Schematic representation of breathing levels during positive expiratory pressure in an obstructed patient. Schematic representation of breathing levels during positive expiratory pressure in an obstructed patient. TV: tidal volume; FET: forced expiration technique; TLC: total lung capacity; FRC: functional residual capacity; RV: residual volume. Courtesy L. Lannefors (Sahlgrenska University Hospital, Gothenburg, Sweden). Maggie McIlwaine et al. Eur Respir Rev 2017;26:160086 ©2017 by European Respiratory Society