Pulmonary Function Tests (PFTs) at the Clinical Center

Patient Information

Preparing for your Pulmonary Function Tests (PFTs)

This information will help you understand and actively take part in your pulmonary function tests (PFTs). With your cooperation, these important tests will provide helpful information for your doctors to use during your stay at the Clinical Center.

What are Pulmonary Function Tests (PFTs)?

Pulmonary function tests (PFTs) tell us how well you breathe. They measure how much air you can breathe in and out, how well your breathing muscles work to move your lungs (like a pump), and how well your lungs exchange gas (move air from the small air sacs in the lungs to the bloodstream). Your doctor uses these tests to screen you for health problems, keep a watch on your condition, and prescribe therapy. A single test or series of tests over time may be done.

Why are PFTs done?

You may have PFTs for many reasons, for example, as a precaution before surgery, to check the status of your lung disease or neurological problems, or as part of your role in research. PFTs also help your doctor know how your medications are working and can help him or her prescribe your medications.

Preparation

There is no preparation for PFTs, but it is best that you be relaxed.  Wear loose-fitting clothing and avoid belts or girdles that may make it harder for you to breathe. Some patients who take breathing medications may not be allowed to take them for 12 hours before the test.  If this is a problem for you, contact your nurse or the pulmonary function technologist.  If you smoke, do not do so for at least 8 hours before testing.  You may want to avoid a large meal before testing.  Ask your doctor for other instructions.

Your PFT

Your PFT will be done in one of the pulmonary function laboratories of the Pulmonary-Critical Care Medicine Branch. Your informed consent for PFTs will be included in a protocol consent document.

First, the technologist will ask you to sit in a comfortable chair next to the pulmonary function machine.

Then, soft clips will be placed on your nose so that you will breathe only through the mouthpiece attached to the PFT machine.  This machine will record the amount of air you breathe (volume) and how fast you breathe (airflow rates).

The technologist will tell you how to do each test, because each one requires you to breathe in and out in different ways. 

For example, you will be asked to breathe normally, slowly, and rapidly. You must give your maximal effort for each test to assure accurate results.

Sometimes, this effort causes patients to have shortness of breath, coughing, dizziness, or light-headedness. These effects do not last long and will go away as you rest between the tests.  If you have these effects, we will help you control them as much as possible.   However, they may be unavoidable for some patients, and though they are not pleasant, your cooperation to put forth the maximal effort will make the tests useful.

You may have one or more of these pulmonary function tests.

Forced Vital Capacity (FVC)

Breathe normally through a mouthpiece attached to the PFT machine.  Maintain a tight seal with your mouth around the mouthpiece.

• Breathe in (inhale) as much air as you can until your lungs are full.
• Breathe out (exhale) as quickly and as forcibly as possible.
• Continue exhaling until the machine says that your lungs are empty.
• While keeping your mouth tight around the mouthpiece, inhale again rapidly.

This test will be repeated until three of these tests show similar results. The technologist will coach you during the test so that you can give your maximal effort each time.

Forced Vital Capacity (FVC), before and after bronchodilators

You may have this test repeated after being treated with a bronchodilator (a drug that opens the bronchi, or breathing tubes), to measure your response to this treatment.  This information is important to determine whether you might benefit from bronchodilator therapy.

Slow Vital Capacity (SVC)

• First, breathe normally. Then, inhale fully.
• Then exhale normally (passively) while keeping your mouth tight around the mouthpiece. Keep exhaling until the machine says that your lungs are empty.

This test will be repeated until three similar results are obtained. You will be coached throughout this test.

Functional Residual Capacity (FRC)

• Breathe through the mouthpiece attached to the PFT machine.
• Breathe normally through the mouthpiece for 3 to 6 minutes. As long as you keep your mouth tightly sealed over the mouthpiece and there are no air leaks, this test will be valid.

Usually, this test needs to be done only once.     

Diffusing Capacity (DLCO)

• Breathe normally through the mouthpiece.
• Inhale maximally and completely, then exhale maximally and completely.
• Inhale again maximally and completely.
• After the second inhalation, hold your breath for 10 seconds before exhaling maximally again.

The entire PFT test session usually lasts about 45 minutes. Your technologist will act as your coach to help you through the tests.

After the Procedure

There are usually no after effects from PFTs. However, some patients feel a little tired when they finish. When the tests are over, you can resume your normal activities.

Please remember, our staff is here to help you. If you have any questions about the tests, please feel free to ask.  Your technologists, doctors, and nurses are here to help you at all times.