Anyone else remember this device from Star Wars - The Phantom Menace when Obi Wan Kenobi and Qui Gon Jinn swim down to Jar Jar's people? lol.

If this were real and it isn't - it sounds like a rebreather (http://en.wikipedia.org/wiki/Rebreather) only several orders of magnitude smaller and without the extra tank full of pure O2.

Fun to think about though.