your lungs. If you are alive, then you metabolize some of the ppO2 of your mix to ppCO2 -- but, because CO2 is more than 20x as soluble as O2 in tissue, the TOTAL tension of dissolved venous gas ~(ppO2 + ppCO2 + ppH2O + ppDiluent) is less than ambient pressure. This difference(gradient) in pressures is the oxygen window. Venous O2 tension indirectly has a lot to do with inert gas management through its absence. Where the oxygen window really makes a difference is on decompression or recompression. On decompression, TOTAL Venous tension is less than ambient, TOTAL Tissue tension is greater than ambient, and TOTAL bubble pressures are (slightly) greater than ambient. Consider the 20ft/6m stop on O2 after an air dive. Your bubbles have a ppN2 ~ 1.7 ata. Your tissues have ppN2 < 1.7 ata that is decreasing with stop time as driven by the tissue-venous ppN2 gradient. Even tho you are breathing O2, your venous ppN2 is not 0-- your blood is carrying ppN2 that was given up by the offgassing tissues. Nonetheless, the venous ppN2, ppH2O, and ppCO2 are small. So, the total tension of dissolved venous gas is much less than ambient pressure and the oxygen window is wide open. Alternatively, if you were on air for the 20 ft stop, the ppN2 of the inspired gas would be > 1.3 ata and the oxygen window is slammed shut. No matter what your mix, if you have bubbles, the O2 window ~(Pambient - Pvenous dissolved gas tension) drives elimination of the free gas. Bubbles offgas to tissue, tissues offgas to veins. _____________________________________________________ Eric Maiken Green Bell 102 Ogigayatsu 2-8-9 Kamakura 248 Japan email emaiken@go*.co* Page http://www2.gol.com/users/emaiken Phone (81) 0467 22 2898 _____________________________________________________ -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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