Relationships Between Outdoor Ambient Air Pollution and Cardiovascular Disorders

Abstract

Most disorders of the circulatory system have a complex etiology, involving genetic and environmental factors, lifestyle, aging, or infections. In recent years, it has been shown that air pollution not only worsens the course of cardiovascular diseases but also contributes to their occurrence. It is also known to increase all-cause and cardiovascular mortality. Although the actual number of deaths caused by air pollution is difficult to determine, the World Health Organization estimates that at least 7 million premature deaths per year may result from the negative impact of air pollution. More than 70% of these deaths are due to cardiovascular complications. The response of the circulatory system to air pollution is modified by the duration of exposure, chemical composition of the pollutants, comorbidities and their treatment, age of an exposed individual, as well as changes of atmospheric conditions such as temperature, humidity, and pressure. The present narrative review discusses the most frequent cardiovascular disorders that are associated with exposure to air pollutants, based on a review of literature. Publications were identified through the search of PubMed, EBSCO, Cochrane, and Science Direct databases. The scope of the chapter was determined by the PECOS search tool, which is generally used to identify the relevant population, exposure, comparison, outcome, and study design. Using the PECOS tool, the following studies were identified and discussed: experimental studies if available as well as epidemiological studies (panel, case-crossover, time-series studies as well as meta-analyses and systematic reviews).

Although the detailed mechanisms underlying the effects of air pollution on the circulatory system are still the subject of research, it is currently assumed that the potential impact is associated with the ability of fine particulate matter, nanoparticles, and some gaseous components to penetrate from the lungs to the blood and vessels, causing inflammation and vasospasm followed by an increase in peripheral resistance and secondary activation of the coagulation system. Although the respiratory system and eye conjunctiva are the major ways by which pollutants enter the circulatory system, the gastrointestinal tract can also be involved, but the exact percentage of pollutants that enter the body via this route has not yet been determined. Some of the chemicals are persistent organic substances that penetrate into the soil, water, crop plants, and animals, thus getting into the body with food, where they accumulate and may affect the circulatory system. The simultaneous effect of various pollutants on the cardiovascular system blurs the fact that particulate matter has a stronger impact than other pollutants according to the available evidence. Numerous studies have reported a relationship between both short- and long-term exposure to air pollution and cardiovascular complications. The strongest evidence exists for an association between air pollutants and global and cardiovascular mortality. Other studies have shown an increased risk of coronary artery disease development and progression. Exposure to air pollution is also currently seen as another cause (in addition to classic cardiovascular risk factors) of a higher incidence of some cardiovascular diseases, such as hypertension and ischemic stroke. A number of studies have indicated a positive association of exposure to particulate matter and selected gaseous pollutants with the risk of hospitalization or death from heart failure. On the other hand, the impact on coagulation disorders, especially venous thrombosis, is less evident and requires further research. It should be emphasized that the occurrence of the above diseases is always multifactorial, and the percentage share of various risk factors is in fact hard to determine. Difficulties in assessing the percentage share of air pollution as a factor contributing to cardiovascular diseases can be clearly seen in large epidemiologic and smaller cohort studies, which often provide significantly different, or sometimes even conflicting, results. This discrepancy is caused by numerous factors. First, there are variations in air pollution and its chemical composition between different parts of the world. Second, air pollution overlaps with different atmospheric conditions, especially heat waves in countries with a mild climate, high humidity and temperature, or sudden temperature drops. Third, potential pollutants are countless and most of them have not been evaluated in terms of their toxicity and health risks. Also epidemiologic studies that contribute to the establishment of dose–response relationships are often subject to errors in the assessment or classification of exposure, errors in the diagnosis or reporting of health outcomes, inadequate sample size, inadequate adjustment for confounding or effect modification by other factors, as well as sampling and statistical bias. There is evidence that air pollution contributes to the risk of cardiovascular diseases and mortality. Therefore, efforts to reduce exposure to air pollution should be urgently intensified and supported by effective legislation. Medical staff plays an important role in educating patients and political decision makers about the harms of air pollution. Further research should explore the optimal methods of air pollution reduction and document its effect on the incidence of cardiovascular disease and mortality.