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
Fun fact: you are now aware of your breathing and will continue to breathe louder and become more aware of your loud breathing.
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.
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.
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).
Some people also just suffer a little brain damage. You can live with a little brain damage.
Free divers do suffer accumulating brain damage even if they don’t black out. Essentially the more they practice the more efficient their bodies become at using oxygen but it does affect some of them negatively.
They will use breathing techniques to improve oxygen utilisation and they will learn to slow their bodies metabolism to use less oxygen.
For some deep dives the pressure can cause blood to enter the lungs and oxygenate them feeding it back to the rest of the body.
Think of it like a survival video game where you have both an oxygen meter and a health meter. When underwater, your oxygen meter depletes slowly. Once the oxygen meter is empty then your health meter starts to go down until you die. The “4-6 minutes without oxygen” is the health meter part, you can’t really train that. You can, however, train your body to use up your oxygen meter more slowly and you can do things like breathing air with extra oxygen for a while to make your oxygen meter bigger. Those two combine so that you can give yourself a long time of oxygen meter before your health meter even comes in to play.
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