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What Is A Pulmonary Function Test, Why is it Performed, What Does It Measure, What Happens During PFT Tests

Pulmonary function tests are diagnostic lung tests. These tests demonstrate how well your lungs are working. These non-invasive tests measure lung capacity, volume, gas exchange, and rates of flow. All this information then helps your doctor diagnose and decide on the treatment plan for whatever lung condition you have. Read on to find more about what is a pulmonary function test, and it can tell you.

Why are Pulmonary Function Tests Performed?

What is a Pulmonary Function Test?

Pulmonary function tests (PFTs) are a group of tests that are used for determining how well your lungs are working. The PFT tests measure lung capacity, volume, rates of gas exchange, and rates of flow. Additionally, the Pulmonary function tests also measure how capable your lungs are at supplying oxygen to the rest of the body and how well you are able to breathe.

The pulmonary function tests are non-invasive, meaning that doctors do not need to cut or insert any medical tools inside the body.

The pulmonary function tests may be ordered in the following conditions:(1)

  • If you are experiencing symptoms of lung problems
  • For monitoring the progression of chronic lung diseases such as chronic obstructive pulmonary disease (COPD or asthma)
  • To monitor your lungs if you are regularly exposed to certain toxic substances in the workplace or the environment
  • To determine how well your lungs are working before you have surgery
  • Pulmonary function tests are sometimes also known as lung function tests.

Why are Pulmonary Function Tests Performed?

Pulmonary function tests may be ordered by your doctor to assess how well your lungs are working. If you already have an underlying health condition that affects your lungs, then your doctor may prescribe this test to check if the disease has progressed or how the conditions are responding to the treatment plan.

Pulmonary function tests can help in the diagnosis of the following conditions:

  • Allergies
  • Asthma
  • Respiratory infections
  • Chronic bronchitis
  • Lung fibrosis
  • Chronic obstructive pulmonary disease
  • Bronchiectasis, a condition characterized by the widening and stretching of the airways in the lungs
  • Sarcoidosis, a condition that causes inflammation of the lungs, lymph nodes, liver, skin, eyes, or other tissues
  • Asbestosis, a condition that is caused by exposure to asbestos
  • Pulmonary tumor
  • Scleroderma, a disease that affects the connective tissue of the body
  • Lung cancer
  • A weakness of the muscles of the chest wall

What Does The Pulmonary Function Test Measure?

The pulmonary function tests measure the following:

  1. Vital Capacity (VC): This is the total amount or volume of air that can be exhaled after inhaling as much air as you can.
  2. Tidal Volume (VT): This is the amount of air exhaled or inhaled during your normal breathing.
  3. Minute Volume (MV): This is the total amount of air you exhale per minute
  4. Residual Volume: This is the amount of air left in the lungs after exhaling as much air as you can.
  5. Functional Residual Capacity (FRC): This is the amount of air left in the lungs after you exhale normally.
  6. Total Lung Capacity: This is the total volume of the lungs when they are filled with as much air as possible.
  7. Forced Vital Capacity (FVC): This is the amount of air exhaled forcefully and quickly after having inhaled as much as you can.
  8. Forced Expiratory Flow (FEF): This is the average rate of airflow during the middle half of the FVC test.
  9. Forced Expiratory Volume (FEV): This is the amount of air expired during the first, second, and this seconds of the forced vital capacity test.
  10. Peak Expiratory Flow Rate (PEFR): This is the fastest rate at which you can force air out of your lungs.

The average values for pulmonary function tests vary from person to person. The amount of air inhaled and exhaled in your individual results are compared to the average values for someone of the same age, gender, height, and race. The results of these tests are also compared to your previous test results. If you have abnormal measurements, or if there is a change in your results, then you may require other tests.

How to Prepare for Pulmonary Function Tests?

If you are on medications for opening up your airways, as is the case in chronic bronchitis or asthma, then your doctor is likely to ask you to stop taking them before the pulmonary function test. Pain medications also have an impact on the test results, and therefore, you must tell your doctor if you are using any over-the-counter or prescription pain medications.

Avoid having a large meal before the test since a full stomach can prevent your lungs from inhaling fully. You also need to avoid having foods and drinks that contain caffeine, such as coffee, tea, and chocolate, before the test. This is advised because caffeine can cause the airways to become more open, affecting the results of the test. You should also avoid smoking at least one hour before the test. Strenuous exercises before the test should also be avoided.

Wearing loose-fitting clothes is best since tighter clothes may restrict your breathing. Also, avoid wearing jewelry that may affect your breath. If you wear dentures, do not remove them during the test. You should wear them to make sure that your mouth fits tightly around the mouthpiece used for the test.

If you have had any type of abdominal, chest, or eye surgery or a stroke or heart attack, then the test will be delayed until you recover completely.(2)

What Happens During Pulmonary Function Tests?

Your doctor will choose your pulmonary tests based on what they are trying to find out. Each of the pulmonary function tests works differently. Here are some of the standard pulmonary function tests.


Spirometry is the most common pulmonary function test. Spirometry helps measure the amount of air you are able to breathe in and out. This test also measures how fast you are able to empty the air of your lungs.(3)

Spirometry helps diagnose many types of breathing problems, such as chronic obstructive pulmonary disease and asthma. If you are already taking medication for a breathing condition, then a spirometry test helps your doctor understand how well the medicine is working.

During the spirometry test, you will sit in front of a machine and will be fitted with a mouthpiece. It is essential that the mouthpiece fits tightly or snugly in your mouth to ensure that all the air you breathe in goes into the machine. You will also need to wear a nose clip to prevent you from breathing the air out through your nose. The technologist administering the test will explain to you how you need to breathe for the test.

Your doctor will ask you to inhale and exhale as deeply or as quickly as you can for several seconds. You may also be asked to breathe in a medication that opens up the airways. You will then proceed to breathe into the machine again to check if the drug has affected your lung function.

Spirometry measures two things:

  1. The maximum amount of air you can breathe out after inhaling deeply. The test results will let you know if you have a decreased ability to breathe normally.
  2. The amount of air you can exhale in one second. The results allow the doctor to know how severe your breathing condition is.

Bronchial Provocation Test

If you have a breathing condition like asthma, you are aware that triggers such as smoke, exercise, and dust that make it difficult to breathe. A bronchial provocation test helps in the diagnosis of asthma. Your doctor may also use this test to measure the severity of your asthma.(4)

During the bronchial provocation test, you will be asked to inhale a medicine that will narrow your airways. Then you will take the spirometry test. You will do this a couple of times. The doctor will use the readings of the test to understand how much your airways narrow when you are having an asthma attack.

Body Plethysmography

A body plethysmography measures how much air is present in your lungs when you take a deep breath in. You will be breathing deeply for this test so that the doctor is also able to determine how much air remains inside the lungs after you breathe out as much air as you can.

The plethysmography test can be used for a variety of reasons, including:

  • To check how a disease such as asthma or chronic obstructive pulmonary disease affects your lungs. The results may indicate that there is a need to change your treatment.
  • To help confirm whether you have lung disease, that is decreasing the amount of space in your lungs. Your doctor is likely to term this as a restrictive disease.
  • To check if your airways have becomes narrow. In this case, the test will also help your doctor determine if you need to be put on lung medications known as bronchodilators to help expand your airways. Bronchodilators are used to open up the airways.(5)
  • To determine how well you will respond if you need surgery for some reason.

This is a painless test and may take around 15 minutes. During body plethysmography, you will be told to sit in a clear plastic box. You will be made to wear a nose clip and told to breathe deeply through your mouth, in and out of a special mouthpiece.

Lung Diffusion Capacity Test

A lung diffusion capacity test measures how well oxygen is able to move from your lungs and into the bloodstream. This test is also quite similar to spirometry.

You will be asked to breathe into a tube that is attached to a machine. The test is used to diagnose a disease of the blood vessels that are located between the lungs and the heart. The test shows the amount of damage that has been caused due to a disease such as emphysema, a condition in which the air sacs gradually get destroyed.

Pulse Oximetry Test

This is another painless test that measures the amount of oxygen present in your blood. The doctor will clip a probe to your earlobe, finger, or another part of the skin. The device makes use of light to measure the amount of oxygen present in the red blood cells.

Cardiopulmonary Exercise Stress Test

This test measures the strength of your lungs and heart. It is usually administered to people who are suspected of having, or already have, lung problems or heart disease. Sometimes such conditions only show up during exercise.

During this test, you will be told to walk on a treadmill or ride a stationary bike. The doctor will keep monitoring your heart rate as your heart starts beating faster and faster. You will then breathe into a tube that is used to measure your lung capacity as they are made to work harder.

Conclusion: Are There Any Risks Of Pulmonary Function Tests?

A pulmonary function test can be a risk in some people:

  • If you have recently had a heart attack
  • If you have recently had chest surgery
  • If you have recently undergone an eye surgery
  • If you have recently had abdominal surgery
  • If you have unstable heart disease
  • If you have a severe respiratory infection

However, pulmonary function tests are typically considered to be safe for most people. But since the test may require you to keep inhaling and exhaling rapidly, it may make you feel dizzy, and there is also a small risk that you may faint. If you start feeling lightheaded, then you should let your doctor or the technician administering the test know.

If you have asthma, then the test may lead to an asthma attack.

In some very rare cases, pulmonary function tests may lead to a collapsed lung.


  1. Miller, J.I., Grossman, G.D. and Hatcher, C.R., 1981. Pulmonary function test criteria for operability and pulmonary resection. Surgery, gynecology & obstetrics, 153(6), pp.893-895.
  2. Ranu, H., Wilde, M. and Madden, B., 2011. Pulmonary function tests. The Ulster medical journal, 80(2), p.84.
  3. Enright, P.L., Linn, W.S., Avol, E.L., Margolis, H.G., Gong Jr, H. and Peters, J.M., 2000. Quality of spirometry test performance in children and adolescents*: experience in a large field study. Chest, 118(3), pp.665-671.
  4. Perpiñá, M., Pellicer, C., de Diego, A., Compte, L. and Macián, V., 1993. Diagnostic value of the bronchial provocation test with methacholine in asthma: a Bayesian analysis approach. Chest, 104(1), pp.149-154.
  5. Cazzola, M., Page, C.P., Calzetta, L. and Matera, M.G., 2012. Pharmacology and therapeutics of bronchodilators. Pharmacological reviews, 64(3), pp.450-504.
Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:August 2, 2021

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