Cerebral blood flow velocity in term newborn infants: changes associated with ductal flow.

The effects of ductal closure on range-gated pulsed Doppler cerebral blood flow velocity (CBFV) patterns in the internal carotid, anterior cerebral, and middle cerebral arteries were studied in 10 normal term infants (mean birth weight 3302 +/- 294 g (SD) and mean gestational age 39.6 +/- 1.3 weeks). Pulsatility was calculated from flow velocities and used as an estimate of cerebral blood flow (CBF). Ductal closure was associated with a rise in mean blood pressure from 45.0 +/- 4.2 to 51.3 +/- 6.5 mm Hg (P less than 0.05) and a significant decrease in pulsatility in all three vessels (mean = 0.77 +/- 0.07 vs 0.70 +/- 0.05 (P less than 0.02]. Changes in pulsatility were correlated with changes in mean blood pressure (P less than 0.02), providing evidence that systemic blood pressure may influence postnatal cerebral arterial pulsatility indices. We also noted significant differences in the velocity and pulsatility of individual vessels that were independent of blood pressure, suggesting that Doppler flow studies may be useful in describing regional CBF patterns. The temporal association between ductal closure and decreased pulsatility suggests that CBFV patterns reflect ductal shunting in normal term newborn infants. Diastolic runoff and reduced systemic blood pressure in the presence of ductal shunting appear to reduce diastolic flow velocity and increase CBFV pulsatility in normal term infants during the first days of life. Normal mechanisms of cerebral autoregulation compensate for decreased flow with vasodilation; therefore the increased pulsatility associated with ductal shunting may be due to diastolic runoff rather than increased cerebrovascular resistance.