Peak flow meters

A peak flow meter is a useful tool for people who have asthma. This hand-held device measures the maximum or “peak” speed at which air can be exhaled from the lungs. During an asthma episode, the peak flow is slowed because the airways are partly blocked.

As early as 24 hours before asthma symptoms appear, your breathing already may be affected. The peak flow meter can detect this change, so you can start medications before wheezing or coughing even begins.

Even children as young as three years old can learn to use a peak flow meter. Usually, the readings are taken right after waking up in the morning and again before going to bed. You also may be asked to take a reading before and after you take inhaled medications. Your doctor can help you determine the best testing times.

Steps for using the peak flow meter

Peak flow zones

Peak flow readings are divided into three zones – green, yellow and red – such as a traffic light. Your doctor will help determine your “personal best” peak flow, then use this number to set the three zones for an asthma action plan. See the chart below for more information about peak flow zones.