Pathophysiology

By definition, bronchiectasis demonstrates localized, irreversible dilatation of bronchi > 2 mm in diameter that results from destruction of the muscular and elastic components of bronchial walls. Damage to these 2 bronchial wall components is caused by an infectious organism and also by the inflammatory cytokines, nitric oxide, and neutrophilic proteases released by the host's immune response to the organism. Additionally, peribronchial alveolar tissue may be damaged, resulting in diffuse peribronchial fibrosis. The result is abnormal bronchial dilatation with bronchial wall destruction and transmural inflammation. The involved bronchi are not only dilated but also inflamed and easily collapsible, resulting in airflow obstruction and impaired clearance of secretions.

The most important functional finding of altered airway anatomy is severely impaired clearance of secretions from the bronchial tree. This altered airway anatomy causes colonization and infection with pathogenic organisms, contributing to the common purulent expectoration observed in patients who have bronchiectasis. The result is a cycle of bronchial damage, bronchial dilatation, impaired clearance of secretions, recurrent infection, and more bronchial damage.

Diseases associated with bronchiectasis are as follows:

•Infection: Typical organisms include Klebsiella species, Staphylococcus aureus, Mycobacterium tuberculosis, Mycoplasma pneumoniae, nontuberculous mycobacteria, Mycobacterium avium-intracellulare complex, measles, pertussis, influenza, respiratory syncytial virus, herpes simplex virus, and certain types of adenovirus.

•Bronchial obstruction: Obstruction occurs as a result of endobronchial tumors, broncholithiasis, bronchial stenosis resulting from infections, encroachment of hilar lymph nodes, and foreign body aspiration.

• Inhalation injuries

• Injury from noxious fumes, gases, or particles

• Inhalation of stomach acid and food particles

•Young syndrome - patients have bronchiectasis (often predominant in the lower lobes), sinusitis, and obstructive azoospermia

· Hereditary conditions

• Cystic fibrosis - CF and its variants are likely the most common cause of bronchiectasis in the United States and other industrialized nations. CF is an autosomal recessive disease. CF is a multisystem disorder that affects the chloride transport system in exocrine tissues, primarily secondary to a defect in the CF transmembrane regulator (CFTR) protein.
• Primary ciliary dyskinesia - manifested by immotile or dyskinetic cilia and/or sperm
• Marfan syndrome

•Allergic bronchopulmonary aspergillosis - Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity reaction to inhaled Aspergillus antigen that is characterized by bronchospasm, bronchiectasis, and immunologic evidence of a reaction to Aspergillus species.

•Immunodeficiency states: The most common congenital conditions involve B-lymphocyte functions—specifically, hypogammaglobulinemia. An aggressive form of bronchiectasis has been described in patients with acquired immunodeficiency syndrome (AIDS).

•Congenital anatomic defects

◦Bronchopulmonary sequestration

◦Williams-Campbell syndrome (congenital cartilage deficiency)

◦Mounier-Kuhn syndrome (tracheobronchomegaly)

◦Yellow nail syndrome

•a 1 -Antitrypsin deficiency

•Lung and bone marrow transplants

•Rheumatoid arthritis and Sjögren syndrome

•Traction bronchiectasis associated with pulmonary fibrosis

In bronchiectasis, mucus production increases, the cilia are destroyed or damaged, and areas of the bronchial wall become chronically inflamed and are destroyed.

Anatomy

Bronchiectasis usually involves bronchi of medium size (>2 mm diameter). The proximal (main, lower, and segmental) bronchi are less affected, because they contain more cartilage than the distal bronchi and because they are more resistant to dilation. However, in patients with allergic bronchopulmonary aspergillosis and cystic fibrosis, the proximal bronchi are typically involved.

Although bronchiectasis caused by bacterial and viral infections usually affects the lower pulmonary lobes, the upper lobes are more frequently affected in patients with allergic bronchopulmonary aspergillosis and tuberculosis. Bronchiectasis is more diffuse in patients with cystic fibrosis and those with immunodeficiency states.

In advanced cases of bronchiectasis, dilated, medium-sized bronchi extend close to the pleura, without side branches and with few normal surrounding lung parenchyma. Focal destruction of part of the bronchial wall, increased mucus secretion and retention, and peribronchial fibrosis occur; the surrounding lung shows volume loss, fibrosis, emphysema, and nodular inflammatory foci.

Symptoms

History

The classic triad of symptoms (chronic cough, excess purulent sputum production, repeated infections) is seen only in the most severely affected patients. Total daily sputum production has been used to characterize severity of bronchiectasis:

• 10 mL/d is defined as mild bronchiectasis.
• 10-150 mL/d is defined as moderate bronchiectasis.
• 150 mL/d is defined as severe bronchiectasis.

Many patients have only mild or intermittent symptoms. Some patients with mild forms of bronchiectasis, as revealed on high-resolution computed tomography (HRCT) scans, may have no symptoms.

Hemoptysis is common and may occur in as many as 50% of patients. Episodic hemoptysis with little to no sputum production (dry bronchiectasis) is usually a sequela of tuberculosis. However, massive hemoptysis may occur; bleeding usually originates in dilated bronchial arteries, which contain blood at systemic (rather than pulmonary) pressures.

Less-specific symptoms include dyspnea, pleuritic chest pain, wheezing, fever, weakness, and weight loss. Significant airway obstruction may occur as a result of the bronchitis, bronchiolitis, or emphysema that frequently accompanies bronchiectasis. Repeated bronchial infection and pneumonia are common.

Дата добавления: 2015-10-30