Hiya
Jenny treats one of my girls who has had something similar to yours. She was getting repeated URI's, hooting, wheezing etc. We were very worried that continued treatment with Baytril would make her resistant to the antibiotics and also was not really making much difference long term.
She is now on Fortekor and Frusemide (the diuretic Pebbles referred to). This has helped her tremendously. She is also on something called 'Nose Relief' a homeopathic treatment for cats and dogs which helps them breath better (
http://www.petplanet.co.uk/shop_store/Homeopet_Nose_Relief_p50570.html)
You have to play around with the doses of Fortekor and diuretic until you get it right (Jenny will tell you what to do if she believes this is the right treatment). I have had two others (sadly now RIP with old age) with the same treatment and all lived healthy and happy lives. Its taken my current little girl a long time to get it right and she still has down days but she is improving a lot.
Hope that helps...Jenny is great is;nt she :-)