Why and how is it possible for one’s lungs to burst from breath-holding against a moderate decompression?
You often hear that you should never, ever hold your breath when the ambient pressure around you is decreasing at a significant rate (for instance, during egress from a submarine ten meters down, or in a pressurised aircraft experiencing a rapid or explosive decompression, lest the expansion of the air trapped in your lower respiratory tract cause your lungs to burst (generally a somewhat undesirable occurrence).1 An analogy often used is that of a sealed balloon in a vacuum pump; as the pressure external to the balloon decreases, the increasing pressure differential across the balloon membrane causes the balloon to be stretched wider and wider as the air inside it expands, until the balloon reaches its breaking point and ruptures.
Which would be perfect for explaining pulmonary breathhold barotrauma, were it not for the fact that the lungs, unlike most balloons, are not free to expand to their alveoli’s content; they can only expand a relatively small amount before running up against the chest wall.
Moreover, the exteriors of the lungs aren’t even exposed to the rapid drop in ambient pressure; instead, they’re exposed to the pressure inside the pleural cavities, which, being sealed, cannot vent to ambient pressure.
A better analogy would seem to be a sealed balloon in a safe in a vacuum pump; the balloon should not burst, no matter how low the ambient pressure, unless its enclosure is ruptured.
Granted, the chest wall, unlike most safes, does have some give to it, but, even with the chest wall deflected outwards to maximum chest size, and with the lungs expanded to fill the entirety of the available space, this still shouldn’t be enough space to allow the lungs to burst,2 barring a wholesale rupture of the chest cavity.34
And, finally, in the event of a large pressure differential between the lungs and the ambient atmosphere (or lack thereof), it would seem that the air trapped in the lungs should be able to force open the epiglottis and escape via the pharynx, mouth, and nose before it would put the lungs in danger of bursting.
What am I missing?
1: In an explosive decompression of an aircraft, this is claimed to often occur even to persons not holding their breath, as the pressure in the aircraft’s cabin decreases faster than air can escape from the lungs.
2: Otherwise, you would risk bursting your lungs any time you breathed in to your maximum lung capacity.
3: In which case you don’t worry about your lungs bursting; you worry about them collapsing.
4: This whole discussion assumes that the pressure drop is not great enough to cause dissolved gasses in the bloodstream to come out of solution; if it is, that’s a whole different ballgame.
(0)Terms of Use Privacy policy Contact About Cancellation policy © freshhoot.com2025 All Rights reserved.