Particle deposition lung airways

Fig. 7-2. Particle deposition as a function of particle diameter in various regions of the lung. The nasopharyngeal region consists of the nose and throat the tracheobronchial region consists of the windpipe and large airways and the pulmonary region consists of the small bronchi and the alveolar sacs. Source Task Group on Lung Dynamics, Health Phys. 12, 173 (1966).

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. 

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 ... 

Cohen, B.S., Harley, N.H., Schlesinger, R.B. and Lippman, M., Nonuniform Particle Deposition on Tracheobronchial Airways Implications for Lung Dosimetry. Presented at Second International Workshop on Lung Dosimetry, Cambridge, England, (September 1985). 

Yeh, H.C. and G.M. Schum, Models of Human Lung Airways and Their Application to Inhaled Particle Deposition, Bull. Math. Biol. 42 461-480 (1980). 

The adult human lung is exposed to more than 10,000 litres of air each day. Thus with each intake of air, the lung receives a high burden of dusts, fumes, pollens, microbes and other contaminants. Efficient defense mechanisms have evolved to minimize the burden of foreign particles entering the airways, and clearing those that succeed in being deposited. 

Aerosol size has an effect on the lung dose. Fine particles breathed through the mouth or the nose from lOOnm to 1,000 nm median size had 5-20 nGy per becquerel. Below 100 nm, this number more than doubled at 25-65 nGy per becquerel at 20 nm median size. Median sizes had an approximate geometric standard deviation of 2, so that the 95% confidence interval of particle sizes ranged from 0.25 to 4 times the stated median size. Very small particles deposited more efficiently in the airways. Lung cancer was related to radiation dose. These dose estimates are important determinants of lung cancer. 

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... 

Calculation of surface area concentrations implies even distribution of particles on the airway wall, but this is probably not the case. Studies of deposition in lung models of large [12,13] and small airways [14] suggest that deposition on airway surfaces is uneven. At all airway generations, it is likely that flow kinetics cause heavy deposition at some points, especially at carinae but also along selected portions of the airways between branches. This creates hot spots and cold spots with respect to particle concentration on airway walls. The importance of uneven deposition with local hot spots with high drug concentration, and also cold spots with low concentration, is not known. That local deposition in the forms of hot spots could be detrimental is made plausible by the evidence that... 

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