Body Plethysmography (Pulmonary Function Test)

Body plethysmography is a type of lung function test. You enter a see-through plastic box, where machines measure how much air goes into and out of your lungs when you breathe. Body plethysmography is safe, but deep breathing may make you feel lightheaded or dizzy. Your healthcare provider will contact you after a few days with your test results.


What is body plethysmography?

Body plethysmography (pronounced “pleh-thiz-mah-graf-ee”) is a noninvasive type of lung function testing known as a pulmonary function test. It can help determine how much air is in your lungs after you take a deep breath in (inhale). It also helps determine how much air remains in your lungs after you take a deep breath out (exhale).

Body plethysmography is safe and comfortable. It gives your healthcare providers critical information about how well your lungs function. This information helps them work with you to create the best treatment plan.

Other names for body plethysmography include lung plethysmography and pulmonary plethysmography.


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Why is body plethysmography performed?

Body plethysmography helps diagnose lung and airway diseases, such as:

Body plethysmography can also:

  • Compare how your lungs function to how well your lungs should be working compared to any previous tests you’ve taken or to standards for your demographic.
  • Measure the effect of chronic (long-lasting) lung diseases on your lung function.
  • Detect early changes in your lung function that might require a change in your treatment.
  • Determine whether substances in your home or work environment have damaged your lungs.
  • Determine your ability to tolerate medical procedures, including surgery.

When would body plethysmography be needed?

Your healthcare provider may order a body plethysmography test if you have lung or airway condition symptoms. Some symptoms for which your healthcare provider may order body plethysmography include:

An abnormal body plethysmography test result can help your healthcare provider confirm that a condition is preventing your lungs from holding as much air as they should.

What are the advantages of body plethysmography?

Body plethysmography is an accurate and relatively quick test — it typically takes fewer than 20 minutes to complete. Your healthcare provider can also get many measurements within just a few minutes.

What are the different types of body plethysmography?

The different types of body plethysmography include:

  • Pressure plethysmograph: A pressure plethysmograph measures your lung volumes by measuring gas pressure changes in a clear, airtight plastic box. The box contains a fixed amount of air. A special machine connected to the mouthpiece called a spirometer measures volume in the area between your neck and abdomen (thorax). A pressure plethysmograph is very sensitive and can measure small changes in volume. Another name for a pressure plethysmograph is a closed-type plethysmograph.
  • Volume plethysmograph: A volume plethysmograph measures gas volume changes by measuring gas displacement in a clear, airtight plastic box. When the gas volume changes in your thorax, the surrounding air in the box exits through a hole in a wall connected to a spirometer. The spirometer measures the airflow. A volume plethysmograph is challenging, so only medical researchers use this test. Another name for a volume plethysmograph is an open-type plethysmograph.
  • Pressure-volume plethysmograph: This test combines elements of a pressure plethysmograph and a volume plethysmograph. As you breathe, any volume changes in your thorax force the surrounding air in the box through a hole in the wall into a spirometer. Your healthcare provider will then add the measurements in pressure change or volume displacement together.


Who performs body plethysmography?

A healthcare provider who helps treat conditions that affect your lungs or breathing (respiratory therapist) usually performs body plethysmography in a lung function lab. A pulmonologist reviews and confirms the findings.

Test Details

How does body plethysmography work?

Body plethysmography takes place in an enclosed, airtight, see-through plastic box. As you breathe into a mouthpiece, a sensor inside the box measures any changes to the air pressure. The mouthpiece also has a sensor that measures your airflow and pressure in your mouth.

As your chest expands and contracts while you breathe, the sensor inside the box registers changes in the amount of air and air pressure in the box. The sensor in the mouthpiece also registers changes in pressure.

What does body plethysmography measure?

Body plethysmography measures the following:

  • Total lung capacity (TLC): TLC is the volume of air in your lungs after taking the biggest breath you can.
  • Functional residual capacity (FRC): FRC is the volume of air that remains in your lungs after breathing out normally.
  • Residual capacity (RC): RC is the volume of air that stays in your lungs after breathing out as much as possible.

How is body plethysmography measured?

Body plethysmography uses the relation Boyle’s law to determine the relationship between gas volume and pressure at a constant pressure. You can use gas volume measurements to determine the gas pressure. Conversely, you can use gas pressure measurements to determine the gas volume.

Other names for Boyle’s law include Boyle-Mariotte law and Mariotte’s law.


What should I expect before body plethysmography?

Your healthcare provider will ask if you’re feeling healthy. You should reschedule your appointment if you have a cold, the flu or another contagious respiratory infection.

Tell your healthcare provider about any medications you’re taking. They may tell you to stop taking certain medications on the day of the test.

Your healthcare provider will give you directions on how to prepare for your body plethysmography. These include:

  • Don’t smoke at least one hour before the test.
  • Don’t drink alcohol at least four hours before the test.
  • Avoid any heavy exercise at least 30 minutes before the test.
  • Wear loose, comfortable clothing that doesn’t squeeze your chest or abdomen. You must be able to breathe comfortably, and tight clothing may alter your results.
  • Don’t eat a large meal at least two hours before the test.

These directions will help ensure that your body plethysmography results are accurate.

What to expect during body plethysmography?

During body plethysmography, you’ll sit in an enclosed, air-tight, see-through plastic box. Talk to your healthcare provider if you’re uncomfortable in confined spaces (claustrophobic). They may prescribe a medication for you to take before the body plethysmography to help calm your nerves. They’ll also talk to you throughout the test, and you can see them and everything else around you in the room while in the box. Let your healthcare provider know if you need a break during testing.

Your healthcare provider will place soft clips on your nose. The nose clips help you breathe out only through your mouth. Your healthcare provider will also give you instructions on how to breathe through the mouthpiece.

Once you’re ready, your healthcare provider will seal the door, and the test will begin.

If you usually get additional oxygen through a storage tank or machine (supplemental oxygen), you won’t be on it during the procedure.

Is body plethysmography painful?

No, body plethysmography isn’t painful.

However, you may feel dizzy, lightheaded or tired from breathing in and out deeply. Blowing into the mouthpiece may also cause you to cough. These symptoms should go away shortly after you complete the test. Let your healthcare provider know if you need a break during testing.

In rare cases, you may get too much carbon dioxide in your blood (hypercapnia) or too little oxygen in your blood (hypoxia). These conditions may occur if you spend a long time in the body plethysmography box.

Body plethysmography can also increase your heart rate. Tell your healthcare provider if you’ve had a heart attack in the past or any other conditions that affect your heart.

How long does body plethysmography take?

Body plethysmography takes about 15 minutes to complete.

What to expect after body plethysmography?

After your body plethysmography, you may return to your normal daily activities.

If you felt dizzy or lightheaded during the test, your healthcare provider will monitor your health until your symptoms go away and you can go home.

Results and Follow-Up

What is a normal body plethysmograph?

A “normal” body plethysmograph depends on a few factors, including your:

  • Age.
  • Height.
  • Race.
  • Sex.
  • Tobacco product use.
  • Weight.

Your healthcare provider will use these factors to determine a typical reading for your demographic. As a result, a normal body plethysmograph result for you may be different from the result of another person.

When should I know the results of body plethysmography?

You should expect your body plethysmography results within a few days after taking the test.

When should I call my healthcare provider?

Your healthcare provider will contact you a few days after your body plethysmography to discuss your results. Reach out to your healthcare provider if you don’t hear from them with your results after a few days.

If your body plethysmography helps your healthcare provider diagnose a chronic lung disease, you may have to schedule lung function tests yearly.

Additional Details

What is the difference between spirometry and body plethysmography?

Spirometry is another type of pulmonary function test. It’s the most common test healthcare providers use to determine lung function.

However, it’s not as accurate as body plethysmography. Spirometry doesn’t measure residual lung volume or total lung capacity.

Body plethysmography also measures other characteristics, such as the pressure difference between your mouth and lungs (airway resistance) and the volume of gases in your thorax (intrathoracic gas volume, or ITGV).

A note from Cleveland Clinic

If you notice any changes in your breathing, it’s a good idea to reach out to your healthcare provider. The changes might not be serious or they might be a symptom of a lung condition. Your healthcare provider can use body plethysmography to help diagnose any possible lung conditions. The test is quick and accurate, it isn’t painful and you should get your results within a few days. A proper diagnosis can help you and your healthcare provider determine a healthcare plan that enables you to improve or maintain your quality of life.

Medically Reviewed

Last reviewed on 12/18/2022.

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