Inhaled particles

In the pages that follow are descriptions of (i) our current understanding of the deposition patterns of inhaled particles, (h) the fate of inhaled fibers and crystals in the limg, (Hi) induction of expression of genes that mediate the fibrogenic diseases, and (iv) how gene expression dictates the patterns of clinical presentation of disease. 

When animals or humans are exposed to aerosohzed fibers or particles, some proportion of the inhaled materials will be deposited in the nasal passages and upper airways. Other particles reach the conducting airways, including the terminal bronchioles, and part of the disease process is manifested there. Finally, a proportion of the asbestos fibers or silica crystals is deposited on the alveolar epithelium. With every breath that contains particles, more are deposited along the respiratory tract, thus triggering a series of pathobiological responses. AU the diseases caused by asbestos and silica are dose responsive, i.e., the more particles inhaled, the more likely it is that the disease will develop and the more advanced the disease will finally appear (2). 

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Mean Chemical Composition and Atmospheric Concentrations of Suspended Particulate Matter Sampled by the United States Environmental Protection Agency s Inhalable Particle and National Air Surveillance Networks—/rg/m and Percentage of Total Mass Sampled, 1980... 

Fine particles (<2.5 yum) coarse particles (2.5-15 /um) inhalable particles (0-15 ixm)... 

The size of inhaled particles varies markedly. The size distribution approximates a log-normal distribution that can be described by the median or the geometric mean, and by the geometric standard deviation. For fibers, both... 

Available information from human exposures indicates that airborne americium-containing particles are deposited in the respiratory tract, cleared to some extent via mucociliary action, and swallowed or expelled (Edvardsson and Lindgren 1976 Fry 1976 Newton et al. 1983 Sanders 1974 Toohey and Essling 1980). Descriptions of human respiratory tract models that can be used for radiation protection also include relevant information regarding biokinetics of inhaled particles (ICRP 1994b, 1995 NCRP 1997). Quantitative data are not available, however. Supporting animal studies include inhalation exposure to aerosols of americium (Buldakov et al. 1972 DOE 1978 Gillett et al. 1985 Sanders and Mahaffey 1983 Talbot et al. 1989 Thomas et al. 1972) or intratracheal instillation of americium compounds (Moushatova et al. 1996). 

Chan TL, Lippman M. 1980. Experimental measurements and empirical modeling of the regional deposition of inhaled particles in humans. Am Ind Hyg Assoc J 47 399-408. 

James AC, Stahlhofen W, Rudolf G, et al. 1994. Deposition of inhaled particles. In ICRP Publication... 

Mercer, T.T. and W.A. Stowe, Radioactive Aerosols Produced by Radon in Room Air Inhaled Particles III (Edited by Walton, W.H.) pp. 839-850, Old Waking Unwin Bros. Ltd., (1971). 

Yeh, H.C. and G.M. Schum, Models of Human Lung Airways and Their Application to Inhaled Particle Deposition, Bull. Math. Biol. 42 461-480 (1980). 

Radford, E. P., and E. A. Martell, Polonium-210 lead-210 ratios as an index of residence times of insoluble particles from cigarette smoke in bronchial epithelium, in Inhaled Particles IV, Part 2 (W. H. Walton, ed.) pp. 567-580, Pergamon Press, Oxford (1977). 

Chan, T. L. and M. Lippmann, Experimental Measurements and Empirical Modelling of the Regional Deposition of Inhaled Particles in Humans, Amer. Ind. Hvg. Assoc. J. 41 399-409 (1980). 

Fig. 1. Deposition of inhaled particles of different sizes (mass median aerodynamic diameters) in the three regions of the respiratory tract. Each shaded area indicates the variability of deposition when the aerosol distribution parameter, o, (geometric standard deviation) was varied from 1.2 to 4.5. The assumed tidal volume was 1450 cm3. (Reproduced from Health Physics, vol. 12, pp. 173-207,1966 by permission of the Health Physics Society).

There are also significant species differences in respiratory tract deposition and clearance of inhaled particles (Thomas, 1972). Data from a number of studies are summarized in Table 14 to assist in evaluating the several factors that influence the retention of inhaled materials. In studies with rats, Syrian hamsters, Chinese hamsters, and mice, the l44Ce was generally lost at a more rapid rate from the pulmonary region than was noted for the dog. A major factor in this difference may be differences in initial deposition sites and perhaps... 

Thomas R. G. (1972). An interspecies model for retention of inhaled particles, page 405 in Assessment of Airborne Particles, Mercer, T. T., Morrow, P. E. and Stober, W., Eds. (Charles C Thomas, Springfield, Illionis). 

Arredouani, M., et al., The scavenger receptor MARCO is required for lung defense against pneumococcal pneumonia and inhaled particles, J. Exp. Med. 200, 2, 267, 2004. 

Bennett, W.D. 1991. Aerosolized drug delivery fractional deposition of inhaled particles. J. Aerosol Med. 7 223-228. 

Brain, J.D. (1971). The effects of increased particles on the number of aveolar macrophages. In Inhaled Particles III, Proceeding of BOHS Symposium. Unwin Brothers Ltd., London, pp. 200-233. 

Davis, C.N. (1961). A formalized anatomy of the human respiratory tract. In Inhaled Particles and Vapours. (Davis, C.N., Ed.). Pergamon Press, London, pp. 82-91. 

Henderson, R.F., Barr, E.B. and Hotchkiss, J.A. (1991). Effect of exposure rate on response of the lung to inhaled particles, (abstr.) Toxicologists 11 234. 

Jones, J.G. (1984). Clearance of inhaled particles from alveoli. In Aerosols and the Lung Clinical and Experimental Aspects (Clarke, S.W. and Pavia, D., Eds.). Butterworth, London, p. 172-196. 

Dust masks, or particulate filter respirators, protect the respiratory system against any kind of inhaled particles. The simplest type, in the form of a cone-shaped fibrous filter that fits over the nose and mouth, is held in place by an elastic band around the back of the head. It is disposable, relatively comfortable to wear, and is useful when the dust is neither excessive nor toxic. It becomes readily clogged and should be discarded and replaced whenever breathing becomes restricted. Its use should not be carried over from day to day. 

Inhaled actinides deposit in the lung as a function of the size of the particle or size of the droplet of actinide salt solution. In the case of larger inhaled particles and... 

The pulmonary lymphatic system contributes to the clearance of fluid and protein from the lung tissue interstitium and helps to prevent fluid accumulation in the lungs [108], The lymphatic endothelium allows micron-sized particles (e.g. lipoproteins, plasma proteins, bacteria and immune cells) to pass freely into the lymph fluid [103], After administration of aerosolised ultrafine particles into rats, particles were found in the alveolar walls and in pulmonary lymph nodes [135], which suggests that drainage into the lymph may contribute to the air-to-blood transport of the inhaled particles. 

Mucociliary clearance Inhaled particles are cleared from the airways through trapping of the particles in mucus upon deposition and subsequent clearance of the mucus (with trapped particles) which is propelled by the coordinated beating of cilia towards the throat. This is termed the mucociliary escalator system. The mucociliary function is regulated by a variety of factors, such as bradykinin, histamine and cytokines [20-24],... 

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