Essentially, the stress on the blood vessels in your lungs is so high and the air pressure so low at high altitudes that the blood vessels burst and fill the lungs with fluid. This is fatal if the victim doesn’t get to a lower altitude very quickly, and one of the things that makes mountain climbing dangerous.

Chapters:
0:00 Intro
0:46 Both your lungs are the same size?
1:22 How much of the air we breath is oxygen?
2:21 Which situation can cause your lungs to stress-fail?
3:35 Outro