Respiratory bronchiolitis following exposures to photochemical air pollutants

W. S. Tyler, M. D. Julian, D. M. Hyde

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Photochemical air pollution, formerly considered to be a problem limited to a very few urban areas, is now known to be widespread, involving both urban and rural populations in many parts of the world. Inhalation of current peak ambient concentrations of ozone, the archetypical component of photochemical air pollution, during normal outdoor work or recreational exercise results in transient changes in pulmonary functions, airway inflammation, and respiratory symptoms. These effects may be intensified by other components of photochemical air pollution, including oxides of nitrogen and acidic aerosols. Long-term consequences in humans of exposure to current ambient concentrations of photochemical air pollutants are uncertain, but there are indications of significant adverse effects. Epidemiologic studies of long-term effects of naturally occurring air pollution have many confounding factors and the strength of associations are difficult to establish. Such studies do suggest the possibility that populations regularly exposed to ambient concentrations of photochemical air pollutants, which often exceed the NAAQS for ozone may be subject to a more rapid deterioration in pulmonary functions with age. The evaluation of children in one epidemiologic study raised the possibility of adverse effects on lung growth and development. The other source of information concerning possible long- term effects in humans is extrapolation of effects from chronically exposed animals. In all species of mammals studied, including nonhuman primates, inhalation of ozone results in changes in the centriacinar airways characterized by epithelial damage followed by changes in epithelial cell populations, inflammatory changes and, in long-term exposures, increases in collagen. In animals, morphologic and biochemical changes continue after pulmonary functions have returned to normal. Morphologic and biochemical changes persist long after the end of an experimental exposure and some biochemical changes actually worsen. Extrapolation modeling has been used to make intra- and interspecies comparisons of the dose delivered to specific target sites, including the centriacinar airways. Related studies of uptake of ozone by the entire respiratory system indicate that the total uptake in humans is double that in rats. Thus, it is likely that humans exposed while exercising may develop centriacinar changes similar to those seen in experimentally exposed animals, especially nonhuman primates. Studies of effects on lung growth and development using young rats and monkeys support the possibility raised by an epidemiology study that inhalation of ozone alters lung growth and development in ways likely to be detrimental. Other studies in nonhuman primates have indicated that intermittent exposures, which model the seasonal nature of photochemical air pollution, result in as much or more damage than daily exposure. Although short-term exposures of humans to ambient concentrations of photochemical air pollution are not life threatening, the long-term effects of a series of exposures are not known, but are likely to be detrimental.

Original languageEnglish (US)
Pages (from-to)94-113
Number of pages20
JournalSeminars in Respiratory Medicine
Issue number2
StatePublished - 1992
Externally publishedYes

ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine


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