Retention of insoluble particles following local intrabronchial
deposition in dogs.
Lay, John C., Clifford R. Berry, Chong S. Kim, William D. Bennett.
Center for Environmental Medicine and Lung Biology, College of
Medicine, University of North Carolina, Chapel Hill, NC 27599,
Department of Anatomy, Physiological Science and Radiology, College
of Veterinary Medicine, North Carolina State University, Raleigh, NC
27606, United States Environmental Protection Agency, Health Effects
Research Laboratory, Clinical Research Branch, Chapel Hill, NC
27599
APStracts 2:0304A, 1995.
Recent studies have challenged the generally accepted hypothesis that
bronchial particle clearance is complete within 24 to 48 hours post
-deposition. We studied bronchial retention of inert particles, using
a bronchoscope and microspray nozzle to localize deposition in a
bronchus while avoiding alveolar deposition. Six-[mu]l aliquots
(444kBq) of submicron (NMD = 0.22 [mu]m, sg=1.75) 99mTc-sulfur
colloid particles (SC, n=6) or the unbound radiolabel, 99mTc
-pertechnetate (99mTcO4-, n=3), were sprayed onto a 5mm diameter
bronchus in Halothane-anesthetized dogs. Radioactivity at the
deposition site and clearance pathway was monitored externally with a
gamma camera, beginning immediately post-spraying. Bronchial
retention of SC was 8.5 +/- 2.4% and 1.5 +/- 0.7%, respectively, at 3
and 24 hours post-spray. Tracheal mucus velocity was measured at 10.4
+/- 2.2 mm/minute. For comparison, clearance of inhaled submicron SC
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 hours, respectively. 99mTcO4- cleared from the bronchi
slightly more rapidly than SC. Radioactivity was readily detected in
the blood following deposition of 99mTcO4-but not SC. Thus, SC
cleared by mucociliary transport, while 99mTcO4-cleared predominantly
by transepithelial absorption. We conclude that clearance of
submicron particles from a 5mm conducting airway is very nearly
complete by 24 hours, with approximately 92% of the clearance
occurring within the first 3 hours post-deposition.
Received 15 February 1995; accepted in final form 7 July 1995.
APS Manuscript Number A185-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.