The human lung comprises about 300 million alveoli which are located on bronchioles between the 17th to 24th generations of the acinar tree, with a progressively higher population density in the deeper branches (lower acini). The alveolar size and aspect ratio change with generation number. Due to successive bifurcation, the flow velocity magnitude also decreases as the bronchiole diameter decreases from the upper to lower acini. As a result, fluid dynamic parameters such as Reynolds (Re) and Womersley (α) numbers progressively decrease with increasing generation number. In order to characterize alveolar flow patterns and inhaled particle transport during synchronous ventilation, we have conducted measurements for a range of dimensionless parameters physiologically relevant to the upper acini. Acinar airflow patterns were measured using a simplified in vitro alveolar model consisting of a single transparent elastic truncated sphere (representing the alveolus) mounted over a circular hole on the side of a rigid circular tube (representing the bronchiole). The model alveolus was capable of expanding and contracting in-phase with the oscillatory flow through the bronchiole thereby simulating synchronous ventilation. Realistic breathing conditions were achieved by exercising the model over a range of progressively varying geometric and dynamic parameters to simulate the environment within several generations of the acinar tree. Particle image velocimetry was used to measure the resulting flow patterns. Next, we used the measured flow fields to calculate particle trajectories to obtain particle transport and deposition statistics for massless and finite-size particles under the influence of flow advection and gravity. Our study shows that the geometric parameters (β and ΔV/V) primarily affect the velocity magnitudes, whereas the dynamic parameters (Re and α) distort the flow symmetry while also altering the velocity magnitudes. Consequently, the dynamic parameters have a greater influence on the particle trajectories and deposition statistics compared to the geometric parameters. The results from this study can benefit pulmonary research into the risk assessment of toxicological inhaled aerosols, and the pharmaceutical industry by providing better insight into the flow patterns and particle transport of inhalable therapeutics in the acini.

References

References
1.
Weibel
,
E. R.
, 1963,
Morphometry of the Human Lung,
Academic Press
,
New York
.
2.
Bleuer
,
B. H.
, and
Weibel
,
E. R.
, 1988, “
Morphometry of the Human Pulmonary Acinus
,”
Anat. Rec.
,
220
, pp.
401
414
.
3.
Zeltner
,
T. B.
,
Caduff
,
J. H.
,
Gehr
,
P.
,
Pfenninger
,
J.
, and
Burri
,
P. H.
, 1987, “
The Postnatal Development and Growth of the Human Lung. I. Morphometry
,”
Respir. Physiol.
,
67
, pp.
247
267
.
4.
Angus
,
G. E.
, and
Thurlbeck
,
W. M.
, 1972, “
Number of Alveoli in the Human Lung
,”
J. Appl. Physiol.
,
32
, pp.
483
485
.
5.
Burri
,
P. H.
, 2006, “
Structural Aspects of Postnatal Lung Development—Alveolar Formation and Growth
,”
Biol Neonate
,
89(4)
, pp.
313
322
.
6.
Federspiel
,
W. J.
, and
Fredberg
,
J. J.
, 1988, “
Axial Dispersion in Respiratory Bronchioles and Alveolar Ducts
,”
J. Appl. Physiol.
,
64
, pp.
2614
2621
.
7.
Tsuda
,
A.
,
Henry
,
F. S.
, and
Butler
,
J. P.
, 2008, “
Gas and Aerosol Mixing in the Acinus
,”
Respir, Physiol, Neurobiol
,
163
, pp.
139
149
.
8.
Darquenne
,
C.
, and
Paiva
,
M.
, 1996, “
Two- and Three-Dimensional Simulations of Aerosol Transport and Deposition in Alveolar Zone of Human Lung
,”
J. Appl. Physiol.
,
80
, pp.
1401
1414
.
9.
Tsuda
,
A.
,
Butler
,
J. P.
, and
Fredberg
,
J. J.
, 1994, “
Effects of Alveloated Duct Structure on Aerosol Kinetics I. Diffusional Deposition in the Absence of Gravity
,”
J. Appl. Physiol.
,
76
, pp.
2497
2509
.
10.
Tsuda
,
A.
,
Butler
,
J. P.
, and
Fredberg
,
J. J.
, 1994, “
Effects of Alveloated Duct Structure on Aerosol Kinetics II. Gravitational Sedmimentation and Inertial Impaction
,”
J. Appl. Physiol.
,
76
, pp.
2510
2516
.
11.
Tsuda
,
A.
,
Henry
,
F. S.
, and
Butler
,
J. P.
, 1995, “
Chaotic Mixing of Alveolated Duct Flow in Rhythmically Expanding Pulmonary Acinus
,”
J. Appl. Physiol.
,
79
, pp.
1055
1063
.
12.
Tippe
,
A.
, and
Tsuda
,
A.
, 2000, “
Recirculating Flow in an Expanding Alveolar Model: Experimental Evidence of Flow-Induced Mixing of Eerosols in the Pulmonary Acinus
,”
J. Aerosol. Sci.
,
31
, pp.
979
986
.
13.
Karl
,
A.
,
Henry
,
F.
, and
Tsuda
,
A.
, 2004, “
Low Reynolds Number Viscous Flow in an Alveolated Duct
,”
J. Biomech. Eng.
,
126
, pp.
420
429
.
14.
van Ertbruggen
,
C.
,
Corieri
,
P.
,
Theunissen
,
R.
,
Riethmuller
,
M.
, and
Darquenne
,
C.
, 2008, “
Validation of cfd Predictions of Flow in a 3d Alveolated Bend with Experimental Data
,”
J. Biomech. Eng.
,
41
, pp.
399
405
.
15.
Sznitman
,
J.
,
Heimsch
,
F.
,
Heimsch
,
T.
,
Rusch
,
D.
, and
Rosgen
,
T.
, 2007, “
Three-Dimensional Convective Alveolar Flow Induced by Rhythmic Breathing Motion of the Pulmonary Acinus
,”
J. Biomech. Eng.
,
129
, pp.
658
665
.
16.
Sznitman
,
J.
,
Heimshch
,
T.
,
Wildhaber
,
J. H.
,
Tsuda
,
A.
, and
Rosgen
,
T.
, 2009, “
Respiratory Flow Phenomena and Gravitational Deposition in a Three-Dimensional Space-Filling Model of the Pulmonary Acinar Tree
,”
J. Biomech. Eng.
,
131
, pp.
1
15
.
17.
Kumar
,
H.
,
Tawhai
,
M. H.
,
Hoffman
,
E. A.
, and
Lin
,
C. L.
, 2009, “
The Effects of Geometry on Airflow in the Acinar Region of the Human Lung
,”
J. Biomech. Eng.
,
42
, pp.
1635
1642
.
18.
Li
,
Z.
,
Kleinstreuer
,
C.
, and
Zhang
,
Z.
, 2007, “
Particle Deposition in the Human Tracheobronchial Airways Due to Transient Inspiratory Flow Patterns
,”
J. Aerosol. Sci.
,
38
, pp.
625
644
.
19.
Li
,
Z.
,
Kleinstreuer
,
C.
, and
Zhang
,
Z.
, 2007, “
Simulation of Airflow Fields and Microparticle Deposition in Realistic Human Lung Airway Models. Part I: Airflow Patterns
,”
Eur. J. Mech. B Fluids
,
26
, pp.
632
649
.
20.
Henry
,
F. S.
,
Laine-Pearson
,
F. E.
, and
Tsuda
,
A.
, 2009, “
Hamiltonian Chaos in a Model Alveolus
,”
J. Biomech. Eng.
,
131
, p.
011006
.
21.
Haber
,
S.
,
Butler
,
J. P.
,
Brenner
,
H.
,
Emaneul
,
I.
, and
Tsuda
,
A.
, 2000, “
Shear Flow Over a Self-Similar Expanding Pulmonary Alveolus During Rhythmical Breathing
,”
J. Fluid Mec.h
,
405
, pp.
243
268
.
22.
Chhabra
,
S.
, and
Prasad
,
A. K.
, 2010, “
Flow and Particle Dispersion in a Pulmonary Alveolus–Part I: Velocity Measurements and Convective Particle Transport
,”
J. Biomech. Eng.
,
132
, p.
051009
.
23.
Chhabra
,
S.
, and
Prasad
,
A. K.
, 2010, “
Flow and Particle Dispersion in a Pulmonary Alveolus–Part II: Effect of Gravity on Particle Transport
,”
J. Biomech. Eng.
,
132
, p.
051010
.
24.
Tsuda
,
A.
,
Filipovic
,
N.
,
Haberthur
,
D.
,
Dickie
,
R.
,
Stampanoni
,
M.
,
Matsui
,
Y.
, and
Schittny
,
J. C.
, 2008, “
The Finite Element 3d Reconstruction of the Pulmonary Acinus Imaged by Synchrotron X-Ray Tomography
,”
J. Appl. Physiol.
,
105
, pp.
964
976
.
25.
Haber
,
S.
,
Yitzhak
,
D.
, and
Tsuda
,
A.
, 2003, “
Gravitational Deposition in a Rhythmically Expanding and Contracting Alveolus
,”
J. Appl. Physiol.
,
95
, pp.
657
671
.
26.
Cunningham
,
E.
, 1910, “
On the Velocity of Steady Fall of Spherical Particles Through Fluid Medium
,”
Proc. R. Soc. A
,
83
, pp.
357
365
.
27.
Pedley
,
T. J.
, 1977, “
Pulmonary Fluid Dynamics
,”
Ann. Rev. Fluid Mech.
,
9
, pp.
229
274
.
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