This chapter defines the functional zones of human lung, describes responses to occupationally polluted air, reviews the adverse health effects caused by environmental air pollution, and considers indoor air pollution.
FUNCTIONAL ZONES OF HUMAN LUNG
The lungs' two regions are the conducting airways and the gas-exchanging alveolar zone. In the former, a mucociliary escalator removes deposited particles. The alveolar zone, which includes alveolarized respiratory bronchioles and alveolar ducts, lacks this ability1 (Fig. 32-1). The two zones differ greatly in defenses and susceptibility to damage. For example, water-soluble gases such as sulfur dioxide and ammonia adsorb to water in proximal conducting airways, while relatively insoluble ozone and nitrogen dioxide damage the nonmucous-covered alveolar zone (Table 32-1). The airways selectively filter particles. Thus large particles (50 μm in diameter) lodge in the nose or pharynx, but particles less than 10 μm (and usually less than 5 μm) reach the alveolar zone.2 Fungal spores with diameters of 17–20 μm affect only proximal conducting airways (Fig. 32-2), while the 1 μm diameter spores of Micropolyspora faeni affect alveoli as well (Fig. 32-3). As a first approximation, reactions to particles can be predicted from their size, which is best defined by the mean median diameter, and from solubility in water. The site of lodgment of fibers and fibrils is predicted from aerodynamic diameter, not from length.
Diagram showing the possible fates and influence of inhaled aerosols and ingested materials. Alv, alveolus; Alv macro, alveolar macrophages; GIT, gastrointestinal tract; Ins, insoluble particles; NP, nasopharynx; RB, red blood cell; RES, reticuloendothelial system; S, soluble particles; TB, terminal bronchioles; TLN, thoracic lymph nodes. (Adapted from Kilburn KH. A hypothesis for pulmonary clearance and its implications. Am Rev Respir Dis. 98:449–63; 1968. Courtesy of the Editor of American Review of Respiratory Diseases.)
TABLE 32-1PROPERTIES, SOURCES, AND TOXICITY OF COMMON GASES ||Download (.pdf) TABLE 32-1 PROPERTIES, SOURCES, AND TOXICITY OF COMMON GASES
|Health Effects |
|Name ||Formula ||Color and Odor ||Sources of Exposure ||Acute ||Chronic ||OSHA [TWA]* (ppm) ||IDLH†(ppm) |
• Asphyxiant Gases
|Carbon dioxide ||CO2 ||c, ol ||M, We, FC ||A, H, D, Ch || ||5000 ||50,000 |
|Carbon monoxide ||CO ||c, ol ||CS, T, FC ||A, H, Cv, Co || ||50 ||1500 |
|Methane ||CH4 ||c, olf ||Ng, D ||A || || || |
|Carbon disulfide ||CS2 ||c, so ||CM ||H, D ||Np ||20 ||500 |
|Hydrogen sulfide ||H2S ||c, re ||Ae, D, Ng, P ||A, Pe, D, H, Co ||Np ||(20) ceiling ||300 |
• Oxidant Gases
|Ozone ||O3 ||c, po ||S, EA, W, AC ||T, Pe, Mm, Tp ||AO ||0.1 ||10 |
|Nitrogen oxides ||NO ||rb, po ||W ||T, Mm, Pe, Tp || ||25 ||100 |