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Pulmonary Function Tests

Pulmonary function tests (also called lung function tests) help measure how well your lungs are working. These tests are done to diagnose lung conditions such as asthma and COPD. They may be done before and after you take certain medications. They may also be used to find out whether you have more trouble breathing with exercise. Over time, pulmonary function tests can help you and your health care providers see how well your treatment is working.

Man pinching nose shut and breathing into spirometer in mouth. Health care provider is monitoring test.

Before Your Test

Follow any instructions you are given to prepare for the test. Otherwise, your test may be canceled:

  • Stop smoking before the test, as directed by your provider.

  • Don't exercise heavily before the test.

  • Follow the instructions from your health care provider for taking your medications, including any breathing medications.

  • Don't eat a large meal right before the test.

  • Wear loose, comfortable clothes.

  • If you wear dentures, make sure you are wearing them for the test. 

  • Don't exercise strenuously for at least 6 hours before the test. 

During Your Test

The health care provider or technician will give you instructions during your test. You may sit in a chair and breathe through a mouthpiece. Or you may sit in a clear plastic box that looks like a phone booth. You will wear nose clips so you only breathe through your mouth.

  • During spirometry, you hold your breath and blow it out fast. Spirometry is repeated at least 3 times to measure your best effort.

  • During diffusion testing, you hold your breath for 10 seconds. The test measures how well your lungs move air into your blood.

  • During lung volume testing, you breathe in different mixtures of air. The amount of air you inhale and exhale and that stays in your lungs is measured.

After Your Test

After the test, you can return to your normal diet, activity, and medications. If you were asked to skip medications before the test, ask when you should take them. Your provider will usually discuss the test results with you at your next office visit.

Pulmonary Testing Terms

Pulmonary function tests measure how much air you exhale, and how quickly. Some of the things that tests measure include:

  • FVC (forced vital capacity). This is the total amount of air you can exhale in a single, prolonged breath.

  • FEV1 (forced expiratory volume in 1 second). This is the amount of air you exhale in the first second.

  • FEV1/FVC. This is the amount of air exhaled in the first second compared to the total amount of air exhaled. It’s given as a fraction or a percentage. In general, the higher the FEV1/FVC, the better.

  • PEF (peak expiratory flow). This is a measure of how fast you can exhale. It can be tested with spirometry or a peak flow meter.


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