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

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology
• Biostatistics

Background:

• Forced expiratory flows (FEFs) near the end of expiration may detect peripheral airway obstruction better than FEV1/FVC.
• FEFs are highly variable, limiting their clinical utility.
• Adjusting FEFs for forced vital capacity (FVC) offers a potential solution to reduce variability.

Purpose of the Study:

• To provide reference equations for FVC-adjusted FEFs (FEF/FVC) at 25%, 50%, 75%, and 25-75% of FVC.
• To evaluate the impact of FVC adjustment on the variability of FEFs.
• To establish a baseline for future research on the clinical application of adjusted FEFs in airway diseases.

Main Methods:

• Linear regression was used to derive reference equations from a large dataset (Lifelines, n=14,472) of healthy adults.
• The derived equations were validated on a separate portion of the Lifelines dataset.
• The coefficient of variation was used to compare the variability of adjusted versus unadjusted FEFs.

Main Results:

• Age, height, and weight were significant predictors in the best-fit models for all adjusted FEFs.
• FVC adjustment minimally reduced the coefficient of variation for FEF75 in males (39% to 36%) and females (43% to 40%).
• The highest explained variance by reference equations was for FEF75/FVC, ranging from 32%-38% in males and 41%-46% in females.

Conclusions:

• Reference equations for FVC-adjusted FEF values were successfully developed.
• A modest but statistically significant improvement in variability was observed with FVC adjustment.
• Further investigation is needed to determine the clinical value of these adjusted FEF measures in obstructive airway diseases.