Pulmonary Function Test

What are pulmonary function tests?

They are noninvasive means to determine lung function. They measure:

  • Capacity
  • Gas exchange
  • Lung volume
  • Rates of flow

This data can help your provider diagnose and treat certain lung disorders.

There are two types of disorders that disrupt lung function:

Obstructive: When airway resistance decreases airflow.

Restrictive: When lung tissue and chest muscles can’t expand enough, leading to lower lung volumes.

There are two pulmonary function test methods — spirometry and plethysmography. Your provider might use them together to conduct different tests.

What do pulmonary function tests measure?

Tidal volume (VT): Amount of air inhaled or exhaled during normal breathing.

Vital capacity (VC): Volume of air exhaled after inhaling as much as possible.

Functional residual capacity (FRC): Amount of air left in the lungs after normal exhaling.

Residual volume: Amount of air left in the lungs after exhaling as much as you can.

Total lung capacity: Total volume of the lungs when filled with as much air as possible.

Forced vital capacity (FVC): Amount of air exhaled with force after inhaling as much as you can.

Forced expiratory volume (FEV): Amount of air expired during the first, second, and third seconds of the FVC test.

Forced expiratory flow (FEF):  Average rate of flow during the middle half of the FVC test.

Peak expiratory flow rate (PEFR): Fastest rate that you can force air out of your lungs.

Normal PFTs values vary. Providers compare data to those of the average for someone of the same age, height, sex, and race. Results are also compared to your previous results.

Why might I need pulmonary function tests?

They can be part of a well-physical. Also, they’re done to test health in coal mines and graphite factories. Other reasons your provider might test:

  • Respiratory infections
  • Trouble breathing from injury to the chest or a recent surgery
  • Chronic lung conditions, such as:
    • Asthma
    • Bronchiectasis
    • Chronic bronchitis
    • Emphysema
  • Asbestosis, a lung disease caused by inhaling asbestos fibers
  • Restrictive airway problems from scoliosis, tumors, or inflammation or scarring of the lungs
  • Sarcoidosis, a disease that causes inflammatory cells around the liver, lungs, and spleen
  • Scleroderma, a disease that causes the thickening and hardening of connective tissue

Providers might check lung function before surgery or other procedures in certain patients. These include smokers, or patients with heart, lung, or other health issues. 

PFTs can help determine treatment for asthma, emphysema, and other chronic lung problems. Your provider might administer PFTs for other reasons, too.

What are the risks of pulmonary function tests?

They aren’t invasive, so they’re safe and quick for most. All that’s required is for the patient to be able to follow clear, simple instructions.

All procedures carry risks. For PFTs, these include:

  • Coughing
  • Dizziness during the tests
  • Shortness of breath

Some people should not have PFTs. Those who shouldn’t include those who have had:

  • A bulging blood vessel (aneurysm) in the chest, belly, or brain
  • Active tuberculosis or respiratory infection, such as cold or flu
  • Chest pain, recent heart attack, or an unstable heart condition
  • Recent belly or chest surgery
  • Recent eye surgery, because of increased pressure inside the eyes during the procedure

Risks may vary because of general health or other factors. Consult your healthcare provider for your risks and concerns.

Are PFTs accurate?

Yes, although some factors can hinder accuracy, including:

  • Degree of patient cooperation and effort
  • Extreme fatigue or other conditions that affect a person’s ability to do the tests (such as a head cold)
  • Stomach bloating that affects the ability to take deep breaths
  • Use of bronchodilators, medicines that open the airways

How do I prepare for pulmonary function tests?

Consult your provider for questions about the tests. He or she might ask you to sign a consent form for the procedure. Ask questions if anything is unclear to you about the tests.

Disclose any medicines you take to your provider, including:

  • Herbal supplements
  • Over-the-counter medicines
  • Prescriptions
  • Vitamins

Before the test, your provider might suggest you refrain from:

  • Smoking (ask how long before the test you should stop)
  • Taking certain medicines
  • Eating a heavy meal

Follow other instructions your healthcare provider gives you. He or she will record your height and weight before the test for accurate test calculations.

What happens during pulmonary function tests?

It’s sometimes outpatient, meaning you’ll go home the same day. It might also be part of a longer hospital stay. It depends on your condition and the provider’s methods.

Usually, it goes like this:

1. He or she will ask you to loosen clothing, jewelry, or other things that may interfere with the procedure.

Note: If you have dentures, you will need to wear them during the procedure.

2. You’ll empty your bladder before the procedure.

3. You’ll sit in a chair. You’ll have a soft clip put on your nose to restrict breathing to your mouth.

4. You’ll receive a sterile mouthpiece attached to a spirometer.

5. You’ll form a tight seal over the mouthpiece with your mouth. You’ll inhale and exhale in different ways with your provider’s guidance. Your provider will watch for dizziness, trouble breathing, and other issues while you’re testing.

6. You might receive a bronchodilator after tests. You’ll repeat tests several minutes later after the bronchodilator has taken effect.

What happens after pulmonary function tests?

You might feel fatigued afterward if you have a history of breathing or lung problems. You’ll have time to rest before your provider discusses test results with you.