Pulmonary Function Tests

What Are Pulmonary Function Tests?

Pulmonary function tests (PFTs) are a group of noninvasive tests that measure how well your lungs are working. These tests evaluate lung volumes, lung capacity, airflow, and gas exchange. PFTs are essential tools in diagnosing and monitoring a wide range of lung and respiratory conditions.

Tests are ordered by your physician to test different aspects of your lungs. Some of the tests that may be included in PFTs include:

Spirometry
A measure of how much air you can inhale and exhale

Lung Volume Measurement
Measures the total volume of air in your lungs (known as total lung capacity) as well as how much air remains in your lungs after you exhale (known as residual volume)

Lung Diffusion Capacity (DLCO)
This measures how well oxygen moves from your lungs to your bloodstream.

Bronchodilator Responsiveness Test
Sometimes performed after spirometry, this test measures the change in your airflow after inhaling a medication known as a bronchodilator (that opens the airways).

Maximal Voluntary Ventilation
This measures the highest amount of air you can inhale and exhale in one minute as an indicator of respiratory strength.

Cardiopulmonary Exercise Test (sometimes called VO2 testing)
This is a type of stress test that measures your ability to exercise. Unlike a stress test done to measure cardiac function, this test is done breathing through special equipment that carefully measures how much air you inhale as well as how much carbon dioxide is exhaled.

Arterial Blood Gas (ABGs)
This is sometimes included with PFTs. It is a measure of oxygen, carbon dioxide and pH levels in arterial blood.

Why Are Pulmonary Function Tests Done?

Doctors may recommend PFTs to:

• Diagnose lung conditions such as asthma, chronic obstructive pulmonary disease (COPD), or pulmonary fibrosis.
• Monitor chronic lung diseases and assess whether they’re improving or worsening
• Evaluate how well treatments, such as inhalers or other medications, are working
• Measure lung function before surgery or lung transplant
• Determine if occupational exposure has affected lung health
• Investigate symptoms such as chronic cough, shortness of breath, or wheezing

Before the Tests

To prepare for PFTs:

• Avoid heavy meals before testing, as a full stomach can affect lung capacity
• Don’t smoke or perform vigorous exercise for several hours before the test
• Wear loose, comfortable clothing
• Let your doctor know about any medications you’re taking, especially inhalers or bronchodilators, which may need to be paused before testing
  
  

During the Tests

Pulmonary function testing is usually performed in a hospital or clinic by a respiratory therapist or trained technician. Depending on the type of test, you may:

• Sit or stand while breathing into a mouthpiece connected to a machine
• Perform a spirometry test to measure how much air you can inhale and exhale and how quickly
• Complete a lung volume test using a body plethysmograph (a sealed booth that measures air in your lungs)
• Undergo gas diffusion testing to see how well oxygen passes from your lungs into your bloodstream
• Repeat parts of the test after using a bronchodilator to evaluate your response to medications

You’ll be coached to breathe in specific ways during each test. The entire appointment usually takes between 30 and 60 minutes.

After the Tests

• Most people can return to normal activities immediately after PFTs
• You may feel slightly tired or lightheaded, especially after forceful breathing maneuvers
• Test results are reviewed by a pulmonologist, and your doctor will discuss what the numbers mean and any next steps needed

Pulmonary function tests are very safe for most people. However, because they require deep or forceful breathing, some patients may experience:

• Brief dizziness or lightheadedness
• Shortness of breath or fatigue
• Coughing during or after the test

People with recent heart attacks, uncontrolled high blood pressure, or other serious heart conditions should consult their doctor before undergoing PFTs. These situations are rare, and medical staff will monitor your safety during testing.