The Mid-Expiratory Flows

Other than the PEF, there are three additional markers of expiratory flow, which can aid spirometry interpretation.

The MEF75 is the flow rate when 75% of the forced vital capacity remains to be exhaled, and is equivalent to the FEF25 (25% of the FVC has been exhaled). The MEF or FEF values therefore reflect the flow capabilities of the peripheral airways; and consequently the cross-sectional area of the bronchioles.

These flow markers are defined by their relationship to the FVC:

The Mid-Expiratory Flow’s (MEF’s) represent the expiratory flow rates when a certain percentage (x) of the FVC remains to be exhaled (MEFx). Where 75% remains this is known as the MEF75, at the half way point is the MEF50 and where the remaining quarter of the FVC remains is known as the MEF25

Alternatively the Forced Expiratory Flow’s (FEF’s) may be used, which represent the expiratory flow rates when a certain percentage x% of the FVC has already been exhaled (FEFx). So, the FEF essentially works in the reverse order to the MEF

The mid expiratory flow rates, particularly the MEF25, can vary between successive spirometry manoeuvres in the same patient; they are sensitive to insignificant fluctuations such as cough, expiratory effort and early termination of the manoeuvre. They depend on the patient performing a technically acceptable FVC manoeuvre since they are the flow rates in proportion to FVC.S

Mark as Understood

© Institute of Clinical Science and Technology.


Tel: 02920 092828