Peak Expiratory Flow and Peak Flow Meter


Peak Expiratory Flow

Peak expiratory flow (PEF) is the maximum speed at which a person can forcibly exhale air from the lungs in a single breath. It helps determine just how open the airways are. Age, gender, size and the condition of the lungs influence normal PEF values.

In healthy people, PEF does not vary much from day to day. In asthmatics however, it will decrease during an asthma attack and when medication is not having the desired effect. The data is particularly useful when several readings can be compared on a daily basis, as it allow asthmatics to monitor whether their respiratory condition is deteriorating and if an attack is imminent. This is why we recommend measuring PEF daily, morning and night.

The data collected is used to determine an asthmatic's personal PEF. A drop that exceeds 10 to 15% of one's PEF - along with symptoms indicating a deterioration of respiratory condition (cough, wheezing, shortness of breath) - is sign of an impending attack or the need to adjust dosage. Dosage adjustments can be made providing they are in line with the doctor's plan of action (see the ACTION PLAN FOR PERSONS WITH ASTHMA handout published by Vigilance Santé).

Peak Flow Meter

PEF is measured with an instrument known as a peak flow meter: a small device fitted with a mouthpiece and a pointer that slides along a graded scale when air is forced out of the lungs.

How to use a peak flow meter

It is recommended that you use your peak flow meter while standing and that you loosen any clothing that may restrict breathing (tie, collar).

  • Make sure the sliding marker is at zero;
  • Take a deep breath;
  • Close lips tightly around the mouthpiece. In one breath, blow as hard as you can;
  • Record result;
  • Repeat 2 other times, making sure the sliding marker is at zero every time;
  • Record the highest of the three readings in your asthma diary (see the ASTHMA DIARY handout published by Vigilance Santé).

Peak Flow Meter Maintenance

To clean the device, leave to soak in warm soapy water for 5 minutes, then rinse under clean running water and allow to dry on a clean towel. The mouthpiece can also be removed and cleaned separately.

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