just a guess here, but was this how that magician held his breath for 17 minutes on Oprah? He gave a ted talk that discussed among other things inserting a breathing apparatus into his body orally. But, I suppose, a magician never reveals his secrets.

Somehow you have to get rid of CO2 though. I'm not sure how you'd do this without breathing.

Hmm, had a thought related to the last paragraph of my post above: don't be stunned if the CIA winds up using this, and I don't mean for covert underwater operations. If I'm right about the stuff supplying oxygen but not sequestering CO₂ then they could shoot someone up with a supply of it and then seal off the nose and mouth, and have themselves safe (sort of), twenty minute long water torture — the urge to breathe, triggered by the carotid bodies, would be overwhelming long before the oxygen ran out and the torturers were forced to allow the person to breathe. Add in the threat that they wouldn't allow the subject to breathe at all (always possible, from the subject's point of view), and I'm sure it would be excruciating.

I assume he was joking; if not, he was wrong.

Though in fact traditional open-circuit scuba is outdated already, because of rebreathers: A few thousand dollars gets you a scrubber/rebreather setup that uses a small bottle of straight oxygen and can last for ~20 hours underwater.

Been complaining forever about it taking too much effort to actually breathe.