Particle penetration and clearance in the human lung. Results in healthy subjects and subjects with chronic bronchitis.

Five-micron diameter radioactive tracer particles have been employed to compare the depth of penetration into the lung during inhalation (by scanning) and the subsequent fast phase clearance (by whole lung counting) in eight healthy aged subjects and nine subjects with chronic bronchitis. All but one subject in each group were smokers. Under standard conditions of inhalation the uniform particles penetrated deeper into the healthy rather than into the bronchitic lung. In the scans in both groups the traverse counts at 1-inch intervals regressed from the hilum laterally to the periphery but the mean regression for the bronchitics (-10.13 ± 0.94 SE) significantly exceeded that for the healthy subjects (-5.26 ± 1.00 SE; P<.005). The particles were cleared from the bronchitic lungs faster than from the healthy lungs (mean retention at six hours 53% in bronchitics as compared with 70% in the healthy group).