Postnatal changes of cerebral blood flow velocity in normal term neonates

Postnatal changes of cerebral blood flow velocity were studied in 43 healthy term neonates using a continuous waveform bidirectional Doppler flowmeter and an ultrasonograph with a pulsed Doppler unit. Pulsatility Index (PI) values of anterior cerebral artery were high within 6 hours after birth, and then decreased in the neonates born by means of both vaginal delivery and caesarean section. These postnatal changes of PI observed with the continuous waveform bidirectional Doppler flowmeter were identical with those with pulsed Doppler technique. The sequential measurement of right radial artery blood flow showed a marked decrease of diastolic flow velocity, which may be due to transient postnatal patent ductus arteriosus. Therefore, this postnatal transient patent ductus arteriosus may be one of the pathogenetic factors for high PI values shortly after birth.