Chronic nonobstructive bronchitis - Causes and pathogenesis

Several factors are important in the development of chronic non-obstructive bronchitis, the main one of which is probably the inhalation of tobacco smoke (active and passive smoking). Constant irritation of the bronchial mucosa by tobacco smoke leads to the restructuring of the secretory apparatus, hypercrinia and increased viscosity of bronchial secretions, as well as damage to the ciliated epithelium of the mucosa, resulting in disruption of mucociliary transport, cleansing and protective functions of the bronchi, which contributes to the development of chronic inflammation of the mucosa. Thus, tobacco smoking reduces the natural resistance of the mucous membrane and facilitates the pathogenic effect of viral and bacterial infections.

Among patients with chronic non-obstructive bronchitis, approximately 80-90% are active smokers. Moreover, the number of cigarettes smoked per day and the total duration of smoking are important. It is believed that smoking cigarettes has the greatest irritating effect on the mucous membrane, and to a lesser extent - pipes or cigars.

The second most important risk factor for chronic non-obstructive bronchitis is long-term exposure of the bronchial mucosa to volatile substances (pollutants) related to industrial and household air pollutants (silicon, cadmium, NO2, SO2, etc.). The implementation of these harmful factors also depends on the duration of the pathogenic effect on the mucosa, i.e. on the length of service or the duration of residence in unfavorable conditions.

The third factor contributing to the occurrence and maintenance of chronic inflammation of the bronchial mucosa is a viral-bacterial infection of the airways: repeated acute tracheobronchitis, acute respiratory viral infections, pneumonia and other bronchopulmonary infections.

The disease is most often caused by:

• respiratory viruses (respiratory syncytial virus, influenza viruses, adenoviruses, etc.);
• pneumococcus;
• Haemophilus influenzae;
• Moraxella;
• mycoplasma;
• chlamydia, etc.

For smokers, the most typical association is between Haemophilus influenzae and Moraxella.

Viral infection is of particular importance. Repeated exposure of the bronchial mucosa to respiratory viruses leads to focal dystrophy and death of ciliated cells. As a result, areas without ciliated epithelium (the so-called "bald spots") are formed on the bronchial mucosa. It is in these areas that the movement of bronchial secretions toward the oropharynx is interrupted, bronchial secretions accumulate, and the possibility of adhesion of opportunistic microorganisms (pneumococci, Haemophilus influenzae, Moraxella, etc.) to damaged areas of the mucosa arises. Thus, a viral infection almost always contributes to bacterial superinfection.

The seeding of the bronchial mucosa with microorganisms, which generally have relatively low virulence, nevertheless leads to the formation of a cascade of humoral and cellular factors that initiate and maintain chronic inflammation of the mucosa.

As a result, a diffuse inflammatory process (endobronchitis) develops in the mucous membrane of large and medium bronchi. The thickness of the bronchial walls becomes uneven: areas of mucous hypertrophy alternate with areas of its atrophy. The bronchial mucosa is edematous, a moderate amount of mucous, mucopurulent or purulent sputum accumulates in the lumen of the bronchi. In most cases, an increase in tracheobronchial and bronchopulmonary lymph nodes is noted. The peribronchial tissue is compacted, and in some cases loses airiness.

Changes in the bronchi in simple (non-obstructive) bronchitis are characterized by the following features:

• predominantly affecting large and medium bronchi;
• in most cases, relatively low activity of the inflammatory process in the bronchial mucosa;
• absence of significant broncho-obstructive disorders.

In addition to the listed main exogenous risk factors leading to the development of chronic endobronchitis (smoking, exposure to volatile pollutants and viral-bacterial infection), so-called endogenous factors are important in the development of chronic non-obstructive bronchitis, which include:

• male gender;
• age over 40 years;
• diseases of the nasopharynx with impaired breathing through the nose;
• changes in the hemodynamics of the pulmonary circulation, primarily in the microcirculation system (for example, in chronic heart failure);
• deficiency of the T-system of immunity and IgA synthesis;
• hyperreactivity of the bronchial mucosa;
• family history of bronchopulmonary diseases;
• disruption of the functional activity of alveolar macrophages and neutrophils

The listed “endogenous” risk factors, and possibly some other “biological defects”, are not among the obligatory (mandatory) mechanisms for the development of endobronchitis, but appear to be important predisposing factors that facilitate the pathogenic effects of tobacco smoke, volatile pollutants, and viral-bacterial infections on the bronchial mucosa.

The main links in the pathogenesis of chronic non-obstructive bronchitis are:

1. Irritating and damaging effects on the bronchial mucosa of tobacco smoke, volatile pollutants of household or industrial origin, as well as repeated viral and bacterial infections.
2. Hyperplasia of goblet cells of the bronchial glands, hyperproduction of bronchial secretions (hypercrinia) and deterioration of the rheological properties of mucus (dyscrinia).
3. Violation of mucociliary clearance, the protective and cleansing function of the bronchial mucosa.
4. Focal dystrophy and death of ciliated cells with the formation of “bald spots”.
5. Colonization of damaged bronchial mucosa by microorganisms and initiation of a cascade of cellular and humoral factors of mucosal inflammation.
6. Inflammatory edema and the formation of areas of hypertrophy and atrophy of the mucosa.

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