Deposition of Ultrafine Particles in the Human Tracheobronchial Tree

Chapter 34

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Deposition of Ultrafine Particles in the Human Tracheobronchial Tree A Determinant of the Dose from Radon Daughters Beverly S. Cohen Institute of Environmental Medicine, New York University Medical Center, New York, NY 10016 The deposition of ultrafine particles has been measured in replicate hollow casts of the human tracheobronchial tree. The deposition pattern and efficiency are critical determinants of the radiation dose from the short lived decay products of Rn-222. The experimental deposition efficiency for the six airway generations just beyond the trachea was about twice the value calculated if uniform deposition from laminar flow is assumed. The measured deposition was greater at bifurcations than along the airway lengths for 0.2 and 0.15μmdiameter particles. pha

ar

Exposure to 2§i P ticle radiation from the short lived daughters of Rn is a recognized cause of bronchogenic cancer in uranium and other underground miners. When Rn decays, the Po and succeeding progeny quickly attach to particles in the air. The activity median diameter of the attached particles varies with indoor, outdoor or underground mining atmospheres but ranges from about 0.1 to 0.4 ym (NCRP, 1984). When these parti cles are inhaled, a fraction deposit on the mucosal surface of the tracheobronchial tree. Subsequent radioactive decay will deliver the significant dose to the sensitive cells of the bronchial epithelium. The radiation dose will depend critically on the efficiency with which the particles are deposited on the airway surfaces. In addition the pattern of deposition is important because substan tial radioactive decay of the short lived radon daughters will take place before the initial particle deposit can be removed by normal clearance mechanisms (Cohen, et al., 1985). Few data are available on the deposition of ultrafine parti cles (d 1 (ultman, 1985). For conditions of these experiments, exceeds one t o beyond t h e t h i r d g e n e r a t i o n . α

Hopke; Radon and Its Decay Products ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


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It is clear that predictions based on uniform deposition from laminar flow are not satisfactory. Current models are not able to incorporate the effects of flow patterns in the upper airways which result in the inhomogeniety of deposition demonstrated in the cast system. It seems remarkable that predictions for dif fusive deposition from laminar flow in cylindrical tubes are so close to those observed in the complex geometry and branching of the human tracheobronchial system. The results of the experiments reported here indicate that the deposition probability for 0.04 to 0.2 ym particles in generations 1-6 of the upper airways is greater than that predicted by equation (1) by a factor of about 2. Until better models are developed the correction factors shown in Figures 2 to 5 are useful for estimating deposition of inhaled pari des in the size range to which the decay products of radon are attached. Acknowledgments This work was supported by Grant No. ES 00 881 from the National Institutes of Environmental Health Sciences (NIEHS) and Special Emphasis Research Career Award Grant No. OH 00022 from the National Institute for Occupational Safety and Health of the Centers for Disease Control. It is part of a Center program sup ported by Grant ES 00260 from NIEHS and Grant CA 13343 from the National Cancer Institute. The author wishes to thank Mr. Robert Sussman who assisted with all of the laboratory studies. Literature Cited Chamberlain, A.C. and E.D. Dyson, The Dose to the Trachea and Bronchi from the Decay Products of Radon and Thoron. Br. J. Radiol. 29: 317-325 (1956). Chan, T.L. and M. Lippmann, Experimental Measurements and Empiri cal Modelling of the Regional Deposition of Inhaled Particles in Humans, Amer. 2nd.Hyg.Assoc. J . 41 :399-409 (1980). Chan, T.L., R.M. Senreck and M. Lippmann, Effect of the Laryngeal Jet on Particle Deposition in the Human Trachea and Upper Bron chial Airways, J. Aerosol Sci. 11:447-459 (1980). Cohen, B.S., Ν.H. Harley, R.B. Schlesinger and M. Lippmann, Nonun iform Particle Deposition on Tracheobronchial Airways: Implica tions for Lung Dosimetry. Ann.Occup.Hyg. (in press). Cohen, B.S., R.G. Sussman and M. Lippmann, Deposition of Ultrafine Particles in Hollow Airway Casts of the Human Tracheobronchial Tree. In Preparation. Gormley, P.C. and M. Kennedy, Diffusion from a Stream Through a Cylindrical Tube, Proc. R. In. Acad. Sect. A52:163-169 (1949).


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Gurman, J.L., R. B. Schlesinger and M. Lippmann, A Variable-Opening Mechanical Larynx for Use in Aerosol Deposition Studies, Am. Ind. Hyg. Assoc. J., 41:678-680 (1980).


Gurman, J.L., M. Lippmann and R.B. Schlesinger, Particle Deposi tion in Replicate Casts of the Human Upper Tracheobronchial Tree Under Constant and Cyclic Inspiratory Flow. I. Experimental, Aero sol Science and Technology 3:245-252 (1984). Harley, Ν.H. and B.S. Pasternack, Alpha Absorption Measurements Applied to Lung Dose from Radon Daughters, Health Phys. 23:771782 (1972). Harley, Ν.H. and B.S. Pasternack, Environmental Radon Daughter Alpha Dose Factors in a Five-Lobed Human Lung, Health Phys 42:789-799 (1982). Ingham, D.Β., Diffusion of Aerosols from a Stream Flowing Through a Cylindrical Tube, Aerosol Science 6:125-132 (1975). f

James, A.C., Bronchial Deposition of Free Ions and Submicron Par ticles Studies in Excised Lung, in Inhaled Particles and Vapours IV, (W.H. Walton, ed.), pp. 203-219, Pergamon Press, New York (1977). Martin, D. and W. Jacobi, Diffusion Deposition of Small-Sized Par ticles in the Bronchial Tree, Health Physics, 23 : 23-29 (1972). National Council on Radiation Protection and Measurements, Evalua tion of Occupational and Environmental Exposures to Radon and Radon Daughters in the United States, NCRP Report No. 78, NCRP, Bethesda, MD 20814 (1984). Nikiforov, A. and R.B. Schlesinger, Morphometric Variability of the Human Upper Bronchial Tree, Respiration Physiology. 59:289-299 (1985). Olsen, D.E., G.A. Dart and G.F. Filley, Pressure Drop and Fluid Flow Regime of Air Inspired Into the Human Lung,J.App.Physiol. 28:482-494 (1970). Olsen, D.E., M.F. Sudlow, K. Horsfield and G.F. Filley, Convective Patterns of Flow During Inspiration, Arch. Intern. Med. 131:51-57 (1973). Schlesinger, R.B. and M. Lippmann, Particle Deposition in Casts of the Human Upper Tracheobronchial Tree, Am. Ind. Hyg. Assoc. J. 33:237-251 (1972). Schlesinger, R.B., D.E. Bohning, T.L. Chan and M. Lippmnn, Parti cle Deposition in a Hollow Cast of the Human Tracheobronchial Tree. J. Aerosol Sci. 8:429-445 (1977).



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Schlesinger, R.Β., J.L. Gurman and M. Lippmann, Particle Deposi tion Within Bronchial Airways: Comparisons Using Constant and Cyclic Inspiratory Flows,Ann.Occup.Hyg. 26:47-64 (1982). Sussman, R.G., B.S. Conen and M. Lippmann, The Distribution of Airflow in Casts or Human Lungs, Presented at the 1985 Annual Meeting of the American Association for Aerosol Research, Albu querque, NM (November, 1985). Ultman, J.S., Gas Transport in the Conducting Airways, in Gas Mix ing and Distributions in the Lung (L.A. Engel and M. Paiva, eds.), pp. 63-136, Marcel Dekker, Inc., New York (1985). Weibel, E. R. Morphometry of the Human Lung, Academic Press, New York (1963). Womersley, J.R., Method for the Calculation of Velocity, Rate of Flow and Viscous Drag in Arteries when the Pressure Gradient is Known, J. Physiol. 127:553-563 (1955). Yeh, H.C. and G.M. Schum, Models of Human Lung Airways and Their Application to Inhaled Particle Deposition, Bulletin of Mathemati cal Biology, 42: 2161-480 (1980). RECEIVED August 20,1986


Deposition of Ultrafine Particles in the Human Tracheobronchial Tree

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