DIFFERENT CEREBRAL HEMODYNAMIC-RESPONSES FOLLOWING FLUID PERCUSSION BRAIN INJURY IN THE NEWBORN AND JUVENILE PIG

The present study was designed to characterize the influence of early developmental changes on the relationship among systemic arterial pressure, cerebral hemodynamics, and cerebral oxygenation during the first 3 h following percussion brain injury. Anesthetized newborn (1-5 days old) and juvenile (3-4 weeks old) pigs equipped with a closed cranial window were connected to a percussion device consisting of a saline-filled cylindrical reservoir with a metal pendulum. Brain injury of moderate severity (1.9-2.3 atm) was produced by allowing the pendulum to strike a piston on the cylinder. Mean arterial blood pressure increased after brain injury in juveniles (68 +/- 4 to 93 +/- 2 mm Hg within 3 min, n = 6), whereas it decreased after injury in newborns (70 +/- 3 to 51 +/- 3 mm Hg within 3 min, n = 6). Fluid percussion brain injury decreased pial artery diameter more in newborns (132 +/- 5 to 110 +/- 5 mu m within 10 min, n = 5) than in juveniles (141 +/- 3 to 133 +/- 3 mu m within 10 min, n = 5). Pial arterioles constricted to a greater extent than small pial arteries following brain injury in both age groups. Within 30 sec, brain injury produced a transient increase in cerebral hemoglobin O-2 saturation (27 +/- 4%, n = 5) that was reversed to a profound decrease in cerebral hemoglobin O-2 saturation (45 +/- 2%, n = 5) in the newborn as measured by near infrared spectroscopy. In contrast, brain injury produced modest increases in hemoglobin O-2 saturation (10 +/- 1%, n = 5), followed by mild desaturation (4 +/- 1%, n = 5) in juveniles. Additionally, regional cerebral blood flow was reduced within 10 min of injury in both newborn and juvenile pigs and remained depressed for 180 min in newborns. In contrast, cerebral blood flow returned to control values within 180 min in juveniles. These data show that the effects of comparable brain injury level were very different in newborn and juvenile pigs. Further, these data suggest that reductions in cerebral blood flow following brain injury are more dependent on changes in reactivity of arterioles. Finally, these data suggest that the decrease in cerebral oxygenation, an index of metabolism, coupled with reduced cerebral blood flow, could result in profound hypoperfusion after brain injury.