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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 primarily use PEFR measurements as a guide for managing asthma symptoms.

However, doctors may also recommend peak flow measurements for people with chronic obstructive pulmonary disease (COPD) to determine an increase in symptoms.

This article looks at how peak flow meters work, their benefits, and how to use them.

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A person may use a peak flow meter to measure the amount of air they can quickly force out of their lungs in one breath.

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.

Recording peak flow measurements is a part of asthma action plans to help treat the condition. A peak flow meter is useful in detecting changes in a person's airway, which could indicate a worsening of symptoms of asthma.

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, and infection can all lead to a change in a person's asthma.

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

A 2012 study involved 53 people with asthma who 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 if they had 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, and 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.

Along with its uses for asthma, a peak flow meter can also be helpful with other lung conditions, such as COPD. People with COPD may also develop 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.

It is vital to use a peak flow meter properly and put forth a good effort to get an accurate measurement. Peak flow meters have slightly different designs depending on the manufacturer, but they all require the same procedure.

People should take a peak flow measurement while standing up. To use a peak flow meter, follow these steps:

  1. Make sure that the indicator or pointer is set to zero.
  2. Take a deep breath.
  3. Put the flow meter in the mouth with the tongue down, out of the way of the mouthpiece, and close the lips around the mouthpiece.
  4. Blow out hard and fast. The indicator will move in response to the exhalation.
  5. Check the number on the scale next to the pointer or indicator. This is the peak expiratory flow.
  6. Move the indicator back to zero and repeat twice more.
  7. Record the best of the three attempts in a chart or notebook.
  8. Measure the peak flow at the same time each day for a few weeks to determine personal best.

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

According to the Asthma and Allergy Foundation of American, people can determine their personal best by using the device daily for a few weeks and recording the highest number they can reach.

Once a person knows their personal best, they can determine whether or not their peak flow changes. The results of a peak flow 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 is getting 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 to follow include:

ZonePercentageWhat it signals
Green80–100% of personal best number
  • Good asthma control.
  • Symptoms are not present.
  • No early warning signs of an asthma flare-up.
Yellow50–80% of 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 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.

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 fast breath. It is one indicator of airways changes that may occur in people with asthma or COPD.

To get a peak flow meter, speak to a doctor. They may give you one or recommend a type to purchase. There are many varieties to choose from online.

A person's peak flow measurement can indicate a worsening of their asthma symptoms or those of a lung condition. Although it is only one test, it can be a useful tool to determine the treatment needed, including emergency medical care.