Peak flow meters are small, hand-held devices that show how well a patient is breathing and is often used as part of an asthma action plan to measure lung function.

The asthmatic patient takes as deep of a breath as possible and blows into a tube to measure how fast they can blow out - resulting in the peak flow number.

It's important that a peak flow meter is used regularly as the values will vary from patient to patient and what's important is how a day's reading compares to the best they've achieved and don't forget to remember what your best is.

The comparison between a reading and this personal best simply and clearly shows whether the asthma is under control or not.

The peak flow meter is able to also help warn of a asthmatic episodes before symptoms occur.

If it is apparent that breathing is deteriorating, via the readings of the peak flow meter, they can immediately follow their plan and take their relief treatments or other medications as the doctor has directed.

Additional peak flow readings can then monitor how well they are responding to the treatment.

As an example (above), if the patient is a woman aged 58, who has a height of 61 inches (5 foot, 1 inch, or 154 cm (1.54 m), then their predicted Peak Flow is roughly 430 litres per minute.