The readings on a peak flow meter tell you how open your airways are, so you can manage your asthma1.
What is a peak flow meter?
A peak flow meter is an inexpensive, portable, handheld device for people with asthma that is used to measure how well air moves out of your lungs. Measuring your peak flow using this meter is an important part of managing your asthma symptoms and preventing an asthma attack and should form part of your personal asthma action plan2.
Why should I measure my breath strength? Peak flow is a measure of how fast you can blow air out of your lungs when you exhale forcefully after inhaling fully. This measure is called a "peak expiratory flow," or "PEF." Keeping track of your PEF, is one way you can know if your asthma are in control or worsening1. Then, in conjunction with your prescribed asthma treatment plan, you can take appropriate action to bring your asthma back under control.
Monitoring asthma If your asthma isn’t affecting you, you will have airways that are open, so you’re able to blow air out of your lungs quickly, which will give you a high peak flow reading. However, if asthma is not controlled, the airways will narrow and you will not be able to blow air out so fast, which will give you a lower peak flow reading.
How is it measured2? Peak flow is measured using a small handheld device called a peak flow meter. The scale is in units of liters per minute (lpm). When you blow into the mouthpiece the small marker will move depending on how fast you are blowing. Where the marker ends up, is your peak flow reading. The highest reading from three attempts should be recorded as your personal best peak flow reading.
Your healthcare professional will set the color zone indicators based on your or your child’s personal best peak expiratory flow rate (the best peak flow measurement achievable when asthma is under control). The peak flow measurement will fall into one of three zones, as shown below.
How is my personal best peak flow number determined?3
The "personal best" peak expiratory flow (PEF) is the highest peak flow number you or your child can achieve over a two to three week period when asthma is under good control. Good control means you feel good and do not have any asthma symptoms.
Your personal best PEF is important because it is the number to which all of your other peak flow readings will be compared. Your asthma action plan, developed along with your healthcare professional, is based on this number.
You should always use the same peak flow meter and write your readings in your peak flow chart. Then, continue to take peak flow readings each morning. Daily readings will help you to recognize early drops in airflow and changes with asthma control.
To find your personal best peak flow number, take peak flow readings:
Twice a day for two to three weeks when asthma is in good control
At the same time in the morning and in the early evening
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