What is COPD?

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COPD – iStock
COPD – iStock
Chronic obstructive pulmonary disease (COPD) is a chronic lung disease characterised by obstruction of airflow that cannot be fully reversed with inhaler medications, called bronchodilators. The most common symptoms of COPD are breathlessness and persistent cough with sputum production. As the condition worsens, even daily activities such as walking up a short flight of stairs or the exertion of washing or dressing become difficult.

The importance of COPD as a global health problem cannot be overstated. According to the latest World Health Organisation (WHO) statistics (2005), approximately 210 million people suffer from COPD worldwide, and 5% of all deaths globally are estimated to be due to this disease. This corresponds to more than 3 million deaths annually, of which 90% are thought to occur in low and middle-income countries. A recent projection published by the WHO Global Burden of Disease Project indicates that COPD will be the 3rd leading cause of death globally by the year 2030.

Cigarette smoking is the major risk factor for COPD, and much of the increase in COPD is associated with projected increases in tobacco use, especially in the developing world. However, recent studies have suggested that a quarter to almost a half of all cases of COPD occur in non-smokers. Other risk factors for the development of COPD include such diverse influences as environmental tobacco smoke exposure (passive smoking), smoke from coal and wood fires, exposure to dust, fumes and vapours, childhood illness, and previous tuberculosis.

Whatever the cause, it seems that chronic inhalation of noxious particles and gases stimulates inflammation in the lung. Unlike the acute inflammation of infection or trauma, this inflammation smoulders on chronically for decades, resulting in progressive damage to the tissue that supports airway structures and the gas exchange surface of the lung. Depending on which part of the lung is predominantly affected can determine whether patients develop either chronic bronchitis or emphysema, two diseases that are now recognised as sub-types of COPD.

Chronic bronchitis occurs when the inflammatory process affects mainly the large airway walls, leading to mucus over-production and inflammatory swelling of the inner layers of the airways, with subsequent obstruction to airflow.  Emphysema, on the other hand, is when the damage involves the delicate gas exchange part of the lungs, the tiny sacs called alveoli. Destruction of these structures leads to large non-functional spaces in the lungs known as bullae, which have a limited capacity to take up oxygen, with subsequent severe exercise impairment in affected individuals. The two different subtypes can also co-exist in the same individual.

The cells involved in the inflammatory response are the normal white cells (neutrophils and macrophages), which should protect the body during infective challenges. The normal defence mechanism of the body, which is aimed primarily at mopping up the invasive substances, attacks normal lung tissue to the detriment of the respiratory system. The toxic substances released by these activated cells, usually produced in response to an infection and designed to destroy bacteria, are unleashed on the lung’s own tissue. Destruction of the fine elastic fibres that support lung tissue leads to an inability to empty the lungs normally, with air-trapping. Thickening of the bronchial walls, formation of scar tissue and eventual destruction of the minute alveoli, which are responsible for oxygen uptake, impairs airflow and the uptake of life-sustaining oxygen and removal of carbon dioxide. The inflammatory response will periodically flare up during attacks of influenza and bronchitis, during which period patients may become acutely ill and very short of breath.

A characteristic of the inflammatory response of COPD is that it is not responsive to long-term medication with drugs such as corticosteroids, which are used successfully for prevention of asthma. When the inflammatory response has, over a period of years, caused extensive damage to the small airways and alveoli, patients will present with respiratory failure due to lack of oxygenation, or right heart failure (See Symptoms and diagnosis of COPD).

The disease is not confined to the lungs; it has systemic (whole body) effects that result in, for example, weight and appetite loss, and particularly a decrease of muscle mass in the limbs of severely ill patients. This leads to a vicious circle, as weakened patients who are extremely short of breath tend to withdraw, become completely inactive and frequently die in isolation.

(Written by Prof J.R. Joubert, MSc, MBChB (Stell), FCP (SA), MMed (Int. Med), MD (Stell.))

(Reviewed by Dr Greg Calligaro, physician at the Lung Unit, Groote Schuur Hospital and University of Cape Town, August 2010)

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