Unknown Woody From “Dive Talk” DCS and Medical Journey

[crofrog]

Can you define your understanding of "supersaturation"?

Supersaturation describes a condition where a liquid contains more of a disolved gas than it can hold under equilibrium conditions, as defined by Henry's Law.

 

[iliketopetsharks]

The way they portrayed DAN in their video was imo not appropriate. And if you take a glance at the comments on Youtube, you'll see that the majority of their audience are very new divers or people who are considering learning to dive. If only some of their viewers don't get DAN or don't renew their membership and then get in a diving accident, they might've done more bad than good with that video.

 

[L13]

Based on my understanding this is not a true statement.

Stable bubble nuclei are likely always present, and bubbles can form under isobaric conditions or in any situation where there is a supersaturation of the dissolved gas.

For any solution of gasses in liquid, nuclei will collapse on or shortly after formation (ie. not stable) unless the total partial pressure of the gasses in solution exceeds the total ambient pressure by enough to offset the additional effect of surface tension (which aids ambient pressure in collapsing bubbles). This is a well established chemistry/physics result.

 

[crofrog]

For any solution of gasses in liquid, nuclei will collapse on or shortly after formation (ie. not stable) unless the total partial pressure of the gasses in solution exceeds the total ambient pressure by enough to offset the additional effect of surface tension (which aids ambient pressure in collapsing bubbles). This is a well established chemistry/physics result.

Are you asserting that stable bubbles can not occur under isobaric conditions?

 

[inquis]

Supersaturation describes a condition where a liquid contains more of a disolved gas than it can hold under equilibrium conditions, as defined by Henry's Law.

You seem to be saying that bubbles are possible and stable when inert tension is greater than the inspired inert gas pressure (i.e., above equilibrium). @L13 is saying it needs to be above total ambient pressure to be stable and that bubbles are not stable in that intermediate region between inspired inert pressure (equilibrium pressure for off/on-gassing) and total ambient pressure.

Consider: my tissues are saturated while sitting in my living room, I will not get bent if I start breathing oxygen, in spite of the fact the nitrogen content in those tissues is now well above equilibrium pressure (i.e., they are supersaturated). Tissues will certainly off-gas, meaning inert molecules will move away from those tissues. Some of those molecules may even form bubbles, but they are not stable because the inert tissue tension of 0.79 atm is less than the 1.0 atm total pressure.

This is why Workman & Buhlmann defined the critical supersaturation (i.e., the M-value) as a multiple of ambient (total) pressure rather than a multiple of the inspired inert pressure. Similarly, Baker put GF=0 at ambient as well.

No one cares about a tissue supersaturation corresponding to a GF of 0%. ETA: a non-diver at equilibrium at sea level reaches a GF above 0% on a 20 minute airplane climbout to 8000 ft.

 

[dmaziuk]

This is why Workman & Buhlmann defined the critical supersaturation (i.e., the M-value) as a multiple of ambient (total) pressure rather than a multiple of the inspired inert pressure. Similarly, Baker put GF=0 at ambient as well.

They did? Does Haldane know?

 

[crofrog]

You seem to be saying that bubbles are possible and stable when inert tension is greater than the inspired inert gas pressure (i.e., above equilibrium). @L13 is saying it needs to be above total ambient pressure to be stable and that bubbles are not stable in that intermediate region between inspired inert pressure (equilibrium pressure for off/on-gassing) and total ambient pressure.

Consider: my tissues are saturated while sitting in my living room, I will not get bent if I start breathing oxygen, in spite of the fact the nitrogen content in those tissues is now well above equilibrium pressure (i.e., they are supersaturated). Tissues will certainly off-gas, meaning inert molecules will move away from those tissues. Some of those molecules may even form bubbles, but they are not stable because the inert tissue tension of 0.79 atm is less than the 1.0 atm total pressure.

I'm unsure if either of you has a subscription to science, but this might be an interesting paper. I had a similar understanding to what you were saying above, but this is showing the formation of bubbles that were detectable on ultrasound during an isobaric switch in vivo. I'm not saying this is what happened during their dive, but I'm saying that is seems to support the formation of stable bubbles in a situation where ambient pressure did not change.

https://www.science.org/doi/10.1126/science.887926

 

[L13]

I'm unsure if either of you has a subscription to science, but this might be an interesting paper. I had a similar understanding to what you were saying above, but this is showing the formation of bubbles that were detectable on ultrasound during an isobaric switch in vivo. I'm not saying this is what happened during their dive, but I'm saying that is seems to support the formation of stable bubbles in a situation where ambient pressure did not change.

https://www.science.org/doi/10.1126/science.887926

I can't read the paper itself, only the summary. However:
Since the diffusion rate of He is higher than N2, the ppHe in the tissue due to the inspired gas would increase faster than the ppN2 would drop. As a result, the Total pressure in the tissue would be greater than ambient. Which is why the paper uses the term "supersaturation" in its description of the condition. This is completely different than the saturated (not supersaturated) condition in our discussion above. Note the bubbles did not occur in the paper's experiment till the inert gas was changed. Saturation on a constant mix caused no bubbles. Which is good, otherwise we would be having bubbles now, sitting at our computers since our tissues are at saturation for the ambient pressure and gas mix.

 

[crofrog]

otherwise we would be having bubbles now, sitting at our computers

We have bubbles right now sitting at our computers. They're just not big enough to matter

 

[KevinNM]

yup - they ignored obvious signs of a potentially serious issue for many hours...

This is very notmal.

I’ve heard 2-3 paramedics and ED nurses describe how they convinced themselves they they were fine for hours despite abvious major cardiac symptoms. One ended up in the cath lab getting ablation due to their racing heart, another in the cath lab getting stents.

If you told them the list of symptoms on duty they would have been getting a stretcher and the 12 lead. But when it was them?

So keep in mind that you are not going to be the best judge of ‘is this serious or not?’ If you think it is possibly bad run with that. Make a call.