What is a peak flow meter and why is it useful?

A peak flow meter is a small plastic device with a measuring gauge along the side, which measures how fast you can blow air out of your lungs. People with asthma can use the meter to get baseline measurements of their normal peak flow, which can then be used to help monitor their condition; to assess the effectiveness of their asthma medicine; and to assist in self-management (by following their doctor's advice for low peak flow readings).

What does a peak flow measurement tell us?

The speed and force that you can blow air out of your lungs depends on how open your airways are. If you are well, the airways are open and your peak flow reading is high. If the airways are tight, such as when your asthma is playing up, your peak flow reading will fall.

Why should I use a peak flow meter?

A peak flow meter will tell you how well your lungs are functioning. However, it is not a standalone tool and it should be used in conjunction with the following symptom assessment:

• are you sleeping through the night and not waking with asthma symptoms?
• are you using your reliever inhaler more than three times a week?
• is asthma stopping you from doing your usual activities? 

What is a normal peak flow reading?

You need to know what your best peak flow reading is when you are well. How fast anyone can blow air out of the lungs depends on:

• size - the taller you are, the faster you blow
• age - the reading gets higher as a child grows up, reaching a peak at about 20 years and falling steadily after that
• sex - males have higher readings than females.

Your doctor, practice nurse or asthma educator (health professional) can work out what your peak flow reading should be, based on your height, age and sex.

Who should use a peak flow meter?

A peak flow meter is useful in asthma management, and not recommended in COPD (chronic obstructive pulmonary disease) management. 

Reliable readings are not usually obtained in very young children (under 6 years). Children should first master the use of their inhaler (inhalation) before using a peak flow meter (exhalation).

Where do I get a peak flow meter?

You can obtain a peak flow meter, free of charge, from your doctor or local medical centre.

What are the benefits of using a peak flow meter?

• It helps you to identify asthma symptoms and triggers
• You can find out if your asthma treatment is having the effect that it should
• Your peak flow diary is a record you can show the doctor on the next visit, especially if you are not as well as usual
• When used with your self management plan, it means that you are in control of your asthma.

How do I use a peak flow meter?

• Sit upright or stand up
• Slide the marker on the peak flow meter to the mouthpiece end (as far as it will go) 
• Hold the meter level
• Keep your fingers from obstructing the marker
• Take a deep breath in
• Put the meter in your mouth and close your lips tight around the mouthpiece, making a good seal. Keep your tongue away from the mouthpiece
• Blow the air out of your lungs as hard and fast as you can, with a strong huff
• Note your reading from the marker level
• Repeat these steps twice more
• Record the highest of the 3 readings
• If you find that your first blow is always the best, then you only need to blow once
• Ask your doctor, nurse or asthma educator to check you are using the meter correctly.

When should I use a peak flow meter?

Initially, you should take your peak flow readings before using your inhalers every morning and again in the evening, for two weeks. Your doctor can then see if your values are as high as they should be. You may choose to either make a graph or keep a diary of these readings and how you feel.

• If your peak flow values are high, your doctor may tell you to reduce your medication.
• If your peak flow values are low, your doctor may change your medication or increase the number of puffs you are taking.
• If your treatment is altered, it is important to keep using your peak flow meter to monitor any changes.

Important times to take readings

When you are well and your peak flow reading is at its best and steady, you won't have to use your meter every day.

Peak flow meters should be used when:

• you have a runny nose or feel a cold coming on
• you just don't feel as well as usual
• you know you've been exposed to one of your asthma triggers (ie, that makes asthma worse) 
• your treatment has been changed
• you have had a recent acute asthma attack (keep recording until readings are normal and symptoms stabilise)
• before you visit your doctor. 

What to do if your readings are down

Ask your doctor to write you a self management plan, which tells you what to do if your readings drop and your asthma symptoms increase. If you follow your plan and your readings still keep dropping, see your doctor. 

Keeping the meter clean

Follow the manufacturer's instructions. Generally, wash it in warm soapy water, rinse, shake and leave to dry. Clean the peak flow meter every few weeks when in use.

Replacement is recommended every one to two years - every year if they are used frequently.

Examples of peak flow readings

There are two main ways of recording, either on a graph or just writing down the figures in columns.

Here are some examples of what to look for in your peak flow diary and the action which may be written in your self management plan.

Related topics

Also see: Puffers and other devices and Asthma medicines

Original material provided by the Asthma Foundation of New Zealand, 2003, 2010. Edited by everybody, November 2010.