Alveolar dust

The alveolar dust is that fraction of the inhalable dust which reaches the alveoh. According to the Johannesburg Convention , all particles with an aerodynamic diameter below 7 pm are regarded as the alveolar fraction. Particles with much smaller diameters have a greater chance of being exhaled without deposition in the respiratory tract. 

The effects of fibers are not fundamentally different from the effects of the alveolar dust. The carcinogenic potency is determined first of aU by... 

Brown, G.M., Li, X.Y. and Donaldson, K. (1991a). Secretion of interleukin 1 and tumour necrosis fector by alveolar macrophages following exposure to particulate and fibrous dusts. In Mechanisms in Fibre Carcint nesis (eds. R.C. Brown, J.A. Hoskins and N.F. Johnson) pp. 499-504. Plenum, New York. 

Nadeau, D., Lane, D.A., Paradis, D. and Fouquette, L. (1989). Effects of nicotinamide on the cytotoxicity of mineral dusts towards pulmonary alveolar macrophages. In Effects of Mineral Dusts on Cells (eds. B.T. Mossman and R.O. Begin) pp. 115-122. Springert Verlag, Berlin. 

Hohansson, A., P. Camner, and B. Robertson. 1981. Effects of long-term nickel dust exposure on rabbit alveolar epithelium. Environ. Res. 25 391-403. 

Animal experiments were undertaken to test the relationship 235 guinea pigs exposed to asbestos dusts were found to have asbestosis but no cancer (Vorwald and Karr, 1938), whereas only two pulmonary carcinomas were reported among ten surviving mice after 240 days of exposure to asbestos dust (Nordman and Sorge, 1941). One fortuitous but often cited animal experiment was that of pulmonary asbestosis reported in a dog who served for ten years as a ratter in an asbestos factory. The animal died of alveolar fibrosis and collapse as a result of diffuse distribution of asbestos in the lungs (Schuster, 1931). 

An immediate response to dust inhalation is the migration of polymorphonuclear leukocytes (PMNs) across epithelial—endothelial junctions to the alveolar space (see Fig. 3.6). Macrophages release a chemotactic factor that mobilizes and attracts PMNs from the pulmonary blood. However, the initial PMN accumulation clears rapidly. 

Inhalation in the form of an aerosol (p. 12), a gas, or a mist permits drugs to be applied to the bronchial mucosa and, to a lesser extent, to the alveolar membranes. This route is chosen for drugs intended to affect bronchial smooth muscle or the consistency of bronchial mucus. Furthermore, gaseous or volatile agents can be administered by inhalation with the goal of alveolar absorption and systemic effects (e.g inhalational anesthetics, p. 218). Aerosols are formed when a drug solution or micron-ized powder is converted into a mist or dust, respectively. 

Fine metallic aluminum powders inhaled by hamsters and guinea pigs caused no pulmonary fibrosis in rats that inhaled the dust, small scars resulted from foci of lipid pneumonitis. Alveolar proteinosis developed in all three species it resolved spontaneously, and the accumulated dust deposits cleared rapidly from the lungs after cessation of the exposure. The failure of inhaled aluminum powder to cause pulmonary fibrosis in experimental animals parallels the clinical experience in the United States, where pulmonary fibrosis has not been observed in aluminum workers. ... 

In rats, inhalation of massive levels of y-alumina with an average particle size of 0.0005-0.04p for up to 285 days caused heavy desquamation of alveolar cells and secondary inflammation, but only slight evidence of fibrosis. The dust concentration in the exposure chamber was described as so high that visibility was reduced a few breaths of the atmosphere by the investigators caused bronchial irritation and persistent cough. 

The inhalation airflow comes to a rest in the alveolar region. In still air, the collision of gas molecules with each other results in Brownian motion. The same happens with sufficiently small particles (which can be seen when the dust particles in a nonventilated room are hit by a sunbeam). For very small or ultrafine particles (when the particle size is similar to the mean free path length of the air molecules), the motion is not determined by the flow alone but also by the random walk called diffusion. The diffusion process is always associated with a net mass transport of particles from a region of high particle concentration to regions of lower concentration in accordance with the laws of statistical... 

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