@mic1953 I have given the “stage” definition an F for clarity . I don’t use the term any more . People hear stage 4 with cancer . I don’t have cancer . It is a miss used term. There is not a stage scale for. Emphysema . The most one can do is describe how much oxygen you require to stay from 90 to 95 on the oxymeter . The usage goes up with activity. I have been on 24/7 oxygen for 3 years. No one at medical care asks you what stage you are. They want to know how much oxygen you use . If you are not using it at times that is great . But if you are not using an oximeter, then you don’t know. I went without oxygen. Not even knowing I had a problem. When they did check , I was immediately put on 24/7 oxygen . So do not rely on your body to tell you . Use the oximeter