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 than could most humans. (BFA: Return of the Krotons) It also allowed them to filter out unpleasant smells. (NA: Cat's Cradle: Witch Mark)

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)

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