Modeling steady state inert gas exchange in the canine trachea.
George, Steven C., Jennifer E. Souders, Albert L. Babb, Michael P.
Hlastala.
Departments of Chemical Engineering, Anesthesiology, Medicine ,
Physiology and Biophysics, University of Washington, Seattle,
Washington
APStracts 2:0196A, 1995.
The functional dependence between tracheal gas exchange and tracheal
blood flow ( O(Q,.)tr) has been previously reported using six inert
gases (sulfur hexafluoride, ethane, cyclopropane, halothane, ether,
and acetone) in a unidirectionally ventilated ( O(V,.) = 1 ml.s-1)
canine trachea (Souders et al. J. Appl. Physiol., submitted as
companion paper, 1995). In order to understand the relative
contribution of perfusion-, diffusion- and ventilation-related
resistances to airway gas exchange, a dynamic model of the bronchial
circulation has been developed and added to the existing structure of
a previously described model (George et al. J. Appl. Physiol.
75(6):2439-2449, 1993). The diffusing capacity of the trachea (ml
gas.s-1.atm-1) was used to optimize the fit of the model to the
experimental data. The experimental diffusing capacities as predicted
by the model, Dexp, in a 10 cm length of trachea are as follows: SF6,
0.000055; ethane, 0.00070; cyclopropane, 0.0046; halothane, 0.029;
ether, 0.10; and acetone, 1.0. The diffusing capacities are reduced
relative to an estimated diffusing capacity, Dest. The ratio
Dexp:Dest ranges from 4-23%. The model predicts that over the range
of O(V,.)/ O(Q,.)tr attained experimentally (10-700), tracheal gas
exchange is limited primarily by perfusion- and diffusion-related
resistances. However, the contribution of the ventilation-related
resistance increases with increasing gas solubility and cannot be
neglected in the case of acetone. The increased role of diffusion in
tracheal gas exchange contrasts with perfusion-limited alveolar
exchange and is due primarily to the increased thickness of the
bronchial mucosa.
Received 1 July 1994; accepted in final form 29 March 1995.
APS Manuscript Number A657-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 16 May 1995.