<prompt> Best denotes airway resistanceVital CapacityMid respiratory flow ratesFEV1Total volume  <response>: 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 