Human respiratory tract particle deposition

The need to determine accurately the phase-specific concentrations of these pollutants reflects several concerns Compared to gaseous materials, particle-phase materials may penetrate more deeply into the human respiratory tract particle-phase pollutants scatter light much more effectively than gaseous materials, and they thus have a greater contribution to visibility reduction gaseous nitric acid has a much higher deposition velocity than particulate nitrates and can be a substantial contributor to the acidification of lakes, streams, forests, and vegetation. 

Scheuch, G., and Stahlhofen, W. (1992). Deposition and dispersion of aerosols in the airways of the human respiratory tract the effect of particle size. Exper. Lung Res. 18, 343-358. 

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). 

Tu and Knutson (1984) also measured the particle deposition of hydrophobic and hygroscopic particles in the human respiratory tract. They showed that the hygroscopic particles grow by a factor of 3.5 to 4.5 at the saturated humidity present in the lung. For the purpose of calculating bronchial deposition for a hygroscopic aerosol we assume an increase in size by a factor of 4 upon entry into the bronchial tree. 

Lippmann, M. (1977). Regional deposition of particles in the human respiratory tract , Section 9, page 213 in HANDBOOK OF PHYSIOLOGY, Lee, H. D. K. Sect. Ed., (American Physiological Society, Bethesda, Md.). 

Stahlhofen, W., Gebhart, J. and Heyder, J. (1980). Experimental determination of the regional deposition of aerosol particles in the human respiratory tract. Am. Ind. Hyg. Assoc. J. 41 385-398. 

The rationale for basing air quality standards on smaller particles is evident from an examination of Fig. 2.12, a diagram of the human respiratory tract. Larger particles that are inhaled are removed in the head or upper respiratory tract. The respiratory system from the nose through the tracheobronchial region is covered with a layer of mucus that is continuously moved upward by the motion of small hairlike projections called cilia. Large particles deposit on the mucus, are moved up, and are ultimately swallowed. 

Hounam, R.F., Black, A. Walsh, M. (1971) The deposition of aerosol particles in the nasopharyngeal region of the human respiratory tract. Journal of Aerosol Science, 2, 47-61. 

Figure 2. Deposition efficiency of particles in the human respiratory tract.

Human Respiratory Tract and Aerosol Particle Deposition... 

HUMAN RESPIRATORY TRACT AND AEROSOL PARTICLE DEPOSITION... 

The probability of deposition of particles in the various parts of the human respiratory tract depends on their aerodynamic diameter, Dae- This parameter in turn is a function of the physical dimensions, shape, and density of the particles. For spherical particles, the aerodynamic diameter is simply... 

REGIONAL DEPOSITION OF INHALED PARTICLES AND DROPLETS IN THE HUMAN RESPIRATORY TRACT... 

Much of our early understanding of deposition of inhaled particles in the human respiratory tract as a function of aerodynamic diameters and breathing parameters... 

Finlay WH, Stapleton KW, Yokota J. On the use of computational fluid dynamics for simulating flow and particle deposition in the human respiratory tract. J Aerosol Med 1996 9 329-342. 

Lippmann M, Albert RE. The effect of particle size on the regional deposition of inhaled aerosols in the human respiratory tract. Am Ind Hyg Assoc J 1969, 30, 257-275. 

Heyder J, Gebhart J, Rudolf G, Schiller CF, Stahlhofen W. Deposition of particles in the human respiratory tract in the size range 0.005-15 xm. J Aerosol Sci 1986, 17, 811-825. 

Interest in particle deposition after World War II was fuelled by concern about possible deposition of radioactive particles. In 1965, The International Radiological Protection Commission (IRPC) Task Force on Lung Dynamics submitted its report Deposition and retention models for internal dosimetry of the human respiratory tract (Task Group on Lung Dynamics, 1966). The Task Force, comprising Bates, Fish, Hatch, Mercer and Morrow, undertook a detailed examination of the area and developed a deposition model using methods of calculation similar to those used... 

If inspired particles were carried only convectively with the bulk of airflow, losses of these particles in the respiratory tract would be negligible. However, all inspired particles experience a nonzero chance of being lost. This is due to particle transport toward airway and airspace surfaces as a result of mechanical and electrical forces acting upon the particles. Upon contact with these surfaces, the particles are deposited. The human respiratory tract can therefore be considered as an aerosol filter, removing particles from the inspired air. The effectiveness of this filter depends on... 

Figure 3 Schematic filter characteristic of the human respiratory tract for aerosol particles. Three domains can be recognized the domain of deposition decreasing with particle size is solely due to diffusional particle transport, the domain of minimum deposition is due to simultaneous diffusional and gravitational particle transport, and the domain of deposition increasing with particle size due to gravitational and inertial particle transport.

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