Human lung clearance of inhaled radioactively labelled particles in horizontal and vertical position of the inhaling person.

When particles are deposited in the respiratory tract, two distinct phases of clearance from the thorax are usually observed. It is generally assumed that the fast phase, which is completed within about a day, represents mucociliary clearance of particles deposited in the tracheobronchial tree, whereas the slow phase represents clearance of the alveolar deposit. Several mechanisms have been proposed which could cause part of the bolus to reach alveoli: the pathways to some alveoli may be relatively short (asymmetric airway branching); the main flow of inspired air in an airway may be confined to the axis (core flow); and some lobes may fill before others (asynchronous or sequential ventilation). In the experiments which are reported here, the administration technique was altered to increase deposition of the bolus in the conducting airways. In addition, another particle material was applied in order to exclude chemical effects on clearance behavior