Unit 4 > Unit 4 > Peak flow Measurements

Peak flow Measurements          

An individual’s lung and airway function can be assessed by using a hand held peak flow meter.  This measurement is often used to diagnose and monitor asthma.  A peak flow meter is a small instrument that an individual blows into.  It measures the fastest rate of air flow that they can blow out of their lungs.  The air flow is recorded in litres per minute(l/min.)


  • Check that the individual does not have a condition  that may be affected by using the peak flow meter
  • Ensure individual is relaxed physically and emotionally
  • The individual must give their consent for their peak flow measurement to be taken
  • Make sure they are not frightened to have their peak flow measurement taken
  • Use a different mouthpiece for each individual or use sterilised wipes to wipe clean

Taking a peak flow reading for an individual

  • Put the marker to zero
  • Get them to take deep breath
  • They must seal their  lips around the mouthpiece
  • Blow has hard and as fast as they can
  • Record the reading
  • Repeat twice more and record the readings.
  • Do the three blows one after the other , the readings should be about the same.  If they are not then the individual may not be blowing into the peak flow meter correctly.
  • The best reading of the three is the one that is used .
  • An error may occur if the individual:
  • Does not blow as hard as they can
  • Does not put their lips right round the mouthpiece

The normal peak flow reading will vary depending upon an individual’s age, size and sex, even the time of day.  In healthy individuals peak flow readings will vary slightly e.g.  in the morning the reading will tend to be higher than in the evening.  In general peak flow readings are higher in men than women due to their physical size and because they are more muscular.  The taller a person is the higher their peak flow.  The highest peak flow reading for an individual occurs between the age of 30-40 years.  A reading of 400- 600 l/min is considered normal.  An individual suffering with asthma would have a lower reading of 200-400 l/min.

Exercise can increase an individual’s peak flow reading.  This is because exercise makes the lungs stronger and this increases the lungs’ ability to take in oxygen.

Normal values for a peak flow reading