ReviewAir pollutants: The key stages in the pathway towards the development of cardiovascular disorders
Introduction
Cardiovascular disorders are becoming a frequent event in modern societies owing to contemporary lifestyles in the developed world. The degree of environmental contamination with toxins and particularly airborne pollution, imposes stress on the heart which promotes the incidence of damaging cardiovascular events like arrhythmogenesis, myocardial infarction and cardiac hypertrophy. Air pollution is one such factor that promotes cardiac stress which leads to cardiovascular damage (Brook, 2008, Simkhovich et al., 2008). Various epidemiological and clinical studies have highlighted the deleterious effects of air pollution on heart disease (Hoek et al., 2002, Miller et al., 2007, Pope et al., 2004).
Air pollutants mainly include carbon mono-oxide, oxides of nitrogen, sulfur dioxide, ozone and particles composed of elemental carbon, organic carbon compounds, transition metals, metal oxides, acid concentrates, sulfates and nitrates (Routledge et al., 2003) (Table 1). Of these, particulate matter has become a major concern of cardiovascular research. There is substantial evidence that indicates the effect of ambient particulate matter on cardiovascular health.
Airborne particulate matter is a heterogeneous mixture of solid and liquid particles of varying size and chemical composition. In 1987, the regulatory focus was on particles that could readily penetrate and deposit in the tracheobronchial tree, or PM10 (PM with a median aerodynamic diameter of <10 μm). In 1997, the US EPA promulgated 24-h and annual average standards for PM2.5 (PM with median aerodynamic diameter <2.5 μm), comprising the size fraction that can reach the small airways and alveoli. The existing federal PM10 standards were retained, however, to address health effects that could be related to the “coarse fraction” (PM10–2.5; World Health Organization, 1987, World Health Organization, 2000). Particles of diameter less than PM10 are considered to have deleterious effects on health. However, ultra fine particles (UFP), which have diameter less than PM0.1 are an interesting area of research owing to their capability of penetrating deep into the lungs and may even pass directly into the circulatory system (Nemmar et al., 2001, Nemmar et al., 2002a). Such particles can thus have harmful effects on cardiovascular health. The present review will focus upon the various mechanisms that will explicate how air pollutants, especially ambient particulate matter is affecting the cardiovascular health and will throw light on various cardiovascular events which have been found to be influenced due to air pollution.
Section snippets
Mechanism
Various studies show that there is a link between the particulate air pollution and the deaths caused due to cardiovascular diseases such as myocardial infarction and arrhythmia. However any definite pathway that can explain the link between the two has not yet been determined. There are two possibilities that link air pollution to heart diseases. These involve the classical pathway that explains the indirect effects mediated through pulmonary oxidative stress and inflammatory responses and the
Linking air pollution to cardiovascular damage
Adverse effects of air pollution on cardiovascular health have been established through various studies. Exposure to air pollutants has resulted in an increased occurrence of various harmful events leading to cardiovascular morbidity. A few major events have been explained further.
Conclusion
The review provides some perspective on the extent of the involvement of air pollutants (especially particulate matter) in various cardiovascular events. The exact mechanisms involved are unknown for majority of events but these processes can be explored in terms of two major categories, i.e. direct translocation or via indirect secondary mediators. Inflammation proves to be the most common mediator of the adverse cardiovascular events of air pollution like thrombosis, vascular dysfunction,
Conflicts of interest
The authors declare that there are no conflicts of interest.
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