An Insidious and Pervasive Component of Cardiac Risk
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It has long been appreciated that fine particulate air pollution contributes to the pathology of respiratory disease and cancer.1,2⇓ The more elusive link to cardiovascular disease, however, has been recognized only in the last decade. Epidemiological1–5⇓⇓⇓⇓ and experimental laboratory6 evidence has been mounting that supports the postulate that elevated concentrations of particulate air pollution contribute to cardiovascular morbidity, hospitalization, and mortality.
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A major challenge to systematic study in this field is the complexity of the particulate components of air pollution. Ambient air particulate matter (PM) consists of a mixture of combustive byproducts and resuspended crustal materials, as well as biological materials such as pollen, endotoxins, bacteria, and viruses. Regulated airborne particulates are generally classified by aerodynamic diameter, as coarse (PM10, 2.5 to 10 μm), fine (PM2.5, <2.5 μm), or ultrafine (PM0.1, <0.1 μm). Ultrafine particles come directly out of smokestacks and tailpipes and grow rapidly into the fine size range. Thus, fine particles result primarily from combustion sources, whereas coarse particles result primarily from mechanical crushing, grinding, or abrasion of surfaces. Particles <10 μm in diameter4 and, especially, finer particles <2.5 μm in diameter1,2,5⇓⇓ have been most commonly associated with cardiovascular risk.
Every geographic region has a unique blend of particulate air pollution. Health risks due to ambient air particles have been documented not only in cities that are considered among the most heavily polluted, such as Los Angeles, Houston, and Steubenville, Ohio,1,4⇓ but also in cities that are considered to have relatively clean air, including Boston,1,5⇓ Seattle, and Minneapolis.4 Current data from the Environmental Protection Agency project that, nationwide, as many as 60 000 deaths annually are related to particulate air pollution.7 …