Journal of Applied Physiology, Vol 80, Issue 4 1165-1172, Copyright © 1996 by American Physiological Society
Assessment of local lung impedance by the alveolar capsule oscillator in dogs: a model analysis
M. Mishima, Z. Balassy and J. H. Bates
Meakins-Christie Laboratories, McGill University, Montreal, Quebec, Canada.
The alveolar capsule oscillator technique has shown that the response of
the lung periphery to intravenous histamine injection in dogs is extremely
inhomogeneous both in terms of local peripheral airway resistance (RA) and
local peripheral elastance (EA) (M. Mishima, Z Balassy, and J. H. T. Bates.
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 K. Horsfield, W. Kemp, and S. Philips (J. Appl. Physiol. 52:
21-26, 1982). The acoustic impedance 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 acoustic impedance between 26 and 200 Hz and
were found to be 492 hPa.s.l-1 and 156,300 hPa/l, 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 approximately 50% of RA is determined by the acinus to
which the alveolar capsule is attached, whereas the remainder is determined
by airways < or = 1 mm diameter that converge on this acinus. By
contrast, EA was determined almost entirely (95%) by the acinus directly
under the capsule. Inhomogeneous peripheral airway constriction altered RA
severalfold but did not affect EA by >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.
