Spirometry is the most common type of pulmonary function or breathing test. This test measures how much air you can breathe in and out of your lungs, as well as how easily and fast you can the blow the air out of your lungs.
Your doctor may order spirometry if you have wheezing, shortness of breath, or a cough. This can help diagnose problems like asthma and COPD, or can be done to check lung function before a surgery. You may also have spirometry done if you are being treated for a chronic lung disease, such as COPD, asthma, or pulmonary fibrosis, to determine if your disease is improving or worsening and whether your medications or inhalers are working properly. Spirometry can be done in the doctor’s office or in a special pulmonary function testing lab.
What to Expect
On the day of the test, you may be asked to not use certain inhalers or medications. Wear loose clothing and avoid big meals before testing.
These tests are not painful. They are performed by a pulmonary function technician. The tests are repeated several times to make sure the results are accurate. When performing the test, keep the following in mind:
- You should take your daily medications prior to testing unless told otherwise.
- Do not smoke for at least six hours prior to testing.
- If you are taking a short-acting inhaler that is used only as needed, do not use for six to eight hours prior to testing, if possible.
- Your doctor may give you other instructions regarding medications.
During the test, you will be sitting upright. A clip is placed on your nose and you will be given a plastic mouthpiece connected to the spirometry machine. You will place your lips tightly around the mouthpiece and be asked to take in as big and deep a breath as possible and then blow out as hard and fast as you can. This maximal effort is very important, and testing will be repeated at least three times to get the best results.
The technician may give you a medicine to help open your airways and then repeat the test to see if your breathing improves with the medicine. The testing takes about 30 to 45 minutes.
Understanding the Results and What Happens Next
Spirometry will give your doctor information about why you may have a cough, shortness of breath, or noisy breathing and help diagnose certain lung problems. After the test, you can return to your normal daily activities.
Normal values are calculated based on age, height and gender. If a value is abnormal, a lung problem may be present. Sometimes a patient with normal lungs may have a breathing test value that is abnormal. Your doctor will explain what your test results mean. Depending on the results of the test, your doctor may prescribe inhalers or medicines to help improve your lung function. The testing may be repeated at future visits to monitor your lung function.
What Are the Risks and When It Should Not Be Done?
During the test, breathing fast and hard can make you feel tired, cough, feel dizzy or light-headed, or have chest tightness or pain. You should let the technician know if you have any discomfort.
You should let your doctor know if you've had a heart attack within the past month. You should also tell your doctor if you have had recent eye, chest or abdominal surgery, have had a collapsed lung or have tuberculosis. If you’ve had any of these, your doctor may wait until you recover before doing the testing.
Special steps are taken to avoid spreading germs between patients who use the same lung function equipment. The technician will change mouthpieces and other equipment between patients. Special filters are also used to prevent the spread of germs.
Be sure to ask if you have any questions before the test is started.
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Updated by: Denis Hadjiliadis, MD, MHS, Paul F. Harron Jr. Associate Professor of Medicine, Pulmonary, Allergy, and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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Updated by: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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.
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