Respiratory bypass system

A respiratory bypass system was a part of Gallifreyan physiology which allowed Time Lords to go without breathing for longer periods of time longer than could most Humans. (BFA: Return of the Krotons)

The Doctor used it to survive on many occasions. The Doctor's fourth self used his respiratory bypass system to survive being strangled by an Osirian service robot. (DW: Pyramids of Mars) He later used it to avoid inhaling helium. (DW: The Robots of Death) The fifth incarnation used it to survive being hanged. (ST: A Town Called Eternity) His sixth persona was able to avoid hypoxia when he shut down atmospheric controls to the mines on the planet Onyakis in order to defeat the Krotons there. (BFA: Return of the Krotons) In his seventh body, the Doctor used his respiratory bypass system to avoid being overcome by ether. (NA: Timewyrm: Genesys)

Although it did not necessarily help him survive, his tenth incarnationwas also helped by it at one point. (DW: Smith and Jones) When stranded on the moon in a hospital with little or no air left, he was able not only to stand and move, but he also picked up one of his companions and carried her the length of a corridor. This was not actually necessary for their survival, but it was quite a feat considering the fact that any humans that were still alive were either passed out or staying still to use as little oxygen as possible.

At least one Human may have developed such a system; Timothy Dean, who gained one when he became infected with the Doctor's DNA. (NA: Human Nature)