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Peak expiratory flow rate
Definition:
The peak expiratory flow rate measures how fast a person can exhale air. It is one of many tests that measure the function of the airways, which are commonly affected by diseases such as asthma, or chronic obstructive pulmonary disease (COPD, usually a combination of emphysema and chronic bronchitis). In these lung diseases, air flow during exhalation is decreased by narrowing or blockage of the airways. The severity of asthma of COPD can change with time, and peak expiratory flow monitoring is used by many patients to monitor their lung function at home. This allows them to anticipate when their breathing will become worse and to take appropriate medications or call their health care providers before symptoms become too severe.

Alternative Names:
Peak flow; peak expiratory flow

How the test is performed:
This test requires a peak expiratory flow monitor, a small hand-held device with a mouthpiece at one end and a scale with a moveable indicator (usually a small plastic arrow). Breathe in as deeply as possible. Blow into the instrument's mouthpiece as hard and fast as possible. Do this 3 times, and record the highest flow rate.
How to prepare for the test:
Loosen any tight clothing that might restrict your breathing. Sit up straight or stand while performing the tests.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test will feel:
There is usually no discomfort. Rarely, repeated efforts may cause some lightheadedness.
Why the test is performed:
Home testing may be useful in monitoring the progress of a disease such as asthma, emphysema, or chronic bronchitis. It can assess the effectiveness of various treatments or detect the onset of an exacerbation or flare (worsening of lung function).
Normal Values:

Normal values vary considerably according to a person's age, sex, and size. Peak flow measurements are most useful when a person is able to compare the peak flow obtained on a day-to-day basis. A fall in peak flow, especially when accompanied by symptoms such as increased cough, shortness of breath, or wheezing, may signal the onset of a flare of lung disease, requiring early treatment to prevent complications.
What abnormal results mean:
If you note that you peak flow is decreasing, you should advise your healthcare provider and take any steps you and your provider have previously outlined.
What the risks are:
There are no significant risks.
Special considerations:

Peak expiratory flow rate measurements are not as accurate as the spirometry measurements performed in a health care provider's office. Small changes in your peak flow may not mean significant changes in your lung function.
Review Date: 2/5/2002
Reviewed By: David A. Kaufman, M.D., Pulmonary & Critical Care Medicine, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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