Air pollution, vascular disease and thrombosis: linking clinical data and pathogenic mechanisms

The public health burden of air pollution has been increasingly recognized over the last decades. Following the first assessed adverse effects on respiratory diseases and lung cancer, a large body of epidemiologic and clinical studies definitely documented an even stronger association of air pollution exposure with cardiovascular mortality and morbidity, particularly related to atherothrombotic (coronary and cerebrovascular) disease. Particulate matter (PM), mainly that with lower aerodynamic diameter (fine and ultrafine PM), is responsible for the most severe effects, due to its capacity to transport toxic substances deep into the lower airways. These effects have been shown to occur not only after short-term exposure to elevated concentrations of pollutants, but even after long-term relatively low levels of exposure. Vulnerable subjects (elderly persons and those with preexisting cardiopulmonary diseases) show the highest impact. Fewer and conflicting data also suggest an association with venous thromboembolism. Although not completely elucidated, a series of mechanisms have been hypothesized and tested in experimental settings. These phenomena, including vasomotor and cardiac autonomic dysfunction, hemostatic unbalance, oxidative stress and inflammatory response, have been shown to change over time and differently contribute to the short-term and long-term adverse effects of pollution exposure. Beyond environmental health policies, crucial for improving air quality and reducing the impact of such an elusive threat to public health, the recognition and assessment of the individual risk, together with specific advice, should be routinely implemented in the strategies of primary and secondary cardiovascular prevention.