If the brain can only survive 4-6 minutes without oxygen, how can freedivers hold their breath for 8+ minutes?

Question

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

Answer 1

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.