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Peak expiratory flow rate

Peak expiratory flow rate

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Overview | Risks | Results

Alternative names:

Peak flow; peak expiratory flow

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.

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). 

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Peak expiratory flow rate

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