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On Tue, 24 Mar 1998, Thomas A. Easop wrote: > To go off on a tangent to this discusssion momentarily, since micro bubble nuclei are > indeed "an a-priori fact of life" wouldn't it make more sense to include the 10ft/3m 02 > deco stop in your schedule since these "bubble seeds" will then have more surface area > to offgass, as oppposed to a higher inner bubble preasure at 20ft/3m? > Actually, that's the subtle part about bubbles. Keep in mind that the key thing (leaving off real complications like protein coating, which mess up the "pure" physics), is that because small bubbles are spherical, the relationship between the volume and the surface area is not linear - the volume grows much more quickly than the surface area does. So, as a bubble grows, it's internal pressure drops, and the surface area increases, and hence, one might be tempted to think that the larger surface area provides better contact for dissolution. BUT, the thing is, the dissolution of the gas in the bubble is not related to bubble surface area like that, it's the partial pressure of the gas that determines how fast it will be absorbed back into the blood - the higher the partial pressure in the bubble vs. the "ambient" partial pressure in the blood, the faster the bubble will dissolve. Since smaller bubbles have a higher surface tension, the partial pressure of the gas inside is higher, (and the volume is lower), the bubble will dissolve more quickly. As a bubble gets larger, the surface tension decreases, and the internal pressure starts to get closer to ambient pressure, which slows the rate of dissolution. In fact, the surface tension is likely to drop so much that ascent is likely to cause the bubble to *on-gas*. Thus, smaller bubbles tend to shrink, while larger bubbles tend to grow. Above a certain critical size, the amount of time it takes for a bubble to shrink goes up fantastically, which is why (some suggest) we see such a long decay curve in Haldanean models - they let the bubbles grow, then deal with longer times it takes to dissolve the enlarged bubbles. That's why you want to do your stops as deep as you can get away with, while at the same time trying to strike a balance with avoiding further raw tissue loading. > Also, Will, do you find the texts of Yount, etc? I still can't find any in the usual > places. No, the mysterious Yount eludes us all - except maybe Rich Pyle. Weinke has Yount's paraphrasings and references all over the place, but I'll be damned if I can find his stuff directly. I wish someone with an actual copy would step up and volunteer to fax the stuff (I'll volunteer to redistribute from there). I'm sure the UHMS library has the goods. Regards, -Will > Bill Mee wrote: > > > <snip> > > > On Mon, 23 Mar 1998, Bill Mee wrote: > > > > > > > The more surface area for gas exchange, the better able for the > > > > system to transport dissolved gas to the alveolar pulmonary circulation > > > > and hence the critical level of dissolved inert gas, where bubble > > > > nucleation occurs, can me minimized. > > > > > > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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