WebMD
Font Size

Peak Expiratory Flow

Peak expiratory flow (PEF) is a measure of how much air a person can exhale while breathing out as hard and fast as possible. PEF is used to evaluate the condition of the airways in people who have asthma or other conditions that affect their ability to breathe.

When the airways become narrowed because of inflammation or disease, the peak expiratory flow drops. Even before symptoms of asthma occur, a decrease in the peak rate can show that the bronchial tubes have narrowed.

Peak expiratory flow may be measured at home using an inexpensive device called a peak flow meter. Or it may be measured in a doctor's office using a spirometer.

ByHealthwise Staff
Primary Medical ReviewerJohn Pope, MD - Pediatrics
Specialist Medical ReviewerLora J. Stewart, MD - Allergy and Immunology
Last RevisedMarch 14, 2013

WebMD Medical Reference from Healthwise

Last Updated: March 14, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.