And what about people like David Blaine or Tom Sietas? Sietas held his breath underwater for over 22 minutes (world record). I know they train for it like months and even years, but doesn’t holding your breath = no oxygen to brain?
Permanent brain damage apparently occurs just after 4 minutes of lack of oxygen to the brain, so why are freedivers left generally unscathed after 8 or 10 minutes without air?
In: Biology
When you breathe in and out, you don’t change 100% of the air in your lungs. Also, the standard air is about 79% nitrogen and only 20% oxygen (and then a bit of carbon dioxide and other stuff).
When the amount of CO2 in your lungs goes up, that compels the need to breathe. But there is still oxygen in your lungs. An exhaled breathe is about 4% carbon dioxide. So you still breathe out lots of oxygen (and nitrogen). So it takes time to actually use up all that oxygen in your lungs, and so even though you aren’t breathing in and out, your blood is still able to switch out oxygen for CO2 for some time. That is significantly expanded if you just breath in pure oxygen before a dive (so instead of 80% nitrogen and a bit less than 20% oxygen, you have a breathe of 100% oxygen).
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