Ventilation distribution and small airway function in patients with systemic sclerosis

Background

Despite the importance of traditional pulmonary function tests (PFTs) in managing systemic sclerosis (SSc), many patients with pulmonary disease diagnosed by computed tomography (CT) present with normal PFTs.

Objective

To evaluate the efficacy of the nitrogen single-breath washout (N₂SBW) test in diagnosing SSc and to correlate N₂SBW parameters with the PFT indexes used in the follow-up of these patients, clinical data, and CT findings.

Methods

Cross-sectional study in which 52 consecutive SSc patients were subjected to spirometry, body plethysmography, analysis of the diffusing capacity for carbon monoxide (DLCO), analysis of respiratory muscle strength, N₂SBW testing, and CT analysis.

Results

Twenty-eight patients had a forced vital capacity (FVC) that was <70% of the predicted value. In the N₂SBW test, 44 patients had a phase III slope (Phase III slope_N2SBW) that was >120% of the predicted value, while 15 patients had a closing volume/vital capacity (CV/VC) that was >120% of the predicted value. A significant difference in Phase III slope_N2SBW was observed when the patients with predominant traction bronchiectasis and honeycombing were compared to the patients with other CT patterns (p < 0.0001). The Phase III slope_N2SBW was correlated with FVC (r_s = −0.845, p < 0.0001) and DLCO (r_s = −0.600, p < 0.0001), and the CV/VC was correlated with FVC (r_s = −0.460, p = 0.0006) and residual volume/total lung capacity (r_s = 0.328, p = 0.017).

Conclusion

Ventilation heterogeneity is a frequent finding in SSc patients that is associated with restrictive damage, changes in pulmonary diffusion, and CT patterns. In addition, approximately one-third of the patients presented with findings that were compatible with small airway disease.