Phenotyping persistent pulmonary hypertension of the newborn: recognition of its persistence across world symposium on pulmonary hypertension classifications.

The earliest clinical sign of pulmonary vascular disease in neonates is persistent pulmonary hypertension of the newborn (PPHN), traditionally classified as World Symposium on Pulmonary Hypertension (WSPH) Group 1. Typical PPHN is defined by the delayed transition from intra- to extra- uterine life with failure of pulmonary artery pressures to fall after delivery. This results in sustained elevation of pulmonary vascular resistance and contributes to hypoxemic respiratory failure (HRF). However, early HRF can also arise from atypical PPHN phenotypes that may persist beyond the expected resolution of typical PPHN and are often classified within WSPH Groups 2, 3 and 5. In addition, a history of PPHN can be associated with the childhood and adulthood PH. In this perspective, we highlight the diverse etiologies contributing to the PPHN phenotype, with a focus on Group 3 disease, and propose a physiology-based framework to classify PPHN and delineate disease trajectories.