Asthma friendly cardio?

I've been on MFP since mid to late December of last year, but have only recently started working out on a regular basis. I usually use the elliptical, for some reason that seems to be one piece of fitness equipment that doesn't often make my asthma flare up. I use stationary bicycles on occasion too, but sometimes after doing either of these for a few days, my knees get a little worn out so I'm looking for other types of cardio that might be a little less intense but still allow me to get in a decent workout. I can't do treadmills at all unless I just do a brisk walk, and I feel like I'm not accomplishing much unless I use a crazy high incline. I tried it out a few days ago just to see if I had gotten more fit since my last attempt and literally made it two minutes at a decent running pace before having to use my inhaler (I can only imagine what would happen if I tried to take an actual run!) I do always have my inhaler with me when I go to the gym, I just prefer not to have to use it if I don't absolutely need to. Stairs are also pretty tough for me, I try to take them instead of the elevator but I'm usually wheezing by about the second or third flight, so stairsteppers probably aren't a good option either. I feel pretty limited and am on my third week of a VERY discouraging plateau and want to try to mix up my workouts and see if that helps.

Does anyone else have this problem or have any recommendations? I'm just getting frustrated and would love any input!