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.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-1952-8) contains supplementary material, which is available to authorized users.

<p>Comparison of impedance measured by the forced oscillation technique and pulmonary functions, including static lung compliance, in obstructive and interstitial lung disease</p>

“…Therefore, the FOT parameters are largely affected by the presence of small airway disease also in ILD. Moreover, it has been demonstrated that there were no significant differences in the indices of respiratory impedance between the airway lesion dominant and interstitial pneumonia dominant groups in patients with rheumatoid arthritis-related pulmonary abnormalities. 29 This indicates the parenchymal abnormalities did not contribute to the changes in respiratory impedance in ILD.…”

Association between chest computed tomography findings and respiratory adverse events in rheumatoid arthritis patients undergoing long‐term biological therapy

“…CT findings related to ILD features (consolidation, ground glass opacity [GGO], reticular changes, nodular opacity, and honeycomb changes) were graded on a 5‐point scale within the whole lung field as follows: grade 0, finding was absent; grade 1, percentage of involvement of lungs between 1% and 25%; grade 2, percentage of involvement between 26% and 50%; grade 3, percentage of involvement between 51% and 75%; and grade 4, percentage of involvement ≥75% according to criteria of CT patterns defined by Tanaka et al With respect to ILD features, CT patterns were categorized into the following six groups: usual interstitial pneumonia (UIP), nonspecific interstitial pneumonia (NSIP), organizing pneumonia (OP), diffuse alveolar damage (DAD), chronic hypersensitivity pneumonitis (CHP), and unclassifiable pattern. AD features (bronchial wall thickening, bronchial mucous plug, bronchiectasis, bronchiolitis, and air trapping) were also graded on a 5‐point scale as follows: grade 0, finding was absent; grade 1, extent of involvement limited to 1 bronchial segment; grade 2, multiple involvement found in 1 side of lung field; grade 3, multiple involvement found in both lung fields; and grade 4, involvement found diffusely in the whole lung field, according to the criteria of CT patterns defined by Sokai et al Total points for the five features were obtained and a cumulative score was obtained (ILD score and AD score; maximum score of 20 per patient) to represent disease severity. For CT scores, patients were categorized into the following four groups: ILD group (n = 29), AD group (n = 76), Co‐existing group (n = 6), and WDC group (n = 221) in the same manner as described in a previous study .…”

“…Other findings observed in pleural lesions (apical cap, pleural thickening, calcification, and pleural effusion) and mediastinal lesions (lymphadenopathy, esophageal dilation, pulmonary artery dilation, and pericardial effusion), as well as nonspecific inflammatory or malignancy findings (intrapulmonary lymph node, calcified nodule, atelectasis, and line shape/cord pattern), were evaluated on a 2‐point scale as follows: grade 0, finding was absent; grade 1, finding was detectable. The extent of emphysema in the whole lung field was also graded according to a previous report on a 5‐point scale, as follows: grade 0, the finding was absent; grade 1, the percentage of involvement of the lungs was between 1% and 25%; grade 2, the percentage of involvement was between 26% and 50%; grade 3, the percentage of involvement was between 51% and 75%; and grade 4, the percentage of involvement was more than 76%. We defined grades 3‐4 emphysema as severe emphysema, and excluded patients with this condition from the study to eliminate the potential influence of chronic obstructive pulmonary disease (COPD) when assessing RAEs.…”

Complex obstructive lung disease – A diagnostic and management conundrum

“…Impulse oscillometry may be useful, where obstruction can be identified as increased resistance values at lower oscillatory frequencies. This pattern was shown to be present in a retrospective cohort of RA patients in Japan [ [8] , [9] ]. Overall, there is no consensus on what defines RA-related obstructive lung disease, and it should be taken into account that confounders are abundant.…”

“…However, some studies have shown increased incidence of obstructive pulmonary function testing in non-smoking RA patients [ 7 ]. In patients where there exist multiple exposures and potential etiologies for pulmonary disease, it can be difficult to isolate and treat a primary diagnosis [ 8 ] With the express consent of the patient, we present a case of complex obstructive lung disease with significant contribution of RA-related small airways disease, which created a diagnostic and therapeutic challenge.…”