COPD Pathophysiology - How Do You Develop COPD?

Chronic Obstructive Pulmonary Disease (COPD) is a chronic, progressive disease of the airways leading to irreversible air flow limitation. COPD encompasses two types of obstructive airway diseases:

1. Chronic bronchitis – An obstruction of the airways

2. Emphysema – An enlargement of air spaces and deterioration of lung tissues.

Chronic bronchitis and emphysema affects different parts of your lungs, but both of them will lead to difficulty in breathing. Cigarette smoking and long-term exposure to irritant smoke released from biomass fuels and other industries, predisposes a person to develop COPD later in life.

According to global statistics, approximately 210 million people are diagnosed with COPD. By 2020, COPD is predicted to be the fifth leading cause of death worldwide. To understand the pathophysiology of COPD, it is important to understand the structures of your respiratory tract.

Normally as you breathe, air moves freely through your trachea (wind pipe), then through large tubes called bronchi and small tubes called bronchioles. From there, the air moves into tiny sacs, called alveoli. When you inhale, each air sac inflates like a small balloon, and when you exhale the air sacs deflate. These air sacs are surrounded by capillaries through which blood flows. The oxygen in your air sacs is exchanged with carbon dioxide in the blood via diffusion. The carbon dioxide released to the air sacs will then be exhaled.

What exactly happens when you have chronic bronchitis?

Chronic bronchitis is 5 to 10 times more common in heavy cigarette smokers. If you are continuously exposed to cigarette smoke, or any other irritant smoke, your airways will become irritated and can develop an inflammatory reaction. This causes the glands in your airways to increase in size (hypertrophy) and number (hyperplasia). The glands found in the airways are mucous secreting cells. As these glands increase in size and number, the amount of mucous secreted also increases. This contributes to the narrowing of the airways.

The ongoing inflammation continuously damages your airways, causing the scarring and the thickening of your bronchial walls. This results in fibrosis of your airways, which also contributes to the narrowing of the airways and limitation of airflow.

This initial inflammation of the small airways is reversible, especially if you quit smoking; yet, as time moves forward, and you reach the late stages of COPD, the inflammation continues even after smoking has ceased.

In smokers, there is hypersecretion of mucous, which predisposes them for recurrent respiratory tract infections. This results in acute exacerbations, and further damage to the airways, contributing to development of COPD.

Emphysema

Emphysema is defined as permanent dilatation of the air spaces distal to the terminal bronchioles. It is a disease of your alveoli. The destruction of lung tissue caused by emphysema is known to be facilitated by the action of proteolytic enzymes (mainly elastases).

The airways are kept open by the radial traction applied by the elastic fibres. When a lung infection occurs, the inflammatory cells release a great deal of proteolytic enzymes. The damage to the elastic fibres by these enzymes makes them less elastic, and causes the airways to collapse, obstructing airflow.

People with the condition alpha 1 antitrypsin deficiency are at a higher risk for developing emphysema. Alpha 1 antitrypsin normally hinders the protease enzymes, which are produced by the inflammatory cells to avoid lung damage. Alpha 1 antitrypsin deficiency is an inherited illness, where there is a deficiency of alpha 1 antitrypsin enzyme. People with this condition are not able to inhibit the protease enzymes, and lead to damage of the elastic fibres and the collapsing of the airways. This results in airflow obstruction.

If you think that you are developing the early stages of COPD, it is important to consult with your doctor.