FLUID-PERCUSSION BRAIN INJURY ADVERSELY AFFECTS CONTROL OF VASCULAR TONE DURING HEMORRHAGIC-SHOCK

To test the hypothesis that brain injury impairs control of vascular t one during compensation from hemorrhagic shock, Sprague-Dawley rats un derwent fluid-percussion brain injury (or sham injury control) followe d by a stepwise hemorrhage period to 1/2 baseline mean arterial pressu re (1/2 MAP), a shock period holding at 1/2 MAP for 30 min, and a resu scitation period. Aortic blood flow (ABF) was measured and vascular co nductance (ABF/MAP) was calculated, No differences occurred between gr oups during the stepwise hemorrhage period. During the 30 min shock pe riod, controls decreased conductance from .2 +/- .07 to .16 +/- .04 an d required repeated additional hemorrhage (3.4 +/- 1.3 cc) to maintain 1/2 MAP, In contrast, brain-injured animals increased conductance fro m .21 +/- .07 to .24 +/- .06 (p < .05) during the shock period and req uired repeated fluid replacements (3.0 +/- 1.3 cc lactated Ringer's (L R), p < .05) to maintain 1/2 MAP. Following resuscitation, conductance appropriately increased to .31 +/- .05 in controls but did not change (.25 +/- .04, p < .05) in brain-injured animals. We conclude that bra in injury adversely affects control of vascular tone during shock and resuscitation in this model.