Peak Expiratory Flow and Personal Best in Asthma
Peak expiratory flow (PEF) measures how fast you or your child can breathe out using the greatest effort. It is used in the monitoring and treatment of asthma to determine how well your lungs are functioning. Your peak flow drops when the tubes that carry air to the lungs (bronchial tubes) narrow. A decrease in the peak flow can show that the bronchial tubes have narrowed even before asthma symptoms develop. Peak expiratory flow is measured with a peak flow meter, an inexpensive device that can be used at home.
Peak expiratory flow is lowest in the early morning
and highest in the afternoon. If you or your child takes the test only one time
during the day, take it first thing in the morning, before using a
bronchodilator medication. Record the PEF in your
asthma diary
(What is a PDF document?).
Developing an Asthma Action Plan
An asthma action plan is a written plan developed by your doctor or asthma specialist to help you or another family member, including teenagers and children, manage asthma and prevent asthma attacks. The plan is designed to tell you or other family members what to do when there are changes in the severity of asthma symptoms and in peak flow numbers.
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PEF varies throughout the day. In a person who does not have asthma, it may vary between 10% and 15%. In a person who has poorly controlled asthma, it may vary more than 20%.
Peak expiratory flow rates are compared with charts that list normal values for sex, race, and height.
Personal best
A person's personal best is his or her highest peak flow. This is the number you use to find the correct asthma zones. The personal best is used in the written plan that says what to do during a sudden increase in asthma symptoms (asthma attacks). If you do not know your or your child's personal best, talk to your doctor.
You determine your or your child's personal best by taking PEF readings over 2 to 3 weeks when the asthma is under control-when you or your child feels good and has no symptoms. During these weeks, peak expiratory flows should be recorded at least twice daily. The personal best is usually reached in the afternoon or evening. Personal best measurements are never measured during an asthma attack.
Your personal best is the highest reading you have over this period of time.
Personal best measurement needs to be evaluated once in a while to see whether it has changed. If it decreases, medicines may need to be changed or increased to prevent asthma from becoming worse. If personal best measurement improves significantly, the amount of medicine may be reduced. Children need to have their personal best measurement checked about every 6 months to account for growth.
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