Aerosols airway

Germany TRK (technical exposure limit) 2mgm inhalable fraction of the aerosol airways and skin sensitizer for Western red cedar. 

As discussed below, airway size, structure, and branching pattern will all influence the delivery and deposition of aerosols. Airway caliber—which may be reduced due to bronchoconstriction, inflammation, edema, increased secretions, or simply age at both ends of the spectrum—is a major influence on site of depo-... 

Single dose or short-term treatment with aerosolized steroids inhibits both the late asthmatic response and allergen-induced bronchial hyperresponsiveness (45,92). However it does not affect the early asthmatic response nor does it induce bronchodilation (45,92). Long-term treatment with steroids protects against both the early and late asthmatic responses and also reduces bronchial hyperresponsiveness (44,71,86,93). Over time, the airways relax (dilate) and measures of airway function, such as forced expiratory volume in one second (FEV ), gradually return to almost normal levels. 

Industrial environments expose individuals to a plethora of airborne chemical compounds in the form of vapors, aerosols, or biphasic mixtures of both. These atmospheric contaminants primarily interface with two body surfaces the respiratory tract and the skin. Between these two routes of systemic exposure to airborne chemicals (inhalation and transdermal absorption) the respiratory tract has the larger surface area and a much greater percentage of this surface exposed to the ambient environment. Or dinary work clothing generally restricts skin exposures to the arms, neck, and head, and special protective clothing ensembles further limit or totally eliminate skin exposures, but breathing exposes much of the airway to contaminants. 

Airstream neutralization of acid aerosols by NH3 present in the airway-lumen reduces the health risk associated with acid particles by reducing the acid concentration prior to particle deposition.- In addition, the liquid lining of the respiratory tract probably acts as a chemical buffer," further reducing the health hazard posed by inspired acid particles. Principal factors controlling airstream neutralization of acid aerosols, which is considered to be a diffusion-limited process, are particle surface area, and particle... 

Guilmette, R. A., Wicks, J. D., and Wolff, R. K. (1989). Morphometry of human nasal airways m vivo using magnetic resonance imaging. J. Aerosol Med. 2, 365-377. 

Larson, T. V., Covert, D.S., Frank, R., and Charlson, R.J. (1977). Ammonia in the human airways neutralization of inspired acid sulfate aerosols. Science 197, 161-163. 

Kaufman, J. W. (1999). The role of upper airway heat and water vapor exchange in hygroscopic aerosol deposition iii the human airway. In Toxicity Assessment Alternatives Methods, Issues, Opportunities (H. Salem and S.A. Katz, Eds.), pp. 63-70. Humana Press Inc., Totow a, NJ. 

Cocks, A, T, and McElroy, W. J. (1984). Modeling studies of the concurrent growth and neutralization of sulfuric acid aerosols under conditions in the human airways. Eimironmefital Res. 35, 79-96. 

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. 

Air contaminants in solid or liquid state (aerosols), e.g., wood dust, welding smoke, or oil mist, are all in principle directly visible. The dispersion of those contaminants and the airflow patterns around the source may therefore be studied without any special tools. It is, however, not always possible to see the contaminant if, for example, the concentration in the air is low, the size of the particles is small, or the lighting is poor. The fact that the contaminant can t be seen may stem from the acceptable low level of the concentration but that can of course not be used to conclude that the control is acceptable. That conclusion depends not only on the contaminant s toxicological qualities but on how visible it is iit air. The ability to see the particles directly is also, as said above, a function of their size. Small particles, able to be transported deep into the thinner airways of the lungs, are many times also difficult to see directly. 

For extrathoracic deposition of particles, the model uses measured airway diameters and experimental data, where deposition is related to particle size and airflow parameters, and scales deposition for women and children from adult male data. Similar to the extrathoracic region, experimental data served as the basis for lung (bronchi, bronchioles, and alveoli) aerosol transport and deposition. A theoretical model of gas transport and particle deposition was used to interpret data and to predict deposition for compartments and subpopulations other than adult males. Table 3-4 provides reference respiratory values for the general Caucasian population during various intensities of physical exertion. 

Guilmette RA, Muggenburg BA, Cuddihy RG. 1988. Systemic absorption of americium from the nasal airways of dogs exposed intranasally to americium-241 nitrate and oxide aerosols. Health Phys 54(Suppl. 1) S27. 

Particulate diffusion does not play a significant role in the deposition of pharmaceutical aerosols. However, it is worth noting the mechanism by which diffusion of particles occurs in the lungs. The principle of Brownian motion is responsible for particle deposition under the influence of impaction with gas molecules in the airways. The amplitude of particle displacement is given by the following equation ... 

The first purified and characterized drug substances were administered as aerosols as a topical treatment for asthma approximately 50 years ago. More recently, drugs have been evaluated for systemic delivery. For each category of drug the mechanism of clearance from the airways must be considered. These mechanisms may be listed as mucociliary transport, absorption, and cell-mediated translocation. The composition and residence time of the particle will influence the mechanism of clearance. 

Most dosimetry models have incorporated the so-called Weibel A airway dimensions (Weibel, 1963) in order to calculate aerosol deposition, clearance and the density of alpha-decays per unit surface... 

Diffusion is the dominant mechanism of lung deposition for radon daughter aerosols. It is generally assumed that airflow is laminar in the smaller airways and that deposition in each airway generation can be calculated adequately (Chamberlain and Dyson, 1936 Ingham, 1975). However, there is no such consensus on the treatment of deposition in the upper bronchi. Some authors (Jacobi and Eisfeld, 1980 NCRP, 1984) have considered deposition to be enhanced by secondary flow, on the basis of experimental results (Martin and Jacobi, 1972). It has been shown that this assumption reduces the calculated dose from unattached radon daughters by a factor of two (James, 1985). 

Figure 5. Doses averaged over all epithelial cells in the bronchial and alveolar regions of the lung per unit exposure to potential alpha-energy as a function of aerosol size, compared with doses to basal cells for several models of airway size and clearance behaviour.

After exposure, the outside surface of the cast was cleansed until the activity of the washes was less than 10X the background of a gamma well scintillation counter. The cast was cut into separate bifurcations and airway sections and each section was counted to determine the amount of aerosol deposited. Sane samples contained both airway and bifurcation sections because of the complex configuration of the cast. For combination samples, the total activity deposited was equally apportioned between each of the airways and bifurcations. End airways were included for determination or total deposition but not in any of the analyses because flow disturbances at open ends may have affected deposition. The surface area of each sample was measured separately. The surface density for each cast segment was calculated by dividing the activity measured in the sample by the interior surface area of that sample. 

Chan, T. L., R. M. Schreck and M. Lippmann, Effect of the Laryngeal Jet on Particle Deposition in the Human Trachea and Upper Bronchial Airways, A Aerosol Sci. 11 447-459 (1980). 

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