I am basically posting to agree with everyone else...

Get your breathing into a rythym... for me I breathe with the pedal stroke - I have a slow cadence up hills so this works.

If its a long hill than about half-way up I "huff" out a few times to get rid of all the air in my lungs.

Also, once over the hill, I do big deep breaths too to get rid of any "dead air" lurking in my lungs, and to get loads of oxygen into my system, before I settle into a downhill breathing rythym, which for me tends to be longer and slower than flats or uphills because I want to lower my heart rate as well as oxynegate (sp?) my muscles.

I also wanted to post that making myself breath in a rythym is hard to do, I have to focus and keep making myself do it.

The first thing when I start to get distressed either on flats or on hills is to check my breathing, and more often than not I am taking short sharp breths. As soon as I change back into a deeper regular pattern, I start to feel better in less than a minute.

Denise, and other asthma gals, I don't know how this fits with that... but it works for me over summer when I get hayfever, and occasional asthma, but my rides do decrease a little in intensity over that time