The interaction between airway lining fluid forces and parenchymal
tethering during pulmonary airway reopening.
Perun, Matthew L., and Donald P. Gaver.
Department of Biomedical Engineering, Tulane University, New
Orleans, Louisiana 70118
APStracts 2:0257A, 1995.
In this study, our goal is to identify the interaction between airway
lining fluid viscous and surface forces and parenchyma tethering
forces during pulmonary airway reopening. The type of closure we
modeled occurs when the airway walls and surrounding parenchyma
collapse and are held in apposition by the lining fluid. We mimicked
this system with a polyethylene tube coated with a Newtonian lining
fluid, supported by open-cell foam. Reopening occurs when a finger of
air travels through the collapsed region. We measured the airway
pressure (PAW) required to open the airway at a constant velocity
(U). Increasing either the foam stiffness (K), lining fluid viscosity
([mu]), and surface tension ( ) results in an increase of PAW.
Furthermore, increasing the downstream suction pressure (PDN),
through tethering, causes an equivalent reduction of PAW. The
upstream radius is the primary length scale, and fluid forces are
represented by Ca = [mu]U/ . Based on these results, we predicted the
likelihood that tethering would begin to reopen collapsed airways in
various disease states. This analysis showed that the ratio of
tethering and fluid forces determines airway patency, as defined by
the parameter = PTRANS/( /R), where PTRANS = PAW - PDN. Finally,
transpulmonary pressure dependent surface tension appears to be
necessary to stabilize the lung.
Received 17 February 1995; accepted in final form 8 June 1995.
APS Manuscript Number A189-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.