What causes chronic bronchitis?
Bronchitis is an inflammatory disorder involving the respiratory channels in the lungs called bronchi. It can be acute with sudden and severe presentation, whereas chronic bronchitis is a low grade and long drawn process.
Chronic bronchitis is defined as production of cough and sputum on most days for at least 3 consecutive months, for at least 2 successive years. This disease forms part of the chronic obstructive pulmonary disease, commonly known as COPD. COPD is defined as a lung disease characterized by airflow limitation that is not fully reversible. The airflow limitation is usually due to an abnormal inflammatory response of the lungs to noxious particles or gases though it is preventable and treatable. It is also associated with other complications like impaired nutrition, weight loss and skeletal muscle dysfunction.
This condition is more common in people who resort to tobacco smoking. The environmental pollution also poses a risk for this condition. In 2005, COPD contributed to more than 3 million deaths, and if it continues at this pace, it is likely to become the third most important cause of death worldwide by 2020. This impact is especially going to be strongest in Asian and African countries due to excessive tobacco consumption.
Causes of bronchitis
Cigarette smoking is the most significant risk factor for bronchitis and is responsible for more than 90% of cases. It is related to the amount and duration of cigarettes smoked by an individual. Though individual susceptibility is important, scientific studies have shown that the risk of chronic bronchitis occurs with more than 10 pack years (1 pack year = 20 cigarettes/day/year).
People in rural areas who use bio-fuels like wood, animal dung, crop residues and coal are at high risk of developing bronchitis due to high levels of indoor air pollution. This is more commonly seen in the rural areas and in snow bound areas. Occupational risk is seen in coal miners. In many patients the condition has hereditary factors. These include deficiency of an enzyme in the lungs called alfa 1 – antiproteinase. This enzyme normally prevents the breakdown of proteins due to release of bacterial enzymes. In the absence of this enzyme, lung infections result in more damage leading to chronic bronchitis.
The genesis of bronchitis
The main initiating factors in the occurrence of chronic bronchitis is long term irritation of the respiratory passage due to smoke from tobacco or environmental pollution caused by sulfur dioxide and nitrogen dioxide. The cigarette smoke interferes with ciliary action of the respiratory epithelium which clears any mucus in the passage; it also inhibits the ability of bronchial and alveolar white blood cells to fight against the bacteria. The exposure of dust from grain, cotton and silica has similar effects. In the early stage of this disease, there is greater production of mucus in the bronchi due to an increase in size of glands in the respiratory epithelial lining. Inflammatory cells like neutrophils release enzymes against proteins called elastase, cathepsin and matrix metalloproteinases which are also responsible for increased mucus production. Special types of cells called goblet cells multiply, and produce more mucus in the small airways resulting in airway obstruction.
The role of infection seems to be secondary as it is not responsible for the initiation of chronic bronchitis, though it plays a great role in maintaining it. Bacterial infections are responsible for acute aggravation of this condition which occurs commonly. Viral infections can also cause exacerbations of chronic bronchitis.
Bronchitis is a chronic health problem and has a rising trend worldwide due to smoking and exposure to pollution. It poses a risk for development of lung cancer. It is preventable by avoidance of risk factors. Public awareness is increased by warning messages shown in the media programs.