The FEF25-75/FVC ratio is associated with methacholine airway responsiveness - The Normative Aging Study

Airway responsiveness is known to be partly explained by geometric and anat omic factors. This cross-sectional investigation was undertaken to determin e whether FEF25-75/FVC as a surrogate measure of airway size relative to lu ng size is associated with airway responsiveness to methacholine. Posteroan terior chest radiographs and spirometry were performed on a group of 929 mi ddle aged and older men from an ongoing longitudinal study, the Normative A ging Study, who returned for their regularly scheduled examination between 1984 and 1989. Subjects had a mean age of 60.5 +/- 7.7 yr. FEV1, FEF25-75, and FVC were taken from spirometric results and FEF25-75/FVC ratios were ob tained. Main bronchus (MB) and tracheal (TR) diameters and lung area (LA) w ere obtained from chest radiographs, and ratios of MB/LA and TR/LA were cal culated for each subject and compared with FEF25-75/FVC as measures of airw ay size relative to lung size. In a multiple linear regression model adjust ing for age, height, initial FEV1, smoking, eosinophil count, and IgE level , FEF25-75/FVC was significantly related to the degree of methacholine airw ay responsiveness as measured by Log,, dose response slope (beta = -0.37, p < 0.001). Controlling for the same variables, both MB/LA (beta = -149.07, p < 0.001) and TR/LA (beta = -125.87, p < 0.001) were significant predictor s of the degree of bronchial responsiveness in separate regression models; however, their effects were greatly attenuated when FEF25-75/FVC was presen t in the same model. Similar results were obtained after excluding subjects with FEV1/FVC less than or equal to 0.70 and subjects who had any smoking history. We conclude that FEF25-75/FVC as a surrogate measure of airway siz e relative to lung size is significantly associated with airway responsiven ess.