Characteristics of Chronic bronchitis
Chronic bronchitis is characterized by the inflammation of the bronchi and bronchioles. It is one of the chronic obstructive pulmonary diseases (COPD) characterized by progressive difficulties in breathing. Irritation in the bronchial tubes carrying air into and out of the alveolar sacs in the lung causes the build-up of mucus. The result is difficulty breathing as the carrying capacity of the bronchial tubes is compromised by inflammation. Categories of chronic bronchitis include simple chronic bronchitis (characterized by mucoid sputum production), chronic mucopurulent bronchitis (characterized by recurrent or persistent sputum production without localized suppurative disease), and chronic bronchitis with obstruction (Rogliani et al., 2016). The onset of either productive cough or wheezing and a long history of the other distinguish chronic bronchitis with obstruction from asthma.
Chronic bronchitis is linked to excessive tracheobronchial mucus production adequate to result in a cough with expectoration for over three months in a year for a minimum of two consecutive years. Symptoms of chronic bronchitis include frequent coughing or a cough with excessive mucus production, wheezing, a whistling or squeaky sound when breathing, shortness of breath (especially with physical activity), and tightness in the chest (Ilchenko & Fialkovska, 2019). Some patients with chronic bronchitis frequently acquire respiratory infections such as colds and flu. In severe cases of chronic bronchitis, patients experience weakness in lower muscles, weight loss, and swelling in the ankles, feet, or legs.
Chronic bronchitis risk factors include smoking, prolonged exposure to lung irritants, age, and genetics. Causes of chronic bronchitis include progression from acute bronchitis or gradual development as a result of heavy smoking or prolonged exposure to contaminated air. The presence of a continuous cough for a smoker indicates the thickening of the bronchial lining, which narrows the airway causing breathing difficulties (MacNee & Rabinovich, 2017).
Normal Anatomy of the Bronchi
The trachea connects the upper airways to the bronchi. Its anterior and lateral walls copies of 16-22 rings made of cartridge and its posterior wall have a thin band of smooth muscle. The set up offers support for the tracheal anatomy during inspiration and expiration (Zhang, Han & Zhang, 2019). The trachea extends 10-12 cm distally before dividing into the right and left mainstream bronchi at the level of the T5 vertebra. The mainstream (primary) bronchi branches into the lobar (secondary) bronchi, which further branch into the segmental (tertiary) bronchi. Bronchi enter the lung at the hilum along with arteries, veins, and lymphatics. Bronchi subdivide an average of 23 times along the bronchial tree with the first 16-17 generations of bronchi making up the conducting zone and do not contribute to gas exchange. Dead space refers to the surface of the airways not engaging in gas exchange. As the bronchi divide, the respiratory epithelium changes to give rise to terminal bronchioles. The 17th-19th generations of bronchioles make up the transition zone. The last 2-3 generations of bronchioles have alveoli in their walls and constitute the respiratory zone. Acinus is the area of the lung that is distal to a terminal bronchiole (Zhang, Han & Zhang, 2019). The respiratory bronchial, which further branches into multiple alveolar ducts, is the final division. Alveoli start appearing at the respiratory bronchioles level and are the functional units of the respiratory system.
Normal Physiology of the Bronchi
Gas exchange does not take place in the bronchi. The conduction zone of the bronchial tree is between the tracheal bifurcation and the terminal bronchial. The conducting zone moistens and warm air and forms part of the dead space. The respiratory zone includes alveoli, alveoli sacs, alveolar ducts, and respiratory bronchioles. During inspiration and expiration, the entire bronchial tree moves with the lung as a result of the thoracic activity. Structural movements are more pronounced in portions of the bronchial tree that are farthest to the pulmonary hilum. The bronchi and bronchioles also constitute the mucociliary escalator that eliminates mucus and pathogens from the lungs. Bronchoconstriction of the bronchi and bronchioles involves tightening of the smooth muscle of the bronchi and bronchioles, leading to coughing, wheezing, and dyspnea (Zhang, Han & Zhang, 2019). It is caused by the release of acetylcholine in the bronchi, activation of the parasympathetic nervous system, overproduction of mucus, inflammation, or allergic reactions. Bronchoconstriction in bronchitis and asthma causes obstruction of the airways and makes it more difficult to breathe.
Mechanism of Pathophysiology
Chronic bronchitis is characterized by inflammation of the central airways. An influx of neutrophil into the airway lumen and inflammatory mononuclear cell infiltrate in the airway are part of the pathology of chronic bronchitis. Researchers are gaining more understanding of the role of molecular events that produce the inflammation in the pathogenesis causing mucus hypersecretion (MacNee & Rabinovich, 2017). Chemotactic and proinflammatory cytokines such as IL-8 and colony-stimulating factors lead to the peribronchial distribution of fibrotic changes and a predominance of neutrophils. In response to inflammatory, infectious, and toxic stimuli, the airway epithelial cells release the inflammatory mediators and also decrease the release of neutral endopeptidase or angiotensin-converting enzyme and other regulatory products. Inflammation in chronic bronchitis is initiated and targets alveolar epithelium. Chemotactic agents derived from tissue fluids, invading microbes, and generated by the affected bronchial epithelium are potentially involved in the inflammatory cell recruitment to the airways. Interleukin (IL-8) is a potent chemoattractant and activator of lymphocyte and neutrophils synthesized by the bronchial epithelial cells. The adhesion of infiltrating leukocytes to resident parenchyma cells in the bronchi and extracellular matrix also contributes to the development of airway inflammation is. Clinical features of chronic bronchitis result from inflammation ((MacNee & Rabinovich, 2017)). Research suggests that neutrophils and lymphocyte constituents play a significant role in the initiation and maintenance of cough and mucus expectoration occurring in patients with chronic bronchitis.
Prevention
Not smoking or cessation of smoking is the best way to prevent chronic bronchitis, as smoking is a significant risk factor for the disease (Ilchenko & Fialkovska, 2019). Other prevention measures include avoiding lung irritants such as dust, chemical fumes, second-hand smoke, and polluted air. Vaccines for the flu and pneumococcal pneumonia are administered to prevent complications since people with chronic bronchitis are more vulnerable to these illnesses.
Treatment
Diagnosis of chronic bronchitis considers medial and family history, symptoms, and lab tests such as lung function tests (spirometry and peak flow), chest x-ray, sputum tests, CT scan, or arterial blood gas tests. Chronic bronchitis has no cure, but treatment aims to relieve symptoms, slow the progression of the disease, and improve patients’ quality of life. Treatment options include medicines, oxygen therapy, lung transplant, and pulmonary rehabilitation.
Bronchodilators help relax smooth muscles around the airways to make breathing easier. The most common for administering bronchodilators is the inhaler. Corticosteroids are administered to reduce inflammation (Ilchenko & Fialkovska, 2019). However, long-term use of steroids is not recommended due to side effects such as weakened bones, diabetes, hypertension, and cataracts. Antibiotics are administered where patients develop lung infections. Nebulizer treatments are used in severe cases. Mucolytics help to thin mucus in the airway, making it easier to breathe (Poole, Sathananthan, & Fortescue, 2019). Oxygen therapy is recommended for patients with severe chronic bronchitis with low levels of blood oxygen. Surgery is recommended for some patients to remove damaged lung tissue. For patients with severe symptoms and fail to show improvement after medication, a lung transplant is an option. Pulmonary rehabilitation programs help people with chronic breathing problems improve their well-being and may include an exercise program, nutritional and psychological counseling, and disease management training.