Lung volume test

A lung volume test is a way of measuring the total amount of air in your lungs. It also measures how much air is left after you have breathed out as much as you can.  The test is sometimes called a body plethysmography.

A lung volume test is used to find out if you have a lung condition that is restrictive or obstructive.  

• If you have an obstructive lung condition, your airways will be narrow. This means your lungs still have air in them after breathing out. Obstructive conditions include COPD and asthma. 
• If you have a restrictive lung condition, your airways won’t expand fully. This means your lungs never fill with air fully. Restrictive conditions include pulmonary fibrosis and sarcoidosis.
   

Your appointment letter will tell you what you need to do to prepare. You may be asked to:  

• take all your medicines as normal, unless your letter tells you not to
• wear loose fitting clothing 
• not smoke 1 hour before the test 
• not drink alcohol 4 hours before the test 
• not eat a large meal 2 hours before the test
• not do any intense exercise 30 minutes before the test.
   

You will sit in a clear box which looks like a shower cubicle. The box is perfectly safe and you will be able to see and speak to your healthcare professional throughout the test. Let them know if you need to stop at any point.

You will wear a clip on your nose to make sure that no air leaves your nose. The test takes between 10 and 30 minutes.

• First, your healthcare professional will ask you to take fast, shallow breaths.
• Then you will breathe in and out normally using the mouthpiece.
• Next you will breathe in fully and blow out to empty your lungs as much as possible. 
• Lastly, you will be asked to take some slow deep breaths in and out.  

The effort you make to breathe changes the pressure inside the box and within your lungs. You will not feel any pressure changes as they are very small. Changes in pressure inside the box are used to find out the amount of air your lungs can hold.

It can take a few tries to get the test right. Don’t worry, your healthcare professional will help you to do this. The test is usually repeated a few times to check that you are getting a true result.
 

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.