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Pulmonary function tests

Pulmonary function tests are a group of tests that measure how well the lungs are working. They measure how much air the lungs can hold and how well the person can let the air out of the lungs. Pulmonary function tests are also called lung function tests.

The most common pulmonary function tests are spirometry and total lung capacity.

  • Spirometry measures how much and how quickly air can be exhaled from the lungs.
  • Total lung capacity measures the total amount of air a person’s lungs can hold.

Why pulmonary function tests are done

Pulmonary function tests may be done to check for any problems with the lungs. They may be done to:

  • assess any effects of medications or chemotherapies that are known to affect the lungs
  • determine a baseline before chemotherapy starts
    • This baseline can be used throughout treatment to monitor the lungs.
  • help decide whether a person is healthy enough to tolerate certain treatments

How pulmonary function tests are done

The procedures for pulmonary function tests are different for adults and young children.

For adults and older children

  • spirometry
    • The person places the mouth around a cardboard mouthpiece on a long tube attached to a computer.
    • A nose clip may be put on to prevent air from leaking out of the nose.
    • The person will first breathe quietly through the mouthpiece.
    • The person will then be asked to take in the biggest breath possible and then blow it out as hard, as fast and as long as possible.
    • The computer measures the amount of air breathed out over time.
    • This test takes 5–30 minutes.
  • total lung capacity
    • The machine used for this test is a confined space with clear walls. The person sits inside the machine.
    • The person will wear a nose plug and blow into a plastic mouthpiece connected to the machine.
    • The machine measures the amount of air breathed in and the force of the air breathed out.
    • The test will have to be repeated a few times to get an accurate reading.

For infants and young children

  • spirometry
    • The child is placed in a special Plexiglas bed and a special mask is placed over the child’s mouth and nose.
    • A loose-fitting jacket is placed around the child’s chest and abdomen.
    • The child is given a few deep breaths from the mask.
    • The jacket is inflated so it gently squeezes the chest, causing the child to blow out.
  • total lung capacity
    • The child is placed in a special Plexiglas bed and a special mask is placed over the child’s mouth and nose.
    • The top of the bed is briefly closed around the child to form a box.
    • The computer calculates lung capacity from pressure and air flow measurements.

Special considerations for children

Being prepared for a test or procedure can reduce anxiety, increase cooperation and help the child develop coping skills. Parents and caregivers can help prepare children by explaining to them what will happen, including what they will see, feel and hear during the test.

  • Special equipment is used for children who cannot perform the voluntary breathing techniques necessary for a pulmonary function test.
  • Sedation may be required for infants and young children.
    • Children cannot eat solid food for 6 hours before the test.
    • They cannot have any liquids for 4 hours before the test.

The preparation you can provide for a pulmonary function test depends on the age and experience of the child. See the following for more age-specific information on helping children cope with tests and treatment.


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