It's true that quitting smoking is the best thing you can do for yourself, no matter how you old you are, or whether or not you have already been diagnosed with chronic bronchitis or emphysema, the two diseases that are classified under the term Chronic Obstructive Pulmonary Disease, or COPD. If you've been smoking for years or even decades, if you quit smoking, you will see a quick change in your breathing and in how well you feel overall.
If you have been diagnosed with COPD, one of the first things your doctor will tell you is you need to quit smoking if you haven't already. Some people might feel that since they've been smoking for so long, quitting smoking won't have make any difference. They might need to use oxygen therapy every day, but once they are done using their oxygen concentrator, they light up another cigarette. The notion that quitting smoking will not have any effect on their current condition isn't true. Even after diagnosis, quitting smoking will slow and even stop the progression of the disease.