Typically the brain performs these basic functions in comatose patients (pic1)
www.brain-injury-law-center.com/practice-areas/coma/
pic2 from: www.webmd.com/brain/coma-types-causes-treatments-prognosis
Not a DrFag, but it looks like the brain (unless your brain dead or have some kind of organ failure, i.e. lung-related) is pretty good at doing these basic things even in a coma.