Shape of concentration-response curves between long-term particulate matter exposure and morbidities of chronic bronchitis: a review of epidemiological evidence

Abstract

Numerous studies have assessed the concentration-response (C-R) relationships between long-term exposure to particulate matter (PM) and mortality from cardiopulmonary diseases, but few studies have evaluated the C-R relationships between PM exposure and morbidity of chronic respiratory diseases or their symptoms, and to date no systematic review has been published on the characteristics of the C-R curves between PM exposure and respiratory disease morbidity. Screening of all available studies in Medline identified ten studies with figures or scatter plots showing the C-R relationships between PM exposure and chronic bronchitis or chronic cough/phlegm. The C-R relationships showed ballistic 'S' shaped curves, linear in the low to moderate PM range and flattening out in the high PM range. Moreover, the shape and level of the C-R curves differed markedly between susceptible and nonsusceptible populations. New evidence from a prospective cohort study confirmed that the C-R relationship between PM reduction and beneficial effects on respiratory health may be due to the decreased incidence of respiratory symptoms and increased recovery in individuals with symptoms of bronchitis. Additional studies are needed to assess the C-R relationships between different PM contents and chronic health parameters, especially in geographic areas with high PM pollution and in more susceptible populations. Evidence from prospective cohort studies in developing countries with areas of high PM pollution may help evaluate the burden of chronic respiratory disease attributable to PM pollution and air quality standards.

Keywords: Particulate matter (PM); bronchitis symptoms; concentration-response curves (C-R curves); morbidity.

Figure 1

Selected C-R relationships from 10 studies relating long-term PM exposure and chronic bronchitis symptoms (appropriate adaptations from original publications rescaled for comparison purposes). Reproduced with permission from Environ Health Perspect for (A) (34), (D) (7) and (G) (38). Reprinted with permission from Elsevier Copyright © 2014 from Environ Res for (B) (5) and Sci Total Environ for (J) (41). Reprinted with permission of the American Thoracic Society. Copyright © 2014 from Am J Respir Crit Care Med for (C) (35), (E) (36), (F) (37) and (I) (40). Reprinted with permission from BMJ Publishing Group Ltd. Copyright © 2014 from Thorax for (H) (39).

Figure 2

Comparison of the C-R curves between two studies of long-term PM exposure and morbidity of chronic cough and mortality of cardiovascular disease (appropriate adaptations from original publications rescaled for comparison purposes). Reprinted with permission from Elsevier Copyright © 2014 from Environ Res for Sci Total Environ for (A) (41), and from Circulation for (B) (19).