Why It Is Done

Testing your peak expiratory flow (PEF) or your forced expiratory volume at 1 second (FEV1) at home may help:

• Measure how well your lungs are working if you have a long-term (chronic) lung disease, such as asthma.
• Guide the treatment and monitor the effectiveness of treatment for asthma. Peak expiratory flow monitoring provides information to help people with asthma make better treatment decisions.
• Monitor your lung function if you are regularly exposed to substances at work that can damage your lungs (occupational asthma).
• Monitor for early signs of rejection if you have had a lung transplant.

How To Prepare

To perform the peak expiratory flow (PEF) test, you need a peak flow meter. A peak flow meter is an inexpensive handheld device you breathe into as hard and as fast as you can.

Read and follow the instructions included with the peak flow meter. Ask your doctor to show you how to use this device before you use it at home. If you have questions about how to use a peak flow meter or how to read the results, talk with your doctor.

If you use medicine to help with breathing (such as for asthma), talk to your doctor about the amount of time you should wait to test your lung function after taking your medicine. You may need to wait a few hours after taking the medicine to do a lung function test. Or your doctor may recommend that you test your lung function in the morning before you take your medicine.

Avoid eating a heavy meal for about 3 hours before performing a PEF test. Be sure to stand up to help you take as large a breath as you can. Use the same position every time you test your PEF. Peak flow monitoring relies on your trying as hard as you can. For accurate results, be sure to give the test your best effort every time.

How It Is Done

Before you begin to test your peak expiratory flow (PEF), remove any gum or food you may have in your mouth. Follow these steps to use your peak flow meter:

1. Set the pointer on the gauge of the peak flow meter to 0 (zero).
2. Attach the mouthpiece to the peak flow meter.
3. Stand up to allow yourself to take a deep breath. Make sure you use the same position each time you test your PEF.
4. Take a deep breath in. Place the peak flow meter mouthpiece in your mouth and close your lips tightly around the outside of the mouthpiece. Do not put your tongue inside the mouthpiece.
5. Breathe out as hard and as fast as you can using a huff. You do not need to breathe out for more than a second.
6. Note the value on the gauge.
7. Move the pointer on the gauge back to 0 (zero) before you blow again.
8. Blow into the peak flow meter 2 more times. Record your values each time you blow. If you cough or make a mistake during the testing, do the test over.
9. After you have blown into your peak flow meter 3 times, record the highest value on your daily record sheet.

How It Feels

Breathing in and out very quickly during these tests may make you feel lightheaded or may make you cough. If you feel like you are going to pass out, stop the test.

What Affects the Test

The accuracy of peak flow monitoring depends on your effort during the test. Results will be inaccurate if you do not follow directions or do not give your best effort during testing. The following factors also may affect the results of peak flow monitoring:

• Using medicine that expands the airways in the lungs within 4 hours before the test may improve test results.
• Using sedatives before the test may worsen test results.
• People who have pain while breathing may not be able to breathe normally. So the results of their tests may be misleading.

What To Think About

• Your doctor may do a complete series of lung function tests to confirm a lung disease, monitor the progression of lung disease, or monitor the effectiveness of treatment. To learn more, see the topic Lung Function Tests.
• Checking your peak expiratory flow (PEF) provides information that may help you decrease your asthma symptoms and keep your lungs as healthy as possible. The benefits of better lung function may include improved quality of life, fewer emergency department visits, greater personal control and confidence, and reduced use of oral steroid medicines, antibiotics, and bronchodilators. To learn more about controlling your asthma, see the topic Asthma in Teens and Adults.
• When using a home peak flow meter, it is best to use the same meter over time. Different brands of meters give different results. If you change your peak flow meter, you need to redetermine your personal best measurement using the new machine.
• Wash your meter according to the manufacturer’s directions to prevent growth of bacteria and fungi.
• PEF is lowest in the early morning and highest in the afternoon. If you measure your PEF only once a day, do so first thing in the morning before using any bronchodilator medicine.
• People with intermittent or mild persistent asthma may not need to check their PEF every day. But if symptoms develop, checking peak expiratory flow often for a period of time may be helpful in bringing asthma under control.