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A peak flow meter is a tool that measures the peak expiratory flow rate (PEFR). The PEFR is the amount of air a person can quickly force out of their lungs in one breath.

People can use a peak flow meter to monitor their ability to exhale (breathe out). This can help people with lung diseases including asthma, chronic obstructive pulmonary disease (COPD), chronic bronchitis, and emphysema:

  • learn to manage their condition
  • track changes in their symptoms
  • support young children with respiratory conditions
  • adjust daily medication if necessary
  • identify and avoid triggers for asthma attacks

A peak flow meter is a handheld device that measures how well someone can move air out of their lungs. People can use peak flow meters to determine and track their “normal” peak flow.

This measurement is the peak expiratory flow rate (PEFR) or the peak expiratory flow (PEF).

For people with asthma, a peak flow meter can detect changes in airways that could indicate the risk of an asthma attack even before individuals might notice symptoms.

When readings show that people are no longer reaching their normal peak flow, they need to take action. This can include taking quick relief medication, seeking medical help, or changing their asthma action plans.

To use a peak flow meter, a person must forcefully blow into the device. The meter measures the forced air in liters per minute.

The indicator on the device moves in response to the exhalation and provides a reading on a numbered scale.

A peak flow meter is useful in detecting changes in a person’s airway function, which could indicate a worsening of symptoms of asthma or other respiratory conditions.

People with asthma may develop narrowing of the airways, which lowers the amount of air they can exhale. The PEFR often changes in response to a flare-up of asthma. Weather, exposure to allergens, infection, or even exercise can all affect asthma symptoms.

Regular monitoring with a peak flow meter can help people detect changes in their airways before other symptoms start. In some cases, a decrease in PEFR is an early sign of an impending asthma attack.

In an older 2012 study, 53 people with asthma recorded their symptoms and peak flow measurements twice daily for 274 days. Researchers analyzed the relationship between changes in peak flow measurements and the participants’ asthma symptoms.

The researchers found that some people incorrectly perceived their symptoms as mild, even with significant airway obstruction. The study also indicated that people with poorly controlled asthma had fluctuations in PEFR even without reported asthma symptoms.

Recognizing the signs of an asthma attack through peak flow monitoring alongside following an asthma action plan can prevent symptoms from becoming severe. A gradual decline in PEFR over time can also indicate a decrease in lung function and help a doctor modify an asthma treatment plan.

Learn more about the signs and symptoms of an asthma attack here.

Peak flow meters can also help with other lung conditions, such as COPD. People with COPD may also develop acute narrowing of the airways and inflammation.

By monitoring their PEFR, people with COPD can determine what is normal for them. Just as with asthma, when there is a significant decrease in the peak flow, this is a red flag that something might be triggering an increase in COPD symptoms.

To use a peak flow meter effectively, people must use it consistently. Regular measurements help people determine their personal best peak flow. When changes develop, people can take action to avoid a serious asthma episode.

A person should follow the steps below to get a good peak flow reading:

  • Always use the same peak flow meter.
  • Take the reading while standing.
  • Move the sliding pointer to the bottom of the numbered scale.
  • Put the meter in the mouth, between the teeth, and close the lips around the mouthpiece.
  • Avoid blocking the mouthpiece hole with the tongue.
  • Take a deep breath.
  • Blow out all the air in one breath as quickly and powerfully as possible, as if blowing out candles on a birthday cake.
  • Write down the number on the scale where the sliding pointer stopped.
  • Take two more readings and record the highest number in an asthma diary.
  • Take peak flow readings every morning, or more often if directed to do so by a doctor.

Peak flow predictions vary based on age, height, and gender. However, it is more important for a person to determine their personal best or what is normal for them.

People can determine their personal best by using the device daily for a few weeks and recording the highest number they reach.

Once a person knows their personal best, they can determine whether their peak flow changes. Peak flow results may indicate different things depending on whether the measurement improved, worsened, or stayed the same.

Changes in peak flow may indicate the following:

  • the need to get emergency medical care
  • a flare-up of asthma symptoms
  • the medication is effective
  • a person has well-controlled asthma
  • a need to change daily medication

By measuring the peak flow daily for a few weeks, a person can identify their personal best. Subsequent monitoring of the peak flow involves determining what percentage of their best a person gets during any given measurement.

Peak flow zones interpret peak flow rates and help an individual know what steps they should take to manage their asthma.

According to the American Lung Association, peak flow zones are as follows:

ZonePercentageWhat it signals
Green80–100% of the personal best number
  • Good asthma control.
  • Symptoms are not present.
  • No early warning signs of an asthma flare-up.
Yellow50–80% of the personal best number
  • Symptoms such as a runny nose, coughing, and fatigue might be present.
  • Follow an asthma action plan.
  • People may need to take a fast-acting inhaler.
  • Call the doctor if peak flow does not improve.
RedLess than 50% of the personal best number
  • Medical emergency.
  • Symptoms such as wheezing, shortness of breath, and coughing are usually present.
  • Use a fast-acting inhaler.
  • See a doctor or call 911 if problems with breathing continue.

Mechanical and digital are two of the main types of peak flow meters. Mechanical peak flow meters only measure PEFR. They frequently come with charts that users fill out while they conduct tests.

Digital peak flow meters can measure both PEFR and FEV1, which is the amount of air individuals can exhale in one second.

Accuracy is an important feature for peak flow meters. Researchers evaluating nine different peak flow meters for accuracy found that only two passed: a mechanical peak flow meter, the Mini Wright, and a digital peak flow meter, the Smart Peak Flow.

There are many varieties to choose from online. However, a person should speak with their doctor about the type of peak flow meter that is most suitable for their health needs.

Please note that the writer of this article has not tried these products. All information presented is purely research-based and correct at the time of publication.

The following are common questions and answers about peak flow meters:

What does a peak flow meter measure?

A peak flow meter measures how forcefully someone can push air out of their lungs.

What is a good peak flow rate?

The typical peak flow measurement is between 400–700 liters per minute for adults.

Age, gender, and height affect what is normal or “good” for an individual. For example, younger, taller people tend to have higher readings. An individual’s peak flow measurements can also change throughout the day or in response to specific events.

Regular measurements help people learn what is best for them. Then they can work with their healthcare professionals to make helpful changes before problems get worse.

Is there a difference between a peak flow meter and a spirometer?

The most significant difference is that a medical professional typically uses a spirometer to diagnose respiratory problems, such as asthma and COPD and monitor the effectiveness of treatment plans. A peak flow meter is generally for home use.

With spirometry, a healthcare professional clips the person’s nose shut, and a machine records the readings. With a peak flow meter, the individual records their measurements, and there is no clip on the nose.

Learn about spirometry here.

How do I improve my peak flow rate?

One of the most important things people can do to improve their peak flow rates is to quit smoking. Exercising can also help people strengthen their breathing muscles. However, individuals with respiratory conditions should do so under the supervision of their healthcare professionals.

If someone using a peak flow meter gets a reading that is 50–80% of their normal peak flow, that means they have entered the “Yellow Zone.” Yellow Zone readings could mean an individual’s airways are narrowing, and their asthma treatment plan needs adjusting.

A peak flow meter reading that is 50% or less of someone’s normal peak flow should trigger a medical alert and means the individual is in the “Red Zone.” People should take their quick-relief medication and call their doctor immediately. If their symptoms do not improve, they should call 911 or go to their nearest emergency room.

A peak flow meter is a small device that measures the amount of air a person can forcefully blow out of their lungs in one rapid breath. It is an indicator of airways changes in people with asthma or COPD.

A person should speak with a doctor to get a peak flow meter. They may provide one or recommend a type to purchase.

A person’s peak flow measurement can indicate a worsening of respiratory symptoms. Although it is only one test, it can be a useful tool to determine the treatment needed, including emergency medical care.