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You wrote:
>
>
>Hey Dan
>
>>
>> So the concept of "Blow and go"
>
>> could be seen as be begging for bigger bubbles, which could be more
>>problematic than the decreased nitrogen absorbtion "Blow and Go"
was
>used to eliminate...
If this 'blow&go' refers to the 'exhale maximally @ depth prior to
ascent' historically used in submarine escape training (not used any
more), I fail to see how this will produce a large gradient.
Irrespective of the amount of exhalation, the residual gas in lungs
(which will be there irrespective of how forcefully one expires) will
have the ppINERT of the absolute pressure @ wh/ that breath was inhaled
at.
Thus the percieved tisssue sat at the aforementioned depth & the
ppINERT of lungs post 'full exhalation' will be comparable. This
assumes no local airway collapse, a problem of blow & go.
>
>Yes. By Causing a large gradient(~5ata) to exist between tissue nearly
>saturated at 260fsw (as all *fast* compartments will be after 25 min)
and
>gas cavities pressurized at the ambient 100 ft stop, you could cause a
>population of bubble nuclei to start growing.
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. Saturation is
intrinsically depth based. That is a compartment saturates for a
certain depth. I presume the implication was not that saturation is
reached faster as depth increases.
Obviously the relative supersaturation that will exist upon arrival at
100 ft (or any shallower depth) from a deeper depth is predicated on
depth & duration of deeper sojourns.
>
>> Typically Blow and go was followed by pure O2 at 20 foot and 10 foot
stops,
>> with some air breaks, and this seemed (at the time) to be effective
in
>> removing or shrinking bubbles...what are your current thoughts on
this. It
>> would seem to me that at the very least, this was probably a great
way to
>> "Farm" bubbles,
>
>It was the opinion of some bubble modelers that the importance of
long,
>shallow stops in traditional deco schedules arose from the need to
treat
>bubbles formed early on in the ascent (by neglecting deep stops).
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. The theory also holds that if one
can reduce volume of bubble sufficiently surface tension (gamma) will
eventually crush it. Hence one presumed utility of O2. This premise
would also imply that starting O2 deeper, should that be possible,
would be more effective.
>
>In addition to radicals like Rich and George who do DEEP stops, the
rest of
>the deco-diving world often employ practices that look good from a
>bubble-reducing standpoint:
>
>> "pull" your 10ft stop at 20ft on O2.
>Supersaturation models (Buhlmann, etc)don't provide rational for the
>efficiency of this practice (the out-gasing should be th same because
>inspired FN2 is zero).
Symmetric models take into consideration of ppINERT thus, de facto,
allow for ppINERT = 0
> Bubble models argue for pulling because the
>increased pressure will help drive gas out of bubbles.
>
The whole concept of O2 deco shows how little we understand bubbles,
bubble formation & DCS.
Frusctus in a very extensive study showed that O2 deco is beneficial
from the stdpoint of DCS (much < cases of DCS in group deco'ing on O2
relative to those deco'ing on air - study used over a 1000 profiles).
All this despite the vasoconstrictive effect of O2!
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. The motive force of
offgassing becomes a ratio of ppCOMP/ppAMB. When breathing pure O2 the
ppAMB of inert gas becomes 0, thus setting up an offgassing rate that
approaches infinity. Obvioulsy this is not observed. 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, yet O2 breathing does set up an infinite ppCOMP/ppAMB.
It appears that a modulating mechansim has to be invoked & that may be
crux of DCI vs no-DCI dilemna of comparable exposures.
>> Use nitrox 80/20 starting at 30fsw rather than O2 starting at 20fsw.
>Opening the O2 window as early as possible will eliminate bubbles.
>
>>IWR relies on bubble squashing ideas.
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. Rapid intervention with high ppO2 appears to be the
principal value of IWR. The presumed benefit (depth 30 ft) is
preventing tissue anoxia and contribute to the prevention of further
bubble formation (bubble formation based on offgassing of supersat
tissue is time dependent & continues after surfacing) by assisting in
offgassing - a result that can be achieved by 100% surface O2.
Again the value of IWR from the stndpt of bubble/DCS theory is not
clear.
>Arguments against IWR based on the supposed inefficiency of Boyle's
law
>in reducing bubble volume are idiotic.
What is the 'inefficiency of Boyle's Law'?
There may be good medical reasons
>to avoid IWR though....
>
>>pause for a minute or two every 30ft from bottom up to your first
>Buhlmann stop.
>
>
The same result could be obtained by slower ascents. The issue here is
the large body of 'no knowldege'. The Haldenian model is based on the
compartment SSat ratio and its reduction. It treats the body as a set
of independent comparments. As this is not reality, it would be
shortsighted to not consider compartment to compartment transfer of gas
during deco, even gas uptake by slower comparments (that R not yet SSat
to the deco depth) while the faster ones are offgassing. In addition
one has to wonder about diffusion & diffusion limited offgassing.
>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
>
>--
>Send mail for the `techdiver' mailing list to `techdiver@terra.net'.
>Send subscription/archive requests to `techdiver-request@terra.net'.
>
Regards
Esat Atikkan
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