Role in Pulmonary Vascular Pathology
Pulmonary vascular pathology accompanies a wide variety of diseases and includes several leading syndromes. In addition to pulmonary hypertension, this group includes pulmonary edema, acute respiratory distress syndrome (ARDS), and pulmonary embolism (PE). Hypertension itself is traditionally divided into two major categories: primary (idiopathic) and secondary, which develops against the background of pre-existing conditions. Regardless of the form, the key hemodynamic consequence is the overload of the right heart chambers.
Primary Pulmonary Hypertension Syndrome
The primary form is extremely rare in clinical practice. The main risk group includes children and women aged 20 to 40 years. Although the exact etiology remains unestablished, pathogenesis is associated with several probable factors:
- Autoimmune reactions. There is considerable evidence linking the syndrome to systemic diseases. Pulmonary arteriopathy frequently develops in patients with scleroderma, rheumatoid polyarteritis, Hashimoto's thyroiditis, and primary biliary cholangitis. In these cases, fibrinoid necrosis is detected within the walls of the pulmonary arteries.
- Genetics. The pathology is classified as a polygenic disease. Familial cases with both dominant and recessive inheritance patterns have been described in literature. Environmental factors are also not excluded.
- Hormonal influence. The association with hormones is supported by the fact that the disease frequently affects women of reproductive age, with pregnancy or oral contraceptive use acting as potential triggers.
- Congenital factors. The syndrome is frequently diagnosed in patients with congenital heart defects and anomalies of the pulmonary artery itself.
Morphological Features of the Primary Form
Macroscopic and microscopic changes strictly depend on the caliber of the affected vessels. Marked atherosclerosis develops in the large branches of the pulmonary artery. Simultaneously, medium- and small-caliber branches undergo fibrosis and significant muscular hypertrophy.
At the microscopic level, a specific symptom complex known as plexogenic pulmonary arteriopathy develops. The spectrum of these morphological changes strictly corresponds to the stages of disease progression:
- The process begins with muscularization of the pulmonary artery wall.
- Migration of dark muscle cells directly into the vascular intima occurs.
- Intimal cells actively proliferate and transform into myofibroblasts.
- Characteristic plexogenic structures are formed.
- Vessel walls undergo dilation, inevitably leading to the formation of microaneurysms.
- At the final stages, microaneurysms rupture, and fibrinoid necrosis develops in the tissue.
Secondary Pulmonary Hypertension Syndrome
The secondary form is always a complication of other pathological processes. Chronic lung diseases, chronic left ventricular heart failure, and repeated episodes of pulmonary embolism (PE) play a leading role in classical etiology. However, in recent years, the connection between secondary hypertension and the dynamics of chronic liver diseases and chronic viral infections has become increasingly relevant.
Morphological changes in lung tissue in secondary syndrome involve the development of pneumosclerosis—the pathological proliferation of connective tissue. Furthermore, if the disease is accompanied by venous congestion, pulmonary vasculitis, or embolism, hemosiderosis (deposition of an iron-containing pigment) joins the morphological picture.