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.
Your doctor may order these tests:
- if you’re having symptoms of lung problems
- as part of a routine physical
- to monitor how effective your treatment is if you have a lung disease, such as asthma
- to assess how well your lungs are working before you have surgery
PFTs are also known as spirometry or 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, which is a condition in which the airways in the lungs stretch and widen
- chronic obstructive pulmonary disease (COPD), which used to be called “emphysema”
- asbestosis, which is a condition caused by exposure to asbestos
- sarcoidosis, which is an inflammation of your lungs, liver, lymph nodes, eyes, skin, or other tissues
- scleroderma, which is a disease that affects your connective tissue
- pulmonary tumor
- lung cancer
If you’re on medications that open your airways, such as those used for asthma or bronchitis, your doctor may ask you to stop taking them before the test. If it isn’t clear whether or not you should take your medication, make sure to ask your doctor. Pain medications may also affect the results of the test. You should tell your doctor about any over-the-counter and prescription pain medications you’re taking.
It’s important that you don’t eat a large meal before testing. A full stomach can prevent your lungs from inhaling fully. You should also avoid food and drinks that contain caffeine, such as chocolate, coffee, and tea, before your test. Caffeine can cause your airways to open. You should also avoid smoking and strenuous exercise before the test.
Be sure to wear loose-fitting clothing to the test. Tighter clothing may restrict your breathing. You should also avoid wearing jewelry that might affect your breathing. If you wear dentures, wear them to the test to ensure that your mouth can fit tightly around the mouthpiece used for the test.
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 ask you to breathe in a medication that opens your airways or breathe in certain gases such as oxygen, helium, or carbon dioxide. You’ll then breathe into the machine again to see if the medication or gases affected your lung function.
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.
A plethysmography test measures the volume of gas in your lungs. 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.
A PFT can cause problems if:
- you’ve recently had a heart attack
- you’ve had recent eye surgery
- you’ve had recent chest surgery
- you’ve had recent abdominal surgery
- you have a severe respiratory infection
- you have heart disease
PFTs are usually safe for most people. However, because the test may require you to breathe in and out quickly, you may feel dizzy and there’s a risk that you might faint. If you feel lightheaded, tell your doctor. The test may cause you to have an asthma attack if you have asthma. In very rare cases, PFTs may cause a collapsed lung.