Longitudinal changes in pulmonary function and respiratory impedance of rheumatoid arthritis.

The aim of this study was to examine long-term changes in pulmonary function and respiratory impedance (Zrs) as assessed by forced oscillation technique (FOT) of rheumatoid arthritis (RA)-related pulmonary disorders. Data of 42 RA patients who underwent pulmonary function tests and Zrs measurements at least twice at a >900-day interval were retrospectively reviewed. Zrs, respiratory resistance (Rrs) and reactance (Xrs), were measured as a function of oscillatory frequency from 4 to 36 Hz. The Rrs and difference between inspiratory and expiratory phases of Xrs were significantly decreased. Annual changes in Xrs parameters significantly correlated with those of spirometric parameters. Zrs parameters were significantly different between the low (the lower 75 percentile of incidence) and high (the top quartile) frequency of adverse respiratory event groups. The Zrs combined with spirometry may be beneficial to evaluate alterations in respiratory functions of RA.