92 Peak expiratory flow (PEF)
Peak expiratory flow (PEF) is the highest speed of air flow during a forceful exhalation that starts after a full breath in. It is measured in litres per minute with a simple peak flow meter or during spirometry. PEF mainly reflects the calibre of the large airways and the strength of the effort. It is especially useful for monitoring asthma at home: a falling PEF can warn of an attack before symptoms become severe, and daily variability supports the diagnosis of asthma. PEF depends on age, height and sex, and the best reference is the person's own personal best.
Measurement
Stand or sit upright, take the deepest possible breath, seal the lips around the mouthpiece and blow out as hard and fast as possible. The best of three attempts is recorded. For monitoring, PEF is measured morning and evening; variability of more than about 10–20% between readings suggests poorly controlled asthma.
Causes of reduced PEF
- Asthma (especially during an exacerbation) and COPD
- Bronchitis, upper airway obstruction (tumour, tracheal narrowing, vocal cord problems)
- Weak breathing muscles or poor effort, chest pain
- Pneumonia and other lung diseases that restrict breathing
if peak flow is below 50% of your personal best, or with severe breathlessness, difficulty speaking, bluish lips or no improvement after reliever medicine.
References
- National Asthma Education and Prevention Program. Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma. Bethesda (MD): National Heart, Lung, and Blood Institute; 2007.
- Graham BL, Steenbruggen I, Miller MR, et al. Standardization of spirometry 2019 update: an official American Thoracic Society and European Respiratory Society technical statement. Am J Respir Crit Care Med. 2019;200(8):e70–e88. doi:10.1164/rccm.201908-1590ST
This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.
Published on 2 May 2024