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Animal lung models for the inhalation of natural radioactive particles and their relevance to man
The biomedical influence of the aerosol
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Fig. 3. Total and regional deposition as function of the aerodynamic particle diameter for one subject (breathing pattern (b)). working subject. In Figs. 2 and 3 representative regional deposition data of a subject are shown as function of the aerodynamic diameter of the particles.
ANIMAL LUNG MODELS FOR THE INHALATION OF NATURAL RADIOACTIVE PARTICLES AND THEIR RELEVANCE TO MAN W. HOFMANN, F. DASCHIL and E. POHL Institute of Biophysics, University of Salzburg, Salzburg, Austria Our knowledge of biological effects caused by inhaled radioactive nuclides in the lung are based primarily on experiments with different kinds of animals. Results obtained in this way are then analyzed for their transferability to man, applying theoretical considerations. Under the assumption of a constant anatomical structure of the respiratory tract deposition in different animal species was determined by using appropriate scaling factors for anatomical and physiological parameters of the human lung, as defined by Weibel (1963). The applicability of this scaling down procedure of the human data for various animals was tested for the rat. Using experimental data on airway dimensions of Raabe et al. (1976) and Kliment (1973) and assuming a structure of the lung analogous to the Weibel model, a suitable anatomical model of the rat lung was developed dividing the respiratory tract into 20 generations. For a defined particle size distribution of the natural aerosol the percentage of particles deposited by diffusion, sedimentation and impaction in the single generations was calculated. These results were compared with those, obtained with the original Weibel data scaled down to the same lung volume. The good agreement between both deposition values justified the application of this scaling procedure to other animal species. As a result of these calculations conversion factors for the activities of the inhaled natural radioactive radon decay products RaA, RaB and RaC, deposited in the tracheobronchial region, are given in Table 1. REFERENCES Kliment, V. (1973) Folia Morphologica 21, 59. Raabe, O. G. et al. (1976) Tracheobronchial Geometry: Human, Dog, Rat, Hamster. Lovelace Foundation LF-53. Weibel, E. R. (1963) Morphometry of the Human Lung, Springer Verlag, Berlin.
236
I HF ANNUAL CONFI REN('E OF THE GAff' Table 1 Scaling factors for activities of RaA, RaB and RaC deposited in the tracheobronchial region for different animal species, normalized for man Species
RaA
RaB
RaC
Mouse Rat Guinea pig Dog Man
2.05 1.6X 1.54 1,14 1.00
3.46 2.56
377 2.75 2.36 1.34 1.00
2.22 1.30 1.00
THE INFLUENCE OF POSTNATAL GROWTH OF THE HUMAN L U N G O N D E P O S I T I O N AND R E T E N T I O N O F RADIOACTIVE AEROSOLS W. HOFMANN, l". SI'E1NH£USLERand E. POHI Institute of Biophysics, University of Salzburg, Salzburg, Austria Calculations of the radiation burden of the human respiratory tract after the inhalation of radioactive parncles arc based primarily on the adult Reference Man with defined anatomical and physiological properties (Reference Man, 1975). However only few individuals of any population will have similar characteristics, especially children a~d youths. The postnatal growth of the human lung from birth up to about 8 years can be characterized by the lormano~ ~i new airways and the lining of the respiratory airways with alveoli. From 8 years onwards the structural developmem of the lung is completed and further growth occurs only by an increase of the linear dimensions. Besides these anatomical alterations also physiological parameters, such as tidal volume and respiratory frequency change with progressing age. From the simulation of the influence of these age-dependent parameters on deposition and retenuon oi radioactive aerosol particles in the human respiratory tract a suitable deposition and retention model, based on the Weibel model A (Weibel, 1963) was developed, For a defined particle size distribution the percentage of particles deposited by diffusion, sedimentation and impaction was calculated. Despite the large anatomical and physiological alterations during postnatal growth, the deposition values do not change significantly with age. The surface activities in the single generations, resulting from the activity deposited, radioactive decay and clearance mechanisms were then obtained as solutions of the corresponding linear differential equation system. In the case t~f the inhalation of natural radioactive radon decay products maximum values were reached at the age of 6 years which are about 3 times higher than that of adults (Fig. 4|. REFERENCES Reference Man (1975) Report of the Task Group on Reference Man, 1CRP No. 23, Pergamon Press, Oxford Weibel, E. (1963) Morphometry qflthe Human Lung. Springer Verlag, Berlin.
f
~,
0.5 RA
u~
RaC
FO
20
Age
30
yr
Fig. 4. Surface activities of radon decay products (RaA, RaB and RaC) in generation 6 of the Weibei model A as functions of age for defined respiration standards and aerosol characteristics.
z o
MEAN RESIDENCE TIME
T
MEAN FLOW RATI~
Q /cm3s "1
I s
235
:
2
:
750
1.0 subject
3
^~
-
~
E
POSIT ION
cu w
0.8 EXTRATHORACIC DEPOSITION
0.6
0.2
-
0
-
TRACHEOBRONCHIAL DEPOSITION
DEPOSIT10N '
t
'
' --
'
'
,0
AERODYNAMIC PARTICLE DIAMETER I I,tm
Fig. 3. Total and regional deposition as function of the aerodynamic particle diameter for one subject (breathing pattern (b)). working subject. In Figs. 2 and 3 representative regional deposition data of a subject are shown as function of the aerodynamic diameter of the particles.
ANIMAL LUNG MODELS FOR THE INHALATION OF NATURAL RADIOACTIVE PARTICLES AND THEIR RELEVANCE TO MAN W. HOFMANN, F. DASCHIL and E. POHL Institute of Biophysics, University of Salzburg, Salzburg, Austria Our knowledge of biological effects caused by inhaled radioactive nuclides in the lung are based primarily on experiments with different kinds of animals. Results obtained in this way are then analyzed for their transferability to man, applying theoretical considerations. Under the assumption of a constant anatomical structure of the respiratory tract deposition in different animal species was determined by using appropriate scaling factors for anatomical and physiological parameters of the human lung, as defined by Weibel (1963). The applicability of this scaling down procedure of the human data for various animals was tested for the rat. Using experimental data on airway dimensions of Raabe et al. (1976) and Kliment (1973) and assuming a structure of the lung analogous to the Weibel model, a suitable anatomical model of the rat lung was developed dividing the respiratory tract into 20 generations. For a defined particle size distribution of the natural aerosol the percentage of particles deposited by diffusion, sedimentation and impaction in the single generations was calculated. These results were compared with those, obtained with the original Weibel data scaled down to the same lung volume. The good agreement between both deposition values justified the application of this scaling procedure to other animal species. As a result of these calculations conversion factors for the activities of the inhaled natural radioactive radon decay products RaA, RaB and RaC, deposited in the tracheobronchial region, are given in Table 1. REFERENCES Kliment, V. (1973) Folia Morphologica 21, 59. Raabe, O. G. et al. (1976) Tracheobronchial Geometry: Human, Dog, Rat, Hamster. Lovelace Foundation LF-53. Weibel, E. R. (1963) Morphometry of the Human Lung, Springer Verlag, Berlin.
236
I HF ANNUAL CONFI REN('E OF THE GAff' Table 1 Scaling factors for activities of RaA, RaB and RaC deposited in the tracheobronchial region for different animal species, normalized for man Species
RaA
RaB
RaC
Mouse Rat Guinea pig Dog Man
2.05 1.6X 1.54 1,14 1.00
3.46 2.56
377 2.75 2.36 1.34 1.00
2.22 1.30 1.00
THE INFLUENCE OF POSTNATAL GROWTH OF THE HUMAN L U N G O N D E P O S I T I O N AND R E T E N T I O N O F RADIOACTIVE AEROSOLS W. HOFMANN, l". SI'E1NH£USLERand E. POHI Institute of Biophysics, University of Salzburg, Salzburg, Austria Calculations of the radiation burden of the human respiratory tract after the inhalation of radioactive parncles arc based primarily on the adult Reference Man with defined anatomical and physiological properties (Reference Man, 1975). However only few individuals of any population will have similar characteristics, especially children a~d youths. The postnatal growth of the human lung from birth up to about 8 years can be characterized by the lormano~ ~i new airways and the lining of the respiratory airways with alveoli. From 8 years onwards the structural developmem of the lung is completed and further growth occurs only by an increase of the linear dimensions. Besides these anatomical alterations also physiological parameters, such as tidal volume and respiratory frequency change with progressing age. From the simulation of the influence of these age-dependent parameters on deposition and retenuon oi radioactive aerosol particles in the human respiratory tract a suitable deposition and retention model, based on the Weibel model A (Weibel, 1963) was developed, For a defined particle size distribution the percentage of particles deposited by diffusion, sedimentation and impaction was calculated. Despite the large anatomical and physiological alterations during postnatal growth, the deposition values do not change significantly with age. The surface activities in the single generations, resulting from the activity deposited, radioactive decay and clearance mechanisms were then obtained as solutions of the corresponding linear differential equation system. In the case t~f the inhalation of natural radioactive radon decay products maximum values were reached at the age of 6 years which are about 3 times higher than that of adults (Fig. 4|. REFERENCES Reference Man (1975) Report of the Task Group on Reference Man, 1CRP No. 23, Pergamon Press, Oxford Weibel, E. (1963) Morphometry qflthe Human Lung. Springer Verlag, Berlin.
f
~,
0.5 RA
u~
RaC
FO
20
Age
30
yr
Fig. 4. Surface activities of radon decay products (RaA, RaB and RaC) in generation 6 of the Weibei model A as functions of age for defined respiration standards and aerosol characteristics.