title: Comparison of maximal midexpiratory flow rate and forced expiratory flow at 50% of vital capacity in children.
abstract: BACKGROUND
  The mid-portion of the maximal expiratory flow-volume (MEFV) curve is often described by values of the mean forced expired flow as lung volume decreases from 75% to 25% of vital capacity (ie, forced expiratory flow, midexpiratory phase [FEF(25-75)]). It is common practice to report also forced expired flow at 50% of vital capacity (FEF(50)).
  
  
  OBJECTIVE
  To investigate whether FEF(50) and FEF(25-75) are highly correlated or whether the difference between them reflects a degree of airways obstruction. Also, we wanted to investigate the correlation between the two in cases of irregularly shaped MEFV curves (ie, "saw-toothing").
  
  
  METHODS
  Analysis of the correlation between FEF(50) and FEF(25-75) in a single determination. We assessed the relationship between the FEF(50)/FEF(25-75) ratio and the degree of airways obstruction, as reflected by other traditional parameters such as FEV(1), FEV(1)/FVC ratio, and specific airway conductance (SGaw).
  
  
  METHODS
  There were 1,350 forced expiratory maneuvers performed by children with a broad range of pulmonary abnormalities.
  
  
  RESULTS
  FEF(50) correlated with FEF(25-75) as follows: FEF(50) (L/s) = 0.041 + 1.136*FEF(25-75)(L/s); r(2) = 0.956; standard error of the estimate = 0.013; p < 0.0001. The FEF(50)/FEF(25-75) ratio remained stable and did not correlate with FEV(1) (r = 0.12), FEV(1)/FVC ratio (r = 0.11), or SGaw (r = 0.02; difference not significant). The correlation between FEF(25-75) and FEF(50) was similar for both the smooth curve (r = 0.97) and the irregular curve (r = 0.96).
  
  
  CONCLUSIONS
  Although not identical, FEF(25-75) and FEF(50) are highly correlated, and the ratio of the two is fairly constant. Therefore, the practice of reporting both of them is unnecessary. We suggest that it is reasonable to prefer FEF(50).
authors.affiliation: Institute of Pulmonology, Hadassah University Hospital, Jerusalem, Israel. EPHRAIMB@CC.HUJI.AC.IL
authors.forename: Ephraim
authors.initials: E
authors.lastname: Bar-Yishay
authors.forename: Israel
authors.initials: I
authors.lastname: Amirav
authors.forename: Shmuel
authors.initials: S
authors.lastname: Goldberg
mesh_terms: D002648:Child; D005260:Female; D005540:Forced Expiratory Flow Rates / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D008171:Lung Diseases / Q000175:diagnosis; D008297:Male; D008448:Maximal Expiratory Flow Rate / Q000502:physiology*; D008954:Models, Biological; D013147:Spirometry / Q000379:methods*; D014797:Vital Capacity