Howard was shocked to learn that Brian still smoked, even if it was only 5 cigarettes a day: "Doesn't that affect your voice?" Brian laughed: "Of course. That's why I keep smoking!"
As such, AC/DC travels with oxygen tanks ("It's a safety thing but we need it...me and Angus move around quite a bit.") and a medical team: "Many a time I'll come off and get some oxygen but then I'll have to sit after a gig with a needle in me arm and a pint of saline drip just to--just to hydrate meself."