Canine cerebral function and blood flow after complete cerebral ischemia: effect of head position.

It has been reported that animals exposed to relatively "bloodless" cerebral ischemia have improved cerebral function post-ischemia. This suggests the possibility that large variations in cerebral blood volume during complete ischemia might affect outcome following reperfusion. The purpose of this study was to determine whether changes in dog head position (and therefore cerebral blood volume) during complete cerebral ischemia produced by occluding the aorta and venae cavae affect post-ischemic cerebral blood flow (CBF), cerebral metabolic oxygen requirements (CMRO2), or neurologic outcome. Two dogs were transfused with 111In-labeled red blood cells. Gamma camera images taken during complete cerebral ischemia showed 45-degree head-up dogs to have 30% of the cranial blood volume of a 10-degree head-down dog. CBF and CMRO2 90 min post-ischemia were not significantly different between the head-up and head-down groups in the 14 dogs studied. There was also no significant difference in neurologic outcome at 48 h post-ischemia between head-up and head-down dogs. The authors conclude that head position during complete cerebral ischemia has a major effect on cranial blood volume, but no effect on post-ischemic CBF, CMRO2, or neurologic outcome.