Immediate Hypertensive Response to Fluid Percussion Brain Injury May Be Related to Intracerebral Hemorrhage and Hypothalamic Damage

Fluid percussion brain injury is associated with an immediate rise in mean arterial pressure (MAP). However, the cerebral morphologic basis for this response is still not clear. Thirty-four anesthetized rats were injured using a lateral craniotomy preparation. In 19 rats, impact level was set at 1.73 +/- 0.04 atm, and impact duration was kept at 25 msec to examine the relationship between postinjury hypertensive response and cerebral lesions. MAP was monitored for 1 hour after impact. Fluid percussion produced an increase in MAP from 99 +/- 3 to 134 +/- 4 mm Hg (p < 0.001), with an increment range of -2 to 87 mm Hg (36 +/- 5 mm Hg) or 0 to 96% increase. The MAP peak occurred at 15 +/- 2 seconds and then rapidly returned to the preimpact level. Histopathological findings, principally hemorrhage, were graded and ranked from 1 to 19 according to relative severity and hypothalamic involvement. There was a significant correlation between MAP rise and the injury ranking (r = 0.52, p = 0.02). No appreciable damage was observed in the brainstem caudal to the diencephalon. Fifteen rats were subjected to higher injury levels. The overall impact magnitude ranged from 1.3 to 3.5 atm. A linear relationship was found between impact magnitude (X, atm) and increment in MAP (Y, mm Hg) (Y = 28.1*X - 14.0, r = 0.62, p < 0.001). Our study indicates that the immediate postinjury hypertensive response is closely correlated with the impact magnitude and may be related to intracerebral hemorrhage and hypothalamic damage but not necessarily to caudal brainstem damage.