Conclusions and Recommendations
Most3–8,81 but not all12,13 studies have found positive associations between several different air pollutants and adverse health outcomes. The results of observational studies are influenced by numerous factors, including characteristics of the air pollution, the population studied, and methodological issues, such as control of relevant confounders. The lack of complete uniformity is not surprising given that numerous variables (atmospheric conditions, geographic locations, cohort characteristics, sample sizes, exposure estimates, and statistical modeling) can affect the results. Our understanding of the relevant biological mechanisms involved also remains incomplete. Nevertheless, the existing body of evidence is adequately consistent, coherent, and plausible enough to draw several conclusions.193 At the very least, short-term exposure to elevated PM significantly contributes to increased acute cardiovascular mortality, particularly in certain at-risk subsets of the population. Hospital admissions for several cardiovascular and pulmonary diseases acutely increase in response to higher ambient PM concentrations. The evidence further implicates prolonged exposure to elevated levels of PM in reducing overall life expectancy on the order of a few years.
On the basis of these conclusions and the potential to improve the public health, the AHA writing group supports the promulgation and implementation of regulations to expedite the attainment of the existing National Ambient Air Quality Standards. Moreover, because a number of studies have demonstrated associations between particulate air pollution and adverse cardiovascular effects even when levels of ambient PM2.5 were within current standards,5,11 even more stringent standards for PM2.5 should be strongly considered by the EPA. Additional approaches to reduce the burden of disease related to air pollution should be highlighted. The levels of O3 and PM in many US cities are published daily by the EPA, along with a health alert system that reflects recommended changes in activity. This information is also available and updated daily on the EPA AIRNow web site (http://www.epa.gov/airnow). The AHA supports these recommendations as guidelines for activity restriction for persons with known heart disease (or with an “at-risk” profile by Framingham or another scoring system), and pulmonary disease, the elderly, and those with diabetes mellitus. A concerted effort should be made to educate healthcare providers and at-risk patients alike about this source of information and about the potential health hazards of elevated air pollution levels. The AHA should also actively work to educate the public and public policy makers about the effects of air pollution on cardiovascular disease by featured presentations at the annual Scientific Sessions, AHA-sponsored public education activities, and advocacy.
In October 2003, the EPA expanded its Air Quality Index program to include information on particle pollution, or fine particles. Next-day forecasts and real-time air quality information about particle pollution are available on the AIRNow Web site for more than 150 cities across the country. Air quality forecasts and reports for particle pollution are available in the local media (newspapers, television, and radio) in these cities and in the national media. The EPA is working to increase the number of state and local air quality agencies that forecast and report real-time particle pollution levels. It is expected that within a few years, this program will mirror the O3 program in terms of geographic coverage and availability to the public. The AIRNow Web site also contains information about the health effects of particle pollution, and the EPA is developing a section with information and tools for healthcare professionals.
Although there is a strong case that air pollution increases the risk of cardiovascular disease, we recognize the need to address a number of remaining scientific questions. Both the US EPA and the National Institutes of Health have increased the priority of research funding in an effort to overcome these shortcomings, and a committee of the National Research Council set out a long-range research agenda in 1998.194 A workshop sponsored by these and other agencies was convened in August 2002 to foster multidisciplinary research on the cardiovascular effects of PM. The AHA writing group supports these measures and recognizes several important areas for future research80,192:
1. Improve our understanding of the underlying biological mechanisms.
• Better describe the basic mechanisms (mediators, cell signaling, pathways) involved in altering HRV (autonomic tone), vascular function, and atherogenesis.
• Increased use of relevant animal models of exposure when investigating cardiovascular outcomes (eg, inhalation chambers at meaningful CAP concentrations). Experiments using intrapulmonary installation provide insight into basic mechanisms; however, the ability to extrapolate findings to humans is limited owing to the route of administration of extraordinarily high quantities of PM.
• Determine the pathophysiological relevance of the many pathways that may contribute to the development of both acute and chronic disease.
• Demonstrate reproducibility of the relevant potential mechanisms under a variety of pollutant regimens and subject risk profiles.
• Demonstrate the occurrence of such cardiovascular end points at environmentally relevant concentrations of ambient pollutants.
• Determine causal pathways, which may become targets for future means of preventive strategies
• Determine whether long-term exposure to PM at environmentally relevant concentrations promotes the genesis/progression of atherosclerosis in humans.
2. Identification of the differential toxicity of various constituents and sources of air pollution, including:
• Specific chemical and biological constituents of PM (eg, metals, carbon, polycyclic aromatic hydrocarbons, endotoxin).
• The role of different PM size fractions, including UFPs (<0.1 μm) and the coarse fraction (PM10 to 2.5).
• The effects of gaseous copollutants alone or in combination with PM.
3. Epidemiological investigations designed to address some of the limitations of prior reports, including studies that involve the following:
• Better characterization of the populations of individuals at high risk related to short-term elevations in PM (eg, comorbidities).
• Improvement of exposure estimates and metrics (eg, use of personal monitoring systems).
• Examination of the relationships between traffic emissions and adverse cardiac effects.
• Investigation of the roles of copollutants and confounders.
• Assessment of the effect of medications on the acute cardiovascular effect of air pollution (eg, HMG-CoA reductase inhibitors).
• Evaluation of the shape of the dose-response curve (identification of any threshold concentrations of various pollutants).
• Improved estimations of the population-wide health benefits of reducing PM and other pollutants.
• More thorough examination of the relationships between ambient air pollution concentrations and adverse reproductive outcomes, including those involving congenital cardiac anomalies
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