Pulmonary Function Testing

Pulmonary means anything that has to do with the lungs. Some diseases and their treatments may affect how well your child’s lungs work. Pulmonary function tests (PFTs) measure how well the lungs work. They also show changes in lung health. 

Services we provide

St. Jude offers the most complete pulmonary function testing available. Most children get a “full study” during their PFT appointment. That study includes these 4 tests:

• Spirometry: This test measures how much air moves in and out of the lungs and how fast the air moves.
• Plethysmography: This test measures how much air your child can hold in their lungs.
• Diffusion: This test measures how well oxygen moves from the lungs into the blood.
• Maximal inspiratory/ expiratory pressure (MIP/ MEP): This test measures lung strength.

Some children may get other lung function tests. One test finds out if medicines called bronchodilators can improve lung function. Another test is a 6-minute walking test. It looks at how well your child can breathe and how tired they are after walking for 6 minutes.

Your pulmonary function test team

Highly trained respiratory therapists coach your child and perform the tests.

How to prepare for pulmonary function tests

Before the test, make sure that you:

• Avoid eating a heavy meal.
• Do not use a bronchodilator for 4 hours beforehand.
• Do not smoke or vape 4 hours beforehand.
• Wear loose-fitting clothes.
• Wear tennis shoes or other shoes good for walking if you are having the walking test. Do not wear flip-flops.
  

What to expect during pulmonary function tests

Children must be able to follow directions to have these tests. So they must be at least 4 or 5 years old to do test.

To be complete and accurate, each test needs 3 attempts that produce similar test results. Your child may have to repeat tasks several times to get 3 efforts that are similar. The tests may take up to 45 minutes.

The respiratory therapist will make the tests like a blowing game as much as possible. The tests are painless. But it may be a little uncomfortable for some.

During the PFT, your child will sit in a chair inside a booth that you can see through. Your child will wear padded nose clips and a special mouthpiece attached to a machine.

This is what happens during each test:

• Spirometer: Your child will take a deep breath in and breathe out as hard as they can. Sometimes children do this test before and after using a bronchodilator.
• Plethysmography: Your child will breathe in and out while sitting in the booth with closed doors.
• Diffusion: Your child will breathe in a harmless gas called a tracer gas.
• Maximal inspiratory/ expiratory pressure (MIP/MEP): Your child will breathe in and out against a closed mouthpiece.
• 6-minute walking test: If your child has the 6-minute walking test, they will walk up and down a hallway for 6 minutes.

What to expect after the tests

Your child may feel lightheaded or dizzy for a few minutes after the tests. Your child’s physician may discuss the results of the tests with you and your child. Results will also be available in the St. Jude MyChart app.

Learn more