What Pulmonary Function Tests Can Tell You About Your Lung Health
Key takeaways:
Pulmonary function tests check lung health and diagnose conditions like asthma, COPD, and restrictive lung disease.
There are different types of pulmonary function tests. The most common are spirometry, lung volume, and diffusion tests.
These tests can be done in a provider’s office or a pulmonary function lab. During the tests, a healthcare professional will ask you to do tasks, like take deep breaths, breathe through a mouthpiece, or exhale quickly.
Pulmonary function tests (PFTs), or lung function tests, check how well your lungs are working. They measure the amount of air moving into and out of your lungs with each breath. The tests also look at how oxygen travels from your lungs to the rest of your body.
You may need complete pulmonary function testing if you have symptoms of a lung condition like asthma or COPD. These tests also help people with chronic lung disease see how well treatments are working.
Let’s look at the different types of pulmonary function tests, how they are performed, and what to expect when you go for testing.
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What are the types of pulmonary function tests?
The three most commonly used pulmonary function tests are spirometry, lung volume testing, and diffusion testing.
1. Spirometry
Spirometry is the most common pulmonary function test. It measures:
Forced vital capacity (FVC): This is the total amount of air you move out of your lungs when you exhale.
Forced expiratory volume (FEV₁): This is the amount of air you can push out of your lungs in 1 second.
To do this test, you take a deep breath in, then breath out as fast as you can through a tube. The tube connects to a spirometer — a machine that measures the speed and amount of air you exhale. Your healthcare provider may ask you to inhale a breathing medication and then repeat the test to see if your results change.
2. Lung volume testing
Lung volume tests measure how much air the lungs can hold and how much air remains after you exhale. The most common test for lung volume is body plethysmography.
For this test, you sit in a see-through booth, place a clip over your nose, and breathe through a mouthpiece. You take several short, shallow breaths, then you breathe normally. The mouthpiece measures pressure changes, which helps calculate your lung volume.
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3. Diffusion tests
When you breathe, you take in oxygen and release carbon dioxide. Diffusion tests measure how well oxygen travels from inside your lungs to the rest of your body.
During the test, you will inhale a mixture of gasses. This includes a small, harmless amount of carbon monoxide. The amount of carbon monoxide that you exhale helps calculate how well oxygen goes from your lungs to your bloodstream.
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Who needs a pulmonary function test?
There are several reasons why you may need a pulmonary function test.
A new lung condition
You may need pulmonary function testing if you have symptoms of a new lung condition. If you have changes on a chest X-ray, these tests can help figure out what is causing these changes. They can also help diagnose a lung condition if you have symptoms like:
Chronic cough
Shortness of breath
Wheezing
Chronic lung conditions
If you have an underlying lung condition, pulmonary function tests can measure how well your lungs are responding to your medication. You may need routine pulmonary function tests if you have:
COPD (chronic obstructive pulmonary disease)
Interstitial lung disease like pulmonary fibrosis
Pulmonary vascular disease
Risk for developing chronic lung conditions
If you are at risk for developing a lung disease, your healthcare provider may recommend routine pulmonary function tests. Testing can help spot signs that you’re developing a lung condition before you start having symptoms. This means you can start treatment earlier to protect your lungs.
You may be at higher risk of developing a chronic lung condition if you were:
Exposed to substances like asbestos that cause lung damage
Treated with medications that can cause lung damage
Treated with radiation therapy
What does your pulmonary function test mean?
Pulmonary function tests offer a look at what’s happening inside the lungs.
Spirometry shows how well air leaves the lungs
Spirometry offers information on how easily air can exit the lungs. This is noted as a measurement called the FEV₁FVC ratio. Here’s how to interpret that number:
FEV₁/FVC less than 0.7: This means air has a hard time getting out of the lungs. This happens when someone has an obstructive lung condition like asthma and COPD.
FEV₁/FVC greater than 0.7: This can mean that air is moving out of the lungs normally. Sometimes it can mean the lungs have a hard time expanding to accept air that you breathe in (restrictive lung disease). Some types of restrictive lung disease include pulmonary fibrosis and sarcoidosis.
Lung volume testing shows lung size
Lung volume testing shows the total amount of space (volume) in the lungs. Lung volume varies from person to person based on age, sex, and height.
Lungs that are much larger than normal can be a sign of obstructive lung disease. This occurs when air gets trapped in the lungs and can’t exit. Small lung volumes can be a sign of restrictive disease because the lungs can’t expand when air enters.
Diffusion testing can show lung scarring
Diffusion testing looks at lungs’ ability to move oxygen into the body and carbon dioxide out of the body. Low diffusion capacity can mean there is scarring of lung tissue or a problem with the blood vessels in the lungs.
Taken together, all three tests give a lot of information about how the lungs work. But these tests are just part of the picture. But along with your history, symptoms, and lung exam, they give a better picture of what’s happening inside your lungs. Some people may need more tests too — like CT scans or bronchoscopy — to give a complete picture of lung health.
How accurate are pulmonary function tests?
Pulmonary function tests are accurate when done right. But they can be tricky to do! You must be able to follow directions and give a good effort when asked to take deep breaths or exhale quickly. With proper coaching, you can correctly do the tests and get useful information about your lung function.
What should you expect during a pulmonary function test?
Sometimes you can do pulmonary function tests, like spirometry, at your provider’s office. For more specialized testing, you may have to go to a pulmonary function lab. Remember these tests aren’t invasive or painful. They’re very safe and don’t expose you to radiation. This is why they’re the first choice for monitoring lung health.
During testing you will have to take deep breaths, push air out of your lungs quickly, and hold your breath. These actions aren’t natural, so expect to practice a little to correctly do these maneuvers. You might have to repeat the test more than once to make sure your results are accurate. The person administering the test can see your results in real time and will give you instructions and coach you through the test.
Here is how to prepare for a pulmonary function test:
Avoid smoking for at least 1 hour before the test.
Do not perform strenuous exercise 30 minutes before the test.
Wear loose-fitting, comfortable clothes that will not restrict you when you try to breathe deeply.
Avoid eating a large meal 2 hours before the test.
Ask your healthcare provider about what medications you can take before pulmonary function testing. If you normally use inhalers, your provider may ask that you not use them for at least 4 hours before the test.
Pulmonary function tests can be very tiring! It is normal to take time to rest and catch your breath in between tests. If you feel lightheaded, dizzy, or like you might faint, you should tell the staff right away. They’ll stop the test so you can rest. You can restart the test when you feel better.
The bottom line
Pulmonary function tests can help diagnose lung conditions. They also can check how well people are responding to treatment for lung conditions. There is more than one type of pulmonary function test. And they all offer different information on how well the lungs work. Pulmonary function tests aren’t painful but are tricky to do correctly. During testing, you will breathe differently than normal. A healthcare professional who is familiar with the test will help coach you through the process.
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References
American Lung Association. (2020). Spirometry.
Asthma and Lung UK. (2020). Lung volume test.
Cheung, H., et al. (2015). Coaching patients during pulmonary function testing: A practical guide. Canadian Journal of Respiratory Therapy.
Decramer, M., et al. (2013). Contribution of four common pulmonary function tests to diagnosis of patients with respiratory symptoms: A prospective cohort study.The Lancet.
Fahy, B., et al. (2019). Pulmonary function tests.American Thoracic Society.
Lamb, K., et al. (2022). Spirometry. StatPearls.
Langan, R., et al. (2020). Office spirometry: Indications and interpretation. American Family Physician.
Moses, S. (2021). Diffusing capacity. FamilyPractice Notebook.
National Heart, Lung, and Blood Institute. (2022). Pulmonary function tests.
Ranu, H., et al. (2011). Pulmonary function tests. Ulster Medical Journal.
