Cor pulmonale: causes and pathogenesis

Causes of pulmonary heart disease

An acute pulmonary heart develops in a matter of minutes, hours or days as a result of massive pulmonary embolism, valve pneumothorax, a severe attack of bronchial asthma, and widespread pneumonia.

Subacute pulmonary heart arises during weeks, months and is observed with repeated small pulmonary embolism, nodular periarteritis, lung carcinomatosis, repeated attacks of severe bronchial asthma, botulism, myasthenia gravis, poliomyelitis.

The chronic pulmonary heart develops for several years. There are three groups of diseases that cause a chronic pulmonary heart.

1. Diseases affecting the airways and alveoli: chronic obstructive bronchitis, emphysema, bronchial asthma, pneumoconiosis, bronchiectasis, polycystic lung disease, sarcoidosis, pneumosclerosis, etc.
2. Diseases affecting the chest with limited mobility: kyphoscoliosis and other deformities of the chest, Bekhterev's disease, post-thoracoplasty condition, pleural fibrosis, neuromuscular diseases (poliomyelitis), paresis of the diaphragm, pikkvik syndrome with obesity, etc.
3. Diseases affecting pulmonary vessels: primary pulmonary hypertension, recurrent thromboembolism in the pulmonary artery system, vasculitis (allergic, obliterating, nodular, lupus, etc.), pulmonary atherosclerosis, compression of the pulmonary artery and pulmonary veins with mediastinal tumors, aortic aneurysm, etc.

Distinguish between the compensated and decompensated subacute and chronic pulmonary heart.

There are also bronchopulmonary (70-80% of cases), vascular and thoracodiaphragmatic forms of the pulmonary heart.

Bronchopulmonary form develops with chronic obstructive bronchitis, accompanied by the development of emphysema of the lungs and pneumosclerosis, with bronchial asthma, pulmonary tuberculosis and other lung diseases, both congenital and acquired character.

Vascular form occurs when the vessels of the small circle of blood circulation, vasculitis, thromboembolism of the pulmonary artery.

The thoracodiaphragmatic form develops with the initial lesions of the spine and thorax with its deformity, as well as in the Pickwick syndrome.

Further, a chronic bronchopulmonary pulmonary heart is discussed.

Pathogenesis of the pulmonary heart

Pathogenetic mechanisms are divided into functional and anatomical mechanisms. This unit is important, since the functional mechanisms are amenable to correction.

Functional mechanisms

Development of the Savitsky-Euler-Lilestrand reflex

In patients with chronic obstructive pulmonary disease, the syndrome of bronchial obstruction leads to vasoconstriction of small branches of the pulmonary artery, precapillaries (Savitsky-Euler-Lilslendar reflex). This reflex develops in response to alveolar hypoxia during hypoventilation of the central, bronchopulmonary or thoracodiafragmal origin. Particularly important is the violation of bronchial patency.

Normally, no more than y, alveoli are ventilated in healthy people, the rest are in a state of physiological atelectasis, which is accompanied by a reflex reduction of arterioles and a cessation of perfusion of blood in these zones, as a result of which the penetration of oxygenated blood into the large circle of blood circulation is prevented. In the presence of chronic bronchial obstruction, alveolar hypoventilation, the reflex becomes pathological, spasm of the majority of arterioles, precapillaries leads to an increase in resistance to movement of blood in a small circle of blood circulation, increased pressure in the pulmonary artery.

Increased minute blood volume

Reducing the oxygen tension in the blood causes irritation of the chemoreceptors of the aortic carotid zone, as a result, the minute volume of blood increases. Passage of increased blood volume through narrowed pulmonary arterioles leads to a further increase in pulmonary hypertension. However, at the initial stage of pulmonary heart formation, the increase in IOC is compensatory, as it helps to reduce hypoxemia.

Effect of biologically active vasoconstrictors

When hypoxia in tissues, including pulmonary, a number of biologically active substances (histamine, serotonin, lactic acid, etc.) that cause spasm of pulmonary arterioles and contribute to the growth of pressure in the pulmonary artery is released. Metabolic acidosis also contributes to vascular spasm. It is also expected to increase endothelial production of the vessels of the lung endothelin, which has a sharp vasoconstrictive effect, as well as thromboxane (produced by thrombocytes, increases platelet aggregation and has a strong vasoconstrictor effect). It is also possible to increase the activity of the angiotensin-converting enzyme in the endothelium of the pulmonary vessels, as a result of which the formation of angiotensin II increases, which leads to spasmodic pulmonary artery and pulmonary hypertension.

Insufficient activity of vasodilating factors

It is assumed that the endothelial relaxing factor (nitrogen oxide) and prostacyclin are inadequate. Both these factors are produced by endothelium, dilate blood vessels and reduce platelet aggregation. When these factors are deficient, the activity of vasoconstrictor substances increases.

Increased intrathoracic pressure, bronchial pressure

In obstructive lung diseases, the intrathoracic pressure significantly increases, which leads to compression of capillaries of the alveoli and contributes to increased pulmonary artery pressure. Increased intrathoracic pressure and pulmonary hypertension is also facilitated by an intense cough, so characteristic of chronic obstructive pulmonary diseases.

Development of bronchial-pulmonary anastomoses and dilatation of bronchial vessels

With pulmonary hypertension, there is an expansion of bronchial vessels and the development of bronchial-pulmonary anastomoses, the disclosure of arteriovenous shunts, which leads to a further increase in pressure in the pulmonary artery system.

Increase in blood viscosity

In the development of pulmonary hypertension, it is important to increase platelet aggregation, the formation of microaggregates in the microcirculation system, which contributes to increased pressure in the small branches of a.pulmonalis. Increased blood viscosity, a tendency to hypercoagulability due to erythrocytosis (due to hypoxia), increased production of thromboxane by platelets.

Frequent exacerbations of bronchopulmonary infections

These exacerbations cause, on the one hand, deterioration in pulmonary ventilation and aggravation of hypoxemia, and, consequently, a further increase in pulmonary hypertension, on the other hand, intoxication, which has an adverse effect on the state of the myocardium, contributes to the development of myocardial dystrophy.

Anatomical mechanism of pulmonary hypertension

The anatomical mechanism of the development of pulmonary hypertension is a reduction of the vascular bed of the pulmonary artery.

Anatomical reduction of the vascular bed of the pulmonary artery occurs as a result of atrophy of alveolar walls, their rupture with thrombosis and obliteration of part of arterioles, capillaries. Reduction of the vascular bed contributes to pulmonary hypertension. The appearance of clinical signs of the chronic pulmonary heart occurs when the total area of the pulmonary capillaries is reduced by 5-10%; a reduction of 15-20% leads to severe right ventricular hypertrophy; a decrease in the surface of the pulmonary capillaries, like the alveoli, by more than 30%, leads to decompensation of the pulmonary heart.

Under the influence of the above-mentioned pathogenetic factors, hypertrophy and dilatation of the right heart with the development of progressive circulatory insufficiency occur. It was found that the decrease in the contractile function of the right ventricular myocardium arises in obstructive forms of CSFN already at the early, transient stage of pulmonary hypertension and is manifested by a decrease in the right ventricular ejection fraction. In the future, as the pulmonary hypertension stabilizes, the right ventricle is hypertrophied and dilated.

Pathomorphology of the pulmonary heart

The main pathomorphological signs of a chronic pulmonary heart are:

• expansion of the diameter of the trunk of the pulmonary artery and its large branches;
• hypertrophy of the muscular layer of the pulmonary artery wall;
• hypertrophy and dilatation of the right heart.

[1], [2], [3], [4], [5], [6], [7]