Chronic Exposure to High Levels of Particulate Air Pollution and Small Airway Remodeling. (Research)
Churg, Andrew, Brauer, Michael, Avila-Casado, Maria del Carmen, Fortoul, Teresa I., Wright, Joanne L., Environmental Health Perspectives
Recent evidence suggests that chronic exposure to high levels of ambient particulate matter (PM) is associated with decreased pulmonary function and the development of chronic airflow obstruction. To investigate the possible role of PM-induced abnormalities in the small airways in these functional changes, we examined histologic sections from the lungs of 20 women from Mexico City, a high PM locale. All subjects were lifelong residents of Mexico City, were never-smokers, never had occupational dust exposure, and never used biomass fuel for cooking. Twenty never-smoking, non-dust-exposed subjects from Vancouver, British Columbia, Canada, a low PM region, were used as a control. By light microscopy, abnormal small airways with fibrotic walls and excess muscle, many containing visible dust, were present in the Mexico City lungs. Formal grading analysis confirmed the presence of significantly greater amounts of fibrous tissue and muscle in the walls of the airways in the Mexico City compared with the Vancouver lungs. Electron microscopic particle burden measurements on four cases from Mexico City showed that carbonaceous aggregates of ultrafine particles, aggregates likely to be combustion products, were present in the airway mucosa. We conclude that PM penetrates into and is retained in the walls of small airways, and that, even in nonsmokers, long-term exposure to high levels of ambient particulate pollutants is associated with small airway remodeling. This process may produce chronic airflow obstruction. Key words: air pollution, chronic obstructive pulmonary disease, COPD, small airways disease. Environ Health Perspect 111:714-718 (2003). doi:10.1289/ehp.6042 available via http://dx.doi.org/ [Online 19 December 2002]
Considerable attention has been devoted to the associations between levels of ambient particulate matter (PM) and acute cardiopulmonary mortality, hospital admissions, and exacerbations of respiratory and cardiac disease (Dockery 2001; Pope 2000). Less is known about chronic effects of high PM exposure, although such exposures have also been associated with increases in cardiopulmonary mortality, including increased rates of lung cancer (Beeson et al. 1998; Pope 2000; Pope et al. 2002). There is a limited amount of evidence to suggest that chronic exposure to high levels of PM may cause chronic airflow obstruction. Abbey et al. (1991, 1995, 1998, 1999) studied a cohort of nearly 4,000 nonsmoking Seventh Day Adventists in California. Significant risks for the development of new cases of chronic bronchitis and obstructive airways disease were associated with increased exposure to ambient PM [less than or equal to] 10 [micro]m in diameter and PM < 2.5 [micro]m in diameter (P[M.sub.10] and P[M.sub.2.5], respectively) (Abbey et al. 1991, 1995). Increased symptom severity correlated with P[M.sub.2.5] and P[M.sub.10] levels. In more recent analyses with this same cohort, long-term increases in P[M.sub.10] concentrations were also associated with lung function decrements (Abbey et al. 1998) and increases in mortality from nonmalignant lung disease (Abbey et al. 1999).
Studies of women in developing countries exposed to very high levels of PM emitted from cooking with biomass fuels also suggest that chronic exposures are associated with the development of chronic airflow obstruction. A case-control study of Mexican women reported an increased risk of chronic bronchitis and chronic airflow obstruction associated with cooking with wood (Perez-Padilla et al. 1996). The risk of chronic bronchitis was linearly associated with hour-years of cooking with biomass fuels. A case-control study conducted in Colombia identified a similar risk in women who cooked with biomass fuels (Dennis et al. 1996).
Because smoke-induced pathologic abnormalities in the small airways are one of the causes of chronic airflow obstruction in cigarette smokers, the observation of chronic airflow abnormalities in individuals with chronic high PM exposures suggests that PM exposure might also produce morphologic changes in the small airways. …