Predicted values for the forced expiratory flow adjusted for forced vital capacity, a descriptive study

Claire A. Cox*, Judith M. Vonk, Huib A. M. Kerstjens, Maarten van den Berge, Nick H. T. ten Hacken

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Background: The forced expiratory flows (FEFs) towards the end of the expiration may be more sensitive in detecting peripheral airways obstruction compared to the forced expiratory volume in 1 s and forced vital capacity (FVC). However, they are highly variable. A partial solution is to adjust the FEFs for FVC (FEF/FVC). Here we provide reference equations for these adjusted FEFs at 25%, 50%, 75% and 25-75% of FVC, which are currently lacking.

Methods: We included pulmonary healthy, never-smoker adults; 14 472 subjects from Lifelines, a biobank for health research, and 338 subjects from the department's control cohorts (NORM and Fiddle). Reference equations were obtained by linear regression on 80% of the Lifelines dataset and validated on the remaining data. The best model was defined as the one with the highest adjusted R2-value. The difference in variability between adjusted and unadjusted FEFs was evaluated using the coefficient of variation.

Results: For all adjusted FEFs, the best model contained age, height and weight. The adjustment improved the coefficient of variation of the FEF75 from 39% to 36% and from 43% to 40%, respectively, in males and females. The highest percentage of explained variance by the reference equation was obtained for FEF75/FVC, 32%-38% for males, and 41%-46% for females, depending on the validation set.

Conclusion: We developed reference equations for FVC-adjusted FEF values. We demonstrated minimally yet significantly improved variability. Future studies in obstructive airway diseases should demonstrate whether it is worthwhile to use these (predicted) adjusted FEF values.

Original languageEnglish
Article numberARTN 00426-2020
Number of pages9
JournalERJ Open Research
Issue number4
Publication statusPublished - 1-Oct-2020


  • FEF25-75/FVC
  • AGE

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