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
They have increased their lung capacity and modified their metabolism through exercise and training. Think of it this way, there are drunks and drug addicts who come into the Emergency Room with blood alcohol levels that would kill an ordinary person, but because they have been abusing themselves for so long their bodies have adjusted. If a person who had never shot heroin took as big a dose as a long term addict, the first timer would die, but the long time user would just be normal.
I want to add to the other comments that when talking about 4-6 minutes without oxygen, it is also without blood supply (e.g. in case of cardiac arrest / ventricular fibrillation). While the divers still have a working circulation, oxygen is still supplied to the brain. Though indeed over time the saturation gets less, it’s not like the moment you hold your breath your saturation becomes 0. So there is technically still oxygen supply there.
It is 4 minutes after the blood oxygen level is below a critical level. Your body doesn’t actually react to lack of oxygen it reactors to increased amount of CO2, that is what gives you the feeling of needing to breathe, it doesn’t mean that you are running out of oxygen.
Now imagine that you are running, you start to breath faster than if you were walking. This is because you are using more oxygen. Now. Try running and hold your breath, as long as you can. You can keep your breath for longer when walking. Makes sense doesn’t it?
Now what free divers and people who do extreme feats that require you to hold breath do is that they relax and calm their bodies, and use breathing techniques to pump as much oxygen in to their body as they can. They have also learned to deal and resist against the urge and struggle caused by build up of CO2.
You can actually try that yourself. Sit on a comfortable chair. Close your eyes, breathe deeply few times and relax as much as you can. Then just hold your breath. You can practice this skill and get quite good at it. This is often used in things like meditation and yoga.
Now. When your body runs out of oxygen, that is below the critical level, you pass out. This is where the timer of 4-6 minutes start. After that it is safe to assume that damage to the brain and other vital organs start to happen. Each passing second increases the probability.
Now. What is interesting is that if you cool your body temperature, the chemical reactions that happen in your cells slow down. This means they’ll use less oxygen. The chemical reactions. This is actually used a lot in medicine, during long surgeries if blood supply has to be cut for some reason, or if there has been severe trauma.
Now. If you do cold water free diving. Your body temperature drops, which gives you an edge. You use less oxygen.
The current world record holder is Finnish Johanna Nordblad (Torille!) who dove 103 meters under ice in the time of 2m 42s, without fins or a wetsuit.
Some people also just suffer a little brain damage. You can live with a little brain damage.
Aside from all the things already mentioned there are specific techniques free divers can use to gather large quantities of oxygen in their lungs and bloodystem prior to diving, like breathing techniques and such.
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.
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.
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