Ambient Air Quality and Cardiovascular Health

Sources of Air Pollution

Air pollution consists of gases and particles present in the atmosphere that are produced from many sources [5]. Motor vehicles, power plants, and industrial facilities are important sources of both gases and particles across the United States, according to EPA's National Emissions Inventory (see Table 1). Particulate matter is also generated through mechanical processes (eg, brake and tire wear) and by particle-forming chemical reactions of atmospheric gases [5]. These gases can be inorganic (eg, SO₂), organic (eg, benzene), and either anthropogenic or naturally occurring (eg, volatile organic compounds emitted from vegetation). Oxidized emissions from combustion of vegetation attendant to uncontrolled wildfires and prescribed burns are a comparatively important source of particulate matter in the southeastern United States [6], including North Carolina. The amount of burned acreage more than doubled between 1986-90 and 2011-15, and changing temperature and precipitation patterns are likely to intensify future fire seasons in many parts of the country [7]. Recent national emissions estimates indicate that wildland fires represent 15-20% of directly emitted PM_2.5 (see Table 1). Prescribed and agricultural burning accounts for approximately another 15% of direct PM_2.5 emissions [8].

While we can be proud of the reductions in emissions and improvements in US air quality since the passage of the Clean Air Act and the creation of the EPA in 1970, work remains to be done to ensure clean air for all. Source emissions have declined nationally by more than 70% since 1970, yet many communities remain affected by local sources [9]. Understanding the impact of air pollution on public health requires consideration not just of air pollution sources, but also factors that affect exposure to air pollution.

Exposure to Air Pollution

People are exposed to air pollution both outdoors and indoors. Most people spend 80-90% of their time indoors, whether at home, school, or work, and outdoor exposure accounts for the majority of air pollution exposure for pollutants that do not infiltrate indoors substantially, such as ozone [10]. PM_2.5, however, does infiltrate indoors, resulting in indoor concentrations that are 50-70% of outdoor concentrations [11]. This is a substantial contribution to exposure to outdoor-generated PM_2.5. Personal activities are another factor contributing to exposure variation among individuals. For example, spending time on or near busy roadways (such as during commuting to work or school) increases exposure to traffic-related air pollution. Living near an industrial facility may also increase air pollution exposure. Exercising in polluted environments compounds exposure by increasing inhaled dose, further raising the potential for health effects.

Cardiovascular Effects of Air Pollution in North Carolina

Many large epidemiology studies, along with smaller panel studies, human challenge studies, and basic toxicological research, have provided unequivocal evidence that both short-term and long-term exposure to ambient air particulate matter is associated with adverse cardiovascular health effects. Over the last several years, thousands of your patients have contributed to the state-of-the-science describing the association between air pollutant exposure and cardiovascular disease as participants in longitudinal national clinical studies such as the Women's Health Initiative (WHI), the Atherosclerosis Risk In Communities (ARIC) Study, and the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air) [12-15], as well as the predominantly North Carolina-based Catheterization Genetics (CathGen) study [16-17]. Ancillary research within these parent studies investigated the impact of ambient air PM_2.5 on cardiovascular health effects, and the findings attest to the relevance of this issue to the citizens of North Carolina. The WHI study showed that long-term exposure to PM_2.5 among post-menopausal women was associated with altered glucose homeostasis, cardiovascular and cerebrovascular events, and death from cardiovascular disease [12, 13]. The ARIC study showed that residents living within 300 meters of a major road were more likely to develop coronary heart disease [14]. MESA Air measured coronary calcium, as well as other biological measures, repeatedly over a period of 10 years for the purpose of answering the question, “Is long-term exposure to air pollution associated with progression of cardiovascular disease? [15].” MESA Air showed that long-term exposure to outdoor PM_2.5 and NO₂ was associated with the accumulation of coronary artery calcium, as well as a number of other anatomic, biochemical, and physiological changes in the heart and blood vessels, a conclusion also reached by McGuinn and colleagues in the CathGen cohort who showed that long-term exposure to ambient PM_2.5 among North Carolinians is associated with the severity of coronary artery disease and the likelihood of having a myocardial infarction in the previous year [16]. Proximity of one's residence to major roads was associated with an increased risk of increased fasting plasma glucose in women, hypertension, and peripheral vascular disease [17-18].

Short-term biochemical and physiological changes have also been observed in the CathGen Cohort in response to ambient air pollution. Brief exposures to outdoor PM_2.5 and ozone were associated with metabolic changes indicating incomplete fatty acid oxidation suggesting dysfunction of the mitochondria [19].

Translating Environmental Health Research into Public Health and Clinical Action

Finding solutions to complex contemporary population health challenges such as chronic cardiovascular disease will require an integrated approach that involves public policy, state and local public health, and systems-level changes that affect communities and clinical practice [20]. Yet, largely overlooked for years has been the potential value of improving the quality of the environment as a means of decreasing the burden of cardiovascular disease. As shown in Figure 1 at the level of the population, attainment of the National Ambient Air Quality Standards as required by the Clean Air Act serves as a primary and secondary prevention strategy for heart and vascular disease. Local improvements in air quality across the United States over the last several decades have resulted in increased longevity, a benefit that is largely attributed to reductions in ambient air PM_2.5 concentrations [21-24]. Through hard work and partnership with local, state, and federal agencies North Carolina has reduced emissions and improved the quality of its air. Yet, for those individuals who are particularly sensitive to the adverse health effects of air pollution—namely older adults, those with chronic heart and lung disease, and children—additional actions to avoid exposure are prudent when air quality is poor.

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FIGURE 1.

Intersection of Environmental and Public Health Policies with Clinical Interventions to Achieve Enhanced Clinical Prevention, Lower Exposures, and Reduced Risk

As recommended by the CDC and CMS in Million Hearts®, health care professionals can play an important role in increasing awareness among the patient populations at highest risk about actions they can take to reduce exposures [2, 25]. Such an approach represents an innovative clinical prevention program to decrease the public health burden of air particle pollution among those at highest risk (see Figure 1).

The most important aspect of the Million Hearts® action plan is the focus on modifying the key risk factors for heart and vascular disease. Achieving their goals will have a collateral benefit of shrinking the portion of the population at risk from the adverse effects of air pollution by improving the overall health of the population. This will entail optimizing both the number of people meeting ideal risk factor parameters and the use of evidence-based medication to prevent progression and clinical events associated with lung and heart disease.

While such recommendations to limit exposures are prudent for those at higher risk for heart attack and stroke, at the present time randomized controlled clinical trials testing whether interventions that decrease exposure—such as in-home high-efficiency particle filtering (HEPA) of indoor air or N-95 respirators that decrease clinical event rates—are lacking (see Figure 1). Yet, many studies do show that reducing exposure improves biochemical measures of inflammation and other biomarkers associated with heart disease during air pollution events. Additionally, a modeling study suggests that instituting in-home HEPA filtering among those at higher risk would reduce clinical events and be cost effective [26, 27].

Greater Engagement of the Health Care System

Increasing awareness among patients who are most likely to benefit from the avoidance of air particle pollution will require greater engagement of the many professionals who contribute to population health. Health care professionals—including health care practitioners, nurses, leaders of professional organizations, health care institutions, and health insurers who deliver health care, health education, or pay for health care and preventive services—play an important role. Increasing environmental health literacy and incorporating environmental health messages into clinical management of the at-risk individual is anticipated to support value-based health care and wellness for individuals and communities.

The 2014–2016 ConsumerStyles surveys showed health care professionals are missing the opportunity to identify and counsel those at higher risk about actions they can take to decrease exposure and potentially reduce adverse health effects of air pollution [28]. Only about one-half of US adults with chronic lung disease were aware of air quality alerts, and those with heart disease were not aware. Only 3% of patients discussed guidance to reduce exposure with a health professional [28]. The results tell us that opportunities exist to raise awareness of air quality alerts and behavior changes to reduce air pollution exposure among adults at risk of worsening lung and heart disease. One of the best sources of up-to-date information about air quality and health is the AirNow website. In partnership with the North Carolina Department of Environment and Natural Resources, EPA's Office of Air and Radiation supports the AirNow website (www.airnow.gov), which is the internet portal for valuable information about local air quality and educational material for public health and health care professionals. The information includes a continuing education course titled “Particle Pollution and Your Patients' Health.”

Likewise health care systems and health insurers can take a more active role in increasing awareness among their patients and communities to promote healthy behaviors and avoidance of exposure among those at highest risk. Regional and city planners and city councils have opportunities to contribute through decisions made to determine the siting of housing, schools, places of business, child and eldercare facilities, as well as acute and chronic health care facilities.

Wildfire Smoke Events Highlight the Value of Translational Environmental Health Science

Extreme air pollutant events attributed to wildfires are frequent in North Carolina and contribute significantly to impaired air quality, clinical symptoms, increased health care utilization, and health care costs [29-34]. Based on the best available evidence, wildfire emissions contribute to all-cause mortality and worsen asthma, chronic lung disease, and childhood respiratory disease [33]. Wildfire smoke also exacerbates bronchitis and pneumonia [40, 44]. Less well-documented are effects on the heart, blood vessels, and birth outcomes. Some populations are more sensitive to the adverse health effects of smoke from wildfires. These include children, older adults, and those with chronic disease [33,34]. The impact of emissions from a peat fire in Eastern North Carolina provided new insights into the effects of air particle pollution on emergency department visits [31].

The public health and clinical burden of wildland fire emissions is anticipated to grow over the next 2 decades as the size of the populations vulnerable to exposure to wildland fire smoke and sensitive to the health effects of wildfire smoke grows. The growth of the at-risk population is commensurate with the changing demographics of North Carolina where over the next 2 decades the population is expected to increase by approximately 2 million, more than half of whom will be aged 65 and older [35]. Moreover, most of the growth is anticipated to be in the major urban centers, thereby bringing larger numbers of at-risk individuals into proximity with wildland fires as the wildland-urban interface increases and as forest health declines.

Recently EPA's Office of Research Development created the Smoke Ready Toolbox for Wildfires to facilitate communication with public health officials, health care professionals, and the public [36]. This website provides the resources health professionals can use to educate the public about the risks of smoke exposure and actions people can take to protect their health.