Chronic Obstructive Lung Disease - Causes

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Causes of Chronic Bronchitis

Biologic Factors and Smoking in Chronic Bronchitis. In chronic bronchitis, smoking triggers inflammation that causes damage in the airways. The processes involved are less clearly understood than those in emphysema, but most likely include the following:

• Damage to the cilia, the hair-like waving projections that move bacteria and foreign particles out of the lungs -- when cilia are injured, such agents become trapped in the lungs and can cause infections that lead to chronic bronchitis.
• Enlargement of the mucus glands in the large airways of the lungs is also involved in the disease process.
• Overgrowth in the smooth muscle cells in the airway.

Bacteria and Viruses. Certain bacteria, particularly Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, are common in the lower airways of nearly half of chronic bronchitis patients. However, the role of bacteria, viruses, and other organisms in causing chronic symptoms, and inflammation is unclear. Some experts believe that a low-level infection in the lungs may trigger an inflammatory reaction that continues to produce subsequent acute attacks.

Review Date: 04/28/2006
Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital