I don't know if you are into meditation or visualization but I'll share this one visualization that has helped me a lot. I learned it kind of from a Chi Gong CD. The CD talks about having each side of your body, (head, feet, front, back, sides) go all the way to the horizon and then collect the "beautiful loving Chi" and have the Chi come back into your body.
So I was trying to do this one day and I centered on my lungs and I just imagined my lungs, say the front, going all the way to the horizon in front and then the bronchi going all the way to the horizon and of course they got real big so I kept imagining that my lungs would go all the way to the front of the horizon, (it helps if you can get a glimpse of the sky first) and the bronchi too. And then I was able to go to the back and do the same. And then I was able to do the sides. Finally I was able to feel like my lungs were as big as the world, 
And I swear if you do it in a peaceful setting you will feel your lungs relax, (you have to learn to do this relaxing but concentrating) and get bigger and take in more air. Well at least it happens for me. Now I am able to do it while walking.
But it sounds like whatever you are doing is working! I'm really happy for you. 
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