Korean J Pediatr 2010;53(6):688-693 • DOI: 10.3345/kjp.2010.53.6.688 689 Table 1. Clinical Classification of Pulmonary Hypertension (Dana Point in 2008) 1. Pulmonary arterial hypertension 1.1 Idiopathic 1.2. Heritable 1.3. Drugs and toxins induced 1.4. Associated with 1.4.1. Connective tissue disease 1.4.2. HIV infection 1.4.3. Portal hypertension 1.4.4. Congenital heart disease 1.4.5. Schistosomiasis 1.4.6. Chronic hemolytic anemia 1’ Pulmonary veno-occlusive disease and/or pulmonary capillary Haemangiomatosis 2. Pulmonary hypertension due to left heart disease 2.1. Systolic dysfunction 2.2. Diastolic dysfunction 2.3. Valvular disease 3. Pulmonary hypertension due to lung diseases and/or hypoxia 3.1. Chronic obstructive pulmonary disease 3.2. Interstitial lung disease 3.3. Other pulmonary diseases with mixed restrictive and obstructive pattern 3.4. Sleep-disordered breathing 3.5. Alveolar hypoventilation disorders 3.6. Chronic exposure to high altitude 3.7. Developmental abnormalities 4. Chronic thromboembolic pulmonary hypertension 5. PH with unclear and/or multifactorial mechanisms patients. Development of PH in the BPD patients According to the classification of PH by the symposium at Dana Point in 2008, BPD is considered to be a class 3 disorder, which is PH with lung disease and/or hypoxia10) (Table 1). Although the exact pathophysiological characteristics of PH in the BPD patients is unknown, several mechanisms have been proposed. Abnormal lung circulation in the BPD patients, including both anatomical and physiologic abnormality, is related to the development of PH. The patients with BPD show reduction of small pulmonary arteries and an altered distribution of pulmonary arteries within the pulmonary interstitium11), which cause reduction of alveolar–capillary surface area. This reduction in surface area causes impairment of gas exchange and increases the requirement for prolonged oxygen and ventilator treatment, which in turn, raise the risk for severe PH. These pulmonary vascular changes, which are characterized by decreased vascular growth and structure, in preterm infants also contribute to the abnormal cardiopulmonary sequelae of BPD12). Physiologic abnormalities of lung circulation include increased vascular tone and reactivity, hypertensive remodeling, and decreased vascular growth12, 13). Previous studies using cardiac catheterization have shown that even mild hypoxia causes marked elevation of pulmonary artery pressure in the patients, including preterm infants with BPD14). To achieve normal gas exchange, the lung tissue must undergo continuous growth and maintenance of the complex system of airways and vessels. However, disruption of angiogenesis and inhibition of pulmonary vascular growth during a critical period of postnatal lung growth impairs pulmonary alveolarization, which contributes to BPD and increases the risk for PH15). Systemic-to-pulmonary collateral vessels, including prominent bronchial arteries, also contribute to PH development in the BPD patients. Significantly large collateral vessels may result in significant shunt f low to the lung and cause pulmonary congestion, ultimately requiring more ventilatory support and medications16). In some cases, patients showed improvement of PH after embolization of large collateral vessels and required less supplemental oxygen and ventilatory support12). Diagnosis of PH in the BPD patients Early detection of PH may lead to earlier treatment with more aggressive respiratory support and cardiac medications, including pulmonary vasodilators, and other procedures to improve the outcome in the BPD patients. However, the diagnosis of PH in BPD patients is difficult because manifested symptoms and signs of PH may be subtle and may sometimes overlap with those of respiratory problems or infection. In this respect, screening of PH in the BPD patients is necessary to decrease morbidity and mortality from PH. PH in the BPD patients is defined as a condition characterized by a mean pulmonary artery pressure greater than 25 mmHg and pulmonary capillary wedge pressure less than 15 mmHg on cardiac catheterization in the resting state10). Cardiac cathe- terization is the gold standard for the diagnosis of PH; however, since this procedure is very invasive and is not performed in all the centers with neonatal intensive care unit (NICU), other diagnostic tools are used for the evaluation of PH in the BPD patients. Electrocardiography (ECG) and echocardiography may be used as screening methods for PH in most centers with NICU. Although ECG can be easily performed, it is known to have low sensitivity and positive predictive value for the diagnosis of RV hypertrophy in the precordial leads reflecting PH. In a recent study, Puchaiski et al. also showed no significant relationship between ECG findings and echocardiographic estimation of pulmonary artery pressure17). Therefore, serial echocardiography, in spite of its several