• Lucas Boeck, Anna Gensmer, Sylvia Nyilas, Bram Stieltjes, Thomas J Re, Michael Tamm, Philipp Latzin, and Daiana Stolz.
• Clinic of Respiratory Medicine and Pulmonary Cell Research, University Hospital Basel, Switzerland.
• Chest. 2016 Nov 1; 150 (5): 1091-1100.

BackgroundCurrent functional assessments do not allow a reliable assessment of small airways, which are a major site of disease in COPD. Single-breath washout (SBW) tests are feasible and reproducible methods for evaluating small airway disease. Their relevance in COPD remains unknown.MethodsWe performed a cross-sectional study in 65 patients with moderate to severe COPD. Phase III slope of nitrogen (SIIIN2) and double tracer gas (SIIIDTG) SBW tests were used as a measure of ventilation inhomogeneity. The association of both markers with established physiological and clinical features of COPD was assessed.ResultsVentilation inhomogeneity as measured by SIIIN2 and SIIIDTG was increased in patients with COPD compared with healthy subjects (P < .001 and P < .001, respectively). SIIIN2 was associated with FEV1 predicted, residual volume (RV)/total lung capacity (TLC) and diffusing capacity of the lung for carbon monoxide (Dlco) (all P < .001). Furthermore, SIIIN2 was related to dyspnea, exercise-induced desaturation, and exercise capacity (P = .001, P < .001, and P = .047, respectively). SIIIDTG was associated with TLC, Dlco, and cough (P < .001, P = .001, and P = .009, respectively). In multivariate regression models, we demonstrated that these associations are largely independent of FEV1 and mostly stronger than associations with FEV1. In contrast, FEV1 was superior in predicting emphysema severity.ConclusionsSIIIN2 and SIIIDTG, two fast and clinically applicable measures of small airway disease, reflect different physiological and clinical aspects of COPD, largely independent of spirometry.Trial RegistryISRCTN99586989, Ethics committee Beider Basel (approval number 295/07).Copyright © 2016 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.

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