Lungs at Work

Peak flow monitoring

What is a "peak flow"?

A “peak flow” is a lung function test which tells us how quickly you can blow air out of your lungs. It is a quick and simple test you can do yourself using a peak flow meter, a small handheld device. 

What is a "peak flow diary"?

A healthcare professional may ask you to complete a “peak flow diary”. This is when you measure and write down your peak flow reading several times a day for a few weeks. This helps us to assess how your lung function might change in different places, such as at and away from work. Completing a peak flow diary can be repetitive, but it is very important to help us diagnose conditions such as occupational asthma.

What do I need to complete a peak flow diary?

We will provide you with a peak flow meter if you haven’t got one, and diary sheets.

Repeat the below steps each time you measure your peak flow:

  1. If safe for you to do so, always measure your peak flow whilst standing up.
  2. Pull the pointer (red arrow) back to the start before every blow. Do not to obstruct the pointer with your hand.
  3. Take a deep breath in, make a tight seal with your mouth around the mouthpiece, then blow as hard and fast as you can into the meter.
  4. Note which number the arrow is pointing to on the scale.
  5. Do this 3 times in a row so you get 3 readings at each hour done. Write down the highest of the 3 readings on your chart – you can round to the nearest ten.

Measure your peak flow 6 times a day, for 4 continuous weeks

You can also watch a video on how to measure your peak flow on the Asthma and Lung UK website.

Remember:

  • Complete the diary sheet correctly and as much as you can every day. This includes your working hours and any relevant exposures, any inhalers used, and any difficulties with your breathing.
  • Do not miss any days. Do measurements every single day in the specified period, including days at and away from work, weekends, and holidays.
  • If you use inhalers, then measure your peak flow just before you use your inhaler rather than immediately after.
  • Only do measurements whilst you are awake.
  • You don’t need to measure at the same time each day – just throughout the whole waking day.
  • You can wash the peak flow meter with warm soapy water if needed, and let it air dry.

As soon as you have completed your peak flow diary, you need to share it with the healthcare professional who requested it so it can be analysed in time for your next clinical review. 

If you are a patient in our NHS Occupational Lung Disease clinic (Royal Brompton Hospital), please send your peak flow diary to the nurse as soon as you have completed it, by any of the following methods:

  • By email: gstt.OCLDAdmin@nhs.net (preferred)

  • By post: If posting the sheets to us, please ensure you keep a copy of the original sheets in case they get lost in the post!

    T Kabir
    Department of Occupational and Environmental Medicine
    National Heart and Lung Institute
    Guy Scadding Building
    Cale Street
    London SW3 6LY