Bronchitis

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Bronchitis

Chronic bronchitis is a persistent inflammation of the bronchial tubes, airways leading to the lungs. The disease is characterized by a daily cough that produces sputum for at least three months each year for two consecutive years, when no other disease can account for these symptoms. The diagnosis of chronic bronchitis is made by this history, rather than by any abnormalities found on a chest x-ray or through a pulmonary function test.

When a person breathes in, air, smoke , germs, allergens, and pollutants pass from the nose and mouth into a large central duct called the trachea. The trachea branches into smaller ducts, the bronchi and bronchioles, which lead to the alveoli. These are the tiny, balloonlike, air sacs, composed of capillaries, supported by connecting tissue, and enclosed in a thin membrane. Bronchitis can permanently damage the alveoli.

Bronchitis is usually caused by cigarette smoke or exposure to other irritants or air pollutants. The lungs respond to the irritation in one of two ways. They may become permanently inflamed with fluid, which swells the tissue that lines the airways, narrowing them and making them resist airflow. Or, the mucus cells of the bronchial tree may produce excessive mucus.

The first sign of excessive mucus production is usually a morning cough. As smoking or exposure to air pollutants continues, the irritation increases and is complicated by infection, as excess mucus provides food for bacteria growth. The mucus changes from clear to yellow, and the infection becomes deep enough to cause actual destruction of the bronchial wall. Scar tissue replaces the fine cells, or cilia, lining the bronchial tree, and some bronchioles are completely destroyed. Paralysis of the cilia permits mucus to accumulate in smaller airways, and air can no longer rush out of these airways fast enough to create a powerful cough.

With each pulmonary infection, excess mucus creeps into the alveoli, and on its way, totally blocking portions of the bronchial tree. Little or no gas exchange occurs in the alveoli, and the ventilation-blood flow imbalance significantly reduces oxygen levels in the blood and raises carbon dioxide levels. Chronic bronchitis eventually results in airway or air sac damage; the air sacs become permanently hyperinflated because mucus obstructing the bronchioles prevents the air sacs from fully emptying.

Chronic bronchitis usually goes hand-in-hand with the development of emphysema , another chronic lung disease. These progressive diseases cannot be cured, but can be treated. Treatment includes avoiding the inhalation of harmful substances such as polluted air or cigarette smoke.

[Linda Rehkopf ]