Effects of surface tension and intraluminal fluid on the mechanics
of small airways.
Hill, Mark J., Theodore A. Wilson, and Rodney K. Lambert.
Department of Aerospace Engineering and Mechanics, University of
Minnesota, Minneapolis, MN 55455; and Department of Physics and
Biophysics, Massey University, Palmerston North, New Zealand
APStracts 3:0450A, 1996.
Airway constriction is accompanied by folding of the the mucosa to
form ridges that run axially along the inner surface of the airways.
Lambert (J. Appl. Physiol. 71: 666-673, 1991) has modeled the muscosa
as a thin elastic layer with a finite bending stiffness and computed
the contribution of its bending stiffness to airway elastance. In
this paper, we extend that work by including surface tension and
intraluminal fluid in the model. With surface tension, the pressure
on the inner surface of the elastic mucosa is modified by the
pressure difference across the air-liquid interface. As folds form in
the mucosa, intraluminal fluid collects in pools in the depressions
formed by the folds, and the curvature of the air-liquid interface
becomes nonuniform. If the amount of intraluminal fluid is small,
< 2% of lumen volume, the pools of intraluminal fluid are
small, the air-liquid interface nearly coincides with the surface of
the mucosa, and the area of the air-liquid interface remains constant
as airway cross-sectional area decreases. In that case, surface
energy is independent of airway area, and surface tension has no
effect on airway mechanics. If the amount of intraluminal fluid is
> 2%, the area of the air-liquid interface decreases as airway
cross-sectional area decreases, and surface tension contributes to
airway compression. The model predicts that surface tension plus
intraluminal fluid can cause an instability in the area-pressure
curve of small airways. This instability provides a mechanism for
abrupt airway closure and abrupt reopening at a higher opening
pressure.
Received 13 March 1996; accepted in final form 9 September 1996.
APS Manuscript Number A251-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996