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Lung Function Tests: About These Tests

What are these tests?

Lung function tests measure how much air your lungs hold and how quickly your lungs can move the air in and out. Spirometry is often the first lung function test that is done. You may also have other tests, such as gas diffusion tests, body plethysmography, inhalation challenge tests, and exercise stress tests. Your doctor will explain which tests you need.

These tests check how well your lungs work. They may also be called pulmonary function tests, or PFTs.

Why are these tests done?

Doctors use lung function tests to find the cause of breathing problems and diagnose lung diseases like asthma or emphysema. You may have lung function tests before you have surgery. Or your doctor may use lung function tests to find out how well treatment for a lung problem is working.

How can you prepare for these tests?

  • Tell your doctor if you have any other medical problems, such as heart disease.
  • Tell your doctor if you are allergic to any medicines.
  • Let your doctor know if you take medicines for a lung problem. You may need to stop some of them before the tests.

What else should you know before these tests?

  • Wear loose clothing that does not restrict your breathing.
  • If you have dentures, wear them during the test to help you form a tight seal around the spirometer's mouthpiece.
  • Do not eat a large meal just before the test. A full stomach may keep your lungs from fully expanding.
  • For 6 hours before the test, do not smoke or exercise hard.

What happens during these tests?

What happens during the test depends on the type of test you have. A respiratory therapist or technician will do the lung function tests.

For most tests, you will wear a nose clip. This is to make sure that no air passes in or out of your nose during the test. You then breathe into a mouthpiece attached to a recording device.

  • For some tests, you breathe in and out as deeply and quickly as you can.
  • You may repeat some tests after you inhale a medicine that expands your airways.
  • You may breathe certain gases, such as 100% oxygen or a mixture of helium and air.
  • For body plethysmography, you sit inside a small booth with windows. The booth measures pressure changes that occur as you breathe.

The therapist may urge you to breathe deeply during some of the tests to get the best results.

You may have a blood test to check oxygen and carbon dioxide levels in your blood before, during, or after your lung function tests.

How long do these tests take?

The testing may take from 5 to 30 minutes, depending on how many tests you have.

What happens after these tests?

  • You will probably be able to go home right after the tests.
  • You can go back to your normal activities right away.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Where can you learn more?

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