It was quite interesting! We did a six minute walk, with an oxygen meter on my finger, so we could see how much air was getting in. That was just fine. Then we did an aspiration test, where I breathed in and out, and then took a big breath and exhaled as quickly as possible. For some reason, I just wasn't exhaling as fast as she wanted, because we did that test several times. The other tests were fine - I'm getting enough oxygen into my lungs, so there's no damage to the lung tissue, and I'm inhaling enough air.
My initial idea was that my diaphragm muscles are weak, causing me to have problems with not getting enough air. I don't know enough to make any educated guesses, so I'll have to wait until the 29th of September!