Bronchiectasis: causes and pathogenesis

Predisposing factors in the formation of congenital bronchiectasis are smoking and drinking by a future mother during pregnancy and virus infections that were transferred during this period.

The development of bronchiectasis is promoted by chronic diseases of the upper respiratory tract (sinusitis, chronic purulent tonsillitis, adenoids, etc.), which are observed in almost half of the patients, especially in children.

Causes of bronchiectasis

The causes of the development of bronchiectasis are not yet fully established. The most important etiological factors, to some extent proven, are the following.

1. Genetically determined inferiority of the bronchial tree (congenital "weakness of the bronchial wall", insufficient development of the smooth musculature of the bronchi, elastic and cartilaginous tissue, insufficiency of the bronchopulmonary defense system - see " Chronic bronchitis "), which leads to disruption of the mechanical properties of the bronchial walls during their infection.
2. Postponed in early childhood (often in the older age group), infectious and inflammatory diseases of the bronchopulmonary system, especially often recurrent. They can be caused by various infectious agents, but the most important are staphylo- and streptococci, hemophilic rod, anaerobic infection, etc. Of course, infectious and inflammatory diseases of the bronchopulmonary system cause the development of bronchiectasis in the presence of genetically determined inferiority of the bronchial tree. Infectious pathogens also play a huge role in the development of exacerbations of the suppuration in already altered and enlarged bronchi.
3. Congenital impairment of the development of bronchi and their branching, which leads to the formation of congenital bronchiectasis. They are observed only in 6% of patients. Congenital bronchiectasis is also characteristic of the syndrome of Cartegener (reverse organ arrangement, bronchiectasis, sinusitis, ciliary stiffness of the ciliated epithelium, infertility in men due to a sharp violation of sperm motility).

Bronchiectasises easily arise in patients with congenital immunodeficiencies and congenital anatomical defects of the tracheo-bronchial tree (tracheobronchomegalia, tracheoesophageal fistula, etc.), with an aneurysm of the pulmonary artery.

Bronchiectasis may accompany cystic fibrosis - a systemic, genetically determined disease with lesions of the exocrine glands of the bronchopulmonary system and the gastrointestinal tract.

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Pathogenesis of bronchiectasis

Pathogenesis includes factors that lead to the development of bronchiectasias, and factors leading to their infection. The development of bronchiectasis leads to:

• obturation atelectasis, which occurs when the bronchial patency is impaired (athetectasis is promoted by a decrease in the activity of the surfactant, compression of the bronchi by hyperplastic radical lymph nodes in the case of the basal pneumonia, tubercular bronchoadenitis, and prolonged blockage of the bronchi by a tight mucous stopper in acute respiratory infections). Obturation of the bronchus causes a delay in the clearance of the bronchial secret distal to the site of bronchial obstruction and, of course, contributes to the development of irreversible changes in the mucous, submucosal and deeper layers of the bronchial wall;
• a decrease in the stability of bronchial walls to the action of bronchodilating forces (increased intrabronchial pressure during coughing, bronchial dilatation with accumulating secretion, an increase in negative intrapleural pressure due to a decrease in the volume of the atelectasized part of the lung);
• the development of the inflammatory process in the bronchi in the event of its progression leads to degeneration of the cartilaginous plates, smooth muscle tissue, replacement of the fibrous tissue and a decrease in bronchial stability.

The following mechanisms lead to infection of bronchiectasis:

• violation of cough, stasis and infection of the secretion in the enlarged bronchi;
• violation of the function of the system of local bronchopulmonary protection and immunity.

According to the data of AI Borokhovai RM Paleeva (1990), in the purulent contents of bronchiectasis, the most frequently found are Klebsiella, Pseudomonas aeruginosa, Staphylococcus aureus, rarely - Proteus, Streptococcus. NA Mukhin (1993) indicates the frequent detection of mycoplasma. In turn, the suppurative process in the bronchi promotes the expansion of the bronchi. Further, blood flow through the pulmonary arteries decreases, and the network of bronchial arteries is hypertrophied, through extensive anastomoses blood is discharged from the bronchial arteries into the pulmonary artery system, which leads to the development of pulmonary hypertension.

Pathomorphology

Expanded mainly bronchus of medium caliber, less often - distal bronchi and bronchioles. Isolate cylindrical, spindle-shaped, saccular, mixed bronchiectasises.

With cylindrical bronchiectasis, bronchial dilatation is moderately expressed, no significant deformation of the bronchial tree occurs. Spindle bronchiectasis is characterized by a moderate expansion and deformation of the bronchi and a decrease in the number of bronchial deletions. Saccharous bronchiectasis is the most severe form of bronchiectasis, with proximal (central) bronchi being affected first, and as the disease progresses, enlargement occurs, followed by damage followed by fibrosis of the distal bronchi. As a result of these pathological processes, bronchiectasis is formed in the peripheral parts of the body in the form of "sacks" filled with pus.

Bronchiectasis is most often localized in the posterior basal segments of the lower lobes of both the lungs and the middle lobe of the right lung.

The most characteristic pathomorphological manifestations of bronchiectasis are:

• expansion of bronchi of cylindrical or saccular form;
• a picture of chronic purulent inflammatory process in the wall of dilated bronchi with marked peribronchial sclerosis;
• atrophy and metaplasia of the bronchial ciliated epithelium into a multi-row or multi-layered flat, in some places - the replacement of the epithelium with a granulation tissue;
• reorganization of the vascular network of bronchi and lungs (opening of reserve capillaries, formation of arteriovenous anastomoses, hypertrophy of the muscular layer of bronchial arteries and their expansion, formation of vein myoelastosis, myoelastofibrosis, elastofibrosis). These changes in the arteries can be the cause of hemoptysis in bronchiectasis;
• changes in pulmonary tissue in the form of atelectasis, pneumofibrosis and emphysema.