What is Pulmonary Function Testing?

Measuring your lung capacity, volume, and rates of flow give our providers a look at how your lungs are working–learn more about these tests before you head into the office.

Aug. 4, 2021 7   min read

Image of lungs being tested for their function

Sometimes, it’s important for your healthcare provider to know how well your lungs are performing. They test this with pulmonary function tests (also called lung functions test or spirometry), which are a variety of tests that check how well your lungs work.

Pulmonary function tests measure your lung volume, capacity, rates of flow, and gas exchange, all while being non-invasive. The information derived from the tests can help your provider diagnose and decide on the best treatment for certain lung disorders. With the assistance of Peter Capucilli, MD, Allergy, Asthma, and Immunology provider, we delved into why you may have lung function tests done, and what will happen when you do.

Two types of disorders cause problems with the air moving in and out of your lungs–obstructive and restrictive disorders. Obstructive disorders occur when air has trouble flowing out of the lungs because of airway resistance, which causes a decreased flow of air. Restrictive disorders are when your lung tissue or chest muscles cannot expand enough, which causes problems with air flow.

Why would I need a pulmonary function test?

There are lots of reasons why your provider might suggest a pulmonary function test. For some, they are done during routine physicals, for others they are routinely offered at work to ensure employee health (especially at coal mines or graphite factories). 

If your provider suspects you may have any of the following problems, they may use pulmonary function tests to diagnose. They’re excellent diagnostic tools for:

  • Asthma
  • Asbestosis
  • Chronic lung conditions like COPD and emphysema
  • Restrictive airway problems from inflammation or scarring of the lungs
  • Sarcoidosis
  • Trouble breathing from an injury or recent surgery

"Pulmonary function tests are safe and quick for most people," explained Dr. Capucilli. "They are a very popular and effective way to measure your lung function and see if drugs or treatments may help you breathe more easily."

Types of Pulmonary Function Tests

The type of test your provider recommends will be based on the results they’re looking for. Some tests are useful for seeing how much air you can get into your lungs while others are useful for understanding how well your lungs work.


One of the most commonly ordered lung function tests, spirometry measures how much air you can breathe into your lungs, and how quickly you can blow air out. This test is performed by having you take in a deep breath, and then blowing all your air out as fast as you can. You’ll be blowing into a tube that’s connected to a machine called the spirometer (hence the name!) To ensure accurate results, this test is repeated three times, with a rest between tests.

Your spirometry test may also be repeated after you are given a bronchodilator (breathing medicine) to find out how much better you could breathe with this type of medicine.

Spirometry tests typically take 30 minutes to complete, and are performed right in your provider’s office.

Diffusion Studies

Diffusion studies are used to find out how well the oxygen you inhale moves from your lungs and into your blood. You will breathe into a mouthpiece that’s connected to a machine, being asked to empty your lungs by gently breathing out as much air as you can. Then, you will breathe in a quick, but deep breath, hold it for 10 seconds, and breathe out when instructed. 

Diffusion tests take about 30 minutes to complete, and you will be asked to do the test several times to ensure accuracy. Please do not smoke and stay away from others who do on the day of your test.

Normal pulmonary function testing values vary person-to-person. Your results will be compared to the average of someone of the same sex, age, height, and race, as well as any previous results.

Body Plethysmography

This test measures how much air is in your lungs after you take in a deep breath, and how much air is left after breathing out as much as you can. No matter how hard you try, you can never get all the air out of your lungs. Measuring the total amount your lungs can hold as well as the amount left after you breathe out gives your provider important information about how well your lungs are working.

During a body plethysmography test, you'll wear a nose clip and be instructed on how to breathe through a mouthpiece. If you use oxygen to supplement your breathing, you may be asked to be off of it during this test. If you have a hard time with that or being in enclosed spaces, please let your provider know before the test–there are other options for testing the total volume of air in your lungs.

What to Expect

Pulmonary function tests are not painful. They will be performed with the help of a pulmonary function technician, and they will ask you to use maximum effort to breathe in and blow out air. You will do this several times to ensure that the results are accurate. 

Keep the following in mind before and during your tests:

  • Take any daily medications before testing unless told otherwise
  • Do not smoke for at least 6 hours before testing
  • If you are using an as-needed, short-acting inhaler, do not use six to eight hours before testing, if possible
  • Ask your doctor about any other medication concerns

Exercise tests are performed on a treadmill or bike, so please wear comfortable, loose-fitting clothes and athletic shoes. After your test or tests, you can safely return to your normal daily activities. 

NEXT STEPS Having Trouble Breathing?

Find an Allergy, Immunology & Rheumatology location close to you and schedule a consultation with our providers. They will work with you to determine any breathing issues quickly, carefully, and thoroughly.

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