Hypothetical question

[doctormike]

the resultant drop in pressure results in bubble formation.

.

Yup, exactly!

Here, the FAA also points out that a drop in ambient pressure alone can cause DCS, even if you don't ongas first.

Interestingly, they recommend treating DCS just like we do, with 100% O2. Which greatly increases that gradient that we keep talking about.

 

[caruso]

After reading 13 pages of this thread and trying to follow the math and science with limited success, my take on the entire thing that unless I'm walking around on the planet's surface breathing 100% pure oxygen, I could get on an airplane, and get bent, without ever setting fin in the water because a) I've got some Nitrogen in my tissues and b) once the plane takes off my body will be exposed to a pressure gradient which makes it possible for gas bubbles to form in my tissues.

 

[dmaziuk]

After reading 13 pages of this thread and trying to follow the math and science with limited success, my take on the entire thing that unless I'm walking around on the planet's surface breathing 100% pure oxygen, I could get on an airplane, and get bent, without ever setting fin in the water because a) I've got some Nitrogen in my tissues and b) once the plane takes off my body will be exposed to a pressure gradient which makes it possible for gas bubbles to form in my tissues.

Yes: Triage and Treatment of Mass Casualty Decompression Sickness After Depressurization at 6400 m. - PubMed - NCBI

 

[doctormike]

After reading 13 pages of this thread and trying to follow the math and science with limited success, my take on the entire thing that unless I'm walking around on the planet's surface breathing 100% pure oxygen, I could get on an airplane, and get bent, without ever setting fin in the water because a) I've got some Nitrogen in my tissues and b) once the plane takes off my body will be exposed to a pressure gradient which makes it possible for gas bubbles to form in my tissues.

Pretty unlikely, given the standard pressurization of commercial air cabins, but as the FAA points out in the link above, this is a real risk in unpressurized aircraft.

Also remember three other things:

1) There is a difference between forming bubbles (which all divers probably do, and maybe some pilots) and getting bent. DCS is the name given to symptoms that are most likely caused by bubble formation, but the vast majority of people who bubble don't get symptoms.

2) Bubbles don't seem to behave in a linear fashion. By that I mean, if you form them, and then ascend again before they are cleared, they may grow and cause more symptoms than they would from a single dive

3) We all tend to be very clever about DCS, figuring that we can precisely determine if we will get bent or not (the "magic bracelet" phenomenon). But there is a lot that isn't known, and in some situations, there are variables that simply haven't been clinically studied or incorporated into our models. Even the USN dive to fly recommendations have to be read in context - they are guidelines for fit young divers balancing the small risk of treatable DCS (they have a lot of chambers), vs whatever impact a flight delay would have on military operations. They are NOT a generalizable guarantee of safety.

I'm also guessing that John's diver will be OK to fly. But there is enough uncertainty about the physiology discussed above that I think that we shouldn't oversimplify.

 

[Storker]

the vast majority of people who bubble don't get symptoms

Could that perhaps have some connection with the fact that sola dosis facit venenum?

 

[tursiops]

Could that perhaps have some connection with the fact that sola dosis facit venenum?

As in climate change, it is not just the dose that makes the poison but the rate at which it is applied.

 

[Dominik_E]

Hi,

coming back to the point that RyanT mentioned, about the location of bubble formation: the underlying reason is that liquids have significant internal cohesion. In order for a bubble to form, not only there must be supersaturation so that free gas could exist, but there also needs to be "room" (as most liquids are basically incompressible, even at the bottom of the deepest ocean trenches the water is only a few percent denser than at the surface). This "room" of course is the bubble. Growing a bubble once a tiny "room" is there is comparatively easy. Gas can diffuse into the bubble, and ambient pressure drop leads to expansion. But making the initial "room" (the nucleus) is decidedly not, because of the comparatively large intermolecular forces. It is of course possible that this would happen inside the liquid itself, if inert gas supersaturation and ambient pressure drop were really huge. But just think of how relatively easy it is to significantly superheat water, without forming gas. So easy that it is a real risk in some applications. It turns out, that in diving such huge differentials are normally never reached.

But here comes some cool observation everyone can do: Next time you see champaigne (or coke) bubbling inside a glass, look closely WHERE the bubbles are coming from. Most of them not from somewhere inside the liquid, but from surfaces of the glass that are in contact with the liquid! This is actually the other process that is often discussed for forming bubble in divers: "heterogeneous" nucleation at surfaces in contact with liquids. And of course, coming back to tribonucleation, muscle power makes it quite easy to create huge local pressure differences in the liquid, "breaking" it and thus nucleating bubbles...

Hope this helps!

 

[J-Vo]

I mostly agree with @doctormike.

DCS & bubble formation are tissue inert gas pressure relevant to total ambient pressure not inspired partial pressure.

The argument is also true that the tissue pressure will never exceed ambient in the described dive.

Therefore, the question is will the ascent pressure drop create tribonucleation? I'm guessing the diver would have to ascend way faster than recommend limits and possibly instantaneously. I don't think this would cause DCS.

I would not hesitate to fly after this dive.

 

[markmud]

Therefore, the question is will the ascent pressure drop create tribonucleation? I'm guessing the diver would have to ascend way faster than recommend limits and possibly instantaneously. I don't think this would cause DCS.

Hi jvogt,

You nailed it. +1

One small, but profound paragraph is the complete answer for this exercise.

fly on,
markm

 

[EFX]

The argument is also true that the tissue pressure will never exceed ambient in the described dive.

Tissue pressure is higher than ambient (or rather the inspired inert gas pressure) on the descent and ascent phases of the dive. During these phases the diver is offgassing. When the diver reaches the bottom at 30 ft. all tissues are saturated at the inspired inert gas pressure of 24.49 fsw. The surface is 24.67 fsw.

Therefore, the question is will the ascent pressure drop create tribonucleation? I'm guessing the diver would have to ascend way faster than recommend limits and possibly instantaneously. I don't think this would cause DCS. I would not hesitate to fly after this dive.

As mentioned earlier tribonucleation creates micro bubbles at local sites by muscle fibers sliding along one another and/or along capillary walls due to turbulent blood flow, among other reasons. These nuclei provide seeds for bubble growth when an offgassing gradient is sufficiently high to overcome the combined internal pressure and surface tension of the bubble.