Features of the course of secondary pulmonary hypertension in a child
Pulmonary arterial hypertension (PAH) is a heterogeneous, often multifactorial condition that can be either an independent, isolated pathology, or a complication of a wide range of diseases, including congenital heart defects, bronchopulmonary dysplasia (BPD), bronchial asthma, genetic and chromosomal diseases, diseases connective tissue and other pathology. According to various estimates, the prevalence of PAH in childhood is rare, approximately 2–16 cases per 1 million children. However, in some risk groups, this pathology occurs many times more often [1, 2]. A significant part, more than 30% of cases, PAH is associated with pathology of the respiratory system, including BPD [3, 4]. Admittedly, the prevalence of pulmonary hypertension is often underestimated. Usually it is regarded as a long-term dynamic process that can occur only in the late stages of chronic bronchopulmonary disease. The initial stage of PAH occurs with a small, often intermittent increase in pressure in the pulmonary artery, which does not require a significant increase in the work of the right ventricle and, as a rule, does not have early clinical manifestations [5, 6]. Therefore, the diagnosis of PAH in the initial stage depends on many factors, including the patient’s age, the severity of the concomitant pathology, the type of heart lesion, and, first of all, the knowledge of specialists about this pathology that occurs in early childhood.
In children of the first months of life, the leading place is given to secondary pulmonary hypertension . The most pronounced changes in pulmonary hemodynamics in infants, as a rule, are with BPD, chronic bronchiolitis, and other chronic obstructive pulmonary pathology [8–10].
In patients with BPD, pulmonary hypertension may be associated with intermittent chronic hypoxia, hypercapnia, damage to lung and airway tissue, diastolic dysfunction, vascular growth retardation, and pulmonary vein stenosis . One of the main causes is arterial hypoxemia due to hypoventilation. Pressure in the pulmonary artery depends on changes in pulmonary blood flow due to damage to the pulmonary endothelium. Endothelial dysfunction of these vessels leads to impaired synthesis of prostaglandins and prostacyclin, as well as to a marked increase in the production of thromboxane and endothelin-1 against the background of a significant decrease in the formation of nitric oxide. These disorders contribute to additional vasoconstriction, an increase in pulmonary vascular resistance, and PAH takes on a chronic character.
As described in the last century W.J. Northway et al. (1967), BPD can occur after prolonged mechanical ventilation (IVL) and oxygen therapy, mainly in premature infants. However, in recent years, against the backdrop of the successes and achievements of perinatology, the problem of nursing premature babies, especially those born with extremely low body weight (ENMT), has become even more urgent due to the high mortality rate in the neonatal period. In this period, in children with low birth weight, the risk of mortality is exacerbated by the development of diseases such as sepsis, congenital infections, pneumonia and BPD, the prevalence of which varies significantly, according to various sources, up to 30% among children who have mechanical ventilation long time . The incidence of BPD in newborns has an inverse correlation with body weight at birth and depends on the timing and modes of mechanical ventilation and oxygen therapy. I want to emphasize that in children with ENMT, the severity of changes in the cardiovascular system and BPD, as well as the progression of retinopathy, as a rule, are links of the same chain, which is based on deep morphofunctional immaturity of organs and systems.
In modern conditions, despite the optimization of the terms of mechanical ventilation, the rational use of surfactant, a high risk of mortality remains, due, in particular, to progressive pulmonary hypertension. Along with this, there are cases of PAH in which a less severe course of the disease can be achieved and, with timely corrective therapy, an outcome in the form of a significant improvement or even recovery. There is still a lack of data on an individual approach and the optimal management of children with pulmonary hypertension [1, 16]. All this determines the urgency of the problem of early diagnosis and adequate treatment of children with PAH on the background of BPD and congenital heart defects.