What is Chronic Bronchitis?
Chronic bronchitis is characterized by a persistent cough with sputum (mucus) production that lasts for at least three months in two consecutive years with no other identifiable cause.
Causes of Chronic Bronchitis?
The primary cause of chronic bronchitis is exposure to irritants and noxious substances. About 90% of individuals with chronic bronchitis are smokers, but the remaining 10% can develop the condition due to exposure to dust from grain, cotton, or silica. These irritants lead to changes in the airways.
Pathogenesis
Exposure to these irritants triggers protective responses in the airways, leading to an increase in the number of goblet cells and the enlargement of submucosal glands. These changes result in the overproduction of mucus, leading to airway obstruction. Smoking also causes inflammation, which can be either acute or chronic. In severe, long-standing cases, this inflammation can lead to fibrosis in smaller airways, further worsening airway obstruction.
Tobacco smoke exposure can also result in acquired cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction. Normally, CFTR regulates mucus production, maintaining proper consistency and hydration. When CFTR doesn’t function correctly, it causes the secretion of dehydrated mucus, impairing mucus clearance from the airways. This makes individuals with chronic bronchitis more susceptible to infections, which can exacerbate their symptoms.
Clinical Features of Chronic Bronchitis
Chronic bronchitis is typically observed in individuals with a smoking history of 40 pack-years or more, meaning they smoked one pack of cigarettes per day for 40 years.
Symptoms, including cough and mucus production, develop gradually and are often worse in the morning.
The hallmark symptom is a persistent cough with mucus production.
Over time, individuals may experience symptoms like cyanosis (bluish skin), hypoxemia (low blood oxygen levels), and edema, which can be a result of heart failure due to increased pulmonary resistance. Hence the name “Blue Bloaters”
Morphological Changes in Chronic Bronchitis
On gross examination, the airway mucous membranes exhibit hyperemia (increased blood flow), swelling, and edema.
Excessive mucus production which can lead to purulent secretions, especially in the presence of an infection.
In some cases, heavy secretions can fill the bronchi and bronchioles
Reid Index in Chronic Bronchitis
The Reid Index is an important histological parameter. It measures the ratio of the thickness of the submucosal glands to the thickness of the airway wall from the basement membrane of the epithelium to the perichondrium of the underlying cartilage. In normal airways, this ratio is typically less than 0.4. In chronic bronchitis, you’ll observe an increased Reid Index, often exceeding 0.5.
Diagnosis and Treatment
Diagnosis of chronic bronchitis relies on clinical symptoms and pulmonary function tests, such as spirometry.
Chest X-rays may reveal increased bronchovascular markings and cardiomegaly.
The mainstay of treatment is smoking cessation.
Medical and supportive therapy includes treating infections with antibiotics, using bronchodilators to relieve airway obstruction, and employing bronchopulmonary drainage in cases of excessive mucus.
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