This document discusses peak expiratory flow rate (PEFR), including its purpose, measurement steps, and significance. PEFR is measured using a peak flow monitor to assess, diagnose, manage, and determine prognosis of lung diseases like asthma. It involves preparing the device, standing up straight, taking a deep breath, and blowing hard into the mouthpiece to measure airflow in L/min. Normal PEFR values vary based on age, sex, and height but are generally above 500 L/min for adult males and 400 L/min for adult females. PEFR tests allow patterns in airflow to be monitored over time to help adjust medications or identify environmental triggers.