Test Overview

A home lung function test uses a peak flow meter or a home spirometer to monitor and evaluate any breathing problems you may have on a day-to-day basis. A peak flow meter allows you to measure your peak expiratory flow. A home spirometer allows you to measure your forced expiratory volume at 1 second (FEV1).

If you have a lung disease, such as asthma, your doctor may test your peak expiratory flow (PEF) to measure the amount of air you can inhale and quickly exhale. This is tracked to see how well asthma is managed.

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 hand-held 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 to learn how long 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 the 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 before performing a PEF test. Be sure to sit up or stand up as straight as possible 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 start, remove any gum or food you may have in your mouth.

1. Set the pointer.

   Be sure the gauge of the peak flow meter is set to 0 or the lowest number on the meter.

2. Attach the mouthpiece to the meter.

   Some meters don't have a separate mouthpiece.

3. Sit up or stand up as straight as you can, and take a deep breath.
4. Close your lips tightly around the mouthpiece.

   Keep your tongue away from the mouthpiece.

5. Breathe out as hard and as fast as you can for 1 or 2 seconds.

   A hard and fast breath usually makes a "huff" sound.

6. Write down the number on the gauge.

   This is your peak flow.

7. Repeat these steps 2 more times.

   Write down the highest of the three numbers in your asthma diary.

If you cough or make a mistake during the testing, redo the test.

How It Feels

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

Risks

There are no significant risks linked with measuring peak expiratory flow (PEF). Breathing in and out very quickly during the test may make you feel light-headed or may make you cough. If you feel light-headed, stop the test.

Results

Results from a peak flow meter or home spirometer can be compared to monitor the progression of disease or help measure your response to medical treatment for a long-term (chronic) lung disease, such as asthma.

Peak flows are compared to charts that list normal values based on age, sex, race, and height. They also can be compared with your personal best measurement. Check with your doctor or read the information included with your peak flow meter to find your normal range, which will vary depending on the type of breathing problems you may have. If you find abnormal results on any of the tests, discuss them with your doctor.

• Normally, peak flows vary slightly throughout the day. They are usually lower in the morning and higher in the afternoon.
• A person with poorly controlled asthma may have peak flows that vary more widely throughout the day.