Rise and Fall of the Bubble (Model) ?

[GJC]

1. Maybe, but it only uses X amount of it, usually quoted number is "about 5%". And I don't believe it goes up with pressure, it's still "about 5%" at 40 metres down.

The model doesn't count everything you have in the mix: if it's 21%, the model says there's 79% of "inert gas" that bubbles. In EAN32, there's 68% "inert gas". And it is multiplied by the pressure in the equations, so at 40 m your body is "using up" all of (32*5)% O2 if you believe the model.

2. I was able to find one paper from last century that claimed oxygen seems to be a little "less bubbly" than nitrogen. Nothing else.

I thought your body used up all dissolved oxygen and all bound to hemaglobin in 5 to 10 min if you stop breathing.

 

[JohnnyC]

Isobaric Counter Diffusion. IBCD.

Isobaric counterdiffusion - Wikipedia

 

[dmaziuk]

I thought your body used up all dissolved oxygen and all bound to hemaglobin in 5 to 10 min if you stop breathing.

Well, don't hold your breath, then.

Seriously, though, at the end of the chain there's chemical reactions that need ingredients other that oxygen, and a sink for the products, and are subject to them pesky laws of thermodynamics. With abundant oxygen, those become your limiting factors. These reactions burn, according to google, about 23 litres of O2 per hour. If you breathe 100% O2 at 5 atm, instead of 21% O2 at 1 atm, they'd still burn about 23 litres/hour of it (if it weren't for the obvious problem). All that O2 you don't burn goes, according to the model, out the "poorly understood" "oxygen window".

 

[GJC]

Well, don't hold your breath, then.

Seriously, though, at the end of the chain there's chemical reactions that need ingredients other that oxygen, and a sink for the products, and are subject to them pesky laws of thermodynamics. With abundant oxygen, those become your limiting factors. These reactions burn, according to google, about 23 litres of O2 per hour. If you breathe 100% O2 at 5 atm, instead of 21% O2 at 1 atm, they'd still burn about 23 litres/hour of it (if it weren't for the obvious problem). All that O2 you don't burn goes, according to the model, out the "poorly understood" "oxygen window".

23 L/hr = 383 ml/min O2 used up by the body at rest

Plasma at sea level only contains 3 ml/L of O2 (hemoglobin binds 203 ml/L and this does not change under pressure)

Assume that half your body is water (50 L) and has the same capacity to absorb O2 as plasma (without hemoglobin)

That gives you 150 ml max total O2 dissolved in the liquids of your body at sea level

At 10 atm (330 ft depth), the max total O2 dissolved in your body would be 1500 ml

Your body would consume all that dissolved O2 in less than 4 min.

I get that you could never go to that depth on 100% O2 and that the other gasses in the mix you breath are the bubble causing culprits, but I don't see how O2 by itself could ever cause bubbles on decompression.

 

[dmaziuk]

Your body would consume all that dissolved O2 in less than 4 min.

... if you stop breathing. If you keep breathing, new oxygen will come in in your breathing gas and keep dissolving in your body.

 

[GJC]

... if you stop breathing. If you keep breathing, new oxygen will come in in your breathing gas and keep dissolving in your body.

You don't have to stop breathing. As you are ascending (decompressing), your body consumes the O2. As the pressure decreases less O2 is dissolving into your body, and unless you ascend really fast I don't see how O2 bubbles will form. Even if you went from 330 ft to sea level in 4 min, your body would have used all the remaining dissolved O2. If you ascend faster than that, I can see the possibility of O2 bubbles.

Again, this is assuming 100% O2 at extreme depths which is just not possible to do. With mixed gas diving, the O2 is significantly less and I can't imagine that O2 plays a factor in bubble formation at all. The other gasses are the problem.

 

[scubadada]

I believe this thread has significantly gone off the tracks. Nearly all your oxygen is bound to hemoglobin, dissolved oxygen is a trivial component. Oxygen does not contribute to DCS. Oxygen is neurotoxic past a certain ppO2. It is generally not used at depth above a ppO2 of 1.4, or for deco beyond a ppO2 of 1.6

 

[dmaziuk]

:sigh: Back when there was IT bubble, this kind of explanation was commonly used in startup business plans and it was referred to as "miracle happens here". Let's just say I fail to see how the numbers in the model could possibly add up, if they accurately represented the actual human body, and leave it at that. As I said before, it doesn't matter: as long as we don't get bent the numbers are good enough.

 

[scubadada]

:sigh: Back when there was IT bubble, this kind of explanation was commonly used in startup business plans and it was referred to as "miracle happens here". Let's just say I fail to see how the numbers in the model could possibly add up, if they accurately represented the actual human body, and leave it at that. As I said before, it doesn't matter: as long as we don't get bent the numbers are good enough.

???

 

[dmaziuk]

???

Look, nobody's arguing that people get bent on oxygen in real life: they don't, evidently. The numbers in Shreiner's equation don't add up to "you metabolize all oxygen" -- because they're a model, not the real thing. That's what I'm trying to say.