Peak Expiratory Flow Rate (PEFR) is an objective measure of the degree of bronchial obstruction. It allows the monitoring of the asthmatic patient on an outpatient basis and must also be part of the clinical examination of all patients in the same way as blood pressure and heart rate. This does not exclude respiratory function controls (one to two per year) in all asthmatics.
The PEFR is the maximum flow obtained during an expiration carried out after the maximum inflation of the chest. The normal PEFR value varies according to age, size, and sex (standards provided with the devices), around 450 I/min for women, and 600 I/min for men. Its value depends on the degree of bronchial obstruction, and the air that is in the rib cage. If the patient has not inflated his chest enough, the peak expiratory flow will be reduced. It also depends on the muscular effort deployed during expiration.
The values given are valid for ages between 15 and 99 years old, and a height greater than 150cm. The values are however very variable according to the individuals, and several tables exist. The table used here is the Nunn and Gregg nomogram.
In the event of an asthma crisis, the severity is assessed based on the predicted percentage of PEFR.