Respiratory Transport and Absorption

This chapter discusses the transport and absorption of ozone and other photochemical oxidants within the respiratory tract. It includes lung morphology and flow aspects of respiratory physiology and emphasizes methodologic approaches to modeling. 

The radical or reactive intermediates discussed in Chapter 2 are included in the term photochemical oxidants for the purpose of this chapter. Of the reactive intermediates discussed, only the hydroperoxy, HO2, and singlet oxygen, O2 (a A), radicals have a lifetime long enough 

This chapter first reviews and discusses selected research on local dose aspects of ozone toxicity, the morphology of the respiratoty tract and mucus layer, air and mucus flow, and the gas, liquid, and tissue components of mathematical models. Next, it discusses the approaches and results of the few models that exist. A similar review was recently done to defme an analytic framework for collating experiments on the effects of sulfur oxides on the lung. Pollutant gas concentrations are generally stated in parts per million in this chapter, because experimental uptake studies are generally quoted only to illustrate behavior predicted by theoretical models. Chapter 5 contains a detailed discussion of the conversion from one set of units to another. 

In this section, sites of action in the respiratory tract are discussed, along with experimental studies of gas uptake in animals. Cumulative dose and dosage at critical sites of action are defined, as well as the general characteristics required for modeling the transport and absorption in the respiratory tract. 

The sites of action and effects of ozone and other photochemical oxidants are described in Chapters 8 and 9. Recent work with primates has suggested that ozone is absorbed along the entire respiratory tract, penetrates more into the peripheral nonciliated airways, and causes more lesions in the respiratory bronchioles and alveolar ducts as the inhaled ozone concentration increases from 0.2 to 0.8 ppm. The most common and most severe tissue damage was observed in the respiratory bronchioles. The ciliated cells in the terminal bronchioles and the Type 1 cells in the epithelial layer of the proximal alveoli of rats were the 

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