Posted by Gerry Smith on March 10, 2001 at 14:05:20:
In Reply to: Re: Lung Overexpansion posted by Steve on March 10, 2001 at 11:48:59:
Steve, I'll try to answer both posts here but keep in mind that my knowledge of anatomy in minimal. I'm just a Dive Instructor.
You're right, the epiglottis is the flap of tissue that closes the airway when you swallow or when you lock your throat while holding your breath. It can be felt just below your adams apple and it can conciously be closed of held open.
The ten percent thing is a supposition. Some amount of overexpansion will cause injury, maybe five percent, maybe twenty. And that percentage will occur at any point in the water column if you ascend far enough. In deeper water the same percentage requires a larger ascent than in shallower so we get the idea that it is OK to hold your breath in deep water. But - and it's a BIG BUT (no comment from you Ken) it's NOT OK. You do get a little wiggle room from the idea that your lungs are rarely filled to capacity, but you never know how much overexpansion it will take to do damage. Your physiology might be a little off - maybe the lung tissue is damaged from a past illness, whatever. The only way you'll ever know is to wake up in a chamber (if you're lucky.) There's also the idea that if you get into the habit of closing the airway in less dangerous conditions, you might be more prone to try it in other situations. So everybody says don't do it, and they're right.
If you have to try not to scare the fish, pause in your breathing but keep the airway open. Better yet, scare the fish and don't chance it.
GS