AC Yao, M Martinussen, AM Brubakk, TD Yanowitz, BS Stonestreet

We studied the early postnatal changes in the intestinal and cerebral circulations of term infants, preterm infants of gestational age 33-35 weeks and very low birth weight (VLBW) infants of gestational age 24-31 weeks and related these changes to the transitional systemic haemodynamics. ECHO-Doppler blood flow velocity of the superior mesenteric and middle cerebral arteries and cardiac output were measured sequentially from the first hours of life to day 7-14. Patency of ductus arteriosus (PDA), heart rate and blood pressure were also monitored. Feeding responses were assessed by pre- and postprandial measurements.

The mesenteric blood flow velocity in term infants decreased from birth to 2-6 hours owing to ductal steal. This was associated with high cardiac output and low blood pressure. The mesenteric blood flow velocity regained birth levels by 24 hours with closure of PDA; it increased on day 3-5 after feeding was established. In contrast, PDA did not affect cerebral blood flow velocity, which remained unchanged in the first 24 hours, then increased on day 3-4. Feeding increased mesenteric blood flow velocity but did not change cerebral blood flow velocity, cardiac output, heart rate or blood pressure. In preterm infants, mesenteric and cerebral blood flow velocity showed similar changes as in the term infants from birth. However, a higher end diastolic mesenteric blood flow velocity was seen from day 3-7. Feeding induced similar increases in mesenteric blood flow velocity as in term infants but was accompanied by increased cardiac output and a fall in blood pressure. In VLBW infants, mesenteric blood flow velocity did not change during the first 54 hours of life, then increased by 54% from 3 to 14 days, coincident with the start of feeding. Postprandial increases occurred as in preterm infants. In contrast, cerebral blood flow velocity increased 71% from 6 to 54 hours of life with no further changes from 3-14 days. Their cardiac output and heart rate increased over the first 14 days of life. No VLBW infants had symptomatic PDA but they were given indomethacin for prophylaxis of intraventricular haemorrhage. We conclude that during the transitional circulatory adaptation after birth, haemodynamic changes are region specific and dependent on developmental age.