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
I really feel like I haven’t seen the real ELI5 answer yet.
It’s because “holding your breath” *doesn’t mean* “no oxygen to your brain.”
Inside your body, oxygen is carried by your blood to all of your different parts. Then, the blood (with some of the oxygen used up) is sent back to your lungs to get more oxygen. But, even if there is no new oxygen in your lungs, you still have a decent reserve of oxygen in your blood for your parts (including your brain) to use up. The only way to *immediately* get to “no oxygen to the brain” is decapitation. Otherwise, as long as your heart is beating (and *all* of the oxygen in your blood hasn’t been used up), your brain will continue to get oxygen.
What freedivers and David Blaine can do is various methods of (1) increasing the amount of oxygen that their blood can carry and (2) decrease the speed at which their body uses that oxygen. So, when they go underwater, they can last longer on the oxygen already stored in their blood until they need to take a breath.
Because they have a beating heart. Apparently there is enough oxygen in the bloodstream to support the brain for a period of time as long as it is actively being moved through the brain. This is why they tried to go to the breathless CPR a few years ago (namely because people wouldn’t do CPR because they didn’t want to put their mouth on another person’s mouth) and it would be better than nothing.
Long story short, holding your breath doesn’t stop oxygen going to your brain. Your blood keeps circulating while your heart is pumping, getting that sweet sweet oxygen to wherever it’s needed.
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).
In the simplest explanation: Holding your breath does NOT mean no oxygen to brain.
Oxygen doesn’t suddenly stop being transported to your brain just because you held your breath. Oxygen is held by the blood and transported to your brain. This is ongoing even when you hold your breath, it takes some time before all the stored oxygen in your blood is used up when you stop breathing and stop restoring oxygen to the blood.
Oxygen is transported to the brain through the blood. You suffer brain damage after there is NO oxygen being transported to it – which means all the oxygen stored in the blood has been used up. How much oxygen your blood is able to store and long it takes for your body to finish using all the stored oxygen is what affects how long you can hold your breath safely.
People train to be able to store more oxygen in their blood, and also use oxygen slower.
People who can hold their breath for 10+ minutes basically means the oxygen supply in their blood is enough for their brain to have access to oxygen for 10+ minutes BEFORE the oxygen runs out.
They breathe funny before diving to oxygenate their blood to an extreme level.
In other words they take some extra oxygen with them, bound to red blood cells, and have trained to use it sparingly.
Also 4-6 minutes is like most of those sort of specs, just an average, not a rule.
Your blood has oxygen in it.
Tonight’s homework, one page, double spaced about hemoglobin
There’s a super interesting video for this. If you’ve got an hour to spare I highly recommend you check out James Nestor. https://youtu.be/aH9boP9pksM
Adding to what other people said, only a minuscule amount of the oxygen in the air we breathe is used in the body. That’s why CPR works, there is still a significant amount of oxygen in exhaled breath that can be breathed into another person for oxygen.
So it takes a while until the body actually needs “fresh” oxygen/until it runs out.
Easy ELI5 boils down to one thing, adaptation. They’ve got factors working for them in their body plus they practiced a lot so their bodies adapted.
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