Pulmonary function tests (PFT’s) evaluate how well your lungs work. They measure the amount of air in your lungs, how well they move the air in and out, and how medications affect them. You may have a PFT to diagnose a lung disease, measure the severity of lung problems, or see if a treatment is working for your lung disease.

A respiratory therapist or technician will guide you through each test in a special exam room that has all of the lung function measuring devices. Most of the tests are quick, easy, and painless, but be sure to tell the technician if you feel light headed, tired, or uncomfortable.

PFT’s always include spirometry. It measures how much air you can inhale and exhale, and how fast you can blow the air out of your lungs. The technician may ask you to place a clip on your nose to prevent air from leaking out. Then you will breathe through a mouthpiece connected to a computer that will measure and record your results.

The technician also may measure the amounts of oxygen and carbon dioxide in your blood. A pulse oximeter can measure the oxygen in your blood without using a needle. If the technician needs more detailed information, they may perform an arterial blood gas. They will draw blood from an artery in your wrist for analysis.

Another important measure is total lung capacity, the total amount of air your lungs can hold. You will perform this test in a body plethysmograph, a clear Plexiglas booth like a telephone booth. You will sit inside and breathe into a tube similar to the one used for spirometry. Then the computer will measure your lung volume.