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 small, airtight room known as a body box. You will breathe or pant against a mouthpiece. Clips will be put on your nose to shut 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 doctors. 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 some medication before the test.
How to Prepare for the Test
Let your doctor know if you are taking any medications, especially ones for breathing problems. You may have to temporarily stop taking certain medications 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.
How the Test will Feel
The test involves rapid and normal breathing, and should not be painful. You may feel short of breath or light-headed. 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 often used because of its technical difficulties.
Normal results depend on your age, height, weight, ethnic background, and gender.
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.
- Anxiety from being in the closed box
- Shortness of breath
Pulmonary plethysmography; Static lung volume determination; Whole-body plethysmography
Hegewald MJ, Crapo RO. Pulmonary function testing. In: Mason RJ, Broaddus VC, Martin TR, et al, eds. Murray and Nadel’sTextbook of Respiratory Medicine. 5th ed. Philadelphia, PA: Saunders Elsevier; 2010:chap 24.
Reynolds HY. Respiratory structure and function: mechanisms and testing. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 85.
Update Date 8/25/2014
Updated by: Denis Hadjiliadis, MD, Associate Professor of Medicine, Pulmonary, Allergy, and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.