Lung plethysmography is a test used to measure how much air you can hold in your lungs.

See also:

• Limb plethysmography
• Plethysmography

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 be breathing against the mouthpiece in both the open and closed positions - they 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.

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.

The test involves rapid and normal breathing, and should not be painful. However, 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.

The test is done to see how well your lungs work. It can help 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).

Normal values depend on your age, height, ethnic background, and gender. Normal results are given as a percentage.

Abnormal results point to a problem in the lungs. This problem can be due to a breakdown of the lung structure, or an inability of the lungs to expand.

Lung plethysmography will not find the cause of the problem. However, it will help the doctor narrow down the list of possible problems.

• Dizziness
• Light-headedness
• Shortness of breath

Gold WM. Pulmonary Function Testing. In: Mason RJ, Murray J, Broaddus VC, Nadel J, eds. Textbook of Respiratory Medicine. 3rd ed. Philadelphia, Pa: Saunders Elsevier; 2005: chap 24.

Wagers SS, Jaffe EF, Irvin CG. Development, Structure, and Physiology in Normal and Asthmatic Lung. In: Adkinson NF Jr., ed. Middleton's Allergy: Principles and Practice. 6th ed. Philadelphia, Pa: Mosby Elsevier; 2003: chap 44.