Pulmonary regions

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).

Lung Clearance Class (fast, F medium, M slow, S)—A classification scheme for inhaled material according to its rate of clearance from the pulmonary region of the lungs to the blood and the gastrointestinal tract. 

Fig. 3 Sites of deposition in the lungs, the oropharynx, tracheobronchial, and pulmonary regions. 

Dosimetric Studies. The main objective of Rn-d dosimetry is to enable the assessment of the observed dose from Rn-d deposited in the respiratory tract from measured Rn-d concentration in the atmosphere. As a consequence of an inhomogeneous Rn-d deposition within the lung, different dosimetric concepts have been developed to describe either regional mean dose values (e.g. for tracheobronchial or pulmonary region) or microdosimetric dose calculations (e.g. for the basal cell layer). Using Monte Carlo calculation methods it is also possible to account for the random nature of cellular hits by deposited alpha particles. The results of such dosimetric calculations should provide the following information needed for Rn-d risk assessment ... 

There are also significant species differences in respiratory tract deposition and clearance of inhaled particles (Thomas, 1972). Data from a number of studies are summarized in Table 14 to assist in evaluating the several factors that influence the retention of inhaled materials. In studies with rats, Syrian hamsters, Chinese hamsters, and mice, the l44Ce was generally lost at a more rapid rate from the pulmonary region than was noted for the dog. A major factor in this difference may be differences in initial deposition sites and perhaps... 

Fig. 17. Biological model recommended for describing the uptake and retention of cerium by humans after inhalation or ingestion. Numbers in parentheses give the fractions of the material in the originating compartments which are cleared to the indicated sites of deposition. Clearance from the pulmonary region results from competition between mechanical clearances to the lymph nodes and gastrointestinal tract and absorption of soluble material into the systemic circulation. The fractions included in parentheses by the pulmonary compartment indicate the distribution of material subject to the two clearance rates however, these amounts will not be cleared in this manner if the material is previously absorbed into blood. Transfer rate constants or functions, S(t), are given in fractions per unit time. Dashed lines indicate clearance pathways which exist but occur at such slow rates as to be considered insignificant compared to radioactive decay of the cerium isotopes.

Gases, vapors, and dust particles can move into the airways from the environment and penetrate to the pulmonary region in several ways. Gases and vapors can move readily through the three regions. 

A concerted effort is needed to increase our understanding of the transfer and uptake of reactive gases in the lung. A program in this field should involve in vitro model studies, animal experiments, and clinical studies. More information is required on the chemical, physical, and morphologic properties of the mucous layer and the kinetics of the reactions of ozone in the mucous and tissue layers. Experimental data on uptake and dosage for ozone and other oxidants are difficult to obtain for the tracheobronchial and pulmonary regions. Such data for animals and humans will be needed to test the present simple transport models, before further refinements are made. 

PULM pulmonary region (alveolated airways and alveoli). 

The physical characteristics of individual particles also are of environmental significance. For example, the smaller particles (diameters on the order of 1 micrometer of less) generally are most important in that they have very long atmospheric residence times (18), are least effectively controlled by pollution control devices (19), are preferentially deposited in the pulmonary regions of the lung (20,21), and may be most enriched in toxic species on a specific concentration (iig/g) basis (22-24). 

Indicates the presence of inhalable and respirable particles. As a rough guide, particles with aerodynamic diameters below 100 p,m have the potential to be inhaled. Particles with aerodynamic diameters of above 1—5 p,m have the greatest probability of settling in the nasopharyngeal region whereas particles with aerodynamic diameters below 1-5 p,m are most likely to settle in the tracheobronchial or pulmonary regions, i.e., are respirable. 

The lower respiratory tract (pulmonary region or alveolar ducts and sacs) is the area where gas exchange occurs. Alveolar sacs, clusters of two or more alveoli, branch from alveolar ducts. It is generally considered that there is a total of approximately 300 million alveoli in the lungs of adult humans. The total alveolar surface area in the lungs of adult humans is... 

In contrast, a decreasing proportion of particles from 1 p (100%) up to lOp (1%) reaches the pulmonary region in the human lung during normal breathing via the nose. Once there, maximum pulmonary deposition occurs for particle sizes of l-4p about 25% of Ip, 35% of2p, 30% of 3p, and 25% of4p. °... 

Mouth breathing by humans during exertion may result in deposition that is distinctly different from that associated with nasal breathing, with increased deposition of the larger particles up to about 15 p in both the tracheobronchial and pulmonary regions. ... 

The human equivalent concentration (HEC) for the LOAEL (LOAELjjec) was calculated by multipl5ung the LOAELadj by the regional gas ratio for the pulmonary region of the respiratory tract (RGDRpu) according to the equation ... 

Used to derive a chronic inhalation Minimal Risk Level (MRL) of 2 x 10" mg/m nickel for soluble nickel salts dose adjusted for intermittent exposure (6/24 hours, 5/7 days), multiplied by the Regional Deposited Dose Ratio (0.9714 for pulmonary region deposition mass median aerodynamic diameter [MMAD] = 2.5 pm, sigma = 2.4 pm), and divided by an uncertainty factor of 30 (3 for extrapolation from animals to humans, and 10 for human variability). 

The exposure concentration was adjusted for intermittent exposure (6 hours/24 hours, 5 days/7 days). A regional deposition ratio of 0.9714 for the pulmonary region for particle size 2.5 pm and sigma 2.4 was used to extrapolate from particle deposition in rats to deposition in humans... 

The pulmonary region concerns exchanging gases with the cells of the body. 

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