Neuropathologic consequences of internal carotid artery occlusion and hemorrhagic hypotension in baboons

We studied eight anesthetized and physiologically monitored adult baboons (Papio cyanocephalus); four were subjected to hemorrhagic hypotension alone and four to hemorrhagic hypotension plus unilateral carotid artery occlusion. Cerebral blood flow was measured using xenon-133, the electroencephalogram was recorded using silver-silver chloride epidural electrodes, and histologic examination was carried out after perfusion-fixation. In the baboons subjected to hypotension alone (mean arterial blood pressure of 28 mm Hg) cerebral blood flow was 28.5 +/- 5.0 ml/100 g/min, whereas in the baboons subjected to hypotension plus unilateral carotid artery occlusion it was 21.8 +/- 1.8 ml/100 g/min at a mean arterial blood pressure of 27 mm Hg. There was no ischemic damage in the former group, but in the latter group there was necrosis in the arterial boundary zones of three baboons and in the distribution of the middle cerebral artery in one. We conclude that, when combined with hypotension, unilateral carotid artery occlusion may lead to hemodynamic ischemia accentuated in the arterial boundary zones of the ipsilateral cerebral hemisphere.