Exploring Right vEntricular Function Applicability in a Prediction mOdel to Identify pReterm infanTs With Early BronchoPulmonary Dysplasia (REPORT - BPD Study): a Mixed Methods Observational Cohort Feasibility Study

RATIONALE The current research findings demonstrated a persistently elevated myocardial performance index of the right ventricle (RV) in the first two weeks of postnatal life (WoPL) in preterm infants with incipient BPD. The identification of the early myocardial dysfunction of RV that is associated with early pulmonary vascular disease (PVD) through echo scan examination in the first two WoPL can potentially serve as a marker for detecting preterm infants with an early BPD.

Data from 1,735 infants born between 23-30 weeks of gestational age (GA) showed that the proportion of preterm infants born < 31 weeks needing oxygen decreases from birth to the 7th day of postnatal life (DoPL). This is followed by a steep rise in the number of infants requiring oxygen in the same cohort at the start of the second week of postnatal life (WoPL). The number of preterm infants needing extra oxygen, peaks at the 14th DoPL. These studies indicate that the pathological pulmonary changes start as early as the first 10 DoPL. Furthermore, studies have identified the end of the first week of postnatal life (WoPL) and the beginning of the second WoPL as the time point when early respiratory problems start to surface. According to the vascular theory, the pathological processes affecting the pulmonary vascular bed are already happening before the appearance of the clinical signs associated with early BPD. The proposed study (REPORT-BPD) aims to capture the early burden exerted on the RV by early BPD and its associated pulmonary vascular changes through performing functional echo examinations at two time points, 5th and 9th day of postnatal life (DoPL) and utilising the findings to construct a prediction model.

To our knowledge, no study has used functional echo examinations to assess extra load or strain imposed by early BPD on the RV on the two time points (5th & 9th DoPL) in the first 10 DoPL.

The cardiac muscle of the preterm infant's heart has premature function. The premature heart reduced contractility is secondary to several reasons such as less myofibrils per cross-sectional area together with immature internal organisation. In addition, there is a lower number of β-adrenergic receptors and underdeveloped sympathetic nervous network. Furthermore, the underdeveloped intrinsic myocardial function following preterm birth is the result of abnormal right ventricle performance with remodelling after birth that persists in the first year of life.

Current research supports the vascular theory as the main pathophysiology of BPD i.e., the pathological process of BPD starts in the pulmonary vascular bed prior to the involvement of the parenchyma of the lungs. So, when the early BPD respiratory insufficiency starts to manifest clinically on 7th day of postnatal life, the adverse haemodynamic changes are already ongoing. In addition, the immaturity of the right ventricle (RV) will render the RV more sensitive to the extra burden imposed by the negative haemodynamic effects of early BPD causing worsening of the RV dysfunction.