title: Retention of insoluble particles after local intrabronchial deposition in dogs.
abstract: 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.
authors.affiliation: Center for Environmental Medicine and Lung Biology, University of North Carolina, Chapel Hill 27599, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Lay
authors.forename: C R
authors.initials: CR
authors.lastname: Berry
authors.forename: C S
authors.initials: CS
authors.lastname: Kim
authors.forename: W D
authors.initials: WD
authors.lastname: Bennett
mesh_terms: D000818:Animals; D001980:Bronchi / Q000502:physiology*; D003102:Colloids / Q000378:metabolism; D004285:Dogs; D005260:Female; D007091:Image Processing, Computer-Assisted; D008168:Lung / Q000502:physiology*; D008297:Male; D009079:Mucociliary Clearance / Q000502:physiology*; D012143:Respiratory Physiological Phenomena; D013997:Time Factors
chemical_list: D003102:Colloids