What is Bronchitis?
Bronchitis is the medical term for inflammation of the lining of the bronchial tree, including the bronchi and/or bronchioles. It often involves the terminal part of the trachea as well. The walls of the bronchi and/or bronchioles become swollen due to inflammation and secrete excessive amounts of mucus. This causes a narrowing of the airway leading to a difficulty breathing (dyspnea), wheeze and a persistent cough.
Bronchitis may be acute, lasting less than 3 weeks (usually 10 to 14 days) or chronic, which is considered as a productive cough present for at least 3 months that recurs in 2 consecutive years. Often acute bronchitis does not occur on its own. It may be preceded or accompanied by inflammation elsewhere in the respiratory tract, namely pharyngitis (pharynx) or laryngitis (larynx).
Acute and Chronic Bronchitis
Acute bronchitis frequently occurs with viral infections, particularly seasonal flu or the common cold, and may often be a complication related to the inadequate treatment and poor management of upper respiratory tract infections. Inflammation that extends further down the respiratory tract, beyond the bronchial tubes and into the lung tissue is known as pneumonia.
Chronic bronchitis is a result of recurrent inflammation of the bronchi and/or bronchioles. Eventually there is degeneration in this part of the airway with subsequent narrowing that is long lasting or sometimes permanent. This ultimately affects the ventilation which is a core function of the respiratory system. Therefore chronic bronchitis falls into the broader category of chronic obstructive pulmonary disease and has to be managed appropriately to prevent long term complications.
Bronchitis and Asthma
These are two airway diseases that are commonly mistaken for each other. Both affect the lower respiratory tract.
Asthma is the narrowing of the airways as a result of bronchospasm (spasm of the muscles lining the bronchial tubes). Similar to bronchitis, mucus secretion and bronchial wall swelling may also occur in asthma. It is mainly a result of immune mediated hypersensitivity (allergies) or heightened airway reactivity. In the past, asthma used to be known as ‘wheezy bronchitis’.
Bronchitis also results in narrowing of the airway as a result of mucus hypersecretion and bronchial wall swelling. Bronchospasm is usually not a key feature of this disease unlike in asthma. It is often a result of infectious and chemical agents irritating the airway.
Abnormal breathing sounds like a wheeze are present in both asthma and bronchitis.
- Laryngotracheobronchitis – inflammation of the lining of the respiratory tract extending from the larynx to the bronchi and/or bronchioles. Also known as croup.
- Tracheitis – inflammation of the lining of the trachea (wind pipe).
- Tracheobronchiolitis – inflammation of the airway lining extending from the trachea to the bronchioles (tracheobronchial tree).
- Bronchiolitis – inflammation of the lining of the bronchioles. Often used synonymously with the term bronchitis because the bronchioles are part of the bronchial tree.
- Bronchopneumonia – inflammation of the lining of the lower airways extending from the bronchi to the lung parenchymal tissue.
Signs and Symptoms
In bronchitis, the irritation to the bronchi and bronchioles triggers the excessive secretion of mucus (hypersecretion). Coupled with the swelling of the wall due to inflammation, the mucus narrows the airway. While a cough is always present, it is not uncommon for other symptoms to be absent in bronchitis.
The main symptom of bronchitis, whether acute or chronic, is a productive cough. This is commonly referred to as a ‘wet cough’. It is episodic and often results in the coughing up of mucus (sputum).
Irritation of the bronchial lining and mucus accumulation within the bronchial tree triggers the cough reflex which aims to expel the irritant and mucus. The mucus expectorated during coughing (sputum) may be clear, yellow, green or brown in color. Brown sputum is usually indicative of an infection. Persistent coughing may cause further inflammation and abrasion of the bronchi, bronchioles, trachea, larynx and/or pharynx thereby causing slight bleeding which is evident as blood-tinged sputum.
In acute bronchitis which is often caused by viral respiratory tract infections, the cough may extend for up to 3 weeks despite the infection having resolved. However, in most cases, it resolves within 10 days. A secondary bacterial infection may also set in during or after the viral infection, especially among immunocompromised patients and cigarette smokers.
In chronic bronchitis, the productive cough lasts for over 3 weeks and recurs for 2 consecutive years or more. It is commonly referred to as a smoker’s cough since cigarette smoking is one of the major causes of chronic bronchitis. The loss of cilia in the respiratory tract epithelium hampers the expulsion of mucus from the traceobronchial tree. Mucus accumulation within the lower respiratory tract may result in rhonchi or crackles as well sometimes changing the typical sound of the cough to a more deep and ‘chesty’ cough.
Bronchitis Short of Breath
Another common symptom of bronchitis is shortness of breath (dyspnea). Ventilation may be adequate but due to the narrowing of the airway, the sensation of shortness of breath is commonly present.
This is a result of mucus secretion and bronchial wall swelling causing narrowing of the airway. In addition, inflammation in the distal parts of the respiratory tract may slightly affect gas exchange. This is further complicated if the mucus is not expectorated efficiently, as is the case with chronic bronchitis, and accumulates lower down the tract or within the lung itself.
Pallor or cyanosis (white to blue discoloration of the skin) due to poor gas perfusion rarely occurs in a case of bronchitis alone and may be an indication of other underlying cardiopulmonary disorders.
Bronchitis Breathing Sounds
The narrowing of the airway often results in a wheeze and other abnormal breathing sounds. This is more pronounced if there is concomitant bronchospasm as is often seen in children with immune mediated hypersensitivity (allergy).
Apart from a wheeze and rhonchi, inflammation higher up the respiratory tract may also cause stridor while mucus accumulation in the lungs may cause crackles.
Asthma should always be excluded in prominent wheezing in children, especially if the onset may have been related to the exposure of known inhaled allergens and irritants, rather than just an infection.
Other Bronchitis Symptoms
Many of the accompanying signs and symptoms may be a result of the respiratory tract infection and not of bronchitis itself. This includes :
- Sore throat
- Runny nose (rhinorrhea) or nasal congestion
- Fatigue, although this may be prominent if the bronchitis is significantly affecting oxygenation
- Muscle aches and pains
Acute Bronchitis Causes
Viruses are the most common pathogen implicated in acute infectious bronchitis. A number of viruses including those associated with the seasonal flu (influenza), common cold, and other acute respiratory tract infections (ARTI) like the respiratory syncytial viruses (RSV’s) are the common cause.
Acute bronchitis often develops along with or towards the latter stages of these viral infections which also affects other parts of the respiratory tract – pharyngitis (sore throat), laryngitis and tracheitis. The symptoms of bronchitis typically commence a day or two after the main symptoms of a cold or flu begins as the infections spreads to the lower respiratory tract. The persistent productive cough associated with acute bronchitis may last for 7 to 10 days.
A bacterial infection may occur secondary to a viral respiratory tract infection. It rarely occurs spontaneously, except in smokers, patients with cystic fibrosis, or following aspiration of gastric contents (acid reflux).
Fungal causes of acute infectious bronchitis is also rare and is more likely to occur in an immunocompromised patient (immune deficiency).
This includes a wide range of non-infectious causes, including mechanical, chemical and allergic causes. Depending on the causative factor, it may lead to recurrent episodes of acute bronchitis which can lead to chronic bronchitis.
Some of the causes include :
- Cigarette smoking
- Environment pollution (air)
- Gastroesophageal reflux disease (GERD /acid reflux)
- Organic and inorganic dust
Chronic Bronchitis Causes
Chronic bronchitis is a productive cough lasting 3 months or more and recurring within 2 consecutive years. There is degeneration of the bronchi and the condition is not solely defined by the episodes of bronchial inflammation and mucus hypersecretion.
Repeated episodes of acute bronchitis may lead to chronic bronchitis. Therefore any of the causes mentioned above for acute bronchitis if persistent or recurrent may lead to chronic bronchitis.
However, of these, cigarette smoking and air pollution has been widely implicated. Most long term cigarette smokers suffer with some degree of chronic bronchitis. The same applies for drug users who consume illicit substances through smoking.
GERD, where there is aspiration of the reflux, is now being implicated more frequently in chronic bronchitis as a result of the airway damage by gastric acid. Long-term allergy-related respiratory conditions, especially if poorly managed, may lead to chronic bronchitis due to the thickening of the bronchial walls as a result of persistent inflammation.
- Bronchitis. Medscape
Last updated on August 31, 2018.