I too have exercise induced asthma. first few miles mean lots of wheezing and phlegm which settles if its not hilly. I also suffer on hills, esp if I have to get out of the saddle. Its not too bad if I can remain seated and control the breathing. Bit frustrating cos people i know I can hammer can leave me on steep hills, which are quite frequent in the peak district.
Someone asked me what it feels like and best analogy I can think of is a mosquito net in the throat. Air can pass through, but inhaling and exhaling feels restricted. The body cant supply enough oxygen to the legs which feel fresh. After about 60 miles, things seemed warmed up tho' and I can at last get some effort from my chest.
Still, gotta crack on with it - at least I'm getting out and having fun and have no real asthma attack type scares. I see people every day I wouldnt wanna swap health/mobility with.
Went to the docs a few years ago, who explained the mechanics, but wont go again cos I have real (seriously) doctor/hospital phobia. daft I know, but cant help it.