Cardiopulmonary Adaptation During First Day of Life in Human Neonates

To characterize the natural history of cardiopulmonary physiology in the first 24 hours after birth.

A prospective observational study of healthy newborns was conducted at a large tertiary perinatal center. Echocardiography was performed at <0.5, 2-3, 7-10, and 22-24 hours of age. Specifically, assessment of pulmonary vascular resistance (PVR) (pulmonary artery acceleration time [PAAT], right ventricular ejection time, right ventricular ejection time:PAAT [PVR index], and PAAT indexed to heart rate [PAATi]), ventricular outputs (right and left), and ventricular function (tricuspid annular planar excursion, right ventricular [RV] fractional area change [FAC], RV/left ventricular [LV] global peak longitudinal strain, and LV ejection fraction) were performed. One-way repeated-measures ANOVA analysis was performed for time-dependent variables.

In total, 15 neonates (9 males), born at 40 ± 0.8 weeks and 3.5 ± 0.5 kg, respectively, were studied. We observed increased PAATi (P < .05) by 2-3 hours, followed by a subsequent decline in all indices of PVR (PVR index, PAATi, midsystolic notching, and right-to-left ductal flow [P < .0001]). Although right and left ventricular stroke volume increased over the study interval (P < .001), LV output remained stable. All indices of RV function (tricuspid annular planar excursion, RV fractional area change 4-chamber, and RV global peak longitudinal strain-3 chamber [P < .001]) increased during the study interval.

The immediate transition after birth is characterized by lower PVR, reversal of the transductal shunt, and increased biventricular stroke volume. The differential adaptive response of the RV and LV is novel and may relate to loading conditions and patent ductus arteriosus closure.