Reference equations to predict forced expiratory flow values adjusted for forced vital capacity resulted in lower sample variability, according to study results published in ERJ Open Research.

Researchers in The Netherlands collected respiratory data from healthy, never-smoker adults with no pulmonary complaints to obtain reference equations by linear regression. This reference equation was then validated against another set of data. The difference in variability between adjusted and unadjusted forced expiratory flow values was then evaluated using the coefficient of variation.

Of the 14,810 adults included, 14,472 were from the Lifelines database, while the remaining 338 were obtained from control cohorts at the researchers’ institution, the University of Groningen. When evaluating reference equations, the best model made adjustments for age, height, and weight. Following adjustment, the reference equations produced a small, but significant reduction in variation — from 39% to 36% and from 43% to 40%, respectively, in men and women.

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Using more than 14,000 healthy individuals, the researchers developed reference equations for forced vital capacity-adjusted forced expiratory flow values. “The next step will be to evaluate the clinical relevance of the obtained reference equations in subjects with established airway disease,” they concluded.

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Cox CA, Vonk JM, Kerstjens HAM, van den Berge M, Ten Hacken NHT. Predicted values for the forced expiratory flow adjusted for forced vital capacity, a descriptive study. ERJ Open Res. 2020;6(4):00426-2020. doi:10.1183/23120541.00426-2020