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Comment by dbatten | Hacker News Reader

PSA: Trying to hold your breath for a long time is dangerous, especially if you hyperventilate first. People die this way.

The hyperventilation thing is because your brain needs oxygen to live, but your impulse to breathe is driven by carbon dioxide saturation. When you hyperventilate, you get rid of a ton of carbon dioxide, and you can get into a situation where you don't have enough CO2 buildup to trigger the signal to breathe, but you have so little oxygen that your brain is dying.

Personally, not something I'd like to mess with.

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It's more than that. Hemoglobin will preferentially release Oxygen in low pH (acidic) conditions and take up Oxygen in high pH (alkaline) conditions. CO2 in the blood increases acidity, so the result of this behavior is that hemoglobin will release Oxygen in parts of the body where CO2 concentrations are higher and will pick up Oxygen in areas where CO2 concentrations are very low. If you hyperventilate then you remove CO2 from your blood, reducing its ability to deliver Oxygen to tissues due to reduced acidity. This conditions, called hypocapnia, leads to vasoconstriction of blood vessels in the brain, which can cause even lower Oxygen uptake in the brain, as well as bronchoconstriction. This can cause you to blackout and can, in combination with the mechanism you've described, result in decreased ventilation when breathing resumes.

I've seen multiple people black out and have blacked out myself under water ... twice? (while training freediving). It comes on slowly and is far easier to do than you'd think.

If you do any of this without supervision it's just a matter of time until you die.

CO2 levels rise to unhealthy levels (700ppm) within a few hours of a typical bedroom if you keep the doors and windows closed. Its also why Submarines have CO2 scrubbers.

Do you have any source for this? A bedroom isn't sealed shut like a submarine would be?

I have a CO2 monitor, and I can confirm that it goes up at least that fast in my home. I can't speak for submarines or healthy levels. I've been wondering for a while why environmental rhetoric only talks about the global rise in CO2 in terms that make people think it's just an atmospheric phenomenon rather than notably changing what they're breathing. It looks like we've nearly doubled the CO2 we're breathing in the past couple centuries, not including our more sealed up lifestyle.

>only talks about the global rise in CO2 in terms that make people think

Because the levels in the global rise are negligible in comparison to what is dangerous for breathing. Here's a hint, if you think you've spotted something blindingly obvious in a field scrutinized by hundreds of thousands of scientists, you're probably making a mistake.

Reminds me of all the bugs in the java compiler I used to find when I first started learning the language and writing Hello World apps.

Thanks for the hint. The thought that the health effects of a waste product from the most profitable of industries may have gone under-reported is indeed preposterous.

Here's a study showing reduced cognitive performance at various CO2 levels in the ranges we're talking about.

https://ehp.niehs.nih.gov/1104789/

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