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On Mon, 22 Dec 1997, Richard Pyle wrote: > > for cases of gross tension differential), the > > whole gradient-participation theory goes right to hell. > > > > In which case, it's all in the lungs, baby. > > I'm not sure I follow you here. > Sorry, it was a semi-obscure reference to the lungs being the primary method of bubble elimination for bubbles of a certain size (before they get too big). > > But it ain't so simple. The question begs: what's "gross"? > > If I understand your question correctly, I believe we are talking > something on the order of 20,000 atmospheres. > Actually, you've mentioned the 20K ATA figure several times. I'm curious where this came from. Surface tension of five gas atoms in a huddle? :) Clearly, even from staring at a champagne glass, it's obvious that some chaotic agent besides surface tension is at work in seeding bubble formation - like, for instance, a microscopic span that only requires X gas molecules to fill, causing just enough of a gas accumulation to act as a seed under conditions of supersaturation. So long before surface tension comes into the picture, there's a seed. Actually, as I recall, there's been some recent work that sheds light on the pure-physics end of bubble seeding, and as I also recall, it had to do with exactly that - cracks or spans in molecular-width ranges - I'll have to go look it up. > The part that I don't understand, however, is that you seem to be > suggesting that abruptly switching from trimix/heliox as a breathing > gas at depth to air/nitorx as a breathing gas during ascent can lead to > spontaneous bubble formation (presumably in the blood adjacent to the > alveoli of the lungs), and such formation is more acute with more > significant gradient steepness? I can envision this process occurring > when a diver whose blood is heavily ladden with N2 abrubtly switches to a > helium-rich breathing gas; but I don't see it happening in the reverse > direction. > Right, here's the thing, and it assumes that bubbles don't just pre-exist, and niggles into the nucleation (seeding) issue, which is admittedly squirrely territory. When we assume that bubble growth at the seed level is a factor of absolute pressure, we are supposing that bubble seeds are comprised of a composite of the representative dissolved gasses, and that supersaturation is acheived for the whole of the composite mix, rather than looking at the possibility that supersaturation occurs for each gas independantly, based upon the relative partial pressure of the dissolved versus inspired gasses. Since we allow on-gassing to be independant for each gas, why don't we make equivalent consideration for off-gassing? On the acuteness issue, I don't think so. It would seem to be more a matter of crossing a single supersaturation threshold for each gas. > Exactly what aspect of the steepeness of the gradient in the former case > (He in blood, N2 in lungs) would cause bubbles to sponatneoulsy form? The lack of He in the lungs increases the partial pressure gradient for *helium* (N2 has nothing to do with it, directly). > Would it be the rate of diffusion across the alveolar membrane? If so, > where do the voids (bubbles) come from, exactly? > I'd have to point back to the seeding issue on this one. -Will > Maybe I'm just not understanding you correctly here. > > Aloha, > Rich > > > Richard Pyle > Ichthyology, Bishop Museum deepreef@bi*.bi*.ha*.or* > 1525 Bernice St. PH: (808) 848-4115 > Honolulu, HI 96817-0916 FAX: (808) 841-8968 > "The views are those of the sender and not of Bishop Museum" > > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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