Pulmonary Function Testing

Pulmonary function tests (PFTs) are different kinds of breathing tests that measure how well your lungs are working. “Pulmonary” (pronounced “PUHL-muh-ner-ee”) means it relates to your lungs.

There are many types of pulmonary function tests. Healthcare providers use them to diagnose asthma, COPD, pulmonary fibrosis and other conditions that affect the lungs and airways. Testing can also help providers figure out the best treatment.

PFTs are safe. And they aren’t invasive. That means providers don’t have to put any tools or instruments in your body.

Other names for pulmonary function tests include:

• Lung function tests
• Functional respiratory tests
• Breathing tests

What are the different types?

Pulmonary function tests include:

• Spirometry to measure lung volume and airflow
• Body plethysmography or lung volumes to measure the amount of air in your lungs, including how much remains in your lungs after a forced breath out
• Lung diffusion testing (DLCO) to measure how much gas moves from your lungs to your blood
• Cardiopulmonary exercise test (CPET) to see how much oxygen your body uses when you exercise and how much carbon dioxide it produces
• Methacholine challenge (bronchoprovocation test) to see if your airways are reactive

Why would it be ordered?

Your healthcare provider may order pulmonary function tests if you have lung or airway symptoms, like:

• Coughing, especially if you cough up mucus or phlegm
• Shortness of breath (dyspnea)
• Difficulty breathing or taking a deep breath
• Wheezing
• Chest tightness, pain or pressure

PFTs also allow your provider to:

• Detect narrowing in your airways, lung weakness or a decrease in your lungs’ ability to get oxygen to your blood
• Determine whether you’re a good candidate for surgery or other procedures
• See if treatment is working
• Understand how tobacco products affect your lungs
• Understand if substances in your environment affect your lungs
• Decide if medications can make it easier for you to breathe

What conditions can it diagnose?

PFTs can help your healthcare provider diagnose:

• Asthma
• Chronic obstructive pulmonary disease (COPD)
• Pulmonary fibrosis
• Weakness of your breathing muscles
• Narrowing of your windpipe (trachea)

How do I prepare for it?

Before testing, your healthcare provider may ask you to:

• Stop taking your breathing medicines for a short period.
• Wear loose, comfortable clothing that doesn’t squeeze your chest.

They also may ask you to avoid:

• Any intense physical activity
• Using tobacco products
• Eating a heavy meal
• Consuming caffeine, including coffee, tea, soda pop and chocolate

These steps ensure your results are the most accurate.

What is done during testing?

You’ll do pulmonary function testing at a hospital or your healthcare provider’s office. A specially trained respiratory therapist usually performs the testing. Tests may involve:

• Breathing through a mouthpiece connected to a machine
• Breathing in medications or gases
• Walking on a treadmill or up and down a hallway
• Riding a stationary bicycle

Before the test, your provider will record some personal information. This allows them to determine a typical value for your demographic. They’ll record your:

• Height
• Weight
• Age
• Sex

Then, they’ll take you to a room with PFT equipment. All PFTs except exercise tests involve breathing through a mouthpiece with soft clips covering your nose. Your provider will give you specific instructions according to your test.

• Spirometry: You take a deep breath in and then breathe out forcefully through a mouthpiece for as long as you can.
• Body plethysmography or lung volumes: You sit in a clear, plastic box and breathe or pant through a mouthpiece. A machine detects pressure or volume changes in the box as you breathe.
• Lung diffusion testing: You breathe in a small, safe amount of carbon monoxide. A machine then measures how much carbon monoxide your lungs absorb.
• Cardiopulmonary exercise test: You walk on a treadmill or cycle on a stationary bike. Machines measure your heartbeat, blood pressure and blood oxygen as you exercise.
• Six-minute walk test: You walk back and forth in a room or hallway. Your provider measures how far you walk in six minutes.

How long does it take?

A PFT may take between 15 and 45 minutes to complete. You may have to do the test a few times to get the most accurate results.

Let your healthcare provider know if you get tired during testing. You can take breaks between parts of the test.

What are the risks or side effects?

Pulmonary function testing is generally safe. While you won’t feel pain, you may feel dizzy or lightheaded from breathing deeply.

Some PFTs can trigger asthma or COPD symptoms. Your healthcare provider has rescue medications on hand. Let them know if you need a break during testing.

PFT can also increase your heart rate. Because of this possible risk, tell your provider if you’ve had a heart attack recently or if you have any other heart condition.

In very rare cases, testing may cause a collapsed lung.

What type of results will I get?

Your healthcare provider will compare your score against the typical scores of your demographic — the expected range of other people who are the same age, height, weight and sex as you. This is your z-score.

You can’t fail a pulmonary function test. If your z-score isn’t in the expected range, your provider may recommend more tests. Additional tests help them diagnose a condition and form a treatment plan.

When should I know the results?

Your healthcare provider should contact you with your results within a few days. Sometimes, you have an appointment right after testing to discuss the results.

When should I call my doctor?

Reach out to your healthcare provider if you don’t hear from them with your results after a few days.

If your provider diagnoses you with a condition, you may need to schedule regular testing. Regular tests allow your provider to see how well your lungs are doing or how you’re responding to medications.

Can a pulmonary function test detect heart problems?

Yes. Pulmonary function testing can help determine if your lungs aren’t expanding as much as they should when you breathe in (restrictive spirometry pattern). This is a risk factor for the development of heart problems, including heart failure.