Doppler flow characteristics in the main pulmonary artery and the LA/Ao ratio before and after ductal closure in healthy newborns.

Echo-Doppler (ED) techniques were used to estimate the time of closure of the ductus arteriosus in 30 normal neonates. We found that after birth there was a left-to-right (L-R) shunt through the ductus, which disappeared within 14 hours in 50% of the neonates investigated. Furthermore, patency of the ductus was not associated with a murmur. After closure of the ductus there was a significant diminution of the echocardiographically determined left atrium/aortic (LA/Ao) ratio, which was used as a measure of the L-R shunt.