I don't know the answer as to why, but it has the same effect on me. I recently began taking adderall for ADHD. It works as well as an albuterol inhaler for me. It was the first, and best, effect I get from it, other than making me sleep
really well.
I found your question because I have "very severe" COPD and wondered if this was a known side effect/advantage. I was prescribed the adderall for ADD (I only take 1/2 the 10 mg prescribed), but I noticed on days I take it, it seems to greatly improve my breathing / inhales. I not only can focus better but have increased stamina just from better breathing (as well as from the speed, I suppose).
Adderall, being an upper (a form of speed), it would produce the effects you describe.
As for your digestion, it makes sense that Adderall would speed it up.
It's entirely possible, although if it is asthma, I've only recently developed it. I'm sort of hoping it's asthma versus something like COPD. I also notice that on a full stomach, I find it hard to breathe, but Adderall not only helps me breathe a little better, but keeps my stomach empty too.
So maybe both of those things...not sure.