An experimental study of clearance of inhaled particles from the human nose

Retention in the extrathoracic airways, and clearance by nose blowing, of monodisperse indium-111-labeled polystyrene particles were followed for at least 2 days after inhalation by healthy volunteers. Nine volunteers inhaled 3-μm aerodynamic diameter particles while sitting at rest, whereas subgroups of 3 or 4 inhaled 1.5-μm or 6-μm particles at rest, and 3-μm or 6-μm particles while performing light exercise. Retention of the initial extrathoracic deposit (IETD) in the extrathoracic airways was described by 4 components: on average 19% IETD cleared by nose blowing; 15% was swallowed before the first measurement, a few minutes after inhalation; 21% cleared by mucociliary action between the first measurement and about an hour later; and 45% subsequently cleared by mucociliary action. Geometric mean times in which 50% and 90% of IETD cleared were 2.5 and 22 hours. The geometric mean retention fractions at 24 and 48 hours were 7% and 2.4% IETD, respectively. No clear trends were found between parameters describing retention and any related to deposition (e.g., particle size). However, the fraction cleared by nose blowing was related to the frequency of nose blowing and therefore appears to be a characteristic of the individual.