PFT
PFT's are pulmonary function tests. FEV1 is how much air you can blow out in the first second (forced expitory volume). FVC is forced vital capacity. The FEV1 is the more important number and gives a better understanding of how your lung disease has progressed. FVC is more effort dependent.
Anyway, it is based on your height. Taller/bigger people can blow out more air so they take that into account. In other words, don't expect your numbers to be the same as guy who is 6ft tall. Ask your RTherapist who gives the PFT to tell you what your score is in terms of percentage, otherwise you will have to do the math. Its easy for them because the computer can covert your score to percentage of what is normal.
Here is the scale for FEV1: 120-70 percent (mild lung disease), 70-40 (moderate lung disease), and anything below 40 percent is considered severe impairment. Some interpretations of this scale may very slightly.
For what its worth, if your fev1 is 50 percent or higher, its likely you may not even notice that you have lost 50 percent of your lung function. At least that was the case with me.