Performance analysis of the Flutter VRP1 under different flows and angles.

Background: The Flutter VRP1 device is used for airway clearance. Its performance is based on 4 basic effects: positive expiratory pressure (PEP), forced exhalations (huff), high-frequency airway flow oscillation, and modification of mucus viscoelasticity. The purpose of this study was to determine the flow and angle conditions in which these effects are optimized.