Supplementary Material for: Positive Expiratory Pressure via Mask Does Not Improve Ventilation Inhomogeneity More than Huffing and Coughing in Individuals with Stable Chronic Obstructive Pulmonary Disease and Chronic Sputum Expectoration

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 (S_acin, S_cond), 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 S_acin immediately following PEP and control conditions was 0.465 and 0.438 litre^-1, respectively (p = 0.45 for comparison between conditions) and mean S_cond 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.