PRINCIPLES OF TOXICOLOGY - Biology East Borneo

9.1 LUNG ANATOMY AND PHYSIOLOGY 179system, before reaching the alveolar regions of the lung. The condition of the alveocapillary membraneis also important. Poor health conditions in a patient might lead to the engorgement of the interstitialspace with fluid, which would impair the diffusion of toxic chemicals across the alveocapillarymembrane. While this protects the affected individual from the toxic effects of the inhaledchemical, it also prevents the free exchange of oxygen and carbon dioxide, which can have obviouslife-threatening outcomes.The degree of uptake of inhaled gases and vapors can be quite significant in workers in manyoccupations. Following the initiation of inhalation, rapid uptake of perchloroethylene, a commonlyused dry cleaning solvent for which there are thousands of potential exposures, can be observed inmany different tissues (Figure 9.10). In this case, the uptake of perchloroethylene in circulating bloodand seven tissues was remarkably rapid, and for many industrial chemicals, it is often within minutesof exposure. It is often interesting to note that the levels of the inhaled solvent remained fairly constantthroughout the inhalation exposure period. This can have important ramifications in occupationalexposures, as workers who enter an environment with a potentially toxic gas can experience systemictoxic effects almost immediately, and these effects can persist for long periods of time (while theinhalation exposure period continues). For instance, many industrial solvents cause neurobehavioraldepression following inhalation exposure, and workers have been known to be injured as a result offalls or mishaps with industrial machinery almost immediately after breathing the chemicals.Obviously, the length of exposure affects the amount of chemical inhaled. However, for many gasesand vapors a steady-state equilibrium can be established after a certain period of inhalation exposure.In this way, the level of chemical in the blood does not continue to increase, despite the continuedinhalation exposure to the compound (Figure 9.10). This has important ramifications in industrialexposures because it helps explain why workers sometimes do not experience toxic effects to certainchemicals despite long-term exposure.Figure 9.10 The uptake and disposition of perchloroethylene (PER) in the blood and seven tissues of laboratoryrats is shown. The animals inhaled 2500 ppm of perchloroethylene for 120 min in dynamic inhalation exposurechambers, and blood and tissues were analyzed for the solvent by electron capture-gas chromatography. (Supportedby US Air Force Grants AFOSR 870248 and 910356.)