Early postnatal changes in intracranial arterial blood flow velocities in term infants.

A range-gated Doppler technique was used to assess intracranial arterial blood flow velocity changes in 20 healthy term infants during the first 3 days after birth. Systolic, diastolic, and mean flow velocity decreased during the first 30 min after birth whereas arterial pressure and heart rate did not change. Mean flow velocity did not change from 30 min to 72 h of life, although systolic and diastolic flow velocity changed in opposite directions. Systolic flow velocity increased to 2 h of age and thereafter decreased. Diastolic flow velocity decreased to a minimum value at 2 h and thereafter increased to 24 h of age. These flow velocity changes suggest an initial decrease in cerebral perfusion, followed by a constant cerebral blood flow during normal circulatory transition after birth.