Airway and alveolar permeability and surface liquid thickness:
theory.
Widdicombe, John.
Dept of Physiology, St George's Hospital Medical School, Cranmer
Terrace, London, SW17 0RE, U.K.
APStracts 3:0458A, 1996.
The thickness of airway surface liquid (ASL) can be calculated as the
ratio of the permeability coefficient of an absorbed inert tracer to
the percentage rate in which it decreases in content in the airway
lumen. The percentage clearance of radiolabelled DTPA from human
airways or lungs has been measured many times, with a mean value of
1.04 +/- 0.25 %.min-1 (SD). Rates of clearance from animal lungs of
most species give values of the same order, although lower in the
sheep and higher in the dog. Permeability coefficients have not been
measured simultaneously with percentage clearances, and not at all
for human tissues. Values for mannitol and sucrose, of which the
former gives a permeability coefficient about 25% greater than for
sucrose and DTPA in airway tubes and isolated mucosal sheets from
experimental animals, give a mean of about 7.1 x 10-7 cm.s-1. This
corresponds to thicknesses of ASL of about 20-150 [mu]m for various
species. The assumptions underlying this estimate are discussed. It
is concluded that ASL thickness in vivo may be considerably greater
than in vitro measurements involving rapid freezing of the airway
wall. Estimates of alveolar permeability suggest that either it is
very considerably lower than that of the airway epithelium, or that
methods to measure alveolar permeability mainly reflect airway
permeability, or both.
Received 27 September 1996; accepted in final form 27 September
1996.
APS Manuscript Number A949-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996