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
Divers can breathe in as much air as possible before diving. That air will supply them with oxygen for a while. Also they can hyperventilate (breathe in and breathe out strongly and rapidly for a while) before diving, so that their blood will become saturated with oxygen, keeping the brain oxygenated even if there’s no more air.
If the brain stops getting its oxygen the person usually loses conscience within mere seconds (like if an airplane depressurizes while at high altitude). Obviously divers don’t want that to happen, so their brain keeps getting oxygen. If a diver has lost conscience they’d quickly drown. The 4-6 minutes survival time means that oxygen supply to the brain has to be restored within that timeframe to avoid death.
Because all the oxygen in your blood isn’t used up immediately once you start holding your breath. Free divers train and perform exercises to increase their lung capacity and lower their heart rates so their bodies use up less oxygen.
The level of oxygen in the body is dependent on two things – how much oxygen is in the bloodstream, and how fast it can be used by the body.
So in the case of David Blaine, he breathed pure oxygen for good period before his record attempt, and through practice increased the time that oxygen could last for by slowing down how much he uses that oxygen.
Free divers also are helped by the body slowing down in cold water their pulse rate, and how their body uses energy. These all slow down so free divers (after much practice) can hold their breath for longer than people on dry land.
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.
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