I'm not a scientist, but I feel confident about this statement: Humans require oxygen to live. The thing is, we don't necessarily need the oxygen to come from air, though that is how our lungs are designed to receive it.
When submerging underwater for extended periods of time, humans have devised ways to bring oxygen with us so we don't drown and stuff, but there's a problem. Breathing air while under the enormous pressure of deep water makes nitrogen in our bodies dissolve, creating air pockets in the blood and organs and causing decompression sickness.
Retired heart and lung surgeon and inventor Arnold Lange has a solution: liquid breathing.