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 do you prepare for these tests?

• Let your doctor know if you take medicines for a lung problem. You may need to stop some of them before the tests.
• Do not eat a heavy meal just before this test. A full stomach may keep your lungs from fully expanding.
• Don't smoke or do intense exercise for 6 hours before the test.
• For the test, wear loose clothing that doesn't restrict your breathing in any way.
• Avoid food or drinks with caffeine. Caffeine can cause your airways to relax and allow more air than usual to pass through.
• If you have dentures, wear them during the test. They help you form a tight seal around the mouthpiece of the machine.

How are these tests done?

What happens during the test depends on the type of test you have.

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 as fast 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 the oxygen and carbon dioxide levels in your blood.

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.