Educational Content: This article is for informational purposes only and does not constitute medical advice. Always consult a healthcare provider for diagnosis and treatment.
Definition of Peak expiratory flow
Medically reviewed by Min Clinic Staff | Updated: January 2026
Peak expiratory flow: Abbreviated PEF. The maximum airflow during a forced expiration beginning with the lungs fully inflated. The PEF is reduced in proportion to the severity of the airway obstruction, as in asthma and COPD (chronic obstructive pulmonary disease).