The FEV ₁ /TLC ratio: Can it differentiate between normal subjects and patients with airflow obstruction and restrictive ventilatory defects - a preliminary analysis?

A reduced FEV 1 is as a marker of airflow obstruction where TLC is normal or increased, whilst both TLC and FEV 1 are reduced in a restrictive ventilatory defect. Aim : To determine the usefulness of the FEV 1 /TLC ratio in determining the presence of an obstructive or restrictive ventilatory defect. Methods : Lung function measurements of FEV 1 , VC and TLC were reviewed and divided into four principle groups - 1) normal (both FEV 1 and TLC > -1.64 SR), 2) airways obstruction (FEV 1 %VC < -1.64SR, TLC normal or > +1.65SR), 3) restrictive defect (TLC < -1.65 SR) and 4) a mixed obstructive-restrictive defect. Results : The group (n = 806; age 20 - 97 yrs) and sub-group analysis is shown in the table. Group and sub-group analysis of data n FEV 1 VC FEV 1 /TLC Entire Group 806 2.85 ± 0.12 3.15 ± 0.04 0.52 ± 0.01 1: Normal 175 3.85 ± 0.07 4.35 ± 0.10 0.68 ± 0.01 2: Airways Obstruction 415 1.65 ± 0.06 3.75 ± 0.05 0.29 ± 0.01 3: Restrictive Defect 174 1.95 ± 0.07 2.55 ± 0.03 0.52 ± 0.01 4: Mixed Defect 42 1.65 ± 0.12 2.65 ± 0.17 0.27 ± 0.02 Data are given as mean ± SEM. The FEV 1 /TLC ratio was significantly lower (p < 0.01) in groups 2, 3 and 4 when compared to group 1. There was no significant difference between groups 2 and 4. On subdividing group 2 into reversible and non-reversible airflow obstruction and group 3 into intrathoracic and extrathoracic restrictive defects (based on TL co and K co ), no significant differences were observed. Conclusion: In this preliminary analysis, the FEV 1 /TLC can differentiate between normal subjects and those with a restrictive and an obstructive ventilatory defect.