Lung volume test (body plethysmography)

A lung volume test measures your total lung capacity. This is the total amount of air in your lungs after you have taken a full breath in.

Lung volume is measured in litres. The average lung capacity of a healthy adult is about 6 litres. But this varies depending on your age, height and sex.

It also measures how much air is left in your lungs after you have breathed out as much as you can.

A body plethysmography (PLETH-iz-MOG-ruh-fee) lung volume test is the best way to measure lung volume.

It can help give healthcare professionals information to help diagnose and manage lung conditions, including asthma and COPD (chronic obstructive pulmonary disease).

A lung volume test is used when healthcare professionals want to know:

• the amount of air you can breathe in and out
• the air left inside your lungs when you take a full breath out.

You may have this test as part of a full lung function test, alongside spirometry and single breath gas transfer tests. But you may also have body plethysmography as a single test.

The test is used for children too.
 

Check your appointment letter carefully for anything you need to do to prepare for the test. You may be able to take all your inhalers and medicines as normal.

If you’ve had a chest infection recently, or you’ve been taking antibiotics, you may need to wait before having the test. You can ask to change your appointment.

Your results are based on your age, height, sex, ethnicity, and level of fitness. Results will change from person to person.

The results may tell you if you have an obstructive or restrictive lung condition. You will then need other tests to see what the main cause of this is.