Chronic Bronchitis
Medical Author:
Charles C. P. Davis, MD, PhD
Medical Editor:
Melissa Conrad Stöppler, MD
What is bronchitis?
Bronchitis is a term that describes inflammation of the bronchial tubes
(bronchi and the smaller branches termed bronchioles) that results in excessive
secretions of mucus into the tubes, leading to tissue swelling that can narrow
or close off bronchial tubes. Bronchial tubes extend from the trachea and
terminate at the alveoli in the lungs; the bronchial system resembles an
inverted tree and is sometimes termed the "bronchial tree." A few authors
include the trachea and upper airway in the definition. There are two major
types of bronchitis, acute and chronic.
What is acute bronchitis?
Acute bronchitis is usually bronchitis that is short-termed; the bronchitis
lasts about two weeks and people recover with no permanent damage to the
bronchial tree. Viruses such as influenza,
respiratory syncytial virus (RSV),
and rhinoviruses cause the majority (about 90%) of cases of acute bronchitis,
while the remainder are caused by bacteria (for example, Mycoplasma, Pneumococcus) or
short-term exposure to chemical irritants (for example,
tobacco smoke,
gastric
reflux contents, inhaled solvents).
Symptoms of acute bronchitis
may include a cough, mild wheezing, fever, chills
and malaise, and shortness of breath especially with exertion. Some people may
cough up phlegm. Chronic bronchitis differs from acute bronchitis in several
ways described below (pathology, progression of disease, major causes,
treatments, and outcomes).
What is chronic bronchitis?
Chronic bronchitis is defined as a cough that occurs every day with sputum
production that lasts for at least three months, two years in a row. This definition was developed to help select uniform patients for research purposes i.e. to study medication therapies for treatment of chronic bronchitis. Many of the
bronchi develop chronic inflammation with swelling and excess mucus production
in chronic bronchitis; 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. 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 epithelial
surface in such structures as the trachea, bronchial tubes, and nasal cavities
to keep these hollow structures clear of particles and fluids. Mucus-producing cells increase due to irritation. These cells produce a viscous fluid that facilitates cleansing of the airway. If the mucus becomes thick (less fluid or viscous, it may contribute to airway blockage.
With long standing inflammation, as can be seen in chronic bronchitis, scarring inside the bronchial tree may develop. These scarred areas do not clear particles and secretions very well, and can result in a fixed, nonreversible narrowing of the airway and the condition,
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.
COPD also includes the entities of
emphysema, chronic bronchitis, and
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.
Next: What are the causes of chronic bronchitis? »
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