Peak flow meters allow patients to monitor their asthma; Peak Expiratory Flow (PEF) is a measurement of how fast a patient can blow out. When a patient is well their PEF is higher, when the airways are narrow (as in asthma) PEF is lower.The first choice for measuring Peak Expiratory Flow of healthcare professionals worldwide, the Mini-Wright is the original portable peak flow meter and has been a globally recognised brand for many years