Pathology and causes of Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease (COPD) is the narrowing of airways caused by chronic bronchitis or emphysema. A common disease among the elderly, it usually gets worse progressively over time.
Chronic bronchitis is caused by the long-term inflammation of the bronchi. As a result, there is more mucus than usual in the bronchi, causing sputum. The disease leads to bronchial wall thickening and swelling, contributing to the narrowing and obstruction of the airways.
Emphysema is a disease of the bronchioles and alveoli. Increased intrapulmonic pressure causes the alveoli to become overinflated, resulting in permanent damage of the elastic fibres. The exchange of oxygen and carbon dioxide is dampened. Patients may experience difficulty breathing and a lack of oxygen.
Statistics in 2007 (1) revealed that COPD was the fifth biggest killer disease in Hong Kong, following cancers, heart disease and stroke. An average of 2,000 people died from this disease annually. A local research study reported that 9% of people aged over 70 had COPD. Hospital statistics in 1997 showed that COPD was the cause of 4% of the emergency admissions and 5.8% of deaths.
The incidence rate of the disease has been increasing. The World Health Organization has predicted that in 2030, COPD would become the third most frequent cause of death around the world. (2)
- Smoking is one of the main causes of COPD and has resulted in 80 to 90% of the fatalities. Long-term smoking contributes to chronic lung inflammation, stimulating the production of mucus, damaging the trachea wall and lung tissues, resulting in chronic bronchitis and emphysema. Breathing in second-hand smoke on a regular basis may also lead to COPD.
- Exposure to cooking fumes or air pollution as a result of urbanization is a common cause of COPD.
- Jobs that require long-term exposure to chemicals or organic dust such as welding, mining, textile and building.
- α1-antitrypsin deficiency is a hereditary disease. α1-antitrypsin stops neutrophil elastase from damaging alveoli. A deficiency of α1- antitrypsin may increase the risk of emphysema.
COPD usually occurs in smokers. Initial symptoms are similar to those of asthma. Long-term exposure to stimulants results in chronic inflammation and fibrosis of trachea and lung tissues, causing thickening of the airway wall; proliferation of goblet cells contributes to increased production of mucus, irreversibly narrowing the airways and resulting in chronic cough and sputum production. Conditions may worsen when exercising, or when there are viral infections, or when the level of humidity changes or air quality becomes poorer. As the disease develops, patients may experience chronic cough, having thick sputum, shortness of breath, difficulty breathing, fatigue and reduced physical ability. Breathing will become more difficult as lung functions weaken. If the condition continues to worsen, patients will find it difficult to breath even when they are still. In a later stage, the reduction of surface area in lungs for the exchange of oxygen and carbon dioxide will gradually develop into hypoxemia and hypercapnia, and even pulmonary heart disease or respiratory failure and death.