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This thread makes my brain hurt:)
Why are O2 and CO2 ignored? Granted they are both part of the metabolic
process, but they both get dissolved in the tissues under hyperbaric
conditions.
If a bubble forms, will it not contain the same gas proportions as were
dissolved?
What percentage of inspired O2 bonds to hemoglobin?
At what PPO2 will the hemoglobin become O2 saturated? Or is it more
related to total ambient pressure?
How much CO2 stays dissolved in the tissues?
On an effective gas exchange in the lungs, what is the PPCO2 remaining?
If a bubble forms containing O2, will the O2 bond to hemoglobin
effectively reducing the quantity of gas in the bubble?
And lastly:
Has anyone done gas composition analysis on bubbles?
Just thinking out loud
David Pearson
Nortel, Public Carrier Networks
Northern Telecom
Ottawa, Ontario, Canada
dpearson@no*.ca*
In message " Deco mix", deepreef@bi*.bi*.Ha*.or* writes:
>
>> See Bennett and Elliot for some discussion of the "window", and
other
>> important issues of ogygen , inert gas, and deco. Don't pay even the
slightes
>> attention to what the agencies say, or the deco weenies. - G
>
>Although I consider myself a deco weenie, I'm going to comment anyway.
>Basically, I think George is right, but I'll try to explain what he
said
>using the English language this time.
>
>Your idea of establishing a high gradient for nitrogen and helium
across the
>alveolar membranes of the lungs by breathing argon is correct; however,
>the gradient accross the alveolar membrane is not the only thing to
>consider for decompression purposes.
>
>The important thing to remember is that oxygen, when breathed at
>sub-toxic levels, is generally not considered in decompression
>calculations. The reasons are primarily: 1) a lot of oxygen is bound in
>Hemoglobin, and thus not contributing to the total dissolved gas load;
>and 2) oxygen is being metabolized ("burned up") by your body. The way
>to think of it is that oxygen is a decompression "freebie".
>
>As George mentioned, maximum allowable tissue tensions for
decompression
>is calculated by combining all of the non-oxygen gasses in solution
>together. If you have loads of N2 and He in your tissues, and you start
>breathing an argon-oxygen mixture, then N2 and He will come out fast,
>but argon will be going *in* fast (there is essentially no argon in
>your tissues to start with, so the argon gradient is big in the
opposite
>direction). At any given time, your total gas load is N2 + He + Ar. So,
N2
>and He are dropping over time because they are coming out through your
>lungs. Argon is increasing over time because it's coming in. So, the
>efficiency of decompression offgasing is measured by relative
difference
>in rates of N2+He loss minus Ar gain.
>
>Now, He is a smaller molecule than N2, and N2 is smaller than Ar, so
>looking only at diffusion rates, you could argue that the N2 and He are
>coming out faster than the argon is going in. Thus, you would have a
net
>drop in total (combined) non-oxygen dissolved gas in your blood over
time.
>However, when you are breathing pure oxygen, your combined gas load
drops
>*MUCH* faster, because it is not off-set by the influx of argon
(remember,
>oxygen is a decompression "feebie"). The point is, from a deco
>perspective, you want as much O2 as you can get.
>
>A better argument for decompression with argon is to use it for
>intermediate stops. For example, switch from He to N2 at 130 feet on
>your way up, then switch from N2 to Ar at 60 feet (Ar is more narcotic
>than N2, so you don't want to breathe it too deep), then O2 at 20 feet.
>The theory is that, because Ar is a "slower" molecule, your net gas
loss
>would be greater during the 60-20 foot stops than it would be breathing
>N2 for the same stops (only because N2 and He would be going out faster
>than Ar would be coming in). However, when you look at almost any dive
>profile, you'll see that the advantages (in terms of reducing deco
times) of
>switching to Ar on deco are pretty slim. The *disadvantages* of using
Ar
>for deco are primarily: 1) there are not enough data on the dynamics of
>Ar and decompression to come up with numbers we can trust; 2) bubble
>dynamics complicate the issue enormously (if bubble composition shifts
>from N2/He to Ar, then the effects of DCS, if they do occur, may be
more
>difficult to treat); and of course, 3) Ar is more expensive.
>
>In short, the theoretical advantages of using Ar for deco are small
>compared to the practical disadvantages.
>
>O.K., so maybe that wan't any more clear than G's explanation....
>
>Aloha,
>Rich
>
>Richard Pyle
>deepreef@bi*.bi*.ha*.or*
>*******************************************************************
>"WHATEVER happens to you when you willingly go underwater is
>COMPLETELY and ENTIRELY your own responsibility! If you cannot
>accept this responsibility, stay out of the water!"
>*******************************************************************
>--
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>
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