Definition of Peak expiratory flow rate:

The peak expiratory flow rate measures how fast a person can breathe out (exhale) air. It is one of many tests that measures how well the lungs are working.

How the test is performed:

This test requires a peak expiratory flow monitor: a small handheld device with a mouthpiece at one end and a scale with a moveable indicator (usually a small plastic arrow).

To perform this test:

• Breathe in as deeply as possible.
• Blow into the instrument's mouthpiece as hard and fast as possible.
• Do this three 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 light-headedness.

Why the test is performed:

The test is commonly used to diagnose and monitor lung diseases such as:

• Asthma
• Chronic obstructive pulmonary disease (COPD)
• Rejection after a lung transplant

Home monitoring can help determine whether treatments are working or detect when your condition is getting worse.