Acute Bronchitis

What is acute bronchitis?

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 describes inflammation of the bronchial tubes (inflammation = itis). The inflammation causes swelling of the lining of these breathing tubes, narrowing the tubes and promoting secretion of inflammatory fluid.
Acute bronchitis describes the inflammation of the bronchi usually caused by a viral infection, although bacteria and chemicals also may cause acute bronchitis. Bronchiolitis is a term that describes inflammation of the smaller bronchi referred to as bronchioles. In infants, this is usually caused by respiratory syncytial viruses (RSV), and affects the small bronchi and bronchioles more than the large. In adults, other viruses as well as some bacteria can cause bronchiolitis and often manifest as a persistent cough at times productive of small plugs of mucus.
Acute bronchitis is as mentioned above, is a cough that begins suddenly usually due to a viral infection involving the larger airways. Colds (also known as viral upper airway infections) often involve the throat (pharyngitis) and nasal passages, and at times the larynx (resulting in a diminished hoarse voice, also known as laryngitis). Symptoms can include a runny nose, nasal stuffiness, and sore throat. Croup usually occurs in infants and young children and involves the voice box and upper large airways (the trachea and large bronchi).
Chronic bronchitis for research purposes is defined as a daily cough with sputum production for at least three months, two years in a row. Chronic bronchitis is a diagnosis usually made based on clinical findings of a long term persistent cough usually associated with tobacco abuse. From a pathologic standpoint, characteristic microscopic findings involving inflammatory cells in seen in airway tissue samples make the diagnosis. When referring to pulmonary function testing, a decrease in the ratio of the volume of airflow at 1 second when compared to total airflow is less than 70%. This confirms the presence of obstructive airways disease of which chronic bronchitis is one type. Certain findings can be seen on imaging studies (chest X-ray, and CT or MRI of the lungs) to suggest the presence of chronic bronchitis; usually this involves an appearance of thickened tubes.

What causes acute bronchitis?

• 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 syncytial virus (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.

What are the risk factors for acute bronchitis?

Bronchitis describes inflammation of the bronchial tubes. Smoking is a key risk factor for developing acute bronchitis. Any other illnesses that predispose to similar inflammation also increase that risk (for example, asthma patients and patients allergic to airborne chemicals).