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Pulmonary Function Test (PFT)

What is a Pulmonary Function Test?

A Pulmonary Function Test is a series of five different tests that measure the different volumes within your lungs, how easily you can move air in and out of your lungs, and how well your lungs are able to transfer oxygen into the rest of your body. The results of these tests can help your doctor assess how your lungs are functioning at rest. If there is a problem, the results will help your doctor determine what is wrong and the appropriate course of treatment.

What conditions can be detected and monitored by a Pulmonary Function Test?

The Pulmonary Function Test is a useful tool to help detect two major types of pulmonary conditions, airflow obstruction and lung volume restriction. Obstructive conditions reduce the ease in which the air flows in and out of the lungs. Restrictive conditions reduce the volume of air that the lungs can take in.

Some examples of Obstructive conditions:

  • Asthma
  • COPD
  • Chronic Bronchitis
  • Emphysema
  • Bronchiectasis
  • Obstructive lesions (Enlarged Thyroid, Paralyzed Vocal Chords, Tumors, etc)
  • Heart failure

Some examples of Restrictive conditions:

  • Occupational lung diseases (Black Lung, Asbestosis, Siderosis, Silicosis, etc)
  • Pneumonia
  • Pulmonary Fibrosis
  • Sarcoidosis
  • Hystoplasmosis
  • Neuromuscular disorders
  • Heart failure
  • Obesity

How is a Pulmonary Function Test (PFT) performed?

A qualified technician will ask you to breath at different speeds and depths through a special device that can measure the airflows and volumes of your lungs. On some tests you will also breathe different amounts of oxygen. The technician will ask you to repeat most of the tests several times, to ensure that the results are repeatable and an accurate and valid reflection of your lung function. To minimize the number of trials you will have to perform, and to get the most accurate results, listen closely to your technician as (s)he guides you through the testing.

How long does the test last?

A pulmonary function test may take 30 to 60 minutes to complete. This will vary according to the amount of trials necessary for you to get repeatable test results.

What are the tests of a Pulmonary Function Test (PFT)?

The five tests that make up a full PFT are:

    1. Forced Vital Capacity (FVC)
    2. Slow Vital Capacity (SVC)
    3. Maximum Voluntary Ventilation (MVV)
    4. Lung Diffusion (DLCO)
    5. Nitrogen Washout

What is the Forced Vital Capacity (FVC)?

The Forced Vital Capacity is perhaps the most important pulmonary test, and it is the most commonly performed. This test measures the maximum amount of air that can be blown out of the lungs, the ease in which the air flows out of the lungs, and various combinations of volume and airflow. The results will be used to assess your body’s ability to ventilate your lungs, which may be affected by lung, heart, neuromuscular or anatomical conditions. To perform the test, your technician ask you to breathe-in as deep and as fast as you can, then force all of the air out of your lungs, as hard as possible. Since this test is so important you will need to do several trials (4-8). Listen closely to the cues your technician gives you to minimize the number of trials you have to do.

What is the Slow Vital Capacity (SVC)?

The Slow Vital Capacity measures the amount of air that you can breathe-in or breathe-out during your largest possible breath. This test requires you to breathe gently. Your technician will ask you to breathe-in as deep as possible, then to relax and let all of your air out easily. Follow your technician’s instructions closely to minimize the number of trials you will be asked to perform.

What is the Maximum Voluntary Ventilation (MVV)?

The Maximum Voluntary Ventilation determines how much air you move in and out of your lungs over period of 10 seconds. During this test, your technician will ask you to breathe-in and out very fast and very deep (but not as fast as possible and not as deep as possible). The technician will give you constant feedback and encouragement during the test to insure that you give your hardest effort. If your first trial is acceptable, you will only be asked to perform this test once. However, most people find that they need one trial to warm-up first before they can meet the acceptability criteria.

What is the Lung Diffusion test (DLCO)?

The DLCO measures how easily oxygen can diffuse from your lungs into your body. Impaired oxygen diffusion into your body may be caused by diseases of the lungs, heart, and blood. During the test, your technician will ask you to breathe-in as deep as possible and then hold your breath for a brief amount of time. This allows the oxygen enough time to move from your lungs into your body. At the end of the breath hold, you will force all of your air out. This test requires good timing between you and your technician, so follow their instructions closely. You will be asked to perform this test 2 to 4 times.

What is a Single Breath O2?

The Single Breath O2 measures how well the air you breathe-in is distributed within your lungs. Once the air enters your lungs it should be distributed relatively evenly to the different parts of your lungs. Various heart and lung diseases may cause the air to be poorly distributed within the lungs, resulting in less oxygen making it into the body. During this test you will breathe-in oxygen as deep as possible. Once your lungs are full, you will let the air out very slowly and controlled. The technician will give you constant feedback to help you maintain the same uniformed speed while you are breathing out. You will only be asked to perform this test 1 to 3 times.

What is the Nitrogen Washout?

The Nitrogen Washout test measures the full volume of the lungs. You are never able to completely blow out all of the air in your lungs, otherwise they would collapse. This test is used to determine the lung volume that cannot be measured during the other pulmonary tests. This test requires that you to breathe-in oxygen to push all of the nitrogen out of your lungs. Since the air in the environment is mainly nitrogen you will need to keep your lips tightly sealed around the breathing device to prevent air from the environment leaking in. This will invalidate your test. The Nitrogen Washout is the longest test you will be asked to perform, lasting 2 to 7 minutes. To get the most accurate test possible, you will need to maintain easy, normal breathing (as if you were watching TV). Your technician will give you constant feedback so that you maintain the appropriate breathing pattern. You will be asked to perform this test 2 to 4 times.

How should I prepare for a Pulmonary Function Test?

Various activities may influence your lung function and should be avoided before testing. For at least 3 hours before your test you should not eat or drink anything (you can drink water). If your stomach is full of food it will press on your lungs preventing them from expanding when you take a deep breath. Additionally, caffeine should not be taken before your test because it can cause the air tubes in your lungs to constrict. If possible, you should not smoke on the day of the test. If you are unable to do this, try to avoid smoking for several hours before your test. This is important because smoking can change the way your lungs function and it influences the blood that flows through your lungs. Be sure not to wear tight clothing that constricts your chest or prevents you from taking a very deep breath. Bring a list of your current medications with you to your test. Your doctor’s office will tell you if you are supposed to take your medications before the test, but if you are unsure, contact your doctor. If you have any questions about your test please contact your doctor’s office and ask to speak with the MET-TEST technician. (S)he will answer any questions you might have, or direct you to the proper person who can answer your questions.
