What exactly is a pulmonary function test?

PFT...: Pulmonary function tests are tests that measure your respiratory functioning. They will show if you have obstructive or restrictive lung disease as well as give information about the size of your lungs and how gases (oxygen, carbon dioxide) are exchanged. It will also show if the disease present is reversible with medicines, like bronchodilators. They are administered by a respiratory therapist.

PFT's: are tests that look at your lung function. They are used to tell if you have obstructive disease by looking at how much air you can blow out; they can tell if you have a restrictive disease by looking at your lung volumes; and they can tell how well you are able to exchange oxygen between your alveoli (air sacs) and capillaries by doing a diffusion test.