title: Respiratory mechanics measured by forced oscillation technique in rheumatoid arthritis-related pulmonary abnormalities: frequency-dependence, heterogeneity and effects of smoking.
abstract: Rheumatoid arthritis (RA)-related pulmonary disorders specifically airway abnormalities and interstitial pneumonia (IP) are important extra-articular manifestations. The forced oscillation technique (FOT) is a useful method to assess respiratory impedance, respiratory resistance (Rrs) and reactance (Xrs), at different oscillatory frequencies during tidal breathing. The aim of this study was to characterize the respiratory mechanics of patients with RA and to relate them to parameters of the pulmonary function test and findings of chest CT images. Respiratory impedance of RA patients (n = 69) was measured as a function of frequency from 4 to 36 Hz using the FOT device and compared with that of healthy subjects (n = 10). Data were retrospectively reviewed. Patients were female-dominant (60.9 %) and 95.7 % had abnormal CT findings including airway and parenchymal abnormalities. Thirty-seven of 69 patients (53.6 %) were smokers. Rrs was significantly frequency-dependent in RA patients but not in the healthy subjects. Xrs were significantly frequency-dependent in both RA and healthy groups. Rrs was significantly higher during an expiratory phase in both RA and healthy groups. Xrs was significantly lower (more negative) during an expiratory phase than that during an inspiratory phase in RA patients but not in healthy subjects. Xrs of the RA group was significantly more negative than that of the normal control. There was no difference in impedance parameters between the airway lesion dominant (n = 27) and IP dominant groups (n = 23) in the RA group. The impedance parameters of the RA group significantly correlated with most parameters of the pulmonary function test. In pulmonary function test results, % of the predicted value for forced expiratory flow from 25 to 75 % of forced vital capacity was significantly lower and % of the predicted value for diffusing capacity of the lung for carbon monoxide was higher in the airway lesion dominant group than those in the IP dominant group. Krebs von den Lungen-6, a serum indicator of IP, was significantly higher in the IP group than that in the airway lesion dominant group. Taken together, the impedance results reflect abnormalities in pulmonary functions and structures in patients with RA.
authors.affiliation: Department of Respiratory Medicine, Nagoya University School of Medicine, Nagoya, 466-8550 Japan.
authors.forename: Risa
authors.initials: R
authors.lastname: Sokai
authors.affiliation: Department of Respiratory Medicine, Nagoya University School of Medicine, Nagoya, 466-8550 Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Ito
authors.affiliation: Department of Radiology, Nagoya University School of Medicine, Nagoya, 466-8550 Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Iwano
authors.affiliation: Department of Clinical Laboratory, Nagoya University School of Medicine, Nagoya, 466-8550 Japan.
authors.forename: Akemi
authors.initials: A
authors.lastname: Uchida
authors.affiliation: Department of Respiratory Medicine, Nagoya University School of Medicine, Nagoya, 466-8550 Japan.
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Aso
authors.affiliation: Department of Respiratory Medicine, Nagoya University School of Medicine, Nagoya, 466-8550 Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Kondo
authors.affiliation: Department of Orthopedic Surgery and Rheumatology, Nagoya University School of Medicine, Nagoya, 466-8550 Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Ishiguro
authors.affiliation: Department of Orthopedic Surgery and Rheumatology, Nagoya University School of Medicine, Nagoya, 466-8550 Japan.
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Kojima
authors.affiliation: Department of Respiratory Medicine, Nagoya University School of Medicine, Nagoya, 466-8550 Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Hasegawa
keywords: Airway; Forced oscillation technique; Impedance; Interstitial lung disease; MostGraph; Rheumatoid arthritis