The assessment of tidal expiratory flow limitation and small airways disease using forced oscillation technique during hospitalization for asthma attacks and recovery.

<bold>Background:</bold> The tidal expiratory flow limitation (EFL_t) has been explored as an additional and important measure during COPD exacerbations. However, this index has not been widely studied in asthma exacerbations (AE), and its association with small airways disease (SAD) is unknown. <bold>Aims:</bold> To describe the proportion of EFL_t and SAD using forced oscillation technique (FOT) among individuals hospitalised with AE. To examine the correlation between EFL_t and SAD and to describe FOT parameters in individuals with and without EFL_t during an AE. <bold>Methods:</bold> Fifty-seven subjects diagnosed with AE were admitted to Nottingham University Hospitals and performed FOT within 24h of their admission (V₁) and 14 days after hospital discharge (V₂). EFL_t were considered when X_5in-X_5exp >2.8 and SAD when R_5-20 < 0.7cmH₂O.s/L. <bold>Results:</bold> Thirty-seven (65%) individuals had SAD and seven (12%) also showed EFL_t at V₁, however 42 (74%) showed SAD at V₂ and only one person retained EFL_t index. Only nine participants improved SAD between visits. The EFL_t index showed significant correlation with R_5-20 (r=0.48 P<0.001) and with AX (r=0.34, p=0.01), but no correlation was found between the index and R₅ (r=0.21, p=0.12). Individuals with EFLt had higher R_5exp (p=0.05); R_5-20 (p=0.026) and AX (p=0.01) compared to the pairs without EFL_t. <bold>Conclusions:</bold> The majority of individuals hospitalised with asthma exacerbations had SAD, with a small proportion also demonstrating EFL_t. FOT is well tolerated during hospitalization following AE and can be a feasible and usable tool for assessment of small airways and expiratory flow limitation.