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Background: Positive expiratory pressure (PEP) has been used to promote airway clearance in individuals with chronic obstructive pulmonary disease (COPD) for many years; however, its mechanism of action and benefits are unclear. Previous authors have suggested that PEP improves collateral ventilation via changes in lung volumes. Objectives: It was the aim of this study to determine whether PEP improves ventilation inhomogeneity more than controlled huffing and coughing in individuals with stable COPD. Methods: Twelve participants with COPD (mean forced expiratory volume in 1 s 45% predicted) and chronic sputum expectoration performed PEP therapy (10-20 cm H2O) or controlled huffing and coughing in random order on alternate study days with a 48-hour washout. Measures of acinar and conductive airway ventilation (Sacin, Scond), lung volumes, spirometry and sputum wet weight were recorded before, immediately after and 90 min following treatment. Ease of expectoration [visual analogue scale (VAS)] and oxyhaemoglobin saturation were assessed immediately following treatment. Results: There were no significant differences between the effect of either test condition at any time point for any test parameter. Mean Sacin immediately following PEP and control conditions was 0.465 and 0.438 litre-1, respectively (p = 0.45 for comparison between conditions) and mean Scond was 0.042 and 0.039 litre-1 (p = 0.55). PEP therapy did not significantly enhance total mean sputum expectoration compared to controlled huffing and coughing (7.06 vs. 6.15 g; p = 0.51) and did not improve ease of expectoration (VAS PEP 4.8 cm vs. control 4.1 cm; p = 0.53). Conclusion: Any therapeutic benefits of PEP in individuals with COPD and chronic sputum expectoration are unlikely to be mediated by improvements in ventilation or lung volumes. Copyright © 2013 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]