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Abstract Background Can physiotherapy with a positive expiratory pressure (PEP) mask improve peripheral ventilation inhomogeneity, a typical feature of children with cystic fibrosis (cwCF)? To answer this question, we used the nitrogen multiple‐breath washout (N 2 MBW) test to measure diffusion‐convection‐dependent inhomogeneity arising within the intracinar compartment (S acin *VT). Methods For this randomized, sham‐controlled crossover trial, two N 2 MBW tests were performed near the hospital discharge date: one before and the other after PEP mask therapy (1 min of breathing through a flow‐dependent PEP device attached to a face mask, followed by three huffs and one cough repeated 10 times) by either a standard (10–15 cmH 2 0) or a sham (<5 cmH 2 0) procedure on two consecutive mornings. Deception entailed misinforming the subjects about the nature of the study; also the N 2 MBW operators were blinded to treatment allocation. Study outcomes were assessed with mixed‐effect models. Results The study sample was 19 cwCF (ten girls), aged 11.4 (2.7) years. The adjusted S acin *VT mean difference between the standard and the sham procedure was −0.015 (90% confidence interval CI: −∞ to 0.025) L −1 . There was no statistically significant difference in S cond *VT and lung clearance index between the two procedures: −0.005 (95% CI: −0.019 to 0.01) L −1 and 0.49 (95% CI: −0.05 to 1.03) turnovers, respectively. Conclusion Our findings do not support evidence for an immediate effect of PEP mask physiotherapy on S acin *VT with pressure range 10–15 cmH 2 0. Measurement with the N 2 MBW and the crossover design were found to be time‐consuming and unsuitable for a short‐term study of airway clearance techniques.
Gambazza et al. (Fri,) studied this question.