Peak Flow Measurement: A Crucial Tool

What is a peak-flow meter?

A peak-flow meter is a small, hand-held device that measures the force of air that your breath blows out. If you have asthma, the meter can tell an important story. A strong, hard breath means your asthma is under control. But if a small, weak breath is all you can muster, asthma may be squeezing your airways.

How do I use a peak-flow meter?

Peak-flow meters are simple to use. Even children as young as three can quickly master them. Each meter has a marker that moves along a numbered scale. (The scale measures the force of your breath in liters per minute.) Move the marker to zero. Then stand up straight, take a deep breath, clamp your lips tightly around the mouthpiece, and blow through your mouth as hard as you can. You want a single, short blast of air, not a long, drawn-out breath. Picture yourself knocking down a house, not cooling off your soup.

After you’ve huffed and puffed, write down the reading from the scale. Then repeat the whole process two more times. If you’ve done it correctly, all three readings should be fairly similar. Ignore the two lowest numbers and record the highest number. This is your “peak flow.”

Who needs a peak-flow meter?

Peak-flow meters can be useful if you have moderate to severe asthma and need to get a better grip on your disease. The meter helps you track your progress, adjust your medications, and even stop attacks before they happen.

For instance, if the readings are high day after day, you may be able to cut back on your medications, according to your doctor’s instructions. But if the meter shows you’re having trouble, you may need extra treatments to manage your disease. A sudden, steep drop may signal an oncoming attack. With the advance warning, you can prevent the attack by inhaling a “quick-relief” medication that opens the airways.

But not every person with asthma needs a peak-flow meter. If your disease is already well-controlled and you rarely have attacks, you may not need to regularly monitor your breathing. Ask your doctor if a meter is right for you.

How often should I use my peak-flow meter?

This is up to you and your doctor. Many people take two measurements each day, one in the morning and one in the evening. Whatever your schedule, you should measure yourself at close to the same time each day.

You should also use your meter during situations that are especially hard on your lungs. For instance, if you sometimes have an attack while exercising, check your breathing before and after you work up a sweat. If your airways are already tight, you may have to skip the workout. You can also check your breath in the middle of the workout to see if an attack is on the way. Likewise, if cat dander makes you wheeze, you may want to check your airways before visiting a house with cats in it.

How should I interpret the results?

To know what your readings mean, you have to know your “normal” peak flow. Your doctor can estimate this based on your age, height, sex, and race. You can also use your personal best as the benchmark. Your doctor can help you decide what’s “normal” for you.

Now you’re ready to interpret the results of your peak-flow meter. If your reading is within 20 percent of normal, you’re in the “green” zone. That means your asthma is under control. If your peak-flow is between 50 percent and 80 percent of normal, the “yellow” zone, your airways are narrowing and you may need a quick relief medication right away to prevent an asthma attack. You should also take other steps — such as adjusting your daily medications under your doctor’s supervision, or avoiding things that trigger attacks — to better control your disease. If your reading is less than half of normal, the “red” zone, you’re having a serious attack and could be in danger. Take your quick-relief medication and call your doctor or an emergency room right away. You and your doctor should discuss how to handle yellow and red zone readings ahead of time, so that you are prepared to act quickly if necessary.

Keep in mind that peak-flow meters can break down from time to time. If your reading puts you in the red zone but you feel fine, take the meter to your doctor for adjustment.


Autio L, Rosenow D, Effectively managing asthma in young and middle adulthood. Nurse Pract 24(1):100-2, 105-6, 108-11; quiz 112-3.

Turner MO, Taylor D, Bennett R, Fitzgerald JM. A randomized trial comparing peak expiratory flow and symptom self-management plans for patients with asthma attending a primary care clinic. Am J Respir Crit Care Med;157(2):540-6.

Stoloff SW, Janson S. Providing asthma education in primary care practice. Am Fam Physician; 56(1):117-26, 131-4, 142.

National Heart, Lung, and Blood Institute and National Asthma Education and Prevention Program. Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma.

American Lung Association. Peak Flow Meters.

© HealthDay