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Asthma and the peak flow meter

A peak flow meter measures how much air a person can blow out of their lungs over a set period of time, and is often an important part of managing asthma.

The peak flow measure checks the peak expiratory flow (PEF).

Keeping track of these readings in a peak flow diary is a useful way check whether asthma symptoms are getting worse or better.

Boy Blowing Into Spirometer

Why use a peak flow meter?

Readings from a peak flow meter can help you or your child recognise early changes that may be signs of worsening asthma. During an asthma attack, the muscles in the airways tighten and cause the airways to narrow. The peak flow meter alerts you to the tightening of the airways often hours or even days before you have any asthma symptoms. This allows you to know when to take your rescue or quick-relief asthma inhaler or other asthma medication. By taking rescue medications before you have symptoms of an asthma attack, you may be able to stop the narrowing of the airways quickly and avoid an asthma emergency.

The peak flow meter can also be used to help you:

  • Learn what triggers your asthma
  • Decide if your asthma action plan is working
  • Decide when to add or adjust asthma medications
  • Know when to seek emergency medical attention

It is important to know that your peak flow meter only measures the airflow out of the large airways of the lungs. Changes in airflow caused by the small airways (which also occur with asthma) will not be detected by a peak flow meter. Early warning signs, however, may be present. Therefore, it is important for you to also be aware of your symptoms and early warning signs to best manage your asthma.

How do I use the peak flow meter for asthma?

A peak flow meter is simple to use for tracking your asthma. Here's what you do:

  1. Stand up or sit up straight
  2. Make sure the indicator is at the bottom of the meter (zero)
  3. Take a deep breath in, filling the lungs completely
  4. Place the mouthpiece in your mouth, lightly bite it with your teeth and close your lips on it. Make sure your tongue is away from the mouthpiece
  5. Blast the air out as hard and as fast as possible in a single blow
  6. Remove the meter from your mouth
  7. Record the number that appears on the meter and then repeat steps 1 to 6 twice
  8. Record the highest of the 3 readings in an asthma diary - this reading is your PEF

To ensure the results of your peak flow meter are comparable, be sure to use your meter the same way each time you take a reading.

How often should I check my peak flow?

Peak flow values are most useful when they are checked at the same time each day, preferably once in the morning and again at night.

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