Single-Breath Washout Tests to Assess Small Airway Disease in COPD.

Boeck, Lucas; Gensmer, Anna; Nyilas, Sylvia Meryl; Stieltjes, Bram; Re, Thomas J; Tamm, Michael; Latzin, Philipp; Stolz, Daiana (2016). Single-Breath Washout Tests to Assess Small Airway Disease in COPD. Chest, 150(5), pp. 1091-1100. American College of Chest Physicians 10.1016/j.chest.2016.05.019

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BACKGROUND

Current 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.

METHODS

We 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.

RESULTS

Ventilation 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.

CONCLUSIONS

SIIIN2 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 REGISTRY

ISRCTN99586989, Ethics committee Beider Basel (approval number 295/07).

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