Particulate Matter and Cardiovascular Diseases - An Overview

Introduction:

Particulate matter or particle pollution denotes microscopic particles (including liquid droplets and solid particles) in the air causing pollution. The particles are inhalable fine particles of varied sizes and shapes and made of various chemicals. Most particulate matter is formed due to various chemical reactions involving pollutants released from industries, power plants, and automobiles. These particles are less than ten micrometers, and some are even smaller than 2.5 micrometers when inhaled can lead to several health problems, including heart disease. Constant and prolonged exposure to particulate matter has the potential to trigger heart disease and increases the chance of death due to heart problems.

What Is Particulate Matter?

Particulate matter (PM) includes tiny, small, inhalable particles with diameters that cannot be seen with the naked eye and can be detected only through advanced microscopes. These are known to cause particle pollution of the air. There are two types of particle pollution:

1. PM10: Particles with diameters less than ten micrometers.

2. PM2.5: Particulate matter with diameters less than 2.5 micrometers.

Their sizes, shapes, and chemical composition vary. Sources of particulate matter include:

1. Directly Emitted From:

   • Construction sites.

   • Unpaved roads or fields.

   • Smokestacks.

   • Fires.

   • Wildfire smoke.

2. Formed Due to Chemical Reactions in the Atmosphere:

   • Pollutants from power plants.

   • Pollutants from industries.

   • Pollutants from automobiles (urban areas, busy roads).

Some of these particles remain in the atmosphere for a long, travel through a large area (thousands of miles), and affect air quality. Hot, humid, stagnant air can further worsen and increase the particulate matter concentration. As these particles are tiny, outdoor particle pollution can lead to indoor pollution in buildings and homes, worsening the situation.

Does Particulate Matter Pollution Increase the Risk of Cardiovascular Disease?

Conditions affecting the heart and blood vessels are termed cardiovascular disease. The buildup of plaque, fat deposits, and clots in the major arteries can block the blood flow leading to medical emergencies such as stroke and heart attacks. Cardiovascular disease is considered the leading cause of death in the US (United States), especially affecting the elderly (over 65 years). The common risk factors for heart and blood vessel diseases include the following:

• Male sex.

• Older age.

• Increased blood pressure.

• High cholesterol.

• Lower levels of high-density lipoprotein (HDL).

• Habits such as smoking.

• Comorbidities such as diabetes.

In addition to the above risks, air pollution, especially particulate matter pollution, can worsen heart and blood vessel problems and contribute to cardiovascular disease development and progression. Fine particulate matter with diameters less than 2.5 micrometers that are inhaled due to outdoor particle pollution exposure increases cardiovascular events risk. Long-term exposure and exposure to increased particulate matter concentrations trigger heart and blood vessel disease-related medical emergencies (such as heart attacks) and can also lead to death.

Though the risk is lesser than the other traditional risk factors of cardiovascular disease, particulate matter exposure has contributed to increased cardiovascular emergencies such as stroke, coronary syndrome, heart attacks, heart failure, heart rhythm problems (arrhythmias), and sudden cardiac death. In addition, those with already existing heart problems may experience worsening of their condition after fine particulate matter exposure. Their symptoms include worsening heart palpitations, chest pain or tightness, lightheadedness, unusual fatigue, and shortness of breath.

How Does Particulate Matter Cause or Worsen Cardiovascular Disease?

Once a person is exposed to fine particulate matter (inhales), there are three ways through which their cardiovascular health is affected. These include the following:

1. Oxidative stress and general systemic inflammation in the body.

2. Entry into the blood.

3. Affecting the autonomic nervous system (directly or indirectly).

Oxidative stress due to particulate matter exposure affects the function of the blood vessel cells (endothelial cells), clotting processes, heart electrophysiology, and fat metabolism. Once the particulate matter particles are inhaled, they reach the lungs and their tiny air sacs and increase the formation of ROS (reactive oxygen species). This process initiates an inflammatory response and increases the production and release of chemicals involved in inflammation (cytokines). These inflammatory chemicals have secondary effects on the blood vessels, heart rate, the contraction of the heart muscles, and heart rhythm. In addition, these insoluble particles deposit and can enter directly into the bloodstream affecting the heart, blood vessels, and the nervous system.

What Are the Cardiovascular Effects of Fine Particle Pollution?

Fine particle pollution increases the risk of hospitalizations for heart and blood vessel related-conditions and mortality (both acute and chronic exposure). The key effects of inhaled particulate matter on the cardiovascular system include the following:

• Acute coronary syndrome (including heart attacks and unstable angina).

• Irregular heart rhythm (arrhythmias).

• Worsening of chronic heart conditions and failure.

• Stroke (due to decreased blood flow to the brain).

• Sudden cardiac death.

• Acceleration of atherosclerosis (fatty plaque or clot deposits in the blood vessels).

• Reduced life expectancy due to worsening of cardiovascular disease.

• Acute Exposure Effects:

• Small changes in blood pressure.

• Affects oxygen saturation.

• Alters endothelial (cells of the blood vessels) function.

• Systemic changes.

• Release of clotting factors.

• Increase in oxidative stress.

• Acute coronary syndrome.

• Heart attacks.

• Arrhythmias.

• Worsening of the heart condition in patients with internal cardiac defibrillators.

• Worsening of heart failure.

• Reduced blood flow to the brain leads to stroke.

• Increased tendency to clot.

• Chronic Exposure Effects: Chronic exposure can occur due to living or working in areas with high particulate matter pollution leading to chronic exposure from months to years. The effects include:

• Reduced life expectancy in patients with cardiovascular disease.

• Worsening of the existing heart and blood vessel diseases.

• Systemic inflammation and oxidative stress.

• Increased plaque turnover.

• Increased fat deposition.

• Altered cardiac autonomic function.

• Heart rhythm irregularities and cardiac arrest.

Conclusion:

Air pollution is becoming a global social and ecological dilemma especially affecting developed and developing countries. Particulate matter particles are tiny particles that, when inhaled, can lead to various health problems. These health problems include not only respiratory diseases but also cardiovascular diseases. Great efforts are needed to combat the problem, from the governments and global health care authorities to lower the risk posed by this particulate matter pollution to the general population's health, including cardiovascular health.