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usual discrete intervals are 25%, 50% and 75% (FEF25, FEF50 and FEF75), or 25% and 50% of FVC that has been exhaled.It can also be given as a mean of the flow during an interval, also generally delimited by when specific fractions remain of FVC, usually 25-75% (FEF25-75%). Average ranges in the healthy population depend mainly on sex and age, with FEF25-75% shown in diagram at left. Values ranging from 50 to 60% and up to 130% of the average are considered normal. Predicted normal values for FEF can be calculated and depend on age, sex, height,

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