Correlation between Computed Tomographic Analysis and Pulmonary Function Measurements in Patients with Relapsing Polychondritis.

BACKGROUND Relapsing polychondritis (RP) is a rare systemic disease of unknown origin, with cartilaginous involvement in multiple organs. Airway involvement is the most important prognostic factor in RP. OBJECTIVES Spirometric measurements and minimum tracheal cross-sectional area (mtCSA) have been reported as useful to assess the degree of airway stenosis. Because the length and severity of tracheal involvement in RP can vary, mtCSA might not provide enough information to assess tracheal abnormalities. We introduced tracheal volume (TrV) as a new method to evaluate correlations between chest computed tomography (CT) measurements and pulmonary function tests, including impulse oscillometry (IOS). METHOD We analyzed chest CT images, spirometry, and IOS collected at our institution from April 2004 to March 2019. We calculated correlations between chest CT measurements using software (TrV, TrV/tracheal length [TrV/TL], and mtCSA) and pulmonary function parameters. RESULTS Twenty-five of 73 clinically diagnosed patients with RP were included. Spirometric findings showed moderate airway obstruction. Peak flow (PEF) was strongly correlated with mtCSA, TrV, and TrV/TL (ρ = 0.74, p < 0.001). FEV1 was significantly correlated with mtCSA (ρ = 0.56, p = 0.004), TrV (ρ = 0.52, p = 0.007), and TrV/TL (ρ = 0.53, p = 0.006). Whereas respiratory resistance at 5 Hz (R5) and 20 Hz (R20) and resonant frequencies (RFs) were significantly correlated with TrV (ρ = -0.46, p = 0.021; ρ = -0.46, p = 0.046; and ρ = -0.42, p = 0.037, respectively), IOS parameters and mtCSA were not. CONCLUSIONS In patients with RP, TrV and mtCSA were strongly correlated with spirometric measurements. Respiratory resistances assessed by IOS correlated only with TrV. This suggests TrV assessment reflects pulmonary function in patients with RP more appropriately than mtCSA.