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Rationale: Residents and area workers who inhaled dust and fumes from the World Trade Center disaster reported lower respiratory symptoms in two World Trade Center Health Registry surveys (2003-2004 and 2006-2007), but lung function data were lacking.Objectives: To examine the relationship between persistent respiratory symptoms and pulmonary function in a nested case-control study of exposed adult residents and area workers 7-8 years after September 11, 2001.Methods: Registrants reporting post September 11th onset of a lower respiratory symptom in the first survey and the same symptom in the second survey were solicited as potential cases. Registrants without lower respiratory symptoms in either Registry survey were solicited as potential control subjects. Final case-control status was determined by lower respiratory symptoms at a third interview (the study), when spirometry and impulse oscillometry were also performed.Measurements and Main Results: We identified 180 cases and 473 control subjects. Cases were more likely than control subjects to have abnormal spirometry (19% vs. 11%; P < 0.05), and impulse oscillometry measurements of elevated airway resistance (R5; 68% vs. 27%; P < 0.0001) and frequency dependence of resistance (R₅₋₂₀; 36% vs. 7%; P < 0.0001). When spirometry was normal, cases were more likely than control subjects to have elevated R₅ and R₅₋₂₀ (62% vs. 25% and 27% vs. 6%, respectively; both P < 0.0001). Associations between symptoms and oscillometry held when factors significant in bivariate comparisons (body mass index, spirometry, and exposures) were analyzed using logistic regression.Conclusions: This study links persistent respiratory symptoms and oscillometric abnormalities in World Trade Center-exposed residents and area workers. Elevated R₅ and R₅₋₂₀ in cases despite normal spirometry suggested distal airway dysfunction as a mechanism for symptoms. [ABSTRACT FROM AUTHOR]