Peak expiratory flow rate

Definition

The peak expiratory flow rate measures how fast a person can breath out (exhale) air. It is one of many tests that measure the how well your airways work.

Alternative Names

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.

How the test will feel

There is usually no discomfort. Rarely, repeated efforts may cause some lightheadedness.

Why the test is performed

The test is commonly used to diagnose and monitor lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), emphysema, or chronic bronchitis. Home monitoring can be used to determine if treatments are working or detect when a condition is getting worse.  

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 take and compare peak flow measurements 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. This may require early treatment to prevent complications.

What abnormal results mean

Air flow during exhalation is decreased when the airways are narrowed or blocked. Peak expiratory flow monitoring can be 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.

If you note that your peak flow is decreasing, you should tell your healthcare provider.

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.