Best denotes airway resistance

The maximal expiratory flow at 50 % of the forced vital capacity (MEF50) is the flow where half of forced vital capacity (FVC) remains to be exhaled . It corresponds to the forced expiratory flow at 50 % (FEF50) and correlates highly with the maximum mid-expiratory flow (FEF25-75 %) Ref: guyton and hall textbook of medical physiology 12 edition page number:326,327,328