I also am very midly asthmatic and was concerned about that aspect of the medical - my peak flow/FEV1s are very good though (have Class 2 medical at the moment for PPL) so I reckon I should be fine.. I just hope they don't make you do the same run-around-the-building-for-10-minutes tests that class 1 pilot medicals get.. If so I'd better get practicing
The reasoning behind that sort of test, I believe, is to test your breathing when confronted with a situation where the amount of oxygen you need or can take in is changed, like in a depressurisation.. and I would hope that wouldn't apply for ATC.
My class 2 doc said I shouldnt have a problem with class 1 (for flying) anyway so I'm quite hopeful that it won't be a problem, if I get that far!!
I've not had an attack or anything ever and have never been hospitalised because of it. I think as long as you're not likely to have any problems operationally, your asthma is well under control, and a doctor can send a note which supports that then you're likely to be fine, but I'm only hypothesising.. I've read that it helps if you have a note from your GP at the time to explain your history.
Has anyone had any experience with asthma first hand in an ATC medical? Do they just check peak flow/FEV1?