Particle deposition in airways

Balashazy 1, Hofmann W. Particle deposition in airway bifurcations—I. Inspiratory flow. J Aerosol Sci 1993 24 745-772. 

Gehr P, Schurch S. Surface forces displace particles deposited in airways toward the epithelium. News in Physiological Sciences 1992 7 1-5. 

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... 

The particle size is the most important factor that contributes to the clearance of particles. For particles deposited in the anterior parts of the nose, wiping and blowing are important mechanisms whereas particles on the other areas of the nose are removed with mucus. The cilia move the mucus toward the glottis where the mucus and the particles are swallowed. In the tracheobronchial area, the mucus covering the tracheobronchial tree is moved upward by the cilia beating under the mucus. This mucociliary escalator transports deposited particles and particle-filled macrophages to the pharynx, where they are also swallowed. Mucociliary clearance is rapid in healthy adults and is complete within one to two days for particles in the lower airways. Infection and inflammation due to irritation or allergic reaction can markedly impair this form of clearance. 

The ICRP deposition model estimates the fraction of inhaled material initially retained in each compartment (see Figure 3-2). The model was developed with five compartments (1) the anterior nasal passages (ET,) (2) all other extrathoracic airways (ET2) (posterior nasal passages, the naso- and oropharynx, and the larynx) (3) the bronchi (BB) (4) the bronchioles (bb) and (5) the alveolar interstitium (AI). Particles deposited in each of the regions may be removed and redistributed either upward into the respiratory tree or to the lymphatic system and blood by different particle removal mechanisms. 

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). 

Bell, K.A. (1978). Local particle deposition in respiratory airway models. In Recent Developments in Aerosol Science (Shaw, D.T., Ed.). Wiley New York, pp. 97-134. 

Kelly, J.T. and B. Asgharian. 2003. Nasal molds as predictors of fine and coarse particle deposition in rat nasal airways. Inhal. Toxicol. 15 859-875. 

Figure 2.13 shows the deposition of particles in various regions of the respiratory tract as a function of particle diameter (Phalen, 1984 Phalen et al., 1991 Yeh et al., 1996). The deposition fraction of PM1() in the pulmonary and tracheobronchial regions can be quite large, so it is not surprising that health effects could be associated with these particles. Deposition in the upper portions of the respiratory system is dominated primarily by the large particles, which are readily taken out in the nose and upper airways. 

Cheng, Y.S., Zhou, Y., and Chen, B.T. (1999). Particle deposition in a cast of human oral airways. Aerosol Sci. Technol., 31, 286-300. 

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. 

Five mechanisms govern particle deposition in lung airways, namely, inertial impaction, gravitational sedimentation, diffusion, interception, and electrostatic attraction.f Electrostatic charges enhance deposition by increasing attractive forces to airway surfaces. Melandri et found that the deposition of... 

Particle deposition in one-dimensional EDMs is dealt with in the same manner as in LDMs, by using exact solutions of the dynamical equations for sedimentation and diffusion in inclined circular tubes and using empirical equations for inertial impaction from experiments in branched-airway replicas. 

Sarangapani R, Wexler AS. The role of dispersion in particle deposition in human airways. Toxicol Sci 2000 54 229-236. 

Oldham MJ, Phalen RF, Heistracher T. Computational fluid dynamics predictions and experimental results for particle deposition in an airway model. Aerosol Sci Technol 2000 32 61-71. 

The site and quantity of particle deposition in the respiratory tract depend mainly on particle size but are also affected by respiratory pattern and airway pathology. Understanding the terminology of particle deposition is essential. Deposition is the capture of particles on a surface. Some inhaled particles are deposited by the respiratory epithelium, and others are exhaled. Clearance is the removal of any deposited particles by any process and is not a major topic of this discussion, although it may be important for the efficacy of inhaled medications. Total deposition is the difference between the inhaled and exhaled mass of the substance of interest. Regional deposition defines mass in various anatomic levels... 

To achieve benefit from aerosolized antibiotic therapy, an adequate amount of medication must reach the site of infection [3,4,8]. Optimal particle size for deposition in the lower respiratory tract and alveoli lies between 1 and 5 micrometers (pm). For alveolar deposition, particle sizes of 1 -2 pm are optimal. Particle diameters of 3 and 4 pm reach the lower airway, while 5-pm particles deposit in the central airways. Particles below this range are likely exhaled, and... 

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