using lungs to mix OC deco gas on the fly?

Drmike

This may seam like a crazy idea at first but bare with me.


Situation: Diver finds himself with considerable OC deco to do but has lost some or all of his intermediate deco gases.

He has left a tank of 100% O2 and a tank of very hypoxic trimix.

Given that the lung doesnt fully exchange all its gas volume on each breath it would I pressume act a bit like an accumilator and to some degree smooth out/mix the gas contents.

You can see this effect to some extent on the surface. Breath in normally (lung full of air) breath out - then breath in O2 and blow contents across a o2 sensor - you dont breathe out 100%.

I pressume it should be easy enough to model if we know the approx exchange rate in the lung.


So given that - could a diver during a dive to some extent 'mix' his own deco gas in his lung (in an emergency) by taking one breath of O2 then one of mix (or whatever ratio gave the right mix)?

Im sure there will still be large fluctuations in ppo2 - but given that we know the human body can tolerate very high ppo2s provided the duration is very short and is interspersed with longer lower ppo2 breathing. )see previous thread here someplace) Im wondering how the balance of risk is doing this compared to the alternative of not being able to complete deco.




[please no dumb ass comments - I know this is not a good idea blah blah blah- I know there are a million ways to avoid ending up in this situation blah blah blah - Ive done my padi nitrox course - Im just looking for info that could lead to any possible real emergency options to keep in the toolkit - you never know when 'crazy' tool may be the only thing that keeps you alive]

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wedivebc

I heard of a tech instructor who taught his students that in an emergency you could breath a bit of O2 then some backgas to extend your dwindling supply.
Is this the sort of thing you have in mind?

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Steve

IIRC Sheck experimented with this concept. Sadly a 2 sec google didn't tum anything up but I think it would be worth your while to look further. I hope this helps.

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dteubner

The problem is that it would be very difficult to do away from a spreadsheet.

Lets say you are at 30m any your hypoxic mix has an FIO2 of 0.04. If you took one breath from the O2 and two from the mix and they are 4 litre breaths from your 7 litre lungs then, at steady state, your fraction of oxygen in the alveoli varies between about 64% after the O2 breath to 14% after the second mix breath and your mean (whatever the hell that means physiologically) PPO2 is 1.44 - which sort of looks like a good number. If you take smaller breaths then the steady state mean doesn't change but the fluctuations are much smaller (1.64 to 0.47 for 1 litre breaths)

I guess what no one can say what the risk of O2 toxicity is when you are at 2.5, 1.2 and 0.6 ATAs for 6 seconds each recurringly, and what the decompression implications of this are is anyones guess.

Of course you can't take exactly 4 litre breaths over and over again so what your PO2 is would be impossible to know and vary accross a very wide range (what's that rule again?)

I think at best you could use the technique to swim from where your dil is too hypoxic to where your O2 is sort of breathable but my gut feeling is you would very likely fit if you tried to do any stops on the way - and you would have no way of knowing what the stops would mean anyway.

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Dave T

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steevke

I wonder if it would be any better doable when breathing mix X for x seconds and mix Y for y seconds - in a single breath I mean.

steven

dteubner

I've changed my mind a bit - I think I was a bit too negative.

Deco planning based on the mean is probably not too far out

Small breaths minimise the big swings

If use the ratio of 1 breath of O2 to (Ambient pressure in ATA) breaths of dil it sort of works quite nicely (on a spreadsheet at least).

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Dave T

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UKSteve

Mike,

Interesting...and tricky too in a human lung I guess...with tidal volumes etc.

But how about a similar approach but using one counterlung? If you have a second manual injector on your "upstream" counter lung then you might be able to add relative volumes of each gas with one or more squirts of O2 and dil into the bag before breathing off it? Could even massage a front mounted lung a little to mix it before breathing it. If at deco / rest then your RMV is ging to be lower - esp at high ppO2s - and so would be time to mix a couple of breaths at a time.

Should be possible to come up with a sort of table for this for different mixes and different depths if we assume that a 1 sec squirt will add a predictable relative volume of each gas.

As someone once said...any gas is a lot better to breath than water...

Steve

decoweenie

Mike,

Here is (hopefully) a tangent out-of-the-box thought...

How about using the wing to blend the 2 gases before breathing it into your lung ?

Some people already learned how to breath off the inflator in case of emergency (IIRC, you have as well), just don't breath it back into the lung.

Use the wing as a blending accumulator and you could learn beforehand what squirt ratio between the 2 tanks gives what fiO2. Or it could even be estimated on-the-fly knowing the fiO2 of the tanks.

The tricky parts are:

• The tanks might not have the inflator hoses connected.
• Buoyancy issue with fluctuating wing volume, but might doable if having access to the downline or cave roof.

Just some food for thoughts...

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dteubner

Spreadsheet at Research etc - last link on the page

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Dave T

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lbihler

If I remember well Mark Elyatt has done it in a real life situation, or at least that's what he wrote

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