Clinical Outcomes Related to Particulate Matter Exposure and Cardiovascular Disease
Hundreds of scientific studies have found that breathing in fine particulate matter (PM2.5) over the course of hours to days (short-term) and months to years (long-term) can lead to a variety of health effects, including harmful effects on blood vessels and the heart.
A large number of these studies were discussed in EPA’s Integrated Science Assessment for Particulate Matter (PM ISA), which was published in 2019 and builds upon the previous PM ISA published in 2009. The 2019 report represents the Agency’s latest evaluation of the scientific literature examining potential relationships between PM exposure and health and welfare effects. The ISA is the scientific foundation of EPA’s review of the National Ambient Air Quality Standards (NAAQS) for six criteria pollutants, including PM, which is required under the Clean Air Act.
The PM ISA concluded that there is extensive scientific evidence that breathing in PM2.5 over the course of a few days and over many years can lead to a range of cardiovascular effects from changes in heart function to more overt effects including atherosclerotic plaque progression and death. The PM ISA characterizes the evidence indicating a relationship between fine particulate matter exposure and a number of clinical cardiovascular outcomes, which are described below.
Clinical Outcomes
Extensive evidence, spanning both experimental and epidemiologic studies, support biologically plausible pathways by which breathing in fine particulate matter (PM2.5) can lead to more overt health effects, including clinical cardiovascular outcomes. These initial effects that may lead to a series of effects culminating in a clinical cardiovascular outcome include:
- inflammation and oxidative stress
- translocation of particles outside the respiratory tract into the blood
- perturbations of the autonomic nervous system
Short-term and long-term exposure to PM2.5 may cause or result in the exacerbation of the following clinical cardiovascular outcomes:
Cardiovascular-related Mortality
Breathing in fine particulate matter may result in changes in the way the heart and blood vessels function, which could result in clinical outcomes leading to death, including heart attacks, stroke, cardiac arrest, and congestive heart failure. Epidemiologic studies conducted in different geographic locations, diverse populations, and using a variety of study designs report increases in cardiovascular mortality for both short-term and long-term fine particulate matter exposures.
Ischemic Heart Disease and Heart Failure
Once inhaled, fine particulate matter may initiate a cascade of events leading to impaired vascular function (alteration of blood vessels), which could result in the formation of blood clots, increases in blood pressure, or a reduction in the heart’s ability to pump blood, all of which could result in the exacerbation of ischemic heart disease and heart failure. Epidemiologic studies examining short-term fine particulate exposure report evidence of increases in emergency department visits and hospital admissions for ischemic heart disease and heart failure. Additionally, evidence spanning both animal toxicological and epidemiologic studies indicates that long-term fine particulate matter exposure may decrease heart function and coronary artery wall thickness, contributing to heart failure.
Heart Attacks (Myocardial Infarction)
Breathing in fine particulate matter may impair vascular function (alter blood vessels), which could include the development of atherosclerosis (clogging of arteries) after long-term exposures or the formation of blood clots after short-term exposures. These changes can result in a decrease in the supply of oxygen and nutrients to the heart and subsequently a heart attack.
Stroke
There are multiple plausible pathways by which breathing in fine particulate matter may cause a stroke. For example, once inhaled particles may trigger systemic inflammation and oxidative stress, which could lead to changes in blood vessel function and the formation of blood clots, and ultimately interrupt the flow of blood to the brain resulting in stroke.
Cardiac Arrest
Among people with advanced heart disease who have internal cardiac defibrillators it has been shown that breathing in fine particulate matter can affect the nervous system resulting in a disruption in the electrical function of the heart for some individuals and leading to potentially fatal abnormal heart rhythms (arrhythmias).
Vascular Function
Once inhaled, fine particulate matter may initiate a cascade of events leading to impaired vascular function (alteration of blood vessels), which may include constriction of blood vessels, development of atherosclerosis (clogging of arteries), formation of blood clots, and coronary artery calcification, which is a strong predictor of coronary heart disease. Changes in vascular function may contribute to a range of cardiovascular outcomes including ischemic heart disease, heart failure, stroke, heart attacks, and death.
Blood Pressure
Short-term fine particulate matter exposure may lead to increases in blood pressure through multiple pathways including impairment in vascular function, which can result in vasoconstriction. Increases in blood pressure in response to short-term exposures are more consistently observed in older adults (i.e., individuals over the age of 65) and people with underlying cardiovascular conditions.
Cholesterol
Elevated cholesterol is a common chronic condition in the U.S. adult population and is an important risk factor for other serious health conditions associated with PM2.5 exposure, such as cardiovascular disease and diabetes. Some studies have examined differences in PM2.5-associated health effects in the context of lipid disorders. This limited epidemiologic research provides some evidence of increased risk with short- and long-term PM2.5 exposure for those with elevated cholesterol compared with those with normal cholesterol.
Overall, the evidence is inadequate to conclude whether adults with elevated cholesterol are at increased risk for PM2.5 -related health effects.
What populations are at increased risk of a clinical cardiovascular outcome in response to PM2.5 exposure?
Broadly, scientific evidence indicates that some populations may be at increased risk of PM2.5-related health effects, which may include clinical cardiovascular outcomes. These populations include:
- Those who are already at greater risk after myocardial infarction and stroke
- Those who have rhythm disorders, heart failure and end-stage-renal-disease