there is a ventilator built into his mask.

i think it's exhale-inhale.

my take:

Herrrrrhphhhhhhhshooooo, ffssss, herrrpphhhhhhhshoooowhooo.

dude's got chronic asthma. give him albuterol stat. or is that contraindicated? i'm stoopid.

i'm a freaking nerd.

Inhale, then exhale. It's the way we all naturally breathe.

Try breathing, but putting a longer pause after you inhale, i.e. exhale-inhale, pause, exhale-inhale, pause, etc. It feels weird.

Now, try the opposite, and it will feel much more natural. Because the pressure is high after an inhalation, your lungs (and the surface tension within them) favor being deflated, just as a balloon does. So the longest pause occurs in the deflated state, after exhaling. Thus, Darth must also be inhaling-exhaling--he is, after all, human.

NOW who's the nerd?

It's definitely inhale, then exhale.

The inhalation cycle on real breathing is longer than the exhalation cycle. Oh wait, Nate just posted that...

Shucks, looks like I'm not the nerd. Do I get nerd points for knowing way too much about the Star Wars universe? Vader can actually take his mask off and use the force to help him breath, but the dark side isn't that good for healing and stuff, so he can't do it very well. He is much better at choking people, so he uses his powers for that mostly I would imagine