There are a lot of factors that go into why your PFTs have gone down or up. It could be allergies, a chest infection, your surrounding environment (weather, dust, pets, etc), time of day that you do your PFTs, etc. Two years ago my PFTs were 89%, and two months ago they were sitting at 69%. Two weeks ago they went down again to 60% while I was in hospital, and my doc said not to be concerned, that it could be all of the above factors I mentioned. It could even be the fact that you're using a different machine to do your pfts each time. He said that they look for a pattern. That if your FEV1 number decreases on a continual basis, then that isn't a good thing. What you're saying, and correct me if I'm wrong, is that your FEV1 number was 99%, then it jumped to 110%, then went down to 80%? You haven't had continual decrease, so I wouldn't think that your lungs are deterioting fastly. My PFTs have gone from 110%, to 90%, to 80%, and then back up to 95% at one time. I've seen people have PFTs that went from high, to 50%, and then back up to 99%. There are even people who have PFTs in their 20s who don't need O2. You only need O2 I think, if breathing is a continual problem for you. I think you know your body better then a doctor does, who sees a ton of patients in one day. Try exercising to bring your PFTs up. Try to reduce allergens in your house i.e. no carpets, buying a hepa filter vacuum if you have carpets, get an air purifier with a hepa filter (this has done wonders for me and my pfts), buy allergen febreeze for your furniture. You can even get allergen carpet powder that you vacuum up. Try to keep dust and pet dander at a minimum by cleaning daily. Hope this helps you out!