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Peak Expiratory Flow (PEF)

The peak expiratory flow (PEF) is the maximum speed that you can forcefully exhale the air from your lungs. It reveals your lung functions and the level of asthma control. When asthma is not under control, the bronchi will contract and the peak expiratory flow will decrease. If it is well controlled, your bronchi will expand, airflow will increase and so will the peak expiratory flow.

How to measure PEF?

A simple way to do this is with a peak flow meter. You can use it in a clinic or at home. Generally, children aged 6 or above can learn to use this meter properly.

PEF helps:

  • Doctors make a diagnosis to determine whether you have asthma.
  • Judge whether your asthma is controlled and monitor how you react to the treatment.
  • Identify any worsening of the asthma condition.

It is sometimes difficult to judge by our feeling whether our asthma is getting worse. Checking our PEF daily will give us more accurate and objective data. If the PEF continues to fall, an attack could take place at any time. We may need extra medicine when asthma starts to worsen. This prevents it from accelerating and triggering a more serious attack.

How to use a peak flow meter?

  1. Set the indicator to zero.
  2. Take a deep breath.
  3. Place the mouthpiece in your mouth; blast the air out as hard and as fast as possible.
  4. Record the reading.
  5. Repeat steps 1 to 3 three times and record the highest of the three readings.
  6. Measure your PEF every morning and evening. If the two readings differ greatly, this shows that the disease is not well controlled.

If you have any questions, please check with you doctor on how to use the peak flow meter and what you should do in case of any worsening of your condition.

Both children and adult peak flow meters are available at The Hong Kong Asthma Society. For enquiries, please call 2895 6502.