This leaflet answers common questions about having a lung function test. If you would like further information, or have any worries, please do not hesitate to ask your nurse or doctor.

In all cases, a respiratory physiologist will explain the tests to you and answer any questions you may have. In most cases it will be possible for a friend or relative to accompany you for all or part of the test. Please ask your nurse or doctor.

What is a lung function test?

Lung function tests (spirometry) are breathing tests to assess how well your lungs are working. Lung function tests are carried out by respiratory physiologists. They aim to measure how well you can get air in and out of your lungs, how well oxygen gets from the lungs into the blood and the total size of your lungs.

What will happen at the appointment?

The tests will last approximately 45 minutes, unless an inhaler is also given, in which case it may last up to 60 minutes. We start by checking your recent medical history to make sure it is safe to perform the tests. We also check your height and weight so that we can interpret the results correctly. The tests are performed using a mouthpiece attached to the measuring equipment, and you will wear a nose clip so that no air can pass through your nose.

Spirometry test

We will ask you to breathe normally through a mouthpiece and then take in as big a breath as you can. When we see that you are completely full of air, we will then ask you to either blow the air out like a sigh or blast the air out as quick as you can until your lungs are empty. Once they are empty, we will ask you to breathe back in as fast as possible until your lungs are full.

Gas transfer test

You will be asked to breathe normally on the mouthpiece, with your lips creating a tight seal with a nose clip on. You will then be instructed to blow all the air out of your lungs until they are completely empty. Then you will be asked to take a breath in until your lungs are as full as possible and hold your breath for up to 10 seconds. Finally, you will blow out till empty, keeping your lips tight throughout.

Lung volume test

You will be asked to sit inside a cubicle with the door closed throughout the test. Please note the door is not locked and can be opened voluntarily at any point if required. You will then be asked to breathe slightly quicker than normal on the mouthpiece whilst holding your 2 cheeks and with a clip on your nose. After 30 to 60 seconds a shutter will block the mouthpiece for two seconds.

During this time, you will be asked to pant softly against the blockage. After two seconds, the shutter will lift and you will then be asked to breathe in fully and then blow all the way out to empty your lungs in a controlled manner, like a sigh. The test finishes with a big breath back in to fill your lungs.

How to prepare for the test

  • Please take all medication including inhalers as normal (unless otherwise stated in your appointment letter).
  • Avoid smoking for 24 hours before the test.
  • Avoid tight clothing.
  • Avoid eating a large substantial meal at least two hours before the test.
  • Avoid drinking alcohol for at least four hours before the test.

After the test

Your results will be sent to your referring doctor for them to review and discuss with you if necessary.

Risks and side effects

Due to the nature of the tests and the exertion required, some patients may feel dizzy or faint during testing. Coughing is also common. Serious complications are rare and risks will be kept to a minimum by your physiologist.

Potential but very rare complications include:

  • Airway narrowing in those with sensitive airways.
  • Heart attack in patients with previous cardiac disease.
  • Sudden changes in blood pressure.
  • Stroke.
  • Collapsed lung.
  • Retinal detachment.

You will be questioned by your physiologist prior to having the tests to check whether you are at an increased risk.