I will try to keep this simple and to the point.
The tests are called Pulmonary Function Tests (PFT), and what I explain below is just the tests blowing into the tube of the smaller machine and not the ones inside the closet. The results can be hard to read, but knowing how they are derived may help. I am not a doctor or a medical practitioner, so please take what follows only as my understanding of these tests.
The machine is called a spirometer and it is used for the tests that take the volume measurements. The FEV1 is one of many tests done on this machine, but it is the one referred to most often. It is popular opinion that you should not only know what these tests mean but you should obtain copies of the results from your doctor for your own records, and it is unfortunate that many doctors don't interpret these results for you, so that you would better understand your condition.
Before I get to numbers, let me offer definition of the terms:
FEV1 - forced expiratory volume 1 = the volume of air that is forcefully exhaled in one second
FVC - forced vital capacity = the maximum volume of air that is forcefully exhaled
FEV1/FVC - ratio of FEV1 to FVC expressed as a percentage
FEF25-75 -forced expiratory flow = the average air flow during the middle part of the exhalation
PEF - Peak expiratory flow rate = the peak air flow during exhalation
Normal values are based on four criteria: gender, race, age, and height. These criteria have all been determined to effect ones lung capacity, and conclude a normal value. The numbers to look at are the % of those predicted normal values. There will often be more than one result listed since it is protocol to give you three testings. Some of you may have a before and after test result, this means you were given a bronchodilator between tests which helps determine your reaction to certain types of medication.
As I mentioned, and without going into a great deal more detail here, the most often used statistic to establish and track one's condition is the FEV1.
These FEV1 values are most often used to describe your condition: normal = above 80% mild = 65-80% moderate = 50-65% severe = below 50%.
I hope this brief explanation will guide you gently toward a better understanding of your test results. Again this is simply my understanding of these numbers and not a medically qualified opinion. You should receive a more complete explanation of your condition from your doctor. In fact, insist on an explanation that you understand.