Many people with asthma use a peak flow meter to help manage their asthma. However, peak flow measuring may not be for everyone — for example, it is often not suitable for young children. Your doctor will advise you if using a peak flow meter should be part of your ongoing asthma management plan.
A peak flow meter is a simple hand-held device that you can use at home to keep track of your asthma by measuring your lung function. A peak flow meter measures how fast you can blow air out of your lungs. As your airways narrow with asthma, the resistance to air flow increases dramatically — the lower the reading is, the greater the narrowing of your airways. The reading on the meter is called your peak expiratory flow (PEF) or ‘peak flow’, and is measured in litres per minute.
Changes in your peak flow, compared to your best ever recorded (‘personal best’) peak flow, show changes in your asthma control: the lower your peak flow compared to your personal best peak flow, the more your airways are narrowed — doctors often use the word ‘constricted’.
Your doctor can read from a chart an expected peak flow rate for someone of your height, age and sex. More importantly, however, your doctor will want to find out the best possible peak flow that you can manage — your personal best peak flow — which will probably be different from an expected peak flow rate.
To do this, your doctor may ask you to measure your peak flow rate at home, in the morning and the evening, over one or more weeks. By writing down your peak flow on a chart as you go, you will have a set of readings that allows your doctor to work out your current personal best peak flow — a key part of your asthma action plan.
Your doctor may also use these readings to:
In the week or so before any appointment with your doctor, it’s always a good idea to record your peak flow morning and evening, at the same time every day.
Regularly checking your peak flow at home (usually on first waking and again in the evening), along with writing down your symptoms, forms the basis of your asthma action plan. Your doctor will help you decide whether you need to do this every day.
It is especially important to check your peak flow when you are:
When your asthma control is worsening, often your peak flow will fall below your personal best peak flow before your usual asthma symptoms appear. In this way, keeping a check on your peak flow rate can help you pick up a small change in your asthma control. Then, by following your doctor’s instructions on your asthma action plan — about how to increase your medicine and when to see your doctor — you should keep well, and have less chance of getting a serious asthma attack.
If your peak flow is below 80 per cent of your personal best peak flow, and if your morning and evening peak flow scores differ by more than 15 per cent (assuming you are an adult), then your asthma is not being well controlled, and you need to adjust your medicine and see your doctor to help get back on track.
For peak flow measurements to be useful, you must always:
If you don’t follow these measures, your peak flow scores may be unreliable, and could lead to you using the wrong amount of medicine, and losing control of your asthma.
Children under 8 years old can’t always use a peak flow meter reliably, so doctors will usually recommend that their asthma be checked at home by watching and recording their asthma symptoms, rather than their peak flow.
Ask your doctor or pharmacist to check your technique for using your peak flow meter.
Here are some pointers to the correct use of your peak flow meter.
Make sure you keep your peak flow meter clean by washing it in warm soapy water every fortnight, rinsing with clean water and allowing it to dry naturally.
Last Reviewed: 29 April 2009