Postnatal adaptation of brain circulation in preterm infants.

Global and regional postnatal cerebral circulatory changes in stable preterm infants were studied, and their relation to brain injury was assessed. Thirty-five preterm infants were studied on the first and second days of age. Cerebral blood flow (CBF) (mL/hg per min) and cerebral blood volume (CBV) (mL/hg) were measured using near-infrared spectroscopy. The cerebral blood flow velocity (cm/second) (peak systolic, diastolic flow, mean flow) and resistance index (RI) were determined in the internal carotid, anterior cerebral, and striate arteries by color Doppler flow imaging. Serial cerebral ultrasound studies were performed to detect changes in brain parenchymal echogenicity or intraventricular hemorrhage (IVH); the maximum severity of these findings was considered. CBF and cerebral blood flow velocity increased significantly with time, and such changes were independent of mean blood pressure, PO(2), PCO(2), hematocrit, or glycemia. In contrast, CBV and RI remained unchanged. According to the results of sonograms, no differences were found in postnatal CBF and cerebral blood flow velocity changes, regardless of whether patients had or did not have parenchymal lesions or IVH. However, higher CBV values were found on the second day in infants with IVH compared with infants without IVH. Early coupling of CBF and metabolic demands is independent of blood pressure. Improved venous return, instead of vasodilation, could be important in this adaptation.