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Comment by simias | Hacker News Reader

Do you really have to pay attention not to hold your breath while ascending?

I'd have thought you'd feel your lungs expanding and you'd have the reflex to let the air go away. Although on the other hand it's probably not a situation common enough for us to have evolved an inate reaction to it.

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Yes and no. If you relax your breathing apparatus, air will escape naturally. However, if you actively hold your breath, the mounting pressure can actually lead to a tighter block. Rapidly expanding lungs are not something that falls within the daily experience of most humans, so it's best to be aware of the complications. Especially when panic sets in (and the journey upward from 30m will be quite long) it can cost a lot of self control to force yourself to exhale.

Especially since if you're doing an emergency ascent, it's quite likely that it's due to having problems with getting air from your cylinder (if your air supply was fine, you'd probably be doing a controlled ascent instead). It's very difficult to avoid holding your breath when you know you won't be able to breathe in again until you reach the top.

Yes for at least two reasons. Firstly, holding your breath can cause you to pass out. Secondly, holding your breath while the pressure is decreasing can cause an embolism (air can enter a blood vessel in the lung) which can form a clot and kill you: http://en.wikipedia.org/wiki/Air_embolism#Gas_embolism_in_di...

You do..(though it's simple, you just sort of humm or go "aaaaah" to yourself, silently.. that keeps your airway open).

No innate reaction - over-inflation would require a positive pressure applied to the lungs - normally as we breathe it's at equilibrium. Your lungs aren't elastic at all - once they are at capacity, over-pressure will rupture them right quick, and you own't feel it coming (but you'll sure feel it happening)

Whether or not you have the reflex to let out the air, the complications are pretty severe, so it's worth covering either way!

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