[K0balt]

It’s the co2 in your blood that you make in your body( not that you breathe in) that makes you want to breathe. You can breathe pure oxygen and you will still feel the need to breathe, because your body uses the oxygen to make co2 which then needs to be expelled.

[hansvm]

That only applies (gives you a trigger that you should breathe when the environment is dangerous) if you never exhale though. Is that really an argument for the technique being safe?