Chaotic mixing of alveolated duct flow in rhythmically expanding
pulmonary acinus.
Tsuda, Akira, Frank S. Henry, and James P. Butler.
Physiology Program, Harvard School of Public Health, The
Biomechanics Institute, Boston, MA 02115 and Department of Mechanical
Engineering and Aeronautics, City University, London, U.K.
APStracts 2:0274A, 1995.
We examined the effects of rhythmic expansion of alveolar walls on
fluid mechanics in the pulmonary acinus. We generated a realistic
geometric model of an alveolated duct which expanded and contracted
in a geometrically similar fashion to simulate tidal breathing. Time
-dependent volumetric flow was generated by adjusting the proximal and
distal boundary conditions. The low Reynolds number velocity field
was solved numerically over the physiological range. We found that
for a given geometry the ratio of the alveolar flow (Qa) to the
ductal flow (Qd) played a major role in determining the flow pattern.
For larger Qa/Qd (as in the distal region in the acinus), the flow in
the alveolus was largely radial. For small Qa/Qd (as in the proximal
region in the acinus), the flow in the alveolus was slowly rotating
and the velocity field near the alveolar opening was complex with a
stagnation saddle point, typical of chaotic flow structures.
Performing Lagrangian fluid particle tracking, we demonstrated that
in such a flow structure the motion of fluid could be highly complex,
irreversible, and unpredictable even though it was governed by simple
deterministic equations. These are the characteristics of chaotic
flow behavior. We conclude that because of the unique geometry of
alveolated duct and its time-dependent motion associated with tidal
breathing, chaotic flow and chaotic mixing can occur in the lung
periphery. Based on these novel observations we suggest a new
approach for studying acinar fluid mechanics and aerosol kinetics.
Received 17 April 1995; accepted in final form 13 June 1995.
APS Manuscript Number A419-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.