Fig. 2From: Exhaled particles and small airwaysAt low specified flow rates the participants exhaled to (a) residual volume (RV), (b) closing point (CP), i.e., the lung volume at which extensive airway closure begins, or (c) normal tidal exhalation to functional residual capacity (FRC). Participants then inhaled to total lung capacity (TLC) and immediately exhaled into the equipment back to FRC. By permission of the authorBack to article page