| Abstrakt: |
Developmental changes in regional cerebral blood flow (RCBF) were determined using radioactively labelled microspheres to measure flow to the cortex (Cx), brainstem (Bs), cerebellum (Cbl), white matter (WM), caudate nucleus (CN) and choroid plexus (CP) in 3 groups of chronically catheterised lambs under physiological and asphyxia, conditions: 90-100 day preterm fetal lambs, 125-136 day near-term fetal lambs and newborn lambs 5-44 days old. In all 3 groups the high flow areas are the CP and CN while the lowest flow area is the WM. There is a different heirarchy of RCBF in utero (Bs and Cbl > Cx) compared to extrauterine life in the newborn lamb (Cx and Cbl > Bs). Analysis of regional cerebral oxygen delivery demonstrated a progressively increasing oxygen transport to the Cx with increasing gestational maturity, and after birth. Oxygen transport to the Bs, Cbl and WM increased with gestational age, but did not increase after birth. RCBF measurements revealed significantly different responses to asphyxia in the 3 groups. With asphyxia, there were significant decreases in oxygen transport to all cerebral regions with the exception of the Bs in the preterm lamb, in contrast to the maintenance of oxygen delivery to the Bs, Cbl, Cx, CN and WM in the near-term and newborn lambs. The response of CBF to hypotension during asphyxia revealed that the preterm brain was the most vulnerable, while the near-term and newborn brains were able to autoregulate regional CBF except in the CP. These experiments demonstrate that maturity of the animal is an important determinant of the response to asphyxia. |
