Lung function tests
What are lung function tests?
Lung (or pulmonary) function tests are performed for a variety of reasons: diagnosing airway obstruction, measuring reactions to treatments for asthma or chronic obstructive pulmonary disease, and determining the severity of your asthma.
Your doctor may ask you to perform tests to help develop an asthma management plan. You may perform peak flow tests yourself at home (using your peak flow meter) as part of monitoring the success of your treatment and the status of your asthma. Your doctor will instruct you in how to do the test and record the results. You may also be tested with a spirometer in your doctor’s surgery or local laboratory.
Who needs lung function tests?
Lung function tests are part of the routine diagnostic work-up and management of patients with respiratory conditions such as asthma and chronic obstructive pulmonary disease (emphysema and chronic bronchitis), and include spirometry tests and peak flow meter measurements.
What is spirometry?
Spirometry is a test of lung function that measures the amount of inhaled and exhaled air using a device called a spirometer. It gives a measure of the maximum amount of air you can breathe out (after taking a deep breath in) and how much you can breathe out in one second. A spirometer issues a graph of respiratory movements and function known as a spirogram.
What is a peak flow meter?
Peak flow meters measure the greatest speed that can be reached when you breathe out through the meter as hard and fast as possible from the biggest breath in you can manage.
Your doctor may use a peak flow meter to monitor your asthma and management progress regularly, but spirometry is the test of choice for doctors to determine the severity of asthma at any given point in time.
You can use your own peak flow meter to conduct peak flow measurements at home as part of your asthma management plan. Peak flow readings should always be done using the same peak flow meter as there is variation among different meters.
What is my doctor measuring when I take a lung function test?
Your doctor or respiratory physician wants to determine how well your lungs are functioning and there are a few measurements they can take using a spirometer, including the following.
- Forced vital capacity (FVC): This is the total amount (volume) of air expelled from the lungs after a full breath into the lungs (to total lung capacity). The person then breathes out quickly and hard, trying to push all the air out of the lungs.
- Forced expiratory volume in one second (FEV1): This is the amount (volume) of air expelled in one second after a full breath into the lungs and then breathing out hard and fast, as above, trying to push all the air out of the lungs.
- Peak expiratory flow (PEF): This is the greatest speed that can be reached when you breathe out through the meter as hard and fast as possible from the biggest breath in you can manage.
Preparing for a lung function test
- You should be aware that the amount of effort you put in can influence the accuracy of your lung function tests.
- You should breathe in as much as you can before exhaling as hard as you can, unless your doctor instructs you otherwise.
- Always sit up straight or stand up, as instructed by your doctor.
- Wear loose clothing that will not interfere with your breathing.
- You may be asked to refrain from using puffers or certain other medicines prior to the test.
- Be aware that your doctor may get you to repeat the test several times to get accurate readings, or to check the effects of your medication.
Last Reviewed: 23 August 2009
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