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.
That surviving “4 to 6 minutes *without oxygen*” means with NO oxygen being supplied. Like, if they cut off your head and kept the blood in somehow.
If you take a deep breath and hold it, your lungs are full of air with oxygen that can be extracted and brought to your brain over the next several minutes. Then once that’s gone, you have 4-6 minutes with “no” oxygen before you’d die.
Pro divers take it further by also hyperventilating until their blood gets saturated with oxygen too, and *then* they take a huge breath. So their blood is full of oxygen, their lungs are full of oxygen, and they’ve trained their bodies to use as little as possible so that more is left to be carried to the brain over those incredible 15-20 minute periods.
But it’s not that their brain is going without oxygen for those 20 minutes. Blaine’s brain needs oxygen at least every 6 minutes too. What the training does is allow them to take in, hold, and deliver that oxygen from their huge breath efficiently.
Basically that clock doesn’t start ticking as soon as you hold your breath.
You have both oxygen in your lungs and oxygen in your blood which will get used.
That 4-6 minute time frame only comes into play after the oxygen in the blood and the lungs has been depleted.
Fun fact: you are now aware of your breathing and will continue to breathe louder and become more aware of your loud breathing.
Oxygen doesn’t travel faster than the speed of light. It diffuses through your body and takes time.
When you read that people cannot survive more than 4-6 minutes without oxygen, it means just that, zero oxygen in the body for that amount of time. It is also referring to normal situations. You can increase the oxygen level in your body by deep breathing. You can slow the exiting of oxygen from your body by slowing breathing and being very still. With practice you can get up to the numbers you mention. Also, some bodies are better and more suited to doing this feat. There are differences between people who are born and live in higher altitudes to those from lower altitudes.
My dad smoked almost his whole life, starting from a very young age. In his 40s he could hold his breath under water for about 4 or 5 minutes. I’ll be 40 this year, never smoked a single cigarette and can only hold my breath under water for about a minute tops.
Everyone else has given great answers, but I’d like to give a simple analogy that may make sense.
We all know a car needs gas to run, just like the brain needs oxygen. Deprive an engine of gas, and it will eventually coast to a stop. If you’re in a moving car, and it runs out of gas, you only have a limited time before it stops moving. This is why cars have gas tanks.
The body is similar – divers take a whole lot of deep breaths before they dive, which is similar to a car filling up with gas. And when they dive, they use up the oxygen stored in their blood like a car uses up the gas in its tank.
The blood running out of oxygen is similar to the car running out of gas – once it’s gone, there’s a time limit. For a moving car that means coming to a stop, and for a human that means brain damage.
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.
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.
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