Chronic obstructive pulmonary disease (COPD) is a group of chronic inflammatory lung disease that causes obstructed airflow from the lungs.
More than 14 million people are diagnosed with COPD and it is the second biggest cause of death in India and third in the world.
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What is Air Pollution?
Air pollution occurs when gases, dust particles, fumes or smoke or odour are introduced into the atmosphere in a way that makes it harmful to humans, animals, and plant. Many of the world’s large cities today have bad air quality owing to urbanization .
Ambient air pollution is simply outdoor air pollution, usually caused by emissions from transportation, power generations, agriculture, and open burning. The chemicals in ambient air pollution are different from that of indoor air pollution.
More than 131 million Americans that are over 40 percent of the nation’s population live in the areas with bad air. Roughly 30 percent of the childhood asthma is due to environmental exposures, costing the nation $2 billion per year.
What is COPD?
Chronic Obstructive Pulmonary Disease (COPD) is an umbrella term used to describe progressive lung diseases including emphysema, chronic bronchitis, and refractory (non-reversible) asthma.
This disease is characterized by increasing breathlessness and is currently incurable.
Emphysema is characterized by the damaged air sacs in the lungs (alveoli). Over time, the inner walls of the air sacs weaken and rupture creating larger air spaces instead of many small ones.
This reduces the surface area of the lungs and, in turn, the amount of oxygen that reaches the bloodstream .
While exhaling the air, the damaged alveoli don’t work properly and old air namely carbon-di-oxide becomes trapped inside the lungs, leaving no room for fresh, oxygen-rich air to enter.
Many people suffering from emphysema also suffer from chronic bronchitis. Chronic bronchitis is the inflammation of the tubes that carry air to the lungs (bronchial tubes), which leads to a persistent cough.
Refractory asthma is a type of non-reversible asthma, like in an asthma attack, bronchial airways tighten up and swell.
Medications can usually reverse this, opening up the airways and returning them to how they were before the asthma attack. In refractory asthma, medications cannot reverse the tightening and swelling of the airways.
COPD is presently the fourth leading cause of death, and it is predicted to become the third leading cause by 2030, making this disease one of the major health challenges in the future.
In addition, COPD is a risk factor for the development of lung cancer, itself a leading cause of death globally.
Smoking is the leading cause of COPD along with other risk factors like air pollution, heredity, and age.
The relationship between Air pollution and COPD
Several studies have reported links between high levels of air pollution and the prevalence of COPD .
Whereas the short-term exposure to air pollution has been studied and associated with acute exacerbation of COPD for many years.
An acute exacerbation of COPD refers to a flare-up or an attack where a person’s breathing becomes worse than normal.
Long-term exposure to traffic-related air pollution has been associated with several cardio-pulmonary diseases like asthma, bronchitis, and COPD .
Researchers in Denmark found that long-term exposure to traffic-related air pollution increases the chance of developing COPD, especially in people with diabetes and asthma.
Another long-term research based in Australia found that poor air quality can contribute to COPD and possibly death.
It was concluded that when residents of Launceston city reduced smoke from burning organic materials such as wood and biofuels, the number of deaths from COPD declined.
The exact cause of development and progression of COPD is not known but scientists around the world have been studying various pathological symptoms related to the disease progression some of the proposed mechanism includes, inflammatory response, oxidative stress, and genetic predisposition.
1. Inflammation and its implication in patients with COPD
The suggested biological mechanism of air pollution damage to the lungs involves a local inflammatory response in the lung tissues with a secondary systemic inflammatory response.
The pathological consequences of the COPD inflammation induce a series of physiological changes which eventually impact the quality of life and survival in the natural progress of COPD .
Chronic inhalation of particulate matters causes injury to both the small airways and lung tissues this is believed to be central to the effects of long-term exposure to air pollution and to the chronic and progressive nature of COPD.
Experimental studies suggest that the deposition of particulate matters (PM) on epithelial cells that line the airways activates both immune response and inflammatory processes.
Studies of lung tissue biopsy specimens from patients with mild to moderate COPD show an increase in inflammatory cell concentration in the central airways when compared with non-smokers as well as smokers who have not developed the disease.
This chronic immunogenic and inflammatory stimulation leads to many structural and molecular disruption in the lung environment that cumulatively leads to the systematic progression of COPD in patients even after cessation of smoking or exposure to air pollutants.
Some of the known pathogenesis of inflammation in COPD are —
1. Elastin degradation: Elastin is a macromolecule and an important architectural component that gives lung air sacs its peculiar property of expanding and relaxing while breathing.
Studies have conclusively shown that elastin degradation is a key step in the pathogenesis of COPD .
Inflammatory cells (macrophages, T lymphocytes, B lymphocytes, and neutrophils) give rise to an enzyme named protease that is responsible for degradation of the elastin molecules in the lungs. Thus rendering lung damaged and functionally impaired .++
2. Cell-death mediators: Inflammatory cells namely T lymphocytes are cytotoxic in nature meaning they are toxic to living cells.
Hence, these inflammatory cells causes’ apoptosis (cell-death) of the alveolar epithelial cells that form the air-sacs in the lungs which is persistent with the symptoms of emphysema.
3. Small Airways Obstruction disease: The small airways are <2 mm in diameter, and there is a dramatic decrease in the diameter in COPD patients compared to the healthy population.
One of the proposed mechanism is that the particulate matters themselves adhere to these small airways tubes thus blocking them.
Another mechanism proposes that the exposure to the particulate matters induces both immune and inflammatory response at the site of adherence.
Thus flooding the site with various immune cells and inflammatory cells blocking the airways.
However, understanding the role of inflammatory cells in COPD is difficult because it is a mixture of diseases that exhibit different patterns of inflammation and different pathology.
Studies show an enhanced or abnormal inflammatory response to inhaled particulate matters or gases, is a characteristic feature of COPD and has the potential to damage lungs permanently.
2. Oxidative stress is another driving mechanism in COPD
Oxidative stress occurs when Reactive Oxygen Species (ROS) are produced in excess of the antioxidant defence mechanisms and result in harmful effects, including damage to lipids, proteins, and DNA. Oxidative stress is a critical feature in patients with COPD .
Inflammatory and structural cells, including neutrophils, macrophages, and alveolar epithelial cells, which are activated in the airways of patients with COPD, produce endogenous ROS .
Whereas, chronic inhalation of pollutants, tobacco, smoke, drugs, etc. produce exogenous ROS .
Studies show that oxidative stress can exert significant functional effects like the constriction of the airways in the lungs (termed as bronchoconstriction) due to the tightening of the surrounding smooth muscle.
ROS have wide-ranging effects on the airways and lung tissues and increase the inflammatory response. ROS activate NF-kB, a protein that controls gene expression that is from DNA to RNA.
Which in turn switches on multiple inflammatory genes, resulting in amplification of the inflammatory response.
Oxidative stress also reduces the expression and activity of sirtuin-1, a key repair molecule that is involved in the aging process.
The reduction in sirtuin-1 in lungs and cells of patients with COPD might be the reason for the accelerated aging response seen in patients with COPD .
Lastly, oxidative stress is also associated with irreversible damage to certain proteins which might stimulate an autoimmune response leading to a persistent inflammatory state in lung tissues .
Environmental exposure contributes to the imbalance of oxidant/antioxidant due to the reactive oxygen species (ROS) inhaled through various pollutants. Moreover, production of the ROS during the inflammatory process and mitochondrial dysfunction also contribute to the disease progression.
Indoor Air Quality & COPD morbidity
Quality of air is of utmost importance especially for patients suffering for COPD and other respiratory diseases. Many people do not realize it but the quality of the air inside the home can be poorer than the air quality outside.
Besides smoking and second-hand smoking, particularly indoor air pollution is one important risk factor for COPD in India and other developing countries.
A number of studies have showed that in India, the incidence of COPD is similar in men and women despite the fact that 75% of the men and only 10% women are smokers. In women, COPD has been credited to domestic air pollution as a result of the burning of solid biomass fuels.
Other allergens and irritants such as pollen, dust mites, molds, and fumes from cleaning products and paint can build up and pollute the air inside the homes.
Therefore, it is imperative to take proper care and precautions to eliminate these threats from the house or work or schools to lessen the burden of COPD and its symptoms.
Chronic obstructive pulmonary disease (COPD) is a progressive inflammatory condition of the airways, pulmonary vessels, and lung tissues (parenchyma).
Cigarette smoking is responsible for the vast majority of COPD, but recent studies have shown that occupational and environmental factors also play important roles.
With rapid urbanization of the world population, a better understanding of the harmful effects of exposure to urban air pollution, mainly from traffic, on COPD is important for urban planning, transport legislation, patient management, and prevention.
In order to avoid the cost of care, an integrated and highly efficient system is required which can promote a healthier lifestyle and an efficient healthcare system.
Moreover, smoking and other risk factors should be controlled considering the future benefits of the nation.
In a recently published Environmental Performance Index 2018, India ranked fourth worst country in the world in terms of environmental health.
In order to improve the burden of COPD, multidimensional strategies should be adopted to promote positive respiratory health not only at the individual level but at the population level.