Body Plethysmography: What It Measures, How It's Done and Results
Updated: 2 days ago
Written and medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: November 2026 · How we review
Quick Answer: What is body plethysmography?
Body plethysmography is a noninvasive pulmonary function test done inside a sealed, see-through booth. As you breathe through a mouthpiece, sensors calculate your total lung capacity, the air left in the lungs after breathing out and airway resistance. It takes about 15 minutes, is painless and helps diagnose and monitor asthma, COPD and pulmonary fibrosis.
What the research says
Plethysmography remains the reference method for static lung volumes. A systematic review of 22 studies found that quantitative CT scans underestimated total lung capacity by an average of 709 mL (12.1%) compared with plethysmography and overestimated residual volume by 603 mL. Spirometry-gated CT narrowed the gap to 70 to 280 mL. (Olsen and Mortensen, European Clinical Respiratory Journal, 2024) [2]
Your "normal" values depend on your height, age and sex. In 244 healthy never-smoking adults, total lung capacity was predicted mainly by height, while residual volume rose with both age and height, which is why labs compare your numbers with reference equations for people like you. (Lessa et al., Jornal Brasileiro de Pneumologia, 2019) [3]
Key takeaways
Body plethysmography measures lung volumes that spirometry cannot, including residual volume and total lung capacity. [1]
You sit inside an airtight, see-through box and breathe through a mouthpiece for about 15 minutes. [1]
It helps diagnose and track asthma, COPD and pulmonary fibrosis, and checks lung function before surgery. [1]
Avoid smoking, alcohol, heavy meals and hard exercise shortly before the test. [1]
Results usually come back within a few days and are compared with values for your age, height and sex. [1]
What is body plethysmography?
Body plethysmography, also called lung or pulmonary plethysmography, is a pulmonary function test that measures how much air your lungs can hold and how hard your airways make it to move that air. You sit inside an enclosed, airtight, transparent box while a mouthpiece sensor and sensors in the box record changes in airflow, pressure and volume. [1]
The test relies on Boyle's law, which links the pressure and volume of a gas. From those pressure changes the machine works out lung volumes that other tests cannot measure directly. [1]
The main measurements a body plethysmography test provides.
What body plethysmography measures
Measurement | What it means |
Total lung capacity (TLC) | All the air in your lungs after the deepest breath in |
Functional residual capacity (FRC) | Air left in your lungs after a normal breath out |
Residual volume (RV) | Air left after breathing out as fully as you can |
Airway resistance | The pressure difference between your mouth and lungs as air moves |
Intrathoracic gas volume | The volume of gas inside your chest |
Sources: [1]
Why is body plethysmography done?
Providers order the test to diagnose lung and airway diseases, compare your results with earlier tests, watch how a chronic lung disease is changing, check whether substances at work or home have harmed your lungs, and judge whether you can tolerate surgery. [1]
You may need it if you have chest tightness or pressure, a cough (especially with mucus), trouble taking a deep breath, shortness of breath or wheezing. Conditions it helps evaluate include asthma, COPD and pulmonary fibrosis. [1]
Body plethysmography vs spirometry
How body plethysmography differs from spirometry.
Spirometry is the most common pulmonary function test, but it measures only the air you can move in and out. It cannot measure residual volume or total lung capacity, and it is less accurate than plethysmography. Body plethysmography also measures airway resistance and the gas volume in your chest. [1] Research confirms it is the preferred method for static lung volumes because it also captures trapped gas, a common finding in COPD. [2]
How do you prepare for body plethysmography?
Reschedule if you have a cold, flu or another contagious respiratory infection. [1]
Tell your provider about all your medicines; you may be asked to skip some on test day. [1]
Do not smoke for at least 1 hour before the test. [1]
Do not drink alcohol for at least 4 hours before the test. [1]
Avoid heavy exercise for 30 minutes and large meals for 2 hours before the test. [1]
Wear loose clothing that does not restrict your chest or belly. [1]
What happens during body plethysmography?
What to expect during the test.
Your provider checks that you feel well and reviews how you prepared. [1]
You sit inside the airtight, see-through box. You can see the provider and the room the whole time. Tell them beforehand if you feel claustrophobic. [1]
Soft clips go on your nose so you breathe only through your mouth, and the provider shows you how to use the mouthpiece. [1]
The door is sealed and the test begins. As you breathe, sensors measure pressure and volume changes from your chest moving, and the mouthpiece measures airflow and mouth pressure. [1]
You can ask for a break at any time. If you normally use supplemental oxygen, you go without it during the test. [1]
A respiratory therapist usually runs the test in a lung function lab, and a pulmonologist reviews the results. The test takes about 15 minutes. [1]
Body plethysmography at a glance
Item | Typical detail |
Test time | About 15 minutes |
Setting | Lung function lab, inside a sealed transparent booth |
Pain | None |
Who performs it | Respiratory therapist; a pulmonologist reviews the results |
Results | Usually within a few days |
Sources: [1]
What are the risks of body plethysmography?
The test is safe and painless. Deep breathing may leave you dizzy, lightheaded or tired, and blowing into the mouthpiece can make you cough; these fade soon after. Rarely, a long time in the box can raise carbon dioxide or lower oxygen in your blood. The test can raise your heart rate, so tell your provider if you have had a heart attack or have a heart condition. [1]
What do body plethysmography results mean?
There is no single normal number. Your provider compares your values with reference ranges based on your age, height, sex, weight and tobacco use. [1] Studies show that total lung capacity depends mainly on height, while residual volume rises with age and height. [3] An abnormal result can confirm that a condition stops your lungs from holding as much air as they should. [1]
Results are usually ready within a few days, and your provider will contact you to discuss them. If the test helps diagnose a chronic lung disease, you may need lung function tests every year. [1]
When should you call a doctor?
Call your provider if you have not heard about your results after a few days, or if you notice any change in your breathing. The change may not be serious, but it can signal a lung condition. [1]
Conclusion
Body plethysmography is a quick, painless way to measure lung volumes and airway resistance that spirometry cannot capture. It helps diagnose asthma, COPD and pulmonary fibrosis, track how they change and judge whether surgery is safe. [1]
Preparing well, by avoiding smoking, alcohol, big meals and hard exercise beforehand, gives the most accurate result. Ask your provider how your numbers compare with the expected range for you. [1]
Keep learning: Read our guide to pulmonary function tests to see how this test fits with spirometry and other lung tests.
Frequently asked questions
What is body plethysmography?
It is a lung function test done inside a sealed, transparent booth that measures lung volumes and airway resistance.
What does body plethysmography measure?
Total lung capacity, functional residual capacity, residual volume, airway resistance and the gas volume in your chest.
How long does body plethysmography take?
The test takes about 15 minutes, and usually fewer than 20.
Is body plethysmography painful?
No. You may feel dizzy or tired from deep breathing, but the test itself does not hurt.
How do I prepare for body plethysmography?
Do not smoke for 1 hour, drink alcohol for 4 hours, exercise hard for 30 minutes or eat a large meal for 2 hours before the test.
What is the difference between spirometry and plethysmography?
Spirometry measures the air you move in and out. Plethysmography also measures residual volume, total lung capacity and airway resistance.
Can I do the test if I am claustrophobic?
Yes. The box is see-through, and your provider may prescribe a calming medicine beforehand.
What conditions does body plethysmography help diagnose?
Asthma, COPD and pulmonary fibrosis, among other lung and airway diseases.
When will I get my results?
Results are usually available within a few days.
What is a normal body plethysmography result?
It depends on your age, height, sex, weight and tobacco use; your provider compares your values with reference ranges.
Related Reading
DLCO Lung Diffusion Test: Purpose, Normal Range and Results explains the breathing test that shows how well oxygen moves into your blood.
Pulmonary Function Tests (PFTs): Types, Preparation and What Your Results Mean explains the full family of lung tests that body plethysmography belongs to.
Spirometry: What the Lung Function Test Measures, How It's Done and What Results Mean covers the most common lung function test and how it differs from plethysmography.
What Is Chronic Obstructive Pulmonary Disease (COPD)? Symptoms, Causes, Stages, and Treatment explains the lung disease that often shows trapped air on plethysmography.
Asthma: Symptoms, Causes, Triggers, Diagnosis & Treatment — Complete Guide covers asthma, one of the conditions the test helps diagnose.
Pulmonary Fibrosis: Symptoms, Causes, Diagnosis, and Treatment Explained describes lung scarring that lowers total lung capacity.
References
Cleveland Clinic. Body Plethysmography: Purpose, Procedure & Results. Cleveland Clinic. Last updated December 18, 2022. https://my.clevelandclinic.org/health/diagnostics/15467-body-plethysmography-pulmonary-function-test
Olsen HJB, Mortensen J. Comparison of lung volumes measured with computed tomography and whole-body plethysmography - a systematic review. Eur Clin Respir J. 2024;11(1):2381898. PMID 39081799. https://doi.org/10.1080/20018525.2024.2381898
Lessa T, Pereira CAC, Soares MR, et al. Reference values for pulmonary volumes by plethysmography in a Brazilian sample of white adults. J Bras Pneumol. 2019;45(3):e20180065. PMID 31166555. https://doi.org/10.1590/1806-3713/e20180065
Medical disclaimer
This article is for general education only and does not replace advice from a qualified healthcare professional. Talk to your doctor about your own diagnosis and treatment, and seek emergency care right away for severe or sudden symptoms.
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