What Is a Body Plethysmography?

Medically Reviewed by Melinda Ratini, MS, DO on August 08, 2023
Written by WebMD Editorial Contributors
4 min read

Body plethysmography is testing that's done to determine how much air your lungs can hold. It goes by other names, too, such as pulmonary plethysmography, static lung volume determination, or pulmonary function testing. It helps doctors diagnose certain conditions, track treatment progress, and more. 

To screen for abnormalities. Medical staff will compare recent test results with previous results or against standards. They'll see if your lungs are working as expected or if there's something new to be concerned about. ‌

To monitor chronic diseases. If you’re currently being treated for a condition involving your lungs, body plethysmography will show how severely the condition affects the lungs themselves. It can help your doctor decide whether your treatments are (still) appropriate.  

Some conditions that may warrant body plethysmography include: 

To assess environmental impact. The results of body plethysmography can show if you’re being exposed to dangerous substances at home or work. Fumes or toxic materials can cause problems with your breathing. 

Chemicals, gases, and toxic dust particles that you come in contact with may produce abnormal results from testing. Your doctor will likely want to explore your situation further.

To determine fitness for other procedures. Body plethysmography can help your doctor decide whether you can go through surgery or other complex medical procedures. If you have problems breathing, you may be at risk for complications. 

You are placed in an apparatus called a volume-constant whole-body plethysmograph. It’s a clear, all-glass box about the size of a telephone booth. It has an airtight seal and a controlled leak that is used to stabilize the pressure within. 

How it works. The plethysmograph measures the changes in pressure and volume of the container as you breathe in and out. A secondary device is used to measure the pressure at your mouth while you breathe. Medical staff study the pressure changes to check for possible abnormalities. ‌

What to expect. You’ll likely be asked to breathe in different ways, such as quickly or at normal speed. Such constant breathing may make you feel faint or short of breath. Trained medical staff will be there throughout the session in case you need help. ‌

The mouthpiece used to measure your mouth pressure may be uncomfortable. But the test should never cause you real pain at any point. ‌

If you have claustrophobia — feel ill at ease or worse than that in tight or enclosed spaces — you may have a problem with the test. The walls of the plethysmograph are clear, so you’ll be able to see outside the box. But you may become anxious.

It typically takes a few minutes for a doctor to get results from body plethysmography. Depending on the results, they may ask you to stay in the plethysmograph longer and provide more evidence. 

Several lifestyle choices can influence the effectiveness of body plethysmography. Your doctor will likely give you this advice: 

  • Don’t wear tight clothing, because it can hinder your breathing. 
  • Report all medications, because there are some you shouldn’t take prior to the test. 
  • Say whether you have the flu, a cold, or other illness. 
  • Don’t drink alcohol for at least four hours prior. 
  • Don’t eat a big meal within two hours prior.
  • Don’t smoke for at least one hour prior.
  • Don’t exercise for at least 30 minutes prior. 

Depending on your situation, your doctor may suggest not smoking or exercising heavily for up to six hours prior. All of these preps will help ensure accurate test results. 

Abnormalities in the results suggest lung problems. Body plethysmography doesn’t find the source of the problems, but it will help your doctor eliminate certain possibilities. 

Problems that can cause abnormal results can include: 

  • A breakdown or deterioration of the lungs
  • Problems with the chest wall muscles
  • Issues that prevent the lungs from expanding and contracting properly

COPD. Body plethysmography is a good test for diagnosing COPD. Since it tests the lung capacity and function of the airways, it’s able to catch a variety of symptoms that COPD causes. 

Symptoms of COPD include: 

  • Difficult breathing 
  • Wheezing
  • Chronic cough
  • Tight chest
  • Chronic respiratory infections

After your test, you may be lightheaded or short of breath. Take the time you need before leaving your doctor to feel like you normally do. 

‌Unless further testing is needed, you can typically return to your daily activities after your test. 

Further testing. If your doctor detects any abnormalities, they may suggest other pulmonary function tests. These include: 

  • Spirometry, a simple breathing test
  • Gas exchange testing, a measurement of how oxygen passes from the lungs into your blood
  • Maximal voluntary ventilation, a test of the maximum amount of air you can breathe in one minute
  • Six-minute walk test, cardiopulmonary exercise testing, and other functional breathing tests
  • Compliance testing, to measure lung elasticity

‌Depending on the results of additional testing, your doctor may suggest a chest X-ray or CT scan to detect severe lung conditions such as emphysema or lung cancer. Body plethysmography is just one of the steps toward a diagnosis.