A study of particulate clearance from the human lungs.

Volunteers were exposed to /sup 54/MnO/sub 2/, iron oxide labeled with /sup 51/Cr, and polystyrene particles labeled with /sup 51/Cr. External counting was done at 7 pulmonary locations. Estimated activity (mass) median diameters for the 3 aerosols were 0.9, 0.8, and 0.5 ..mu..m, respectively. Clearance was described by a series of exponentials: one each for tracheal and upper bronchial and 3 for lower bronchial and parenchyma. Biological halftimes for the 5 phases were 2.7, 24 to 29, 80 to 120, and approx. 300 min and 35 to 65 days, respectively. Computed mean velocity (cm/min) of the particles would be 1.4, 0.1, 0.05, 0.01, and not stated, respectively. Clearances of the 3 aerosols were kinetically similar.

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