Pulmonary Function Test

What are breathing tests? — Breathing tests are a group of tests that measure how well your lungs are working. The terms doctors use for these tests are “pulmonary function tests” or “PFTs.” Specifically, breathing tests measure:

  • How much air you can breathe in and out of your lungs
  • How fast you can breathe the air out of your lungs
  • How much oxygen gets into your blood from your lungs

Why might my doctor order breathing tests? — Your doctor might order breathing tests to:

  • Find the cause of symptoms such as a long-term cough, noisy breathing (wheezing), or trouble breathing
  • Check if a known lung condition is mild or severe, or changes over time – Lung conditions that are commonly followed with breathing tests include asthma, chronic bronchitis, pulmonary fibrosis, and chronic obstructive pulmonary disease (also called “COPD”).
  • Check how well your inhaler medicines are working
  • Check how well your lungs are working before you have surgery

How do I prepare for breathing tests? — Your doctor or nurse will tell you if you need to do anything special to prepare for your breathing tests. If you take an inhaler, your doctor might have you wait to take your medicine after the test (instead of before).

What are the different breathing tests and what do they involve? — The different breathing tests include:

  • Spirometry – This is the breathing test most commonly done. It involves breathing in as deeply as you can, and then breathing out as hard and as fast as you can into a tube (figure 1). The tube is attached to a machine called a “spirometer.” The doctor, nurse, or technician will give you specific directions about how to breathe for the test. Spirometry measures how much air you can breathe in and out of your lungs and how fast you can breathe the air out of your lungs.

During this test, the doctor, nurse, or technician might give you medicine to open up your airways. This medicine comes as an inhaler that you breathe in. Then, you will repeat the spirometry test to see whether the medicine has affected your breathing.

  • Lung volume measurement – This test measures how much air is in your lungs. Some lung diseases increase the amount of air in your lungs. Other diseases decrease the amount of air in your lungs. The test involves sitting in a large glass box that looks like a phone booth. While you are in this box, you will breathe in and out through a tube. The technician might ask you to pant (breathe in and out quickly) during the test.
  • Diffusing capacity – This test measures how well oxygen gets from your lungs into your blood. It involves breathing in a certain gas, and then breathing out into a tube.