Pulmonary function tests (PFTs) are a group of tests that measure how well your lungs work. This includes how well you’re able to breathe and how effective your lungs are able to bring oxygen to the rest of your body. PFTs are also known as lung function tests.
Your doctor will order these tests to determine how your lungs are working. If you already have a condition that’s affecting your lungs, your doctor may order this test to see if the condition is progressing or how it’s responding to treatment.
PFTs can help diagnose:
- Chronic bronchitis
- Respiratory infections
- Lung fibrosis
- Bronchiectasis, a condition in which the airways in the lungs stretch and widen
- COPD, which used to be called emphysema
- Asbestosis, a condition caused by exposure to asbestos
- Sarcoidosis, an inflammation of your lungs, liver, lymph nodes, eyes, skin, or other tissues
- Scleroderma, a disease that affects your connective tissue
- Pulmonary tumor
- Lung cancer
- Weaknesses of the chest wall muscles
Your PFTs may include spirometry, which measures the amount of air you breathe in and out. For this test, you’ll sit in front of a machine and be fitted with a mouthpiece. It’s important that the mouthpiece fits snugly so that all the air you breathe goes into the machine. You’ll also wear a nose clip to keep you from breathing air out through your nose. The respiratory technologist will explain how to breathe for the test. You may then breathe normally. Your doctor will ask you to breathe in and out as deeply or as quickly as you can for several seconds. They may also ask you to breathe in a medication that opens your airways. You’ll then breathe into the machine again to see if the medication affected your lung function.
- Plethysmography test
A plethysmography test measures the volume of gas in your lungs, known as lung volume. For this test, you’ll sit or stand in a small booth and breathe into a mouthpiece. Your doctor can learn about your lung volume by measuring the pressure in the booth.
- Diffusion capacity test
This test evaluates how well the small air sacks inside the lungs called alveoli, work. For this part of a pulmonary function test, you will be asked to breathe in certain gases such as oxygen, helium, or carbon dioxide. You may also breathe in a “tracer gas” for one breath. The machine can detect when you breathe out this gas. This tests how well your lungs are able to transfer oxygen and carbon dioxide to and from your bloodstream.
The tests measure lung volume, capacity, rates of flow, and gas exchange. There are 2 types of disorders that cause problems with air moving in and out of the lungs and PFT helps to diagnose these:
- Obstructive: This is when air has trouble flowing out of the lungs due to airway resistance. This causes a decreased flow of air.
- Restrictive: This is when the lung tissue and/or chest muscles can’t expand enough. This creates problems with airflow, mostly due to lower lung volumes