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Vol. 83, Issue 6, 2029-2036, December 1997
1 Department of Medicine, University of California, San Diego, La Jolla, California 92093-0931; and 2 Biomedical Physics Laboratory, Université Libre de Bruxelles, Brussels, Belgium
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
APPENDIX
ACKNOWLEDGEMENTS
FOOTNOTES
REFERENCES
ABSTRACT 
Darquenne, Chantal, Manuel Paiva, John B. West, and G. Kim
Prisk. Effect of microgravity and hypergravity on deposition of
0.5- to 3-µm-diameter aerosol in the human lung. J. Appl. Physiol. 83(6): 2029-2036, 1997.
We
measured intrapulmonary deposition of 0.5-, 1-, 2-, and 3-µm-diameter
particles in four subjects on the ground (1 G) and during parabolic
flights both in microgravity (µG) and at ~1.6 G. Subjects breathed aerosols at a constant flow rate (0.4 l/s) and tidal
volume (0.75 liter). At 1 G and ~1.6 G, deposition increased with
increasing particle size. In µG, differences in deposition as a
function of particle size were almost abolished. Deposition was a
nearly linear function of the G level for 2- and 3-µm-diameter
particles, whereas for 0.5- and 1.0-µm-diameter particles, deposition
increased less between µG and 1 G than between 1 G and ~1.6 G. Comparison with numerical predictions showed good agreement for 1-, 2-, and 3-µm-diameter particles at 1 and ~1.6 G, whereas the model
consistently underestimated deposition in µG. The higher deposition
observed in µG compared with model predictions might be explained by
a larger deposition by diffusion because of a higher alveolar
concentration of aerosol in µG and to the nonreversibility of the
flow, causing additional mixing of the aerosols.
aerosol deposition; gravity; human lung
INTRODUCTION THE DEPOSITION OF AEROSOLS in the human lung is
primarily due to the mechanisms of inertial impaction, sedimentation,
and Brownian diffusion. Inertial impaction causes most of the particles >5 µm to deposit in the upper airways. Brownian diffusion affects smaller particles (<0.5 µm), which deposit mainly in the alveolar region. Sedimentation is the gravitational settling of particles and
mainly affects particles in the size range 1-5 µm. Of these three mechanisms, sedimentation is a gravitation-dependent process and
is therefore expected to be changed in altered gravity (G) environments. Besides affecting sedimentation, G is also responsible for regional differences in ventilation. Because the lung distorts under its own weight, the alveoli at the base of the lung are relatively compressed compared with the apical alveoli, and, because poorly expanded alveoli are more compliant, ventilation is greatest near the bottom of the lung and becomes progressively reduced near the
top. Changes in the G level (i.e., in lung weight) will affect the
distribution of ventilation and are therefore expected to affect the
distribution and deposition of aerosols.
In a theoretical analysis in 1967, Muir (15) examined the influence of
G on aerosol deposition in the lungs of subjects on the surface of the
moon ( In a spacecraft environment, the potential for significant airborne
particle concentrations is high because the environment is closed and
no sedimentation occurs. Measurements in the US Space Shuttle air
environment have shown a substantial increase in microbial counts
during missions (9, 14), and a large variety of airborne particles,
including hair, food, paint chips, and synthetic fibers, has been
found. It is therefore of considerable interest to determine the fate
of inhaled aerosols in an environment that has altered gravitational
levels, and hence altered deposition, and a potentially large airborne
particulate load. Furthermore, many drugs are now administered by
aerosolized drug-delivery systems, and a further understanding of how
gravity affects aerosol deposition is clearly desirable in the
terrestrial environment.
In the present study, we measured total deposition in normal subjects
of aerosols having a diameter spanning the range from 0.5 to 3 µm.
Data were collected on the ground (in 1 G) and aboard the NASA
Microgravity Research Aircraft during parabolic flights in both the
weightless phase (microgravity; µG) and the ~1.6-G pullout phase.
The data are compared with the previous studies (2, 13, 15) and with
predicted numerical values from Darquenne and Paiva's model (3). The
comparison of data obtained in µG and ~1.6 G with deposition at 1 G
helps to elucidate the impact of gravitational sedimentation on
deposition processes. For convenience, the ~1.6 G condition will be
referred to as 1.6 G in the text.
METHODS
G) for particle sizes up to 8 µm. On the basis of
knowledge of such deposition on Earth, he predicted a reduction in the
overall deposition but an increase in deposition in the alveolar
region. He suggested, therefore, that astronauts might be more
susceptible to infection by bacteria penetrating more deeply into the
lung. Beeckmans (2) developed a computer program based on experimental
data available at 1 G to predict deposition within the respiratory
tract. He computed deposition for particle size ranging from 0.2 to 15 µm at decreased G levels, and his computations suggested a lower alveolar deposition than that suggested by Muir (15) at G. Hoffman and Billingham (13) conducted the only experimental study to
date to obtain deposition data at various G levels on a National
Aeronautics and Space Administration (NASA) LearJet. They measured the
deposition of only 2-µm-diameter particles in three different
subjects. They found an almost linear increase in deposition, with
increasing G in the range 0-2 G. However, at 0 G, deposition was
lower than that predicted by Beeckmans (2). Thus the amount of
deposition of aerosol particles of different sizes in the absence of G
is largely unknown.
Fig. 1.
Schematic representation of experimental setup. Subject breathes
aerosol from a reservoir. A 2-way nonrebreathing valve allows subject
to inhale from reservoir and to exhale into room through a filter. An
additional 3-way valve is connected to inhalation port of
nonrebreathing valve, allowing subject to breathe pure air through a
filter before start of experiment. Measurement of aerosol concentration
and flow rate is provided by a photometer and a pneumotachograph
(Fleisch no. 1), respectively. A diffusion dryer is located between
photometer and mouthpiece to remove water vapors from exhaled air.
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(1) |
RESULTS
The effect of G level and particle size on deposition is displayed in
Fig. 2. In Fig.
2A, total deposition averaged over the four subjects (mean ± SD) is plotted as a function of the particle size for each G level. In Fig. 2B,
deposition values are plotted as a function of the particle size for
each G level. The open symbols refer to our data, and the closed
circles refer to data obtained by Hoffman and Billingham (13) by using
2-µm particles. At 1 and 1.6 G, deposition is strongly size
dependent, with the greatest deposition occurring for the largest
particle sizes. Deposition ranged from 16.5 to 44.0% at 1 G and from
20.0 to 60.7% at 1.6 G. In µG, differences in deposition between
particle sizes are almost abolished, with deposition ranging from 12.9 to 14.9%.
, microgravity (µG); 
, 1 G; 
, ~1.6 G. B: total deposition
as a function of G level. 
, 0.5 µm particle diameter
(dp); 
,
dp = 1 µm; 
,
dp = 2 µm; 
,
dp = 3 µm; ,
data from Hoffman and Billingham obtained with 2-µm-diameter
particles (13).
For a given particle size, significant
(P < 0.01) variations from one G
level to the other was found, with lower deposition being present at
lower G levels. Significant (P < 0.03) differences in deposition were also present between different
particle sizes at each G level, except for the deposition of 2- and
3-µm particles in µG, which was not different. Although differences
are smaller in µG, deposition of 0.5-µm particles was found to be
significantly larger than deposition of 1-µm particles. Intrasubject
variability is illustrated in Fig. 3, where
total deposition in each subject is plotted as a function of particle
size for each G level. Intrasubject variability was sufficiently low so
that clear differences in deposition were visible among G levels.
, µG; , 1 G; ,
~1.6 G.
Our data were compared with numerical results obtained by using a
one-dimensional (1D) model developed by Darquenne and Paiva (3). In
that model, a 1D equation describing the transport and deposition of
aerosols is solved in a lung structure based on data of Haefeli-Bleuer
and Weibel (8). The main equations used in the simulations are
summarized in the APPENDIX. The
comparison between the numerical and experimental results is shown on
Fig. 4 for each G level. For
the experimental data, the mean values averaged over the four subjects
are displayed as well as the standard deviation (SD;
left bar of each pair), whereas the
numerical results (right bar of each
pair) are shown with the contribution of each mechanism of deposition
considered in the numerical simulations: impaction is represented by
the open segment, sedimentation by the hatched segment, and diffusion
by the solid segment. In 1 and 1.6 G, the experiments agree with the
numerical data within 1.5 SD, except in the case of 0.5-µm particles
in 1.6 G, for which the simulations predict a lower deposition than we
measured. In µG, the numerical data significantly underestimate
measured deposition for each particle size except 3 µm. Although the
model underestimates deposition in µG, it should be noted that the
model predicts a minimum deposition for 1.0-µm-diameter particles,
and this is consistent with the experimental observations.
Figure 5 shows the total
deposition values obtained on the ground. In Fig.
5A, deposition data are shown for each
subject separately. They are represented by their mean and SD, the SD being an indication of the intrasubject variability. In Fig.
5B, our data averaged over the four
subjects () are compared with experimental data of Heyder et al.
(11, 12): data obtained for a tidal volume of 0.5 liter and a flow rate
of 0.25 l/s () and data obtained for a 1-liter tidal volume and a
flow rate of 0.5 l/s (). Note that these protocols do
not exactly match ours in either flow rate or tidal volume. The last
set of data () in Fig. 5B refers to
data obtained in 20 subjects for a flow rate of 0.4 l/s and a tidal
volume of 0.8 liter (12), a protocol very similar to ours, although
these data are only available for 1- and 3-µm particles. For the
purpose of clarity, this last set of data has been slightly shifted to
the right. Note that in Fig. 5B, the
SD in our data reflects both the intersubject and intrasubject variability.
) is 0.4 l/s. ,
Subject 1; ,
subject 2; ,
subject 3; ,
subject 4.
B: comparison with data of Heyder et
al. (11, 12). , Data from this study averaged over 4 subjects; ,
data from Heyder et al. (11) with
VT = 0.5 liter and
= 0.25 l/s; , data from Heyder et al. (11) with
VT = 1 liter and
= 0.5 l/s; , data from Heyder et al. (12) with
VT = 0.8 liter and
= 0.4 l/s (for clarity, data have been slightly shifted to right).
DISCUSSION
) in Fig.
2B. Although both sets of data show an
almost linear increase of deposition with increasing G level, the
increasing rate is higher in our study than in Hoffman and
Billingham's study.
If the different mechanisms of deposition were independent, the change
in G level would only affect deposition by sedimentation, which is a
gravitational process. According to Stokes' law, particles sediment
with a velocity
(vs)
|
(2) |
p is particle density,
dp is particle
diameter, and µ is gas viscosity. With the assumption of an unlimited
source of aerosols, deposition by sedimentation should increase
linearly with G and in a quadratic way with
dp. For the
biggest particles (2 and 3 µm), diffusion may be neglected and
deposition is mainly due to sedimentation in the distal airways and
impaction in the upper airways. Impaction is gravity independent and
increases also in a quadratic way with
dp (see
Eq. A4). For a given particle size,
deposition by sedimentation should increase linearly and deposition by
impaction should be constant. Therefore, total deposition should
increase linearly with G.
On the other hand, for a given G level, both deposition by
sedimentation and impaction should vary in a quadratic way with the
particle size. Deposition by impaction occurs in the upper airways and
affects the number of particles available for deposition by
sedimentation in the smaller airways. Thus the number of particles available to deposit by sedimentation decreases with increasing particle size, and the use of Eq. 2 to
describe total deposition is no longer as straightforward as it was for
a given particle size at different G levels.
As we would expect, deposition of 2- and 3-µm particles varies almost
linearly with altered G level (Fig. 2). For 0.5- and 1-µm particles,
however, if we assume that the relationship between 1 and 1.6 G defines
the gravitational influence, then the extrapolation to µG predicts a
deposition less than that measured, especially for 1.0-µm-diameter
particles, where deposition in µG would be expected to approach zero.
Because the deposition by impaction is negligible for these small
particles, a plausible explanation for the results in µG might be a
larger deposition by diffusion because sedimentation is absent in µG.
The absence of deposition by sedimentation increases the aerosol
concentration in the small airways, leaving a larger number of
particles available for deposition by diffusion and/or for
being transported more deeply in the lung, where deposition by
diffusion may also occur. This is reflected in the results of the
simulation, which show a much increased deposition component because of
diffusion in µG compared with 1 and 1.6 G (Fig. 4). Deposition by
diffusion decreases from 8.4% in µG to 7.3% at 1.6 G for 0.5-µm
particles, from 5.6 to 3.6% for 1-µm particles, from 3.8 to 1.4%
for 2-µm particles, and from 3.0 to 0.6% for 3-µm particles.
Despite this, deposition is still underestimated by the model. A
possible effect is the nonreversibility of flows in the airways of the
human lung (19). During reciprocal tidal breathing, unequal time
constants in different parts of the lung and other perturbations, such
as the mechanical pulsations of the heart, all serve to make flow
reversals within the lung asymmetric. Thus an additional mixing effect
is introduced that will serve to move the particles in the direction of
the alveoli. This would have the effect of increasing the apparent
contribution of diffusional loss of particles in the lung. In the
absence of gravity, with the reduction in losses due to sedimentation,
this effect will become more prominent than in 1 G.
Another factor that may explain that deposition in µG is larger than
we expected is the reduction in the functional residual capacity (FRC)
that occurs in the weightless environment (6, 7, 16, 17). Elliot et al.
(7) found that during sustained periods of µG, FRC decreased
significantly by 15% (500 ml) compared with 1 G standing FRC. Paiva et
al. (16) and Edyvean et al. (6) also demonstrated a 200- to 500-ml
decrease in FRC during short periods of µG. Davies et al. (5) and
Heyder et al. (10) showed that deposition increased as the resting
expiratory reserve volume was decreased. For 0.5-µm-diameter
particles, Davies et al. (5) found an ~2.5% increase in deposition
when the tests were performed from (FRC 
500 ml) instead of FRC.
Therefore, the reduction in FRC observed in µG likely contributes to
the higher deposition than would be expected if the tests were
performed from the same FRC as in 1 G. However, this increase remains
lower than what we observed in our measurements. Thus, even if we
correct for the reduction in FRC in µG by using a controlled
protocol, deposition will still be higher than that predicted by the
model.
An interesting observation shown in Fig. 3 is the very small
intrasubject variability of the µG data. This result seems
surprising, in view of the more difficult experimental conditions
during a parabolic trajectory than on the ground. A potential
explanation may be the sensitivity of deposition by gravitational
sedimentation to the conditions of the test, such as flow or tidal
volume. This observation is very promising in the sense that
experiments in µG will help in studying the different mechanisms
(except gravitational sedimentation) that affect aerosol behavior in
the lung without the disturbing influence of gravity. In particular,
the use of aerosol boli in µG will allow the determination of
deposition at different depths within the lung. Performing the bolus
tests with small or large particles will allow better estimates of
deposition by diffusion or impaction, respectively. These experimental
data could also be used to improve present 1D models, and, more
particularly, the deposition functions used in the 1D equation
describing aerosol transport and deposition in the bronchial tree.
These improvements, in conjunction with further developments of the 1D
models suggested by multidimensional studies on aerosol transport in
the alveolar zone of the lung (4, 21, 22), will allow more accurate predictions of deposition in the respiratory tract.
Figure 3 shows that in subjects 2,
3, and
4, the largest difference between 1 G
and µG occurs for the largest (3-µm) particles, whereas in
subject 1 the difference seems to
plateau between 2- and 3-µm-diameter particles. This difference is
consistent with the results of the simulation (Fig. 4), which show that
deposition due to sedimentation is greatest for the largest particles
at the highest G level. It is predictable, also on the basis of Fig. 4,
that in µG, for particles larger than 3 µm, deposition would increase due to impaction. Comparisons between simulations and experiments in 1 G (Fig. 4B) show an
almost linear increase of deposition with particle diameter for the
simulated results, whereas the experimental observations show higher
deposition for the smallest particles than predicted, and lower
deposition for the largest particles. The higher deposition for the
smallest particles might be explained by the additional diffusional
losses because of the nonreversibility of the flows, as already
discussed above.
Figure 4 shows the contribution of each mechanism of deposition as
computed by the numerical model. In µG, there is, by definition, no
deposition by sedimentation. Small particles (0.5 and 1.0 µm) deposit
almost only by diffusion, whereas deposition by impaction becomes more
and more predominant with increasing particle size. For each particle
size, the fraction of particles that deposit by impaction (open segment
of right bar of each pair) is
independent of the G level, whereas deposition by diffusion decreases
with increasing G level, i.e., when deposition by sedimentation
increases. The interdependence of deposition by diffusion and
deposition by sedimentation might be explained by the fact that they
both take place in the same region of the lung (the distal airways), whereas deposition by impaction occurs in the first generations of the
respiratory tract.
Comparison with previous studies.
Particle deposition at 1 G was compared with data previously obtained
by Heyder et al. (11, 12) for slightly different breathing patterns
(Fig. 5). The first of the three protocols has higher tidal volume and
flow rate than ours, the second one has lower tidal volume and flow
rate, and the last one is similar to ours. In all their protocols,
however, the residence time, defined as the duration of one breath, is
the same and is equal to 4 s. In our protocol, the residence time of
3.75 s is similar. We found particle deposition similar to the data of
Heyder et al., with the exception of 0.5-µm particles, whereby our
results show a slightly higher deposition: 16.2 ± 3.0% compared
with 12%. However, given the intersubject and intrasubject
variability, there are no significant differences between our results
and those of Heyder et al. The large dispersion of aerosol deposition
in different subjects is one of the reasons for the difficulties in the
interpretation of aerosol data. Comparing the first two breathing
protocols, Heyder et al. found the same average deposition for 0.5- and
1-µm particles. For 2- and 3-µm-diameter particles, deposition is
higher for the larger tidal volume, higher flow rate protocol because
these particles deposit mainly by inertial impaction and gravitational
sedimentation. Deposition by inertial impaction increases with the
flow. Sedimentation is a time-dependent process that mainly occurs in
the distal generations of the lung, where the airway dimensions are
smaller. Because the residence time in both protocols is the same, the
increase in deposition in the larger tidal volume, higher flow rate
protocol could be attributed in the higher tidal volume, allowing
particles to reach more distal airways than in the smaller tidal
volume, lower flow rate protocol. In the third protocol, which closely
approximates our protocol of a 0.4 l/s flow rate and 0.75-liter tidal
volume, Heyder et al. (12) measured a total deposition of 15 ± 4%
for 1.0-µm-diameter particles and 45 ± 6% for 3.0-µm-diameter
particles. Our data show a deposition of 17.0 ± 5.8 and 44.4 ± 11% for 1.0- and 3.0-µm-diameter particles, respectively, suggesting
that our results may safely be compared with those of previous
terrestrial studies of total intrapulmonary deposition.
Effect of altitude.
Four flights (1/particle size) were performed to collect all the data.
During each flight, before the start of the first parabola, we were
able to collect data at 1 G with one subject and compare the deposition
with that obtained on the ground with the same subject. These values
are shown in Table 2. The data obtained in
the aircraft refer to 6-10 breaths, whereas the data on the ground
refer to over 50 breaths. Because the order in which the subjects
performed the tests differed on each flight, the data do not
necessarily correspond to a single subject. Data for the subject in
whom these measurements were made are shown in Table 2. The comparison
shows that analogous results are obtained in both environments, with no
statistical differences between aircraft and ground data. This means
that there were no systematic differences in our data introduced by the
lower barometric pressure in the aircraft cabin and that we may
therefore valuably compare aircraft and ground data.
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ACKNOWLEDGEMENTS
We acknowledge Jeff Struthers, Janelle Fine, Bob Williams, and Lynette Bryan for collaborating. We also thank Mary Murrell, Marsha Dodds, Christa Roth, and Raoul Ludwig for technical and administrative assistance.
FOOTNOTES
Address for reprint requests: C. Darquenne, Physiology/NASA Laboratory 0931, Dept. of Medicine, UCSD, 9500 Gilman Drive, La Jolla, California 92093-0931 (E-mail: cdarquenne @ucsd.edu).
Received 24 March 1997; accepted in final form 20 August 1997.
APPENDIX
The Numerical Model
A 1D equation of aerosol transport and deposition is solved in a human lung model (3). The lung model is a trumpet model based on morphometric data of Weibel (23) and Haefeli-Bleuer and Weibel (8). This structure is referred as model C in Darquenne and Paiva's paper (3). The equation incorporates aerosol bulk flow, convective mixing, and deposition and is written as
|
(A1) |
is the flow rate, and
L is a deposition term.
Diffusion coefficient.
D incorporates both Brownian diffusion
(DB) and
convective mixing
(Da) and is
expressed by
|
(A2) |
|
|
(A3) |
|
|
(A4) |
p
d2pu/18µd;
u is the mean gas velocity in the
airway, and d is the airway diameter).
The higher the value of the Stokes' number, the more readily particles
will diverge from the airflow streamlines and the more likely they are,
therefore, to deposit by impaction on the airway walls.
The functions describing deposition by gravitational sedimentation and
Brownian diffusion are derived from a theoretical approach (1, 20). The
deposition functions are expressed
by
|
(A5) |
|
(A6) |
is fraction of alveolated surface of airway,
N(z)
is the number of airways in generation
z,
vs is gravitational settling velocity, 
s is deposition rate by
sedimentation, Na(z)
is number of alveoli in generation
z,
d is deposition rate by
diffusion, and sa
is inner surface area of alveolus.
REFERENCES
| 1. | Beeckmans, J. M. The deposition of aerosols in the respiratory tract I. Mathematical analysis and comparison with experimental data. Can. J. Physiol. Pharmacol. 43: 157-172, 1965[Medline]. |
| 2. | Beeckmans, J. M. Alveolar deposition of aerosols on the moon and in outer space. Nature 211: 208, 1966[Medline]. |
| 3. |
Darquenne, C.,
and
M. Paiva.
One-dimensional simulation of aerosol transport and deposition in the human lung.
J. Appl. Physiol.
77:
2889-2898,
1994 |
| 4. |
Darquenne, C.,
and
M. Paiva.
Two- and three-dimensional simulations of aerosol transport and deposition in alveolar zone of human lung.
J. Appl. Physiol.
80:
1401-1414,
1996 |
| 5. |
Davies, C. N.,
J. Heyder,
and
M. C. Subba Ramu.
Breathing of half-micron aerosols I. Experimental.
J. Appl. Physiol.
32:
591-600,
1972 |
| 6. |
Edyvean, J.,
M. Estenne,
M. Paiva,
and
L. A. Engel.
Lung and chest wall mechanics in microgravity.
J. Appl. Physiol.
71:
1956-1966,
1991 |
| 7. |
Elliott, A. R.,
G. K. Prisk,
H. J. B. Guy,
and
J. B. West.
Lung volumes during sustained microgravity on spacelab SLS-1.
J. Appl. Physiol.
77:
2005-2014,
1994 |
| 8. | Haefeli-Bleuer, B., and E. R. Weibel. Morphometry of the human pulmonary acinus. Anat. Record 220: 401-414, 1988[Medline]. |
| 9. | Henney, M. R., K. D. Kropp, and D. L. Pierson. Microbial monitoring of orbiter air (Abstract). Aviat. Space Environ. Med. 55: 466, 1984. |
| 10. | Heyder, J., L. Armbruster, J. Gebhart, E. Grein, and W. Stahlhofen. Total deposition of aerosol particles in the human respiratory tract for nose and mouth breathing. J. Aerosol Science 6: 311-328, 1975. |
| 11. | Heyder, J., J. Gebhart, G. Rudolf, C. F. Schiller, and W. Stahlhofen. Deposition of particles in the human respiratory tract in the size range 0.0005-15 µm. J. Aerosol. Sci. 17: 811-825, 1986. |
| 12. |
Heyder, J.,
J. Gebhart,
W. Stahlhofen,
and
B. Stuck.
Biological variability of particle deposition in the human respiratory tract during controlled and spontaneous mouth-breathing.
Ann. Occup. Hyg.
26:
137-147,
1982 |
| 13. |
Hoffman, R. A.,
and
J. Billingham.
Effect of altered G levels on deposition of particulates in the human respiratory tract.
J. Appl. Physiol.
38:
955-960,
1975 |
| 14. | James, J. Environmental health monitoring results for STS-40/Space Life Sciences (SLS-1) (Abstract). Spacelab Life Sciences-1 180-Day Preliminary Results 4: 4.1.3-4.1.3-34, 1992. |
| 15. | Muir, D. C. F. Influence of gravitational changes on the deposition of aerosols in the lungs of man. Aerosp. Med. 159-161, 1967. |
| 16. |
Paiva, M.,
M. Estenne,
and
L. A. Engel.
Lung volumes, chest wall configuration, and pattern of breathing in microgravity.
J. Appl. Physiol.
67:
1542-1550,
1989 |
| 17. |
Prisk, G. K.,
H. J. B. Guy,
A. R. Elliott,
M. Paiva,
and
J. B. West.
Ventilatory inhomogeneity determined from multiple-breath washouts during sustained microgravity on Spacelab SLS-1.
J. Appl. Physiol.
78:
597-607,
1995 |
| 18. | Schlesinger, R. B., and M. Lippmann. Particle deposition in casts of the human upper tracheobronchial tree. Am. Ind. Hyp. Assoc. 33: 237-251, 1972. |
| 19. | Schroter, R. C., and M. F. Sudlow. Flow patterns in models of the human bronchial airways. Respir. Physiol. 7: 341-355, 1969[Medline]. |
| 20. |
Taulbee, D. B.,
and
C. P. Yu.
A theory of aerosol deposition in human respiratory tract.
J. Appl. Physiol.
38:
77-85,
1975 |
| 21. |
Tsuda, A.,
J. P. Butler,
and
J. J. Fredberg.
Effects of alveolated duct structure on aerosol deposition in the pulmonary acinus. I. Diffusional deposition in the absence of gravity.
J. Appl. Physiol.
76:
2497-2509,
1994 |
| 22. |
Tsuda, A.,
J. P. Butler,
and
J. J. Fredberg.
Effects of alveolated duct structure on aerosol deposition in the pulmonary acinus. Part II: Gravitational sedimentation and inertial impaction in the absence of diffusion.
J. Appl. Physiol.
76:
2510-2516,
1994 |
| 23. | Weibel, E. R. Morphometry of the Human Lung. New York: Academic, 1963. |
| 24. | Westenberger, S., J. Gebhart, S. Jaser, M. Knoch, and R. Köstler. A novel device for the generation and recording of aerosol micro-pulses in lung diagnostic. J. Aerosol Sci. 23, Suppl.: S449-S452, 1992. |
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 A. Graebe, E. L. Schuck, P. Lensing, L. Putcha, and H. Derendorf Physiological, Pharmacokinetic, and Pharmacodynamic Changes in Space J. Clin. Pharmacol., August 1, 2004; 44(8): 837 - 853. [Abstract] [Full Text] [PDF]
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 A. Tsuda, R. A. Rogers, P. E. Hydon, and J. P. Butler Chaotic mixing deep in the lung PNAS, July 23, 2002; 99(15): 10173 - 10178. [Abstract] [Full Text] [PDF]
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C. Darquenne, M. Paiva, and G. K. Prisk Effect of gravity on aerosol dispersion and deposition in the human lung after periods of breath holding J Appl Physiol, November 1, 2000; 89(5): 1787 - 1792. [Abstract] [Full Text] [PDF]
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G. K. Prisk Physiology of a Microgravity Environment: Invited Review: Microgravity and the lung J Appl Physiol, July 1, 2000; 89(1): 385 - 396. [Abstract] [Full Text] [PDF]
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C. Darquenne, J. B. West, and G. K. Prisk Dispersion of 0.5- to 2-µm aerosol in µG and hypergravity as a probe of convective inhomogeneity in the lung J Appl Physiol, April 1, 1999; 86(4): 1402 - 1409. [Abstract] [Full Text] [PDF]
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A. Tsuda, Y. Otani, and J. P. Butler Acinar flow irreversibility caused by perturbations in reversible alveolar wall motion J Appl Physiol, March 1, 1999; 86(3): 977 - 984. [Abstract] [Full Text] [PDF]
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C. Darquenne, J. B. West, and G. K. Prisk Deposition and dispersion of 1-µm aerosol boluses in the human lung: effect of micro- and hypergravity J Appl Physiol, October 1, 1998; 85(4): 1252 - 1259. [Abstract] [Full Text] [PDF]
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