Bronchitis is an inflammation of the air passages within the lungs. It occurs when the trachea (windpipe) and the large and small bronchi (airways) within the lungs become inflamed because of infection or other causes. Air is pulled into the lungs when we breathe, initially passing through the mouth, nose, and larynx (voicebox) into the trachea and continues en route to each lung via either the right or left bronchi (the bronchial tree - bronchi, bronchioles, and alveoli). Bronchi are formed as the lower part of the trachea divides into two tubes that lead to the lungs. As the bronchi get farther away from the trachea, each bronchial tube divides and gets smaller (resembling an inverted tree) to provide the air to lung tissue so that it can transfer oxygen to the blood stream and remove carbon dioxide (the waste product of metabolism).
Bronchitis causes inflammation of the bronchial tubes. The inflammation causes swelling of the lining of these breathing tubes, narrowing the tubes and promoting secretion of inflammatory fluid.

• The thin mucous lining of these airways can become irritated and swollen.
• The cells that make up this lining may leak fluids in response to the inflammation.
• Coughing is a reflex that works to clear secretions from the lungs. Often the discomfort of a severe cough leads you to seek medical treatment.
• Both adults and children can get bronchitis. Symptoms are similar for both.
• Infants usually get bronchiolitis, which involves the smaller airways and causes symptoms similar to asthma.

Bronchitis describes inflammation of the bronchial tubes .The inflammation causes swelling of the lining of these breathing tubes, narrowing the tubes and promoting secretion of inflammatory fluid. Bronchitis can be classified into two categories, acute and chronic, each of which has unique etiologies, pathologies, and therapies.
Acute bronchitis is characterized by the development of a cough, with or without the production of sputum, mucus that is expectorated (coughed up) from the respiratory tract. Acute bronchitis often occurs during the course of an acute viral illness such as the common cold or influenza. Viruses cause about 90% of cases of acute bronchitis while bacteria account for less than 10%.
Chronic bronchitis, a type of chronic obstructive pulmonary disease, is characterized by the presence of a productive cough that lasts for 3 months or more per year for at least 2 years. Chronic bronchitis most often develops due to recurrent injury to the airways caused by inhaled irritants. Cigarette smoking is the most common cause, followed by air pollution and occupational exposure to irritants, and cold air.

Acute bronchitis

• Occurs most often due to a viral infection that causes the inner lining of the bronchial tubes to become inflamed and undergo the changes that occur with any inflammation in the body. Common viruses include the rhinovirus, respiratory (RSV), and the influenza virus.
• Bacteria can also cause bronchitis (a few examples include, Mycoplasma, Pneumococcus, Klebsiella, Haemophilus).
• Chemical irritants (for example, tobacco smoke, gastric reflux, solvents) can cause acute bronchitis.
• People at increased risk both of getting bronchitis and of having more severe symptoms include the elderly, those with weakened immune systems, smokers, and anyone with repeated exposure to lung irritants.

Chronic Bronchitis

• Family History
• Cigarette smoking
• Long-standing Acute bronchitis
• Also, underlying disease processes (for example, asthma, cystic fibrosis, immunodeficiency, congestive heart failure,)

Bronchitis Symptoms
Acute bronchitis most commonly occurs after an upper respiratory infection such as the common cold or a sinus infection. You may see symptoms such as fever with chills, muscle aches, nasal congestion, and sore throat.

• Cough is a common symptom of bronchitis. The cough may be dry or may produce phlegm. Significant phlegm production suggests that the lower respiratory tract and the lung itself may be infected, and you may have pneumonia.
• The cough may last for more than two weeks. Continued forceful coughing may make your chest and abdominal muscles sore. Coughing can be severe enough at times to injure the chest wall or even cause you to pass out.
• Wheezing may occur because of the inflammation of the airways. This may leave you short of breath.

Inflammation of the bronchial tubes narrows the inside opening of the bronchial tubes. Narrowing of the bronchial tubes result in increased resistance, this increase makes it more difficult for air to move to and from the lungs. This can cause wheezing, coughing, and shortness of breath. The cough may consist of sputum due to the secretions from the inflamed cells that line the bronchi. By coughing, the body attempts to expel secretions that clog the bronchial tubes. If these secretions contain certain inflammatory cells, discoloration of the mucus may result often in a green or yellow color. Sometimes the severity of the inflammation may result in some bleeding. As with any other infection, there may be associated fever, chills, aches, soreness and the general sensation of feeling poorly or malaise.

Doctors diagnose bronchitis generally on the basis of symptoms and a physical examination.

• Usually no blood tests are necessary. In severe cases CBC count can be done.
• If the doctor suspects the patient has pneumonia, a chest x-ray may be ordered.
• Doctors may measure the patient's oxygen saturation (how well oxygen is reaching blood cells) using a sensor placed on a finger.
• Sometimes a doctor may order an examination and/or culture of a sample of phlegm coughed up to look for bacteria.