As someone with
asthma, you know how important it is to monitor your
condition. You need to know how well your lungs are "working." Is their ability
to move air in and out staying the same, or is it getting better or
When you monitor your asthma, you can control it. When you
control your asthma, you also control your life—you do what you want to do, and
your asthma does not limit you.
Peak expiratory flow
(PEF) measures how much air you breathe out when you exhale. It tells you
how well your lungs are working. You measure PEF with a
peak flow meter, an inexpensive device that you can use at home.
If you can breathe out quickly and with ease,
you will have a higher number (higher peak flow rate). Your lungs are working
well, and your asthma is not bothering you.
If you can only
breathe out slowly and with difficulty, you will have a lower number (lower
peak flow). This usually means that your lungs are not working well, even if you
don't have any usual asthma symptoms.
You measure PEF as liters of air per minute.
How often should I measure PEF?
How often you
measure your PEF depends on how severe your asthma is and how often you have
asthma attacks. If you have severe asthma or cannot
tell when you are having asthma symptoms, you may need to check your PEF twice
a day, in the morning and in the evening. If you have mild asthma, you may not
need to check your PEF daily and can instead monitor it by paying attention to
symptoms. But if any asthma symptoms develop, you may need to check your
PEF. Talk with your doctor about how often you check your
Measuring your PEF is important, because it lets you:
Determine your asthma zones, which you use in
your asthma action plan. During an acute asthma attack, the zone you are in
determines your medicine and action.
Know whether an acute asthma attack is going to occur and how
severe it may be. If you know you are going to have an asthma attack, you can
take medicine to prevent it or make it less severe. This may help you avoid
having to go to the emergency room.
Identify things that may
trigger an asthma attack, such as pollen, cigarette smoke, or
Measure changes in your
breathing. This can help your doctor to:
Decide whether you need to change,
increase, or decrease the long-term medicine used in your daily asthma
Tell which medicines are helping your breathing and
which are not.
Test Your Knowledge
Measuring your PEF can help you know if you may have
an asthma attack.
have never used a peak flow meter, talk with your doctor about how
to use it correctly, and then practice using it.
Measure your PEF
regularly, even if you are feeling good. PEF is
lowest in the early morning and highest in the afternoon. When you measure your
PEF once a day, it needs to be done first thing in the morning before you use
your asthma medicine.
It's very important to record the results of
your PEF measurements in your asthma diary. This will help you notice changes
in your breathing. Take your asthma diary with you when you see your doctor so you can review it together. It's very important to review the
diary with your doctor whenever you feel your lung function is
Measuring your peak expiratory flow
any gum or food you may have in your mouth.
Then use your peak flow meter to:
If you have questions about this information, take
it with you when you visit your doctor. Make notes about what you
would like to ask about or discuss.
If you would like more information on asthma, the
following resource is available:
Asthma and Allergy Foundation of America
1233 20th Street NW
Washington, DC 20036
The Asthma and Allergy Foundation of America (AAFA)
provides information and support for people who have allergies or asthma. The
AAFA has local chapters and support groups. And its Web site has online
resources, such as fact sheets, brochures, and newsletters, both free and for
How this information was developed to help you make better health decisions.