Minimum depth change required for an AGE?

[Capt Jim Wyatt]

Yes indeed--I have been told that a 1.5 PSI pressure increase can lead to AGE.

 

[Akimbo]

A colleague of mine was on surface-supplied air at about 25 feet, squatted down to pick up a heavy object on the bottom, held her breath when she stood up with the object, maybe 2 1/2 feet of depth change, and suffered a gas embolism.

It is easy to understand how a 1.1124 PSI or 0.0767 Bar pressure difference is enough to over-pressure the lung but the volume change would require her to be significantly hyper-inflated before standing up. I have to wonder if she had an undetected tissue weakness that failed.

Have you ever heard of an AGE caused by voluntary lung-packing that is still commonly done by freedivers? I was never a fan of lung-packing since it takes time and energy to complete for a very marginal increase in volume.

 

[Subcooled]

Depth is irrelevant here.

Roughly speaking, pressure times volume is constant. Half the pressure twice the volume. This is why bubbles are a problem indeed. Ascent from 1m or 1.1 ATM to 1.0 ATM is a very small relative pressue change. Hence, lung expansion will be minimal!

 

[peterak]

I've personally seen it happen in less than a meter. A colleague of mine was on surface-supplied air at about 25 feet, squatted down to pick up a heavy object on the bottom, held her breath when she stood up with the object, maybe 2 1/2 feet of depth change, and suffered a gas embolism. That was in relatively shallow water, which makes a difference as @Akimbo pointed out.

Best regards,
DDM

I wonder if straining to lift the heavy object contributed--perhaps in a major way.

 

[Dr Simon Mitchell]

Depth is irrelevant here.

Roughly speaking, pressure times volume is constant. Half the pressure twice the volume. This is why bubbles are a problem indeed. Ascent from 1m or 1.1 ATM to 1.0 ATM is a very small relative pressue change. Hence, lung expansion will be minimal!

Hello Subcooled,

Aspects of your post are correct, but your initial claim isn't. Depth is very relevant, and the reason is embodied in your summary statement of Boyle's law. The predicted change in volume of a compressible or expandable gas space is proportional to the change in pressure. The change in pressure associated with a 1m ascent from 50m to 49 m is only 608 kPa to 598 kPa, a 1.6% decrease, which would be matched by a 1.6% increase in the volume of (eg) a bubble. In contrast, the change in pressure associated with a 1m ascent from 1m to the surface is 111 kPa to 101 kPa, a 9% decrease, which would be matched by a 9% increase in the volume of a bubble. Thus, the 1m ascent very shallow provokes a > 5x increase in volume than the same ascent performed deep.

You are right that lung expansion from 1m to the surface will still be relatively small, but if you start with very full lungs and don't vent gas during the ascent, experience tells us that it may be sufficient to provoke pulmonary barotrauma and arterial gas embolism in some cases. For an example, see here:

Arterial gas embolism breathing compressed air in 1.2 metres of water - PubMed

The same journal (Diving and Hyperbaric Medicine) is about to publish (in two weeks) another case that occurred very shallow (~1m) during helicopter escape training.

Simon M

 

[duke dive medicine]

It is easy to understand how a 1.1124 PSI or 0.0767 Bar pressure difference is enough to over-pressure the lung but the volume change would require her to be significantly hyper-inflated before standing up. I have to wonder if she had an undetected tissue weakness that failed.

Have you ever heard of an AGE caused by voluntary lung-packing that is still commonly done by freedivers? I was never a fan of lung-packing since it takes time and energy to complete for a very marginal increase in volume.

Weird. I thought I'd replied to this. Re lung defects, possible but unlikely.

There are documented cases of lung packing causing pulmonary barotrauma. It's a dangerous practice.

Best regards,
DDM

 

[duke dive medicine]

I wonder if straining to lift the heavy object contributed--perhaps in a major way.

It's possible, with enough of an increase in intrapulmonary pressure.

Best regards,
DDM

 

[Miyaru]

With a freediver technique call lung packing or buccal pumping, you can inflate your lungs to the maximum volume.

The easy way to achieve the same is to go ~86cm below the surface (body horizontal) and breathe in completely from your scuba regulator . If you hold your breath and surface, your lungs likely won't be damaged.

For AGE, you'll have to go deeper. The 1.2m mentioned in the article that Simon referred to, is probably enough for most people.

 

[duke dive medicine]

The easy way to achieve the same is to go ~86cm below the surface (body horizontal) and breathe in completely from your scuba regulator . If you hold your breath and surface, your lungs likely won't be damaged.

@Miyaru I'm going to respectfully disagree with you here. 86 cm is about 2.8 feet, enough of a depth change to result in pulmonary barotrauma on a full breath.

Best Regards,
DDM

 

[tbone1004]

somewhat relevant anecdote about lung packing and this.

I am a bagpiper and I play on what is considered very strong reeds. The goal of all bagpipers is to get to the strong reeds because they are more stable, sound better, and are significantly louder. We typically measure with a manometer and "wimpy" beginner reeds are around 20" of water or 0.7psi, and the big boy reeds are around 40" of water or about 1.5psi. The big boy reeds are about at the limit of what your lungs are able to generate from a pressure perspective and after I had a bad bout of COVID-19 last February I had to go back to beginner reeds because I was not able to generate the pressure anymore.
This is the pressure generated by your diaphragm and putting positive pressure on your lungs that they can withstand and what is interesting is seeing how over the last year my lungs were able to recover back to their initial strength, but also relating that "workout" of the lung tissue when we see new pipers grow in reed strength in their ability to generate pressure and withstand that pressure.
With lung packing in free divers, they are using their tongue to generate positive pressure in the lungs and you can definitely generate more pressure than your lungs can withstand.
Sneezing is apparently around 1psi

All this to say that I've seen an AGE in the shallow end of a pool, and that the specific depth is going to be largely dependent on what kind of shape your lungs are in based on the type of activities you do. If you play instruments like clarinet, bagpipes, french horn, oboe, or trumpet where you are generating a lot of positive pressure in your lungs to play or you are practicing lung packing, your lungs are probably going to fare much better than someone who doesn't. Your lungs don't experience any real positive pressure under normal circumstances except when you sneeze which is relatively infrequent.