What is a peak flow meter?

October 5, 2017
A peak flow monitor helps asthma patients manage their health from home.

Measuring lung function is important for people with asthma. Frequent testing allows you to have a better understanding of your asthma and identify any chances in your condition. A peak flow meter provides a fast and simple way of measuring whether or not your airways have narrowed.

Here’s everything you need to know about a peak flow meter.

A peak flow meter is a handheld device used to measure how fast you can exhale air.

What is a peak flow meter? 

A peak flow meter is a handheld device used to measure how fast you can exhale air from your lungs. The test involves blowing as hard as you can into the device, with the resulting score measuring the number of litres of air breathed out per minute.

The test measures your peak expiratory flow (PEF). When asthma is well controlled and your airways are open, your PEF will be higher. If airways are narrowed as a result of asthma, the PEF reading will fall, as it is more difficult to exhale with force.

As well as being inexpensive and portable, the peak flow meter is easy to use, allowing asthma sufferers to take daily recordings of their peak flow from home. This enables closer monitoring of breathing capacity and is superior to a single recording taken under the supervision of a doctor.


People with asthma can monitor their condition closely with a peak flow meter.

Why is it important to measure peak flow?

The peak flow meter is a useful tool to determine treatment options, whether your medication is working and even what triggers your asthma attacks.

Your doctor can use your monitoring results to make a more accurate diagnosis of asthma and act as a gauge to understand the severity of the condition. Using a peak flow meter to measure your PEF in your day-to-day life can give your doctor a more accurate overview of lung function than by only taking readings in the clinic. The peak flow readings patients take themselves can help to assess the best course of medical care and their subsequent response to that treatment.

Peak flow readings can also help to identify when asthma is getting worse. The readings may alert you and your healthcare team that you require an increase in medication to effectively manage your condition. The early warning signs flagged by the peak flow meter can be a good indicator of when you need to seek emergency care. Relying solely on changes in symptoms to treat asthma attacks can delay increasing or starting medication, which can be dangerous for patients.

Changes in asthma symptoms can be triggered by a change in treatment, other health issues such as a common cold, or external factors such as a change in the weather. Measuring peak flow before and after exposure to one of these triggers may help you to identify whether or not it is affecting you.

Knowing your personal best peak flow reading makes it easier to identify when your asthma is worsening.

Regular monitoring also helps determine the best PEF you can achieve. Knowing your personal best peak flow reading makes it easier to identify when your asthma is worsening and to put together an action plan that involves increasing treatment when symptoms start to decline. An action plan laid out by your doctor empowers you to make decisions about your treatment at home and also makes it clearer when you should seek emergency help.

Who should measure peak flow? 

Patients with any degree of asthma can benefit from using a peak flow meter to manage their symptoms and possibly even prevent asthma attacks.

While patients with mild asthma may only need to take a PEF reading when their asthma flares up, a regular PEF recording is a good idea for anyone suffering from moderate to severe asthma. People who have recently experienced an acute asthma attack should continue measuring their peak flow until readings have returned to a more normal level and symptoms have stabilised.

Keeping a peak flow diary with a record of each reading is an effective way of understanding when your asthma is well managed, and when you may need to take action.

Monitoring your PEF can help you understand when your asthma is under control and when you need to take action.