Inhaled particle deposition and clearance from the normal respiratory tract

Tracheo-bronchial and pulmonary deposited fractions of inhaled insoluble particles and their clearances rates were studied in 16 healthy non-smokers. After oral inhalation of radioactive particles (Mean Mass Aerodynamic Diameter (MMAD) = 3 microns, sigma g = 1.4 labelled with 111In) incorporated radioactivity was measured for each subject both by a gamma camera from to until the 3rd day, then from the 3rd until the 5th day first by a gamma camera and then by a low background profile scanner and from the 5th until the 35th day by a low background profile scanner alone. Clearance rates were calculated from the biological half lives of the deposited tracers. All subjects performed respiratory function tests. Experimental data were fitted to a two-compartment exponential system with two biological half lives: T1 = 76 min for 30%, T2 = 3.15 days for 40% of the deposited material. The delayed clearance phase for the remaining 30% of the deposited material approaches a constant rate. Our clearance values were compared with those of the Task Group of Lung Dynamics (T.G.L.D.) and other authors' results, especially for T1 and T2. These values are analyzed in terms of mucus velocity and mucociliary transport in distal conductive airways. Impaired transport reduces natural defenses and increases toxicological hazards. Therefore reliable techniques for detecting such impairment may be important in evaluating pulmonary involvement in environmental respiratory disease.