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Morphology of the guinea pig respiratory tract.

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THE ANATOMICAL RECORD 196:313-321 (1980)
Morphology of the Guinea Pig Respiratory Tract
JAY P. SCHREIDER AND JOHN 0. HUTCHENS
Department of Pharmacological and Physiological Sciences,
University ofChicago, Chicago, Illinois 60637
ABSTRACT
A morphologic description of the airways of the guinea pig was
developed from measurements of casts of the lungs and nasal cavity and from
measurements of frozen sections of the lungs. The lengths, diameters, branching
pattern, and numbers of elements of the respiratory tract formed the basis for a
representative model of the system. The branching pattern is irregular to the
pulmonary region but regularly dichotomous thereafter. The nasopharyngeal-tracheobronchial region contributes 2.64 cm3of the total respiratory volume of 21.62
cm". The alveoli contribute 16.31 cm:' of the 18.98 cm' pulmonary region. The nasal
region consists of convoluted and irregular airways with a functional volume of
0.48 cm3.
Small rodents, including the guinea pig, are
commonly used in inhalation toxicology research. The toxicity of an inhaled aerosol depends partially on the extent and loci of deposition in the respiratory tract. The disposition
depends on particle characteristics (size, density, and shape), on physical characteristics of
the respiratory system, and on the kinetics of
gas flow within the system. Differences in deposition characteristics between humans and
experimental animals will influence extrapolation of toxicity results obtained with small
animals to humans. This study was performed
to contribute to a n understanding of these factors.
Findeisen ('35) derived equations describing
particle deposition in the lungs by impaction,
sedimentation, and diffusion. These equations,
along with a model of the human respiratory
tract, were used to calculate the deposition
characteristics for man. That simple model assumed regular dichotomous branching of the
airways. Landahl ('50, '63) derived a different
set of equations governing particle deposition.
Using these equations, along with a modified
form of Findeisen's model, Landahl recalculated particle deposition characteristics for the
human respiratory tract. Weibel ('63) also assumed dichotomous branching when developing a detailed model of the human respiratory
system. Krahl ('64) and Davies ('61) presented
models in which dichotomous branching was
not assumed for the whole lung and the presence of side branching was considered.
The structure of the respiratory systems and
particle deposition characteristics have been
established for only a few experimental animals. Hutchens and Sharp (unpublished data)
developed a schematized model of the respiratory tract of the rat. Based on this model,
particle deposition characteristics were calculated for the rat (Granito, '71). Raabe et al. ('71)
presented measurements of the tracheobronchial portions of the respiratory tract of two
rats, two beagle dogs, two humans, and one
hamster. Kliment et a1 ('721,from latex casts of
guinea pig lungs, measured lengths, diameters,
and branching angles of the elements. Based on
those measurements, a model of the respiratory
tract was derived and the deposition characteristics were calculated. However, their results differed significantly from the results in
this study and with the work of other authors
(Tenney and Remmers, '63;Forrest and Weibel,
'75).
This study was part of a comprehensive effort
a t the University of Chicago to establish the
aerosol deposition characteristics of a number
of laboratory animals commonly used in toxicology studies. Through the use of epoxy casts
of the respiratory system and examination of
the alveolar regions of fast frozen sections of the
lungs, the morphology of guinea pig airways is
reexamined. Based on these measurements, a
000-3276W80/1963-0313$01.700 1980 ALAN R. LISS, INC.
Jay P. Schreider's present address is Radiobiology Laboratory, University of California, Davis, CA 95616, (916) 752-6918.
Received May 15, 1979; accepted August 20, 1979.
313
314
JAY P. SCHREIDER AND JOHN 0. HUTCHENS
model of the respiratory tract is presented. The
anatomical nomenclature used is taken from
Cooper and Schiller (’75).
MATERIALS AND METHODS
Guinea pigs of an unspecified strain, weighing about 600 g, were killed by a n intraperitoneal injection of 300 mgkg of sodium
pentobarbital (USP “injection,” 5% solution).
The animals died within five minutes of injection and did not exhibit any obvious respiratory
trauma. Reflex bronchial constriction, a major
problem in preparing guinea pig lung casts,
was prevented by exposing the guinea pigs to
an aerosol of epinephrine, generated by blowing oxygen through a modified DeVilbis type
nebulizer containing an epinephrine solution
(USP “injection”1mg/cc),from one minute preceding pentobarbital injection until respiration
ceased. The effectiveness of the epinephrine
pretreatment in preventing bronchial constric-
tion was demonstrated by the observed uniformity of the resulting casts. Casts made from
the epinephrine-treated animals showed no obvious differencesfrom the few satisfactory casts
or portions of casts made from untreated animals.
After death of the animal, the trachea was
exposed and cannulated. The cannulation tube
was connected to a n air pressure head of 15 cm
of water. The chest cavity was opened (lungs
still under pressure) and the lungs and heart
removed by severing the mediastinal pleura,
the esophagus, and the blood vessels leading to
the heart (with the exception of the pulmonary
vessels). The pressure of 15 cm water caused
the lungs to just fill the opened (but not distorted) chest cavity and the edges of the lungs to
overlap the heart. The lungs, still under pressure, were immersed in a saline solution (leaky
specimens were discarded).
Lung casts (Fig. 1) were prepared by with-
Fig. 1. Undissected epoxy cast of guinea pig lung. Dorsal view.
GUINEA PIG RESPIRATORY MORPHOLOGY
drawing a volume of air through a syringe attached to the clamped tracheal cannula and
then injecting a n equal volume of casting medium over a two minute period. The casting
compound was prepared by mixing a two-part
epoxy resin (No. 6201, High Strength Plastics,
Chicago, IL), which was put under vacuum for
1-3 minutes to remove air bubbles. For some
preparations, Lucite beads about 200 pm in
diameter (separated by sieving from Lucite 40
Bead Polymer, E. I. Du Pont De Nemours and
Co., Polychemicals Department, Wilmington,
DE) were mixed 1:2 with the resin. The beads
were used to prevent the resin from filling
many of the smaller airways. After casting, the
lungs were hung vertically, supported by the
tracheal cannula, in a moist chamber overnight. The tissue then was digested in a bath of
hot 2 N NaOH. The casts were washed in water
and allowed to dry.
A few lung casts were prepared by allowing
epoxy resin t o flow into evacuated lungs supported by an artificial thorax. The artificial
thorax was formed from W o agar poured into a
paper cup mold containing the inflated lung
specimen. The agar hardened around the
buoyant lung, and only the clamped tracheal
cannula, extending through a paraffin-sealed
hole in the bottom of the cup, was exposed. The
lung was then evacuated through the tracheal
cannula with a water aspirator, a syringe containing epoxy resin was attached to the cannula, and resin was allowed to flow into the
lung and harden overnight. After removal from
the agar, the lung tissue was digested in the
usual way. Measurements were made on the
larger branches where distension might be expected to occur during injection under pressure.
Casts prepared in this way were identical to
those prepared by the injection method, indicating that the method (and injection pressures) did not cause distended or stretched
branches.
Lung casts were dissected under a binocular
dissecting microscope. Beaded casts were used
for studying the larger airways because the
beads prevented filling of many of the smaller
airways and thus simplified the dissection.
Branches 200 microns and smaller that were
filled with resin were removed, leaving a cast
such as that pictured in Figure 2. The dissected
fragments were saved for study of the smaller
airways. When unbeaded resin was used, casting of the smaller airways was more frequent.
Alveolar bundles (Fig. 3) were isolated from
such casts. Several dozen casts were made. The
best casts were dissected. One beaded cast was
315
completely dissected and measurements made
on all lobes. A number of casts were partially
dissected. Measurements made on the dissected
portions served to clarify some measurements
made on the completely dissected cast.
Lung elements were measured with a linear
micrometer occular on a dissecting microscope.
The measurements were accurate to within
i 50 microns under x 10 magnification, i 16
microns under x 30 magnification (used for
most measurements), and ? 8 microns under
x 60 magnification (used for pulmonary region
measurements). All ducts through three orders
of branching were measured, but measurements for the remaining orders were based
on a random sampling of at least ten elements
of each order.
Lengths and diameters of ducts were
recorded. Duct diameters were measured a t the
midpoint. The size and number of ducts branching off a given element also were recorded. The
largest diameter ducts branching from an element were designated as the next smaller
order. When regular dichotomous branching
began, the branching orders became obvious.
The branching angle was defined as the
angle between the axes of the parent duct and
the daughter branch. A branch was designated
as a side branch if the axis of the major daughter did not appreciably change in direction from
the axis of the parent duct. A branch was designated as an end branch if the axes of both
daughters changed direction from the axis of
the parent duct. The angles were estimated
through the dissecting microscope; however,
orientation problems made exact measurement
difficult. In addition, the branching angles of
the larger branches may have been somewhat
distorted by hanging the lungs by the trachea
during curing. Therefore, an overall estimate
was made of the angle for a side branch and for
a n end branch.
Although they are extensions of the primary
bronchi, the left and right posterior bronchi
were treated as branches (branching angle of
0")of the first order bronchi and were grouped
with the other second order bronchi. Therefore,
the lengths of the first order bronchi were
measured from the tracheal bifurcation to the
point where the first side branch was given off
in the posterior lobes. This resulted in seemingly short lengths for the first order bronchi,
but the model was easier to treat.
Measurements of the smaller elements were
made on many isolated fragments of the unbeaded casts. Measurement of the length of the
alveolated ducts was complicated by orienta-
316
JAY P. SCHREIDER AND JOHN 0. HUTCHENS
Fig. 2. Dissected cast of guinea pig lung. Dorsal view.
Fig. 3. Fragment of alveolar bundle.
GUINEA PIG RESPIRATORY MORPHOLOGY
317
which supply the cranial, middle, and accessory
lobes, and then terminates with the right caudal lobe. The left first order bronchus (0.20 cm
diameter) supplies branches to the left cranial
and the left middle lobes, and then terminates
in the left caudal lobe. The lobes are classified
on the basis of their air supply. A section of the
lung is considered to be a lobe if it is supplied by
a second order bronchus. This treatment is unambiguous except in the case of the right cranial and middle lobes. Although the second
order bronchi supplying these lobes are separate, there are tissue connections between the
two lobes.
The pictures of a nasal cast (Fig. 4a, b) show
that the right and left passages are separate for
about 25 mm. There is a bend of approximately
40"at the external nares. The sinus portion of
the cast forms several dead pockets. The volume of the entire nasal cavity is 0.883 cm",
while the volume of the nasal cavity minus the
sinus or ethmoid area is 0.483 cm'.
The measurements are summarized in a
schematization of the respiratory tract
presented in Tables 1and 2. Table 1illustrates
the branching pattern of the ducts from the
second order bronchi through the alveolated
ducts. Smaller airways have fewer side
branches. The branching pattern is irregular to
the level of the 0.014 cm ducts. Three 0.009 cm
ducts branch from each of the 0.014 cm ducts.
The branching pattern is regularly dichotomous thereafter. The branching angle is 15" for
the tracheal bifurcation. For the rest of the
system, the angles are about 30" for an end
branch and 60" for a side branch. As a duct gives
off side branches, it decreases in diameter.
From the branching pattern and the anatomical measurements, a model of the lung (Table 2)
is generated in which a duct is placed in a given
order according to its diameter and not its origin. Duct diameters did not occur as a continuum of sizes, but fell into fairly well defined
ranges. Therefore, the diameters were recorded
as grouped data with the midpoint of the group
being listed in the tables. Because of their small
diameter, the right cranial and left middle
bronchi were grouped with the third order
bronchi. With the exceptions of the fourth order
alveolated duct and the second order bronchi,
the volume of each element decreases with each
order of branching. The volume of an order or
region is a function of the number and volume
of the elements in that region.
RESULTS
The alveoli are closely packed on all alveolThe guinea pig lung is divided into seven
lobes. The right first order bronchus (0.23 cm ated elements, suggesting the absence of respihrnnchinles.
- -._- - - ~ ~ -- ~ - Because the surface area of
diameter) branches t o three secondary bronchi, rat,nrv
tion illusions. Since the alveoli were closepacked on the surfaces of the alveolated ducts,
the lengths of the airways were calculated by
multiplying the number of alveoli along the
lengths of the ducts by the alveolar diameter. In
some cases, it was possible to count the total
number of alveoli on a duct. The alveolar
number was also estimated by calculating the
number of spheres of a given radius that could
be packed on the surface of a duct. There was
good agreement between the two methods of
estimation.
Because the alveolar casting often was incomplete, alveolar dimensions were also estimated from frozen sections of lungs. Lungs
were removed under pressure in the same
manner used in preparing the casts, and
quickly frozen in liquid nitrogen. Such fast
freezing did not collapse the lungs because of
the immediate formation of a frozen shell.
Thick sections were taken from the frozen tissue and examined in a cryostat under a dissecting microscope. Because the alveoli were sectioned at random distances from their centers,
the largest diameters found were accepted as
the diameters of the alveoli. This method assumes that the alveoli are uniform in size in the
frozen specimen. Examination of the alveolar
bundle fragments supported this assumption.
For the preparation of nasal casts (Fig. 41, the
anterior end of the trachea was cannulated and
epoxy resin injected towards the cranial region.
After the mouth had filled, the jaws were tied
shut. The head was suspended vertically with
the nose pointing up, and resin was injected
until it began to emerge from the nares. After
the resin hardened, loose tissue was stripped
from the head, and the remaining tissue was
digested in hot 2 N NaOH. Pieces of bone
adhering to the cast were digested with 1N
HCL.
The length of the nasopharynx on the nasal
cast was measured from the choanae to the
pharynx, using a micrometer occular and a dissecting microscope. The shape of the duct varied along its length, so a vernier caliper was
used to measure twenty different diameters
along the length. Acrylic molds (reverse casts)
of the nasal cavity were prepared (Hutchens
and Schreider, manuscript in preparation) and
the volume of the nasal region measured from
the amount of water needed to fill one of the
molds.
-
J
318
JAY P. SCHREIDER AND JOHN 0. HUTCHENS
A
B
Fig. 4. Epoxy cast of nasal cavity. (A) side view, (B) dorsal view.
the alveolated ducts is constant, the number of
alveoli per duct remains about t h e same
throughout the pulmonary region.
Total respiratory volume is 21.62 cm”. The
dead air space (nasopharyngeal-tracheobronchial region) has a volume of 2.64 cm”. The
pulmonary region has a volume of 18.98 cm:’,
the majority of which is contributed by the alveoli (16.31 cm”).
Examinations of the epoxy casts and the frozen sections indicated that the alveoli have the
shape of a % sphere or a polyhedron (minus one
side occupied by the alveolar opening) with a n
average diameter of 80 microns. As the alveoli
inflate, the shape may more closely approach
that of a sphere with a narrow-necked opening
to the duct. All alveoli are assumed to be in the
same state of inflation.
DISCUSSION
Anatomists classify the airways of the lungs
according to the amount of smooth muscle and
cartilage contained in the walls and according
to the types of cells lining the walls. In the
classification presented here, histological
make-up of the elements is not considered, and
3 R.C.
=
Right Caudal. R.Cr.
R.C. bronchus (0.20)
R.Cr. bronchus (0.11)
R.M. bronchus (0.13)
R.A. bronchus (0.15)
L.C. bronchus (0.15)
L.Cr. bronchus (0.15)
L.M. bronchus (0.11)
0.10
0.065
0.050
0.040
0.030
0.023
0.014
0.009
0.007
0.006
0.006
Parent duct*
(diameter, cm)
=
3.0
1.0
1.0
1.0
4.0
0.10
=
2.6
1.7
3.0
3.0
7.0
Right Middle. R.A.
6.0
2.0
3.0
3.0
5.0
6.0
(no side branches)
3.0
6.0
Right Cranial. R.M.
-.
=
Right Accessory. L.C.
1.0
3.0
3.0
2.6
2.4
1.0
1.1
3.0
4.0
4.0
4.0
4.0
4.0
1.9
1.3
3.0
3.0
=
.-
of
=
0.10
0.10
0.10
0.10
0.10
0.065
0.065
0.065
0.050
0.040
0.030
0.023
0.014
0.009
0.007
0.006
0.006
0.005
0.005
0.065
0.10
0.065
0.065
0.065
0.065
0.050
0.050
0.040
0.030
0.023
0.014
0.014
0.009
0.007
0.006
0.006
0.009
Average diameter of ducts branching
off end of duct of origin (cm)
guinea pigs
Left Cranial. L.M. = Left Middle.
2.0
2.0
2.4
1.0
0.014
Left Caudal. L.Cr.
2.0
1.6
1.0
Average no. ducts of given diameter
branching off side of duct of origin
diameter of branching duct (cm)
0.065
0.050
0.040
0.030
0.023
TABLE 1 . Branching pattern of ducts in the respiratory tract
e
0
0
$
8z
z
@
cn
M
8a
3>
320
JAY P. SCHREIDER AND JOHN 0. HUTCHENS
TABLE 2. Schematic representation of respiratory tract
Region
Diameter of
duct or
alveolus (cm)
Cross-sectional
area (crnl) of
duct
Nasal cavity
Nasopharynx
Trachea
1st order bronchi
2nd order bronchi
3rd order bronchi
4th order bronchi
5th order bronchi
6th order bronchi
7th order bronchi
8th order bronchi
9th order bronchi
1st alveolated duct
2nd alveolated duct
3rd alveolated duct
4th alveolated duct
5th alveolated duct
Alveoli
0.32
0.30
0.22
0.16
0.10
0.065
0.050
0.040
0.030
0.023
0.014
0.009
0.007
0.006
0.006
0.005
0.008
7.9 x 10-2
7.1 x lo-'
3.7 x 10-2
2.0 x 10-2
7.9 x lo+
3.3 x lo-:'
2.0 x lo-:'
1.3 x lo-:'
7.1 x
4.0 x
1.5 x
x
x
x
x
x
6.4
3.9
2.8
2.8
2.0
the ducts are classified only according to their
diameters and the presence or absence of alveoli on their walls.
During nasal deposition studies (Hutchens
and Schreider, manuscript in preparation), no
material was ever recovered in the ethmoid
area. Because the ethmoid area forms dead
pockets, any material entering it should be deposited there. The conclusion is that very little
or no tidal air enters the ethmoid area and that
the ethmoid area is not part of the functional
volume of the respiratory system.
In this model of the lungs, all members of the
same size are treated as members of the same
order with identical paths from the trachea
through the various branches and branching
angles to that order. Examination of the lung
cast shows that the anatomical paths to the
various pulmonary regions may be quite different. However, the scheme presented is based on
average values and should be a realistic model
of the respiratory system.
Tenny and Remmers ('63) related lung volume to body weight, and alveolar diameter and
surface area to metabolic rate for several laboratory animals. Computations based on those
formulas yield values of 25.3 cm' for total lung
volume, 76.8 pm for the alveolar diameter, and
0.79 m2for total alveolar surface area. Forrest
and Weibel ('75) estimated the pulmonary diffusion capacity of guinea pigs. From their
graphs, extrapolations can be made to yield
values for a 600 g guinea pig of 21.5 cm" total
-
lo-*
10
10-5
10-5
lo-'
10-5
of guinea pig
Length (em)
of duct
2.5
4.5
1.2
1.9
0.85
0.53
0.26
0.19
0.10
0.066
0.045
0.024
0.024
0.024
0.024
0.032
vol. of
duct or
alveolus (cm0
0.48
0.20
0.32
0.042
0.037
6.6 x lo-'
1.8 x
5.1 x
1.9 x 10-4
7.1 x
2.6 x lo-'
7.0 x
1.6 x
9.2 x 10-7
6.8 x lo-'
6.8 x 10
6.3 x lo-'
2.0 x 10-7
no. of
ducts or
alveoli
1
1
1
2
5
17
86
312
1.0 x 103
3.0 x 10'
9.5 x 10'
4.2 x 104
1.3 x lo5
2.5 x 105
5.0 x 1oj
1.0 x 108
2.0 x 10"
8.2 x 107
lung volume, 15 cm3alveolar air space volume,
and 1.3m ' alveolar surface area. Data from this
study show values of 21.6 cm'j total lung volume, 16.3cm" total alveolar volume, and 1.1m2
alveolar surface area (80 pm alveolar diameter).
Kliment et al. ('72) presented a model of the
respiratory tract of the guinea pig based on
measurements of latex corrosion casts, but
their values (extrapolated to a 600 g animal) for
number of alveoli (6.8 x lo6),alveolar diameter
(92 pm), calculated alveolar surface area assuming spherical alveoli (0.18 m2), and total
lung volume (9.11 cm:')are quite different than
the values of this paper, or values reported by
Tenney and Remmers ('631, and Forrest and
Weibel('79, and are not consistent with established relationships correlating alveolar surface area and lung volume with respiratory requirements and body weight. Kliment et al.
('72) also list fewer orders, fewer members of
each order, and smaller dimensions of the elements of each order than were found in this
investigation. Incomplete casting could have
resulted in low numbers of alveoli and distal
airways, leading to a low lung volume. In addition, the treatment of the nasal cavity as a
straight cylinder is not appropriate for the convoluted and irregular shape of the nasal casts
(Fig. 4).
The model presented in this paper forms the
basis for calculations of the aerosol deposition
characteristics of the guinea pig using the di-
32 1
GUINEA PIG RESPIRATORY MORPHOLOGY
TABLE 2lcont.) Schematic representation
of
respiratory tract of guinea pig.
Region
VOl. of
region (cm")
Cumulative
vol. of
ducts (cm')
Nasal cavity
Nasopharynx
Trachea
1st order bronchi
2nd order bronchi
3rd order bronchi
4th order bronchi
5th order bronchi
6th order bronchi
7th order bronchi
8th order bronchi
9th order bronchi
1st alveolated duct
2nd alveolated duct
3rd alveolated duct
4th alveolated duct
5th alveolated duct
Alveoli
0.48
0.20
0.32
0.084
0.19
0.11
0.15
0.16
0.19
0.21
0.25
0.29
0.19
0.23
0.34
0.68
1.24
16.31
0.48
0.68
1.00
1.09
1.27
1.39
1.54
1.69
1.89
2.10
2.35
2.64
2.83
3.06
3.40
4.07
5.31
21.62
ameters, lengths, and numbers of the ducts of
the respiratory tract; the branching angles and
branching pattern of the ducts; the size, shape,
and number of the alveoli; the extent of alveolation of the ducts; and the physics of aerosols and
airflow (Schreider and Hutchens, '79). These
calculations are used to predict regions of the
respiratory airways in which particles of a
given size or distribution may deposit in inhalation toxicology studies. The results of these
calculations are generally in line with the results of exposure studies on man and various
experimental animals (Schreider and Hutchens, '79).
Alveoli/
duct
Alveoli/
region
Alveolar
vol. (cm%
region
23
21
19
19
23
2.88 x 106
5.41 x lo6
9.46 x lo6
1.89 x loG
4.55 x 10"
0.57
1.08
1.88
3.76
9.05
Davies, C.N. (1961) A formalized anatomy of the human
respiratory tract. In: Inhaled Particles and Vapors. Proc.
Int. Symp., Br. Occupational Hygiene SOC.,Oxford, March
29-April 1, 1960. Pergamon Press, London, pp. 82-91.
Findeisen, W. (1935) Uber das absetzen kleiner, in der luft
suspender teilchen in der menschlichen lunge bei der atmung. Arch. Ges. Physiol., 236t367-379.
,Forrest, J.,and E. Weibel(1975) Morphometric estimation of
pulmonary diffusion capacity. VII. The normal guinea pig.
Lung. Respir. Physiol., 24: 191-204.
Granito, S. (1971) Calculated Retention of Aerosol Particles
in the Rat Lung. MS. dissertation, Department of Physiology, University of Chicago.
Kliment, V., J. Lihich, and V. Kandersova (1972) Geometry
of guinea pig respiratory tract and application of Landahl's
model ofdeposition of aerosol particles. J. Hyg. Epidemiol.
Microbiol. Immunol., 16: 107-115.
Krahl, V. (1964) Anatomy of the mammalian lung. In:
Handbook of Physiology: Respirations. Am. Physiol. SOC.,
Washington, D.C., vol. 1, pp. 213-284.
Landahl, H. (1950) On the removal of airborne droplets by
ACKNOWLEDGMENTS
the human respiratory tract: I. The lung. Bull. Math.
Biophys., 1243-56.
The research for this study was supported by
H. (1963) Particle removal by the respiratory sysPublic Health Service grant PHS R01- Landahl,
tem. Note on the removal of airborne particulates by the
ES00855 from the National Institutes of
human respiratory tract with particular reference to the
Health.
role of discussion. Bull. Math. Biophys., 25:29-39.
JPS. received personal support from Na- Raabe, O., H. Yeh, and G. Schum (1971) Tracheobronchial
geometry; human, dog, rat, hamster-A compilation of
tional Institutes of Health National Research
selected data from the project respiratory tract deposition
Service Award PHS 5-T32 GM-07151from the
models. U S . Govt. Printing Office, Washington, D.C.
National Institute of General Medical Services. Schreider, J., and J. Hutchens (1979)Particle deposition in
the guinea pig respiratory tract. J. Aerosol Sci., (In press).
Tenney, S., and J. Remmers (1963) Comparative quantitative morphology of the mammalian lung: Diffusion area.
LITERATURE CITED
Nature, 197:54-56.
Cooper, G., and A. Schiller, (1975) Anatomy of the Guinea Weibel, E. (1963) Morphometry of the Human Lung.
Academic Press, New York.
Pig. Harvard Univ. Press, Cambridge.
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Теги
guinea, morphology, respiratory, pig, trace
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