Chronic bronchitis

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What is Chronic bronchitis?

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Chronic bronchitis is a disease of the lung. The lungs consist of a series of folded membranes (the alveoli) which are located at the ends of very fine branching air passages (bronchioles).

Chronic bronchitis is a persisting infection and inflammation of the larger airways of the lungs - the bronchi. There are two main bronchi in the lungs (the right and left) which divide from the trachea, as seen in the figure to the right. Chronic bronchitis occurs as part of the disease complex known as chronic obstructive pulmonary disease (COPD) which also includes emphysema and small airways disease. Chronic bronchitis specifically refers to chronic cough and daily mucus production for at least three months of two or more consecutive years. Other causes of chronic cough must be excluded before making the diagnosis.

Who gets Chronic bronchitis?

COPD (which includes chronic bronchitis and emphysema) is a common disease in Australia and a major cause of disability, hospital admissions, and mortality. It is considered to be ranked third in the overall burden of disease after heart disease and stroke. More than half a million Australians are estimated to suffer from moderate to severe disease, and COPD ranks fourth among the common causes of death in Australian men, and sixth in women. Rates are even significantly higher in the Australian Aboriginal population.

Chronic bronchitis is common among smokers. In Western countries it is estimated that chronic bronchitis occurs in approximately 18% of male and 14% of female smokers compared to 7% and 6% of non-smokers, respectively.

Predisposing Factors

Chronic bronchitis can affect both males and females of all ages but it tends to be most common in middle-aged males. The following predisposing factors have been identified:

Cigarette smoke- This is by far the most important factor in the development of chronic bronchitis. The disease is 4 to 10 times more common in heavy smokers regardless of age, sex, occupation, and place of dwelling. There is a direct relationship between intensity of smoking and reductions in lung function and mortality from disease. Those who smoke 30 cigarettes per day are 20 times more likely to die from chronic bronchitis and COPD than non-smokers.
Pollution- Non-smokers exposed to heavy atmospheric pollution may occasionally develop chronic bronchitis. This results due to irritation of the airways from inhalation of toxins and fumes.
Family history- There is some role of family history in the development of COPD and chronic bronchitis.
Airway infections- Although infection is not considered responsible for the initiation of chronic bronchitis, it is important factor in maintaining disease and causing exacerbations.

Progression

Early on in chronic bronchitis you usually will have symptoms of cough productive of significant amounts of sputum without any significant breathlessness. The excess mucus production is caused by enlargement of mucous glands and increased numbers of mucus-secreting goblet cells in the airways. The small airways themselves then become inflamed but at this stage the disease is considered largely reversible. Cessation of smoking will resolve the airway inflammation.

As the disease progresses there is progressive abnormal cell growth (called squamous metaplasia) and fibrosis (hardening) of the bronchial walls. This causes airflow limitation and symptoms of shortness of breath. Symptoms of breathlessness are usually present on exertion. You may develop other signs of COPD such as cyanosis (bluish discolouration of the lips and skin). Emphysema may also be present at this stage, causing more severe shortness of breath and chest tightness.

If your chronic bronchitis remains severe some other complications can develop including:

Secondary polycythaemia- This is an increase in the number of red blood cells in the blood to try to compensate for reduced oxygen levels. The blood subsequently becomes 'thicker' with sluggish flow which can lead to clotting.
Right heart failure.
Pneumothorax (punctured lung).
Respiratory failure- This is often caused by acute infective exacerbations. Death can sometimes occur from severe declines in respiratory function.

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