Lung tissue resistance and the hysteretic moduli of lung
parenchyma.
Kimmel, Eitan, Michal Seri, Jeffrey J. Fredberg.
Department of Agricultural Engineering, Technion, Haifa 32000,
Israel, Physiology Program, Department of Environmental Health,
Harvard School of Public Health, Boston MA 02115, USA
APStracts 2:0158A, 1995.
Lung tissue resistance Rtis represents a large and labile component of
total pulmonary resistance, but mechanism is unknown. One hypothesis
that has received some support in the literature is that upon
exposure to contractile agonists airway smooth muscle shortens and
then, by the agency of elastic interdependence, induces distortion in
surrounding parenchyma. Parenchymal distortion induced in the
vicinity of a constricted airway is a pure shear deformation, but
currently there are no data available for shear hysteresivity. Guided
by a microstructural model we have assigned stiffness and
hysteresivity to microstructural elements and then computed how those
properties are expressed at the macroscale in bulk hysteresivities
for both shear and volumetric expansion. Hysteresivity for volumetric
expansion is shown to be a stiffness-weighted average of
hysteresivities of all microstructural components. But as the
hysteresivity of microstructural elements increases, that for shear
deformation increases to some degree but eventually attains a
plateau. Blunted hysteretic response in shear seems to be an
intrinsic property of pressure-supported structures, like the lung,
that require an inflating pressure to ensure mechanical stability.
The analysis indicates that that part of Rtis attributable to
parenchymal distortion can be at most a small fraction of that
attributable to volumetric expansion. These results are purely
theoretical in nature and this suggests that caution is necessary in
their interpretation. However, the mechanical basis of the results is
sufficiently general to conclude that the hypothesis that parenchymal
distortion secondary to bronchoconstriction can account for Rtis and
its changes seems to be implausible.
Received 3 June 1994; accepted in final form 15 March 1995.
APS Manuscript Number A549-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 19 April 1995.