Exactly as melissa said. If you're going to play a wind instrument I would highly suggest a flute. I attribute it to giving me a few more years before needing a transplant. Played it for 6 years give or take. *thinks of it sitting in the closet* hmm. Should start again.
Then again any wind instrument would help, clarinet or oboe I'm not sure would help as much as a flute, since that is in fact played with a reed so as far as I know (and correct me if I'm wrong) it's more like taking a breath and blowing it through the reed (your breath is controled by the reed, so it's not forcefully expelling the air in one shot). The flute is more like taking a deep breath and blowing over the top of a coke bottle, since you're blowing over an open hole you're expelling air a lot faster then you would any other instrument, thus you have to take in air faster, which equals more lung exercise.
I should really take my flute out of the closet. Esp. with my pft's going down a little bit.