Does the nitrogen single-breath washout test contribute to detecting pulmonary involvement in rheumatoid arthritis? A pilot study

OBJECTIVE: There has been growing interest in studying small airway disease through measures of ventilation distribution, thanks to the resurgence of the nitrogen single-breath washout (N(2)SBW) test. Therefore, this study evaluated the contribution of the N(2)SBW test to the detection of pulmonary involvement in patients with rheumatoid arthritis (RA). RESULTS: Twenty-one patients with RA underwent clinical evaluation, pulmonary function tests (PFTs), including the N2(S)BW test, and computed tomography (CT). The main tomographic findings were air trapping and bronchiectasis (57.1% and 23.8% of cases, respectively). According to the phase III slope of the N(2)SBW (phase III slope), 11 and 10 patients had values < 120% predicted and > 120% predicted, respectively. Five patients with limited involvement on CT had a phase III slope > 120%. The residual volume/total lung capacity ratio was significantly different between patients with phase III slopes < 120% and > 120% (P = 0.024). Additionally, rheumatoid factor positivity was higher in patients with a phase III slope > 120% (P = 0.021). In patients with RA and airway disease on CT, the N(2)SBW test detects inhomogeneity in the ventilation distribution in approximately half of the cases, even in those with normal conventional PFT results.