Holding your breath on ascent...

[elmer fudd]

Have you ever done the experiment of filling a plastic bottle at 10 meters below, seal it and let it surface. You will be amazed what the expansion of air can do!

I'm a bit dubious about this. Releasing a plastic bottle full of air from 10m would mean that at the surface it would have a maximum pressure of 14.7 PSI. In reality however, plastic bottles bulge and expand somewhat when under pressure, so the pressure would likely be somewhat less. In any event though, 14.7 PSI isn't much for a plastic bottle. People routinely charge them to 100 PSI or more when using them for water rockets.

 

[friscuba]

I'm a bit dubious about this. Releasing a plastic bottle full of air from 10m would mean that at the surface it would have a maximum pressure of 14.7 PSI. In reality however, plastic bottles bulge and expand somewhat when under pressure, so the pressure would likely be somewhat less. In any event though, 14.7 PSI isn't much for a plastic bottle. People routinely charge them to 100 PSI or more when using them for water rockets.

He never claimed it'll explode, just that you'd notice the expansion. I've done it and it's definitely noticeable, the bottle expands quite a bit, all of the indentations will bulge at any rate. Thing is, you're lungs are nowhere near as capable of handling additional pressure as a plastic water bottle is, they're probably a heck of a lot closer to a soaking wet paper sack in strength than a bottle.

 

[stargazer61]

Breath holding during ascent isn't an issue in an aircraft as the cabin is pressurized. The pressure drop even at 30k feet is not that much. I'm sure I must be correct on this as I've never heard anything about it during the safety announcements!

Perhaps they will have to add a bit to cover the situation where someone panics on seeing the masks drop and holds their breath until they get it fitted on!

 

[bleeb]

Breath holding during ascent isn't an issue in an aircraft as the cabin is pressurized. The pressure drop even at 30k feet is not that much.

As has been mentioned here on SB before, the 'record' for the shallowest water depth causing an AGE is I think something like 3-4'. When I took OW, my instructor had a saying: 1' might cause injury. 3' probably will. As some of the medical types have mentioned in this thread, they normally try not to exceed about 1.15' H2O with mechanical ventilators.

Commercial aircraft are typically pressurized to the equivalent of 8,000' or about 0.75 ata. This is equivalent to about 7.5' H2O, which is well into the dangerous range. The thing that makes AGE problems unlikely is that you'd have to hold your breath for the typical 5-10 min it takes to get there.

At 30,000', the outside air pressure is typically about 0.3 ata. Blowing down from 0.75 ata is equivalent to rising another 15' H2O. Although more catastrophic failures are possible, the most 'common' major ones would be something like a window blowout, which IIRC still takes a minute or two to blow down a plane to ambient pressure, since a window is still pretty small compared to the total volume of a plane. And you're not holding your breath if you're busy screaming or hyperventilating.

So plane depressurization is certainly large enough to cause problems, but because of other aspects of Real Life(tm) actual instances of AGE seem generally significantly less likely.

 

[Hoomi]

It should be stated as well that risk analysis isn't a precise science. We can predict the possibility, for example, of suffering a broken leg on a jump from a given height, and even with ample data to draw upon concerning that threshold height above which it's a good bet a bone will be broken, and below which a break will not occur, we'll still find cases that buck the odds. There are so many variables involved, that an absolute prediction is nearly impossible.

I don't know about the rest of you, but what I took from my training was that holding the breath on any part of a dive significantly increases the risk of an over-expansion injury. As has been mentioned already in this topic, we're going to find reports of people who held their breath and somehow escaped injury, while also reading of those who consciously focused on keeping their airway open, and still ended up with a problem. What we want to do is develop habits and practices that maximize our odds for a safe dive, while minimizing the chances for any form of injury.

 

[g1138]

I'm still slightly unsure of the process that occurs in a lung over expansion scenario. If the alveoli were to expand and pop then I would expect blood to be coughed up by a victim. I've never heard of blood being expelled as a result so is it that the pressure in the lungs collapses the alveoli rendering them useless?

The alveoli are the last stage of the lungs internal "piping"
They're basically small sacs that AREN'T made or suppose to expand. They covered in capillaries. Capillaries are the smallest blood vessels in the human body, only 1 cell "thick" meaning only one blood cell can pass through at a time (in single file).
The alveoli are covered in capillaries so when air enters the alveoli it diffuses into the red blood cells in the capillaries, since they area between the two is so close.

Red blood cells contain hemoglobin, which binds to oxygen, or worst case scenario, binds permanently to CO (carbon monoxide).

If the alveoli burst then there is no chance for oxygen diffusion, and therefore oxygen transport. Even is the alveoli just expand there is a chance for the capillaries to tear.

If your victim is coughing up foamy blood then it's safe to assume that the alveoli have burst.