Assessment of local lung impedance by the alveolar capsule
oscillator in dogs: a model analysis.
Mishima, M., Z. Balassy, and J. H. T. Bates.
Meakins-Christie Laboratories and Department of Biomedical
Engineering, McGill University, Montreal, Quebec, H2X 2P2, Canada
APStracts 2:0527A, 1995.
The alveolar capsule oscillator technique has shown that the response
of the lung periphery to i.v. histamine injection in dogs is
extremely inhomogeneous both in terms of local peripheral airway
resistance (RA) and local alveolar elastance (EA) (Mishima et al., J.
Appl. Physiol., 77: 2140-2148, 1994). To assess the physical extent
of the local lung region identified by this technique we performed
computer simulations using an asymmetrical branching model of the
canine lung proposed by Horsfield et al. (J. Appl. Physiol. 52: 21
-26, 1982). The acoustic impedance (ZA) of the model from 26 to 200 Hz
as seen from the alveolar capsule oscillator was calculated. RA and
EA were estimated from the simulated ZA between 26 and 200 Hz, and
were found to be 492 hPa.s.l-1 and 156,300 hPa.l-1, respectively.
These values are similar to those found experimentally in previous
studies. By simulating data using the model in various stages of
completeness we determined that about 50% of RA is determined by the
acinus to which the alveolar capsule is attached, while the remainder
is determined by the airways of diameter 1 mm or less that converge
upon this acinus. By contrast, EA was determined almost entirely
(95%) by the acinus directly under the capsule. Inhomogeneous
peripheral airway constriction altered RA by several fold, but did
not affect EA by more than 5%. This suggests that the previously
observed changes induced in EA by bronchial challenge reflect real
changes in intrinsic tissue elastance rather than merely regional
mechanical inhomogeneities.
Received 26 June 1995; accepted in final form 20 November 1995.
APS Manuscript Number A688-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95