Recent reviews by USEPA and WHO have shown that the long-term exposure to ambient air pollution is responsible for increased mortality and morbidity from respiratory and cardiovascular diseases, lung cancer and shortens life expectancy. In addition, epidemiological studies have shown that airborne particulate matter (PM) is associated not only with respiratory diseases but also with cardiovascular diseases.
Cardiovascular effects of Ambient Air Pollution
The Cardiovascular System
The cardiovascular system is also known as the circulatory system and includes includes the heart, arteries, veins, capillaries and blood. These vital structures are critical in the process of pumping deoxygenated blood to the lungs for gas exchange as well as pumping oxygenated blood to the body's tissues to support their metabolic functions. The cardiovascular system has three major functions:
- transportation of materials - The cardiovascular system transports blood to almost all of the body’s tissues. The blood delivers essential nutrients and oxygen and removes wastes and carbon dioxide to be processed or removed from the body.
- protection from pathogens - The cardiovascular system protects the body through its white blood cells. White blood cells clean up cellular debris and fight pathogens that have entered the body. Platelets and red blood cells form scabs to seal wounds and prevent pathogens from entering the body and liquids from leaking out. Blood also carries antibodies that provide specific immunity to pathogens that the body has previously been exposed to or has been vaccinated against
- regulation of the body’s homeostasis - The cardiovascular system is instrumental in the body’s ability to maintain homeostatic control of several internal conditions. Blood vessels help maintain a stable body temperature by controlling the blood flow to the surface of the skin. Blood vessels near the skin’s surface open during times of overheating to allow hot blood to dump its heat into the body’s surroundings. In the case of hypothermia, these blood vessels constrict to keep blood flowing only to vital organs in the body’s core. Blood also helps balance the body’s pH due to the presence of bicarbonate ions, which act as a buffer solution. Finally, the albumins in blood plasma help to balance the osmotic concentration of the body’s cells by maintaining an isotonic environment \cite{innerbody2018}.
How do pollutants enter the cardiovascular system
The most common route for pollutants to enter the cardiovascular system is via inhalation whereby air travels from the upper respiratory tract which includes the nasal cavity, pharynx, glottis and larynx to the lower respiratory tract consisting of the trachea, bronchi, bronchioles and lungs. Of all the pollutants that pass through the respiratory system (refer to Figure 6), particulate matter with an aerodynamic diameter of <2.5 and <0.1\(\mu\)m has the ability to penetrate the lung alveoli (where gas exchange of oxygen and carbon dioxide occurs) and enter the bloodstream whereby it exerts the adverse health effects\cite{Franck_2011}. Because of its small aerodynamic diameter (AD) most particulates with an AD range of 2 to 10\(\mu\)m are deposited in the nasal cavities and upper airways. Particulate matter has been recognized as being associated with inducing adverse health effects because it may contain toxic substances that can be transported to the respiratory tract\cite{Lee_2014}. In addition, animal studies have shown that particulate matter with an aerodynamic diameter < 2.5\(\mu\)m can have direct health effects when taken up by alveolar macrophages and endothelial cells.