Ductal left-to-right flow and pulmonary circulation in normal neonates: pulsed Doppler echocardiographic evaluation

To determine whether ductal left-to-right flow affects pulmonary circulation in the neonatal period, ductal patency and flow patterns of the right ventricular outflow tract were studied using Doppler echocardiography in 40 normal neonates. The ductus arteriosus was defined as being patent when diastolic or continuous flow could be detected at the pulmonary end of the ductus. Evaluation of pulmonary circulation was carried out by examining the flow velocity pattern of the right ventricular outflow tract; pulmonary hypertension was considered to be present when the Doppler echocardiogram pattern was triangular with peak velocity in early systole. Neonates were initially examined within nine hours (mean 5.3 hrs) after birth, and two to three times daily thereafter, until no ductal flow could be detected. In all the neonates, the ductus arteriosus was patent at the initial examination. The predicted time of closure of the ductus arteriosus was within seven hours after birth in 5% of the neonates, within 21 hours in 50%, and within 65 hours in 95%. The flow velocity pattern of the right ventricular outflow tract changed from a triangular shape with peak velocity in early systole soon after birth to a dome-like contour with peak velocity in mid-systole: thus the mean ratio of acceleration time to right ventricular ejection time increased with age. In neonates with patent ductus arteriosus at age 13.6-20.7 hours, the mean ratio of acceleration time to right ventricular ejection time was less than in age-matched neonates with closed ductus arteriosus. These results indicate that the ductal left-to-right flow affects the pulmonary circulation.