Hi. This is jeff, Diana's husband. DMG and any other immune boosting agent will provide your cat with better ability to fend off and/or deal with disease. DMG, also improves cardiovascular function which will be stressed during asthmatic episodes. Also, Grape Seed extract is another good supplement to help improve circulation in the body. And, Beta-Thym (beta sitosterol) is a natural anti-inflammatory to help inflammed areas (bronchil path). You can view this on www.bestforyourpet.com. Finally, and most importantly is good nutrition. Get your cat on a good natural diet - preferably raw or all cans. Not kibble. Then there are environmental considerations. Humidifiers, air purifiers are always good to use. Litter should be dust free. Do you smoke? Or, do you live in an Old house? Just consider every possible thing that could contribute to breathing. Well, hope this helps.
Jeff