Lung plethysmography is a test used to measure how much air you can hold in your lungs.
How the Test is Performed
You will sit in a large airtight cabin known as a body box. The walls of the cabin are clear so that you and the health care provider can see each other. You will breathe or pant against a mouthpiece. Clips will be put on your nose to close off your nostrils. Depending on the information your doctor is looking for, the mouthpiece may be open at first, and then closed.
You will breathe against the mouthpiece in both the open and closed positions. The positions give different information to the doctor. As your chest moves while you breathe or pant, it changes the pressure and amount of air in the room and against the mouthpiece. From these changes, the doctor can get an accurate measure of the amount of air in your lungs.
Depending on the purpose of the test, you may be given medicine before the test to most accurately measure the volume.
How to Prepare for the Test
Let your doctor know if you are taking any medicines, particularly ones for breathing problems. You may have to temporarily stop taking certain medicines before the test.
Wear loose clothes that allow you to breathe comfortably.
Avoid smoking and heavy exercise for 6 hours before the test.
Avoid heavy meals before the test. They can affect your ability to take deep breaths.
Let your doctor know if you are claustrophobic.
How the Test will Feel
The test involves rapid and normal breathing, and should not be painful. You may feel short of breath or lightheaded. You will be monitored at all times by a technician.
The mouthpiece may feel uncomfortable against your mouth.
If you have trouble in tight spaces, the box might make you anxious. But it is clear and you can see outside at all times.
Why the Test is Performed
The test is done to see how much air you can hold in your lungs during rest. It helps your doctor determine if a lung problem is due to damage to the lung structure, or a loss of the lungs' ability to expand (get bigger as air flows in).
Although this test is the most accurate way to measure how much air you can hold in your lungs, it is not always used because of its technical difficulties.
Normal results depend on your age, height, weight, and sex.
What Abnormal Results Mean
Abnormal results point to a problem in the lungs. This problem can be due to a breakdown of the lung structure, a problem with the chest wall and its muscles, or a problem with the lungs being able to expand and contract.
Lung plethysmography will not find the cause of the problem. But it helps the doctor narrow down the list of possible problems.
Risks of this test may include feeling:
- Anxiety from being in the closed box
- Short of breath
Pulmonary plethysmography; Static lung volume determination; Whole-body plethysmography
Bhakta NR, Kaminsky DA. Pulmonary function testing: physiologic and technical principles. In: Broaddus VC, Ernst JD, King TE, et al, eds. Murray and Nadel's Textbook of Respiratory Medicine. 7th ed. Philadelphia, PA: Elsevier; 2022:chap 25.
Chernecky CC, Berger BJ. Pulmonary function tests (PFT) - diagnostic. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:944-949.
Review Date 7/31/2022
Updated by: Denis Hadjiliadis, MD, MHS, Paul F. Harron Jr. Professor of Medicine, Pulmonary, Allergy, and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.