The peak flow meter measures the amount of airflow in the airways (breathing tubes). The peak flow rate is the rate of airflow in the breathing tubes when a person inhales fully and blows the air out as quickly as possible. For the test to be useful, the peak flow rate must be reproducible (the person must be able to repeat the same flow rate at least three times).

There are many kinds of peak flow meters. The same peak flow meter must be used every time to make sure the changes in airflow are measured correctly. Peak flow rate measurements help determine if the airway is closing or opening up.

Peak flow rates decrease (the numbers on the scale go down) when your child's asthma is getting worse or is out of control. Peak flow rates increase (the numbers on the scale go up) when the asthma treatment is working and the airways are opening up. The use of peak flow rate measurements can help you to recognize when your child's airway is narrowing, so asthma treatment can be started early. Peak flow rates also will help you identify some of the "triggers" (causes) for your child's asthma, so they can be avoided.

There are differences in peak flow rate measurements at different times of the day. Measuring your child's peak flow rate twice a day shows how much your child's peak flow rate changes throughout the day. Children of different sizes and ages have different peak flow rate measurements.

How To Measure the Peak Flow Rate

1. Have your child take a deep breath and fill his or her lungs with air.

    

2. Have your child blow into the peak flow meter as fast and as hard as possible.

    

3. Read the number on the peak flow meter scale and write the number down on a piece of paper.

    

4. Measure the peak flow rate again and write the numbers down (measure the peak flow rate a total of three times.)

    

5. At a time when your child is able to do his best, draw a circle around the best (highest) of the three measurements. This is your child's "personal best" peak flow rate. This value may need to be changed periodically as your child grows or improves, or both.

Your pediatrician suggests you measure your child's peak flow rate:

_____twice daily, morning and evening

_____at the time of asthma symptoms

Your child's personal best peak flow rate is:__________

Green (safety) asthma zone: __________
(80 percent or more of personal best peak flow rate)

Yellow (caution) asthma zone: __________
(50 percent to 80 percent of personal best peak flow rate)