What are pulmonary function tests?
Pulmonary function tests (PFTs) measure how well your lungs take in and exhale air and how efficiently they transfer oxygen into the blood. There are several different tests:
- Spirometry measures how well the lungs exhale (breathe out).
- Lung volume measures how much air the lungs can hold.
- Testing the diffusion capacity of carbon monoxide (DLCO) shows how efficiently the lungs transfer oxygen from the air into the bloodstream.
Why are these tests done?
Pulmonary function tests help:
- Diagnose diseases of the lung such as asthma, chronic bronchitis, and emphysema.
- Determine the cause of shortness of breath.
- Measure the effects of exposure to chemicals, coal dust and other toxins on your lung function.
- Measure the effectiveness of medicines and other treatments.
- Detect lung disease at an early stage before you have symptoms.
How do I prepare for these tests?
Eat a light meal and do not smoke for four to six hours before your test. If you have asthma, ask your health care provider if you need to stop using asthma medicine before the test.
How is the test done?
Spirometry—You breathe into a mouthpiece that is connected to an instrument called a spirometer. The spirometer measures the volume of air that you can force out of your lungs in one second after having inhaled as much as you can. You will be asked to hold the tube of a spirometer in your mouth, inhale as much air as possible, then blow out as hard as you can into the spirometer for one second. The amount of air you can force out is called your forced expiratory volume, or FEV1.
Lung volume—You breathe nitrogen or helium gas through a tube for a certain amount of time. Then the concentration of the gas in a chamber attached to the tube is measured.
Diffusion capacity—You breathe carbon monoxide for a very short time (often one breath). The concentration of carbon monoxide in the air you exhale is then measured. The difference in the amounts of carbon monoxide inhaled and exhaled shows how quickly gas can travel from your lungs into the blood.
PFTs are painless, and you will have time to rest between the different breathing measurements. The measurements may be repeated two or more times.
- You breathe into a mouthpiece that is connected to an instrument called a spirometer. The spirometer measures the volume of air that you can force out of your lungs in 1 second after having inhaled as much as you can. You will be asked to hold the tube of the spirometer in your mouth, inhale as much air as possible, then blow out as hard as you can into the spirometer for 1 second. The amount of air you can force out is called your forced expiratory volume, or FEV1.
- Lung volume. You breathe nitrogen or helium gas through a tube for a certain amount of time. Then the concentration of the gas inside the full body box attached to the tube is measured.
- Diffusion capacity. You breathe carbon monoxide for a very short time (often 1 breath). The concentration of carbon monoxide in the air you exhale is then measured. The difference in the amounts of carbon monoxide inhaled and exhaled shows how quickly gas can travel from your lungs into the blood.
