The Diagnostic Importance of a Reduced FEV1/FEV6

Background: On spirometry the FEV1/FEV6 ratio has been advocated as a surrogate for the FEV1/FVC. The significance of isolated reductions in either the FEV1/FEV6 or FEV1/FVC is not known. Methods: First-time adult spirograms (n = 22,837), with concomitant lung volumes (n = 12,040), diffusion (n = 14,154), and inspiratory capacity (n = 12,480) were studied. Four groups were compared. 1) Only FEV1/FEV6 reduced (n = 302). 2) Only FEV1/FVC reduced (n = 1158). 3) Both ratios reduced (n = 6593). 4) Both ratios normal (n = 14,784). Results: In patients with obstructed spirometry (either a reduced FEV1/FVC and/or FEV1/FEV6), 3.8% only had a reduced FEV1/FEV6, while 14.4% only had a reduced FEV1/FVC. The mean FEV1 was lower when both ratios were reduced. The group with only a reduced FEV1/FEV6, compared to only the FEV1/FVC reduced, had a lower FEV1, FVC, BMI, Expiratory Time, and IC (p values < 0.0001). DLCO was also lower (p = 0.005), and the FEV1/FVC and RV/TLC were higher (p values < 0.0001). When the patients with only a reduced FEV1/FEV6 had a subsequent spirogram, 60% had a reduced FEV1/FVC when their mean expiratory times were 3.5 seconds longer. Ninety percent of this group had strong clinical evidence of airways obstruction. Conclusions: The FEV1/FEV6 is not as sensitive as the FEV1/FVC for diagnosing airways obstruction, but in the presence of a normal FEV1/FVC, subjects have greater physiologic abnormalities than when only the FEV1/FVC is reduced. The FEV1/FEV6 ratio should not replace the FEV1/FVC as the standard for airways obstruction, but there is benefit including this measurement to identify individuals with greater air trapping and diffusion abnormalities.