Particle deposition, factors affecting

A second factor in the deposition process is the physical size of the radioaerosol particles deposited during dry deposition. Particle size affects the efficiency of foliar collection of dry aerosol particles and may also be important in determining the rate of solution of soluble constituents within the aerosol particle. Lockhart et al. (7) indicated that nuclear debris in surface level air is generally associated with aerosol particle sizes about 0.5-1.0p in diameter. Martell (8) stated that high yield detonations causing condensation of "Sr at stratospheric altitudes leads to the formation of particles with diameters less than 1 fi. Hence,... 

Physiological factors affecting particle deposition in the airways... 

While chemical composition is important in determining the toxicity of particles and fibers, it is equally or more important to determine where a particle or fiber will deposit in the respiratory tract and how long it will stay there. The quantity and location of particle deposition in the respiratory tract depends on factors related to both the exposed individual and the inhaled particles. The mechanism of deposition is determined by the physical (size, shape, and density) and chemical (hygroscopicity and charge) characteristics of the inhaled particles. Particle deposition is also affected by biological factors inherent to the exposed individual such as breathing pattern (volume and rate), route of breathing (mouth versus nose), and the anatomy of the airways. 

Agnew JE, Pavia D, Clarke SW. 1985. Factors affecting the alveolar deposition of 5 microns inhaled particles in healthy subjects . Clin. Phys. Physiol. Meas. 6 27-36. 

Schulz H. Mechanisms and factors affecting intrapulmonary particle deposition implications for efhcient inhalation therapies. Pharm Sci Technol Today 1998, 1, 336-344. 

Many chemical component-s present in such aerosols are relatively stable they can be measured long after (days, week.s, or more) the aero.sol has been collected on a filter or impactor plate, for example. Short-lived reactive and/or volatile species such as peroxides and aldehydes are not usually determined. This may make it difficult to evaluate the health and ecological effects of aerosols because chemically reactive chemical species tend to be the most active biochemically. The chemical components present in the particles collected on a filter or impactor plate may react with each other when they are in close proximity. Particle deposits in filters or on surfaces may also react with molecular components of the gases flowing over them. Chemical reactions between the gas and aerosol may not affect mea.surement.s of metallic elements but may modify chemical speciation (compound form) on the collector surface. All of these factors must be taken into account in selecting sampling and measurement methods for aerosol chemical properties. 

Inhaled particles vary both in shape and density and these factors affect their capacity to be deposited by sedimentation. The behaviour of such particles can be determined by converting their actual diameter(s) to their aerodynamic diameters). What does this mean Imagine a low-density particle of irregular shape - this will be characterized by a certain terminal velocity as it settles in air. The aerodynamic diameter of the particle is defined as the actual diameter of a spherical particle of unit density with the same terminal velocity. 

While the product is in the aerosol can or nebuliser vial, the dosage form that the patient experiences is a dynamic aerosol cloud. For example, the quality of the cloud from a DPI is often dependent on the airflow through the device, and a MDI cloud rapidly evaporates as it travels through the air. These factors affect the particle size distribution in the aerosol cloud, and the particle size is the critical parameter for lung deposition. 

Particles (such as those present in mists, and in fumes, smokes, and dusts) present a more complex distribution pattern because the particle size affects its deposition at various levels of the airway. Such factors as sedimentation and impact rates also control particle deposition. Therefore, heavier particles may settle in the nasopharynx or upper airways, whereas lighter or smaller particles may reach more-peripheral airways. Once they have impacted, particles are susceptible to a variety of respiratory defense mechanisms. These mechanisms determine the efficiency with which particle removal progresses, thereby determining the particle s ultimate degree of adverse effects. 

Schiller et al. (1986) analyzed factors affecting ultraline aerosol deposition in the human airway. Deposition of ultrafine particles in replicate cast models of the human nasal cavity is measured by Cohen et al. and Swift et among... 

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