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Chest Clinic - Pulmonary Function Test

Pulmonary function tests are several tests done to show us how well your lungs are working. They help us find the cause of shortness of breath, and diagnose new lung disorders such as asthma, COPD, emphysema, and bronchitis. In people with known lung disorders, the tests help us determine how well your medicines are working or if your lung disorder is worsening.

Preparing for your PFT

No smoking (1) one hour prior to the test.
You can take all of your medications except:

  • DO NOT take inhalers or nebulizers four (4) hours before the test
  • DO NOT take Advair, Serevent, Spiriva or other long acting broncodilators for (12) twelve hours prior to the test

What to Expect

Pulmonary function tests are done in a special area of the hospital or clinic by a respiratory therapist. You will wear a clip on your nose so air doesn't escape from your nose. You will also have a mouthpiece in your mouth that is a attached to a recording device.

Pulmonary function tests usually consist of the following:

1) Incentive Spirometry- This test measures how much air you can breathe in and out over a specific amount of time. You will breathe into a mouthpiece that is connected to a recording device, called a spirometer.

2) Lung Volume Measurement - This test measures how much air your lungs can hold. It also measures how much air is left in your lungs after you have exhaled (breathed out), called your "residual volume". Lung volume can be measured in a couple of ways:

You may breathe in a certain gas, such as nitrogen, helium or 100% oxygen from a container through your mouthpiece for a specific amount of time. The change in the concentration of gas remaining in the container is measured. This allows us to calculate your lung volume, or amount of air your lungs can hold.

You may also sit in an airtight booth, called a plethysmograph. This is similar to a telephone booth, with windows so we can see in and you can see out. You will breathe in and out through a mouthpiece. We will adjust the pressure in the booth, which helps us measure the total amount of air your lungs can hold.

3) Diffusion capacity - This tests measures how quickly oxygen and carbon dioxide travel from your lungs into your blood. You will breathe in a very small amount of carbon monoxide through your mouthpiece. We will measure the amount of carbon monoxide that you breathe out and assess the difference in the carbon monoxide level.


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Wentworth-Douglass Hospital
789 Central Avenue, Dover, NH 03820
Phone: (603) 742-5252
Toll free: 1 (877) 201-7100