Temporal dynamics of acute isovolume bronchoconstriction in the
rat.
Bates, Jason H. T., Thomas F. Schuessler, Carrie Dolman, David H.
Eidelman.
Meakins-Christie Laboratories and Department of Biomedical
Engineering, McGill University, Montreal, Quebec, H2X 2P2, CANADA
APStracts 3:0412A, 1996.
The time-course of lung impedance changes following i.v. injection of
bronchial agonist have produced significant insights into the
mechanisms of bronchoconstriction in the dog (Bates et al., J. Appl.
Physiol. 76:616-626, 1994). We studied the time-course of acute
induced bronchoconstriction in five anesthetized, paralyzed, open
-chest rats injected i.v. with a bolus of methacholine. For the 16 s
immediately following injection we held the lung volume constant
while applying small-amplitude flow oscillations at 1.48, 5.45 and
19.69 Hz simultaneously, which provided us with continuous estimates
of lung resistance (R) and elastance (E) at each frequency. This
procedure was repeated at initial lung inflation pressures of 0.2,
0.4 and 0.6 kPa. Both R and E increased progressively following
methacholine administration, but the rate of change of E increased
dramatically as frequency was increased whereas R remained relatively
independent of frequency. We interpret these findings in terms of a
three compartment model of the rat lung, featuring two parallel
alveolar compartments feeding into a central airway compartment.
Model simulations support the notions that both central airway
shunting and regional ventilation inhomogeneity developed to a
significant degree in our constricted rats. We also found that the
rates of increase in both R and E were greatly enhanced as the
initial lung inflation pressure was reduced, in accord with the
notion that parenchymal tethering is an important mechanism limiting
the extent to which airways can narrow when their smooth muscle is
stimulated to contract.
Received 19 March 1996; accepted in final form 26 August 1996.
APS Manuscript Number A272-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996