What is a lung volume test?
A lung volume test is a way of measuring the total amount of air in your lungs, and how much air is left after you have breathed out as far as you can.
What’s it used for?
A lung volume test helps your health care professional to find out more about what’s happening in your lungs. It can tell them if your lung condition is restrictive or obstructive:
- If you have an obstructive lung condition, there is a narrowing of the airways inside your lungs. Your lungs never empty of air completely and more air than normal stays in your lungs after you breathe out. Examples of obstructive conditions are COPD, asthma, bronchitis and bronchiectasis.
- If you have a restrictive lung condition, you cannot fill your lungs fully with air. That’s because your lungs are restricted from expanding fully, as they have lost their elasticity. Examples of restrictive conditions are pulmonary fibrosis and sarcoidosis. Sometimes this may also be seen in people who have a curvature of the spine or changes to shape of their ribcage, or in people who are obese.
What happens during a lung volume test?
To measure your lung volume, you will sit in a sealed, clear box which looks like a shower cubicle. It’s sometimes called a body-box which can sound a bit alarming, but it is perfectly safe. You’ll wear a clip on your nose to make sure that no air escapes from your nose.
People sometimes worry that they will have to sit in a box. You’ll be able to talk through an intercom to the health care professional performing the test throughout. Let them know if you are anxious. The tests only takes about 5 minutes.
During the test you will be asked to pant, taking rapid shallow breaths for a few seconds. You will also be asked to put your hands firmly onto your cheeks, to stop them puffing in and out. You will then breathe in and out normally using a mouthpiece for a short time and then take some slow deep breaths in and out.
The effort you make to breathe causes changes in the pressure inside the box, as well as within your lungs. You will not feel any pressure changes, as they are very small. Changes in pressure inside the box are measured, and used to calculate your lung volume.
It can take a few goes to get the technique for the test right. Don’t worry, the health care professionals are very experienced at helping people to do this. The lung volume test is usually repeated 3 to 5 times to check that you are getting a consistent result. You may be asked to practise the breathing technique before the actual measurement starts.
The method used to measure lung volumes may vary depending on your condition or the equipment that is available at your hospital.
What will the results look like?
Lung volume is measured in litres. Your predicted total lung capacity (TLC) is based on your age, height, sex and ethnicity, so results will differ from person to person. Normal results typically range between 80% and 120% of the prediction.
If your lung volume results fall outside of this normal range, this may suggest you have an obstructive or restrictive lung condition.
High lung volume
When the lung volume is higher than normal, this may mean there is too much gas in your lungs - called lung hyperinflation. This is when gas gets trapped in the lungs and makes them inflate too much. Lung hyperinflation can happen with obstructive conditions like COPD, bronchitis and bronchiolitis.
In people with COPD, if the tests show that there is a lot of trapped gas, bronchodilators may help to reduce this.
If you have chronic bronchitis or bronchiectasis, tests will indicate mucus in the airways. In this case, physiotherapy is the solution.
Low lung volume
If your lung volume is lower than normal, this may be a sign of a restrictive lung condition such as pulmonary fibrosis or sarcoidosis.
We're currently reviewing this information. An updated version will be available soon.