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Peak flow meter


Related terms
Author information
How it works
Types of peak flow meters
How to use it
Determining personal best reading
Managing asthma

Related Terms
  • Allergens, allergic asthma, asthma attack, asthmatic, bronchodilator, bronchospasm, chronic lung disease, extrinsic asthma, green zone, inflammation, inflammatory lung disease, lungs, inhaler, intrinsic asthma, lung capacity, lung disease, non-allergic asthma, peak expiratory flow rate, PEF, personal best reading, red zone, spirometer, spirometry, trigger avoidance, wheezing, yellow zone.

  • Asthma is a chronic, inflammatory lung disease that may or may not be triggered by allergens. The air passages within the lungs are constantly swollen, restricting the amount of air allowed to pass through the trachea. Asthmatics have recurrent breathing problems and a tendency to cough and wheeze.
  • While there is currently no cure for asthma, proper treatment and management can help alleviate symptoms.
  • A peak flow meter helps patients monitor their asthma and prepare for asthmatic exacerbations. This portable device measures how well the lungs are able to expel air.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (

  1. American Academy of Allergy Asthma and Immunology. .
  2. American Lung Association. Peak Flow Meter. .
  3. Asthma and Allergy Foundation of America. Asthma. .
  4. Centers for Disease Control. Surveillance for Asthma - United States, 1960-1995, MMWR. 1998; 47 (SS-1). .
  5. Natural Standard: The Authority on Integrative Medicine. .
  6. Ohio State University Medical Center. Peak Flow Meter. .

  • Dr. B.M. Wright created the first meter specifically designed to measure the airflow of the lungs in the late 1950s. Today, the device has evolved to a more portable and cost-affordable version. Currently, there are several different types of peak flow meters, which are available over-the-counter. Individuals should consult their healthcare providers to determine which is best for them.

How it works
  • A peak flow meter is made of a plastic tube with a mouthpiece on the end. A scale is located inside the device to measure the force of air that is expelled from the lungs and blown through the tube. This force, measured in liters per minute, is known as the peak expiratory flow (PEF).

Types of peak flow meters
  • Peak flow meters are most helpful for asthmatics who take asthma medication daily. Children as young as three years old have been able to use a peak flow meter safely and effectively.
  • There are several types of peak flow meters, which are available over-the-counter. A low-range peak flow meter is used for small children, and a standard-range meter is used for older children, teenagers and adults. A physician or pharmacist can help patients determine which type to use. Examples of peak flow meters include: ASSESS®, AsthmaCheck®, POCKETPEAK® and MicroPeak®.

How to use it
  • To use the device, first slide the pointer all the way down to the bottom of the scale. Then stand up, remove any gum or food from the mouth, and take a deep breath. Place the lips over the mouthpiece, making sure there are no gaps for air to escape. Do not put the tongue inside the hole. Blow as quickly and as forcefully as possible into the tube. Do not breathe out slowly or for a long period of time because the device is designed to measure how fast and hard the individual can expel air out of the lungs.
  • Once the air is expelled, take the meter of the mouth, and note the number next to the pointer. If the individual coughs or makes a mistake, the number is not considered an accurate reading. Repeat the procedure twice more, and then record the highest of the three readings. Do not calculate the average. It is recommended that individuals keep a chart, including the date and time of each peak flow reading.

Determining personal best reading
  • Individuals should determine their personal best peak flow reading. This is the highest number the individual can achieve when the asthma is under good control. Good control means that the patient feels healthy and is not experiencing asthma symptoms.
  • Take peak expiratory flow (PEF) readings at least twice a day for two to three weeks. It is recommended that individuals measure their peak flow in the morning and evening, after taking short-acting inhalers, when asthma symptoms occur and any other time the physician suggests. Record the readings when PEF is measured.
  • After two or three weeks, look at the recorded numbers and find the highest reading. This number is considered the personal best peak flow reading. Personal best readings vary among individuals, even if they are the same age, weight and height.
  • Three numbers are calculated from the personal best reading, and they are used to establish three separate "zones." These zones are based on percentages of the personal best reading and are merely guidelines.
  • Green zone: The green zone is more than 80% of the personal best reading. Readings in this zone signal that the asthma is under good control. Medications should be taken as usual.
  • Yellow zone: The yellow zone is 50-80% of the personal best reading. This zone indicates caution because there is some airway narrowing. Individuals are recommended to take a short-acting, quick-relief medication right away to prevent asthma symptoms. Individuals should also consult their healthcare providers to determine whether daily medicines should be altered.
  • Red zone: The red zone is less than 50% of the personal best reading. This signals a medical alert because there is significant narrowing of the airway passages. Individuals should take their quick-relief medication immediately (e.g., oral steroids), and call their physicians or go to the emergency department at the hospital to determine the best course of action.
  • If an individual's peak flow reading increases 20% or more after taking a short-acting inhaled quick-relief medicine, a qualified healthcare provider should be consulted to determine whether another medication or higher doses would help control the asthma symptoms.

Managing asthma
  • The muscles in the upper airways contract during an asthma attack, making it difficult for the lungs to take in and release air. However, this narrowing of the airways does not happen suddenly. In fact, the airway may start to narrow hours before the first symptoms of asthma arise.
  • The peak flow meter can help a patient determine when the airway begins to narrow, possibly before symptoms occur. A 20-30% decrease in an individual's PEF might indicate that asthma mediation is necessary to prevent an asthma attack. Taking medications before symptoms appear may help prevent severe exacerbations.
  • In addition, a peak flow meter can help patients and physicians learn what makes triggers the asthma (makes the asthma worse), decide whether the current treatment plan is working, decide when to add or stop medication(s), and decide whether emergency care is necessary.

Copyright © 2011 Natural Standard (

The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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