The Section of Pulmonary Hypertension, Division of Cardiology, has been involved in the Pulmonary Hypoplasia Program (PHP) since its inception. Of our current 567 pediatric patients with pulmonary hypertension (PH), 51 percent have neonatal lung diseases as the primary etiology of the PH, many of whom are patients of the combined PHP. We are consulted on admission to assist in the diagnosis of cardiac diseases, heart failure and the evaluation and treatment of PH. In addition, we see all PHP children as outpatients and assist in managing the cardiac complications of lung hypoplasia.
Although the normal ranges of pulmonary artery pressures are lower in children than in adults, the current definition of pediatric PH is the same as in adults: a mean pulmonary artery pressure > 25 mm Hg with an increased pulmonary vascular resistance > 3 WUi and a normal left ventricular filling pressure. These values are greater than 2 standard deviations above the mean for children, and clearly define a pulmonary vascular bed that is high in resistance and low in the capacity to increase pulmonary blood flow if metabolically needed. This decrease in capacity is associated with right ventricular failure,
both the hallmark of PH and the principal cause of morbidity and mortality.
The presence of PH at 3 weeks of age is a significant predictor of survival in congenital diaphragmatic hernia Congenital diaphragmatic hernia (CDH). Dillon, et. al., published the survival of 47 CDH infants as a function of the presence of PH at 3 weeks: no PH, 100 percent survival; improved PH but not normal, 75 percent survival; and resistant PH, 100 percent mortality (J Pediatric Surgery, 2004). The recent CHOP data is better than this older data; however, the existence of PH clearly increases morbidity and mortality as well as increases the utilization of complex care. The sheer number of patients in our program has led to significant discoveries that have, in turn, led to improved survival and a lower incidence and severity of PH in children with lung hypoplasia.
It is important to understand that most PH in this population is not caused by vasoconstriction. It is not the classic persistent pulmonary hypertension of the newborn associated with prenatal insults as in meconium aspiration. Instead, lung hypoplasia, especially from CDH, is associated with PH because of four overlapping mechanisms: developmental arrest; abnormal myofibroblast proliferation and arteriolar occlusion; left ventricular diastolic dysfunction possibly associated with hypoplasia; and lastly, inflammatory lung destruction (from hyperoxia, ventilator shear forces, infection and/or micro-aspiration).
In addition to serial physical exams, our team utilizes serial B-type naturetic peptide to follow the right ventricular dysfunction that is inherent with PH. Echocardiograms and cardiac catheterization have a limited but important role in the ongoing assessment of neonatal PH, especially in those infants that require PH-directed therapies, as in sildenafil, endothelin-1 receptor antagonists and prostacyclin analogues.