Peak expiratory flow (PEF)
Peak expiratory flow (PEF) is the maximum flow generated during expiration performed with maximal force and started after a full inspiration. Close attention has to be paid to the correct performance of the test. The highest value of three accurately completed manoeuvres is recorded.
Due to stress relaxation of viscoelastic lung elements PEF is considerably larger if the test is performed without pause immediately after inspiration. Contrary to popular belief PEF is not effort dependent: if the manoeuvre is performed sufficiently forcefully in most subjects PEF is determined by flow limitation in central, possibly also in more peripheral airways.
Predicted values of PEF are of little use in detecting lung disease, since variability between healthy subjects is large. Therefore a value within the normal range does not rule out the presence of airway obstruction. In severe obstructive lung disease rapid and extensive dynamic airway compression during the forced manoeuvre contribute appreciably to initial maximum expiratory flow from the lungs; the severity of airway obstruction then tends to be underestimated from PEF.
An abnormally low PEF may be caused by:
obstructive lung disease
prior inhalation not to total lung capacity
restricted lung expansion (e.g. stiff chest cage, muscular or neurogenic disorders)
Pedersen OF, Brackel HJL, Bogaard JM, Kerrebijn KF. Wave-speed-determined flow limitation at peak flow in normal and asthmatic subjects. 1997. Journal of Applied Physiology; 83: 1721-1732
Quanjer PH, Lebowitz MD, Gregg I, Miller MR, Pedersen OF. Peak expiratory flow. Conclusions and recommendations of a working party of the European Respiratory Society. 1997. Eur Respir J; 10 (Suppl. 24): S2-S8
Expiratory flow correlated to lung volumes