Respiratory oscillometry findings in World Trade Center-exposed rescue/recovery workers

Background Persistent respiratory symptoms are common in Fire Department of the City of New York (FDNY) rescue/recovery workers following the World Trade Center (WTC) collapse on 11 September 2001 and some continue to experience symptoms despite normal spirometry without bronchodilator response. Respiratory oscillometry is a sensitive method for detecting small airways dysfunction and identifies abnormalities undetected by spirometry. This study evaluated whether respiratory oscillometry is associated with respiratory symptoms among workers with normal spirometry, and qualitatively assessed this association stratified by serum eosinophilia. Methods We analysed a cohort of FDNY WTC-exposed rescue/recovery workers who completed same-day respiratory oscillometry, spirometry and symptom questionnaires. We included only those with normal spirometry without obstruction, defined as forced expiratory volume in 1 s (FEV 1 ), forced vital capacity (FVC) or FEV 1 /FVC greater than the lower limit of normal and no bronchodilator response. Logistic regression estimated associations between oscillometry z-scores (as continuous variables in separate models) and symptom burden. Models were adjusted for age, race, WTC arrival time, smoking status and body mass index. Analyses were also stratified by eosinophilia status. Results Resistance at 5 Hz (R5) was associated with persistently high symptom count (odds ratio (OR) 1.36, 95% CI 1.11–1.66) and high symptom severity (OR 1.32, 95% CI 1.05–1.67). Frequency dependence of resistance (the difference between resistance at 5 Hz and resistance at 20 Hz (R5–R20)) was also associated with persistently high symptom count (OR 1.31, 95% CI 1.11–1.56). Associations for R5 and R5–R20 were greatest in those with eosinophilia (≥300 cells·μL −1 ). Conclusion In symptomatic individuals with normal spirometry, oscillometry is sensitive for detecting airways dysfunction, supporting our hypothesis that persistent, severe symptoms are attributable to disease in the small airways. Larger associations with eosinophilia identify a phenotype that may inform early intervention and treatment.