The World Trade Center (WTC) destruction released dust and fumes into the environment. Although many community members developed respiratory symptoms, screening spirometry was usually normal. We hypothesised that forced oscillation testing would identify functional abnormalities undetected by spirometry and that symptom severity would relate to magnitude of abnormalities measured by oscillometry. A symptomatic cohort (n=848) from the Bellevue Hospital WTC Environmental Health Center was evaluated and compared to an asymptomatic cohort (n=475) from the New York City Department of Health WTC Health Registry. Spirometry and oscillometry were performed. Oscillometry measurements included resistance (R₅) and frequency dependence of resistance (R_5-20). Spirometry was normal for the majority of subjects (73.2% symptomatic versus 87.6% asymptomatic, p<0.0001). In subjects with normal spirometry, R₅ and R_5-20 were higher in symptomatic versus asymptomatic subjects (median (interquartile range) R₅ 0.436 (0.206) versus 0.314 (0.129) kPa·L^-1·s^-1, p<0.001; R_5-20 0.075 (0.085) versus 0.004 (0.042) kPa·L^-1·s^-1, p<0.0001). In symptomatic subjects, R₅ and R_5-20 increased with increasing severity and frequency of wheeze (p<0.05). Measurement of R_5-20 correlated with the presence and severity of symptoms even when spirometry was within normal limits. These findings are in accord with small airway abnormalities as a potential explanation of the respiratory symptoms.

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