Relationship between frequency and amplitude dependence in the
lung: a nonlinear block-structured modeling approach.
Suki, B[acute]ela, Qin Zhang, Kenneth R. Lutchen.
Department Biomedical Engineering, Boston University, 44 Cummington
St., Boston, MA 02215
APStracts 2:0144A, 1995.
During lung constriction there is an increase in both the frequency
and tidal volume (VT) dependences of lung tissue resistance (Rti) and
elastance (Eti). This suggests that a) significant alterations take
place in the mechanisms contributing to both the linear and nonlinear
characteristics of lung tissues; and b) the frequency and VT
-dependences of Rti and Eti are coupled. We examined these issues for
the case of sine wave and special pseudorandom inputs by utilizing
the theory of nonlinear block structured systems. Two basic model
structures were considered: the Hammerstein and the Wiener
structures. The Hammerstein structure is a cascade connection of a
nonlinear zero-memory (N) system and a linear dynamic process (L).
This structure predicts that frequency and VT dependences of Rti and
Eti are decoupled. The Wiener structure is an inverse cascade of
these two blocks (i.e., L-N) in which the frequency and VT
dependences of Rti and Eti are coupled. These two structures were
combined with a nonlinear airway compartment and fitted to measured
airway opening and alveolar capsule pressure-flow time domain data in
dogs before and after histamine induced constriction. The best lung
model was a linear airway compartment combined with a Wiener
structure consisting of a constant phase linear tissue impedance in
cascade with a polynomial nonlinearity suggesting that frequency and
VT dependences of Rti and Eti are indeed coupled during control and
constricted conditions. Moreover, histamine caused much larger
changes in the linear tissue parameters than in the nonlinear
coefficients. We suggest that the primary cause for the increased VT
dependence during constriction is not a change in the nonlinear
mechanisms but rather the inherent nonlinear mechanisms become
exacerbated through an increase in the magnitude of the linear tissue
impedance.
Received 1 September 1994; accepted in final form 27 March 1995.
APS Manuscript Number A920-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 April 1995.