Yes I have asthma also, I was smoking real cigs for about 8 years until I started vaping a little over a month ago. On real cigs I had to use my inhaler basically every night/every morning when I woke up. Since vaping I really haven't had to use it at all, much much less than I used to at least, and I can breathe a million times better, with MUCH better lung capacity. My lung capacity seems even HIGHER now without even using an inhaler than it was right after I used the inhaler while smoking real cigs.
One thing though, I noticed PG liquids make me not able to breathe, like really really bad, I can't breathe deep at all and feel like I need an inhaler right away with 100% PG liquids...I don't know if it is just me or not, but I would be careful about that. My girlfriend said fog machines and the like, which use PG, is bad for asthma, so obviously vaping with PG would do the same thing. I don't know where she read that, or if it is true, but it seems to be true for me at least. Other than that, vaping 100% VG juices is working wonders, can breathe better, I can walk up stairs without losing my breath now, etc. I am smoking 20%PG/80%VG right now and that seems to be fine also, I haven't tried any higher PG concentrations so far, but I would stick on the high side with VG.