Journal of Applied Physiology, Vol 79, Issue 6 1921-1929, Copyright © 1995 by American Physiological Society

ARTICLES

Retention of insoluble particles after local intrabronchial deposition in dogs

J. C. Lay, C. R. Berry, C. S. Kim and W. D. Bennett
Center for Environmental Medicine and Lung Biology, University of North Carolina, Chapel Hill 27599, USA.

Recent studies have challenged the generally accepted hypothesis that bronchial particle clearance is complete within 24-48 h postdeposition. We studied bronchial retention of inert particles using a bronchoscope and microspray nozzle to localize deposition in a bronchus while avoiding alveolar deposition. Six-microliter aliquots (444 kBq) of submicrometer (number mean diameter = 0.22 microns, geometric standard deviation = 1.75) technetium-99m-labeled (99mTc) sulfur colloid (SC) particles (n = 6) or the unbound radiolabel 99mTc-pertechnetate (99mTcO4-; n = 3) were sprayed onto a 5-mm-diam bronchus in halothane-anesthetized dogs. Radioactivity at the deposition site and clearance pathway was monitored externally with a gamma camera beginning immediately postspray. Bronchial retention of SC was 8.5 +/- 2.4 and 1.5 +/- 0.7% at 3 and 24 h postspray, respectively. Tracheal mucus velocity was measured at 10.4 +/- 2.2 mm/min. For comparison, clearance of inhaled submicrometer SC particles was also measured in the same dogs. Retention of inhaled aerosolized SC (peripheral lung deposition) was 98.1 +/- 1.1 and 76.3 +/- 1.8% at 3 and 24 h, respectively. 99mTcO4- cleared from the bronchi slightly more rapidly than did SC. Radioactivity was readily detected in the blood after deposition of 99mTcO4- but not of SC. Thus SC cleared by mucociliary transport, whereas 99mTcO4- cleared predominantly by transepithelial absorption. We conclude that clearance of submicrometer particles from a 5-mm conducting airway is very nearly complete by 24 h, with approximately 92% of the clearance occurring within the first 3 h postdeposition.

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