Mailing List Archive Mailing List Archive
> > If this 'blow&go' refers to the >submarine escape Not what Dan was talking about....you can't *escape* from 25min at 260 on air--no matter how narced you are. > > According to the Haldenian concept, it takes the t1/2=5 min compartment > 30 minutes to 'sat'. THus no 'fast', or, for that matter, no > compartments are saturated in 25 min @ any depth. ?????? ...ah you must be a splitter, while I must be a lumper...you're correct the 5 min compartment would not be *saturated,* it would only be 96.87% loaded in 5 half-times.... And, then of course only a dead diver can be fully *saturated.* The oxygen window, water vapor, etc keeps the sum of inert gas partial tensions in tissue less than the corresponding inspired partial pressures. 'So what' about a "5 min" tissue per-se--the relavent time scale is the fast ascent up to the first stop (1 or 2 min let's say)--so after a *long* time at depth (not just a bounce), tissues are heavily loaded and a large gradient exists between ambient pressure cavities and tissue tension. > > It has been theorized that the inert gas within a bubble & wh/ makes it > up, will diffuse out more readily when dissolved identical inert gas is > lowered, thus reducing bubble size. yes. each partial tension (gas in tissue) must balance the partial pressure of the same gas in the bubble--so you have a coupled set of diffusion equations for each bubble. See H. Van Liew's work of the past 10yrs-- he plays "what if" games with bubble growth. Physical bubble growth is very well understood experimentally in simple non-perfused systems (like gelitin)--less well in living systems. > > Yet we also have evidence that bubble formation is dependent on the > saturation level of the compartments & the partial pressure (of the > homologous inert gas) at the 'shallower' depth. did we just say the same thing different ways? For instance, a stable bubble exposed to a gas-switching diver's tissues (constant depth) can grow by amplification. For eg: As a new inert diffuses into a bubble, the bubble grows. The skin tension then decreases lowering the internal pressure. More gas diffuses in due to the lowered pressure. the bubble grows, skin tension is reduced...and the bubble grows.... >The motive force of > offgassing becomes a ratio of ppCOMP/ppAMB. No. Sounds like you're using Haldane to attack bubbles. The motive "force" (per unit area) for bubble growth/shrink is a gradient of pressures (Pbubble - Psurrounding) as found in the time dependance of a diffusion equation. It is true that consideration of the chemical potential of free gas in equalibrium with disolved gas should depend on a ratio of pressures--but that would be energetics--not the kinetics we care about--the ultimate question is: "WHEN can I get out of the water!". > When breathing pure O2 the > ppAMB of inert gas becomes 0, thus setting up an offgassing rate that > approaches infinity. Sounds like you're mixing M's (ratios) up with G's (gradients) This is a common mistake in trying to generalize M values and Haldane ideas to hypobaric deco situations (altitude). See Bruce Wienke's papers (ca. early 1990s) to see the correct extension of allowable supersaturation to zero ambient pressure. M's always remain bounded. Of course, M's don't determine "rates" of offgassing--they set limits on allowable supersaturation in each compartment (supposedly to avoid bubble formation). As you know, at a given supersaturation, the rates are set by 1/2 times. >Obvioulsy this is not observed. Right. It's not "allowed" by our common sense either. >The scary > thought is that theory of bubble formation also holds that bubble > formation is dependent on rate of gas evolution & is driven to some > extent by the above ratio. The faster the rate of offgassing, the more > bubbles formed, No. The distribution of growing bubbles (number) depends on HYDROSTATIC pressure changes rather than tissue tension. The rate of growth of individual bubbles does depend on local tissue tensions and no doubt about it, the faster the rate of offgassing the more existing bubbles stop growing and start shrinking. > yet O2 breathing does set up an infinite ppCOMP/ppAMB. No. You need to re-normalize your theory. Infinity is non physical. BTW, whats COMP? > We have had this discussion with Pyle. I think that ascribing the > value derived from IWR solely to bubble 'crushing' may be an over > simplification. Yes. But crushing is one of the few options available to the bent diver (and offers near instantaneous relief).Considering the alternative it makes sense to use repressurization as a tool. Regards, EM _____________________________________________________________ Eric Maiken email: ebmaiken@ea*.oa*.uc*.ed* Dept. of Physics o: 714 824-6621 U. of California fax: 714 824-2174 Irvine, CA 92715-4575
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]