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What is chronic bronchitis?
Chronic bronchitis is defined as a cough that occurs every day with sputum
production that lasts for at least 3 months, two years in a row. This definition was developed to help select uniform patient
populations for research purposes, for example, to study medication therapies for treatment of chronic bronchitis.
Many of the
bronchi develop chronic inflammation with swelling and excess mucus production. The inflammation causes a change in the lining cells of the airways to varying degrees. Many cells that line the airway lose the function of their cilia (hair-like appendages that are capable of beating rapidly), and eventually the ciliated cells are lost. Cilia perform the function of moving particles and fluid (usually mucus) over the lining surface in such structures as the trachea, bronchial tubes, and nasal cavities to keep these hollow structures clear of particles and fluids. These ciliated cells that help in clearance of secretions are often replaced by so-called goblet cells. This group of cells secretes mucus into the airway. The warm moist environment of the airway along with the nutrients in the mucus is an excellent medium for growing bacteria. The mucus often becomes infected and discolored from the bacterial overgrowth and the body's inflammatory response to it. The inflammation, swelling, and mucus frequently and significantly inhibit the airflow to and from the lung alveoli by narrowing and partially obstructing the bronchi and bronchioles.
The muscles that surround the some of the airways can be stimulated by this airway irritation. This muscular spasm also known as bronchospasm can result in further airway narrowing. With long standing inflammation, as can be seen in chronic bronchitis, this muscular spasm and inflammation results in a fixed, nonreversible narrowing of the airway and the condition is termed
chronic obstructive pulmonary disease (COPD).
Chronic coughing develops as the body attempts to open and clear the bronchial airways of particles and mucus or as an overreaction to ongoing inflammation. Chronic bronchitis can be a progressive disease; symptoms (listed below) increase over time. Some NIH investigators consider chronic bronchitis a type of COPD.
COPD also includes the entities of
chronic asthma. These
conditions are not always separable and patients often have components of each.
In the case of chronic bronchitis, the fixed airway obstruction, airway
inflammation and retained secretions can result in a mismatch of blood flow and
airflow in the lungs. This can impair oxygenation of the blood as well as
removal of the waste product, carbon dioxide.
Although people of any age can develop chronic
bronchitis, the majority of people diagnosed with the disease are 45 years of
age or older.