Effects of aortic occlusion on regional spinal cord blood flow and somatosensory evoked potentials in sheep.

Somatosensory evoked potentials (SEPs) were recorded continuously during aortic occlusion in sheep, with simultaneous measurement of spinal cord blood flow (SCBF) by radiolabeled microspheres. Aortic occlusion was associated with disappearance of the SEPs in seven of nine sheep in 7.8 +/- 4.1 (SD) minutes. SCBF at the time of initial cross clamping and 30 minutes after the onset of ischemia revealed a severe reduction in white and gray matter flow in the thoracolumbar cord. Release of the aortic clamp was associated with reactive hyperemia in these ischemic regions. In two animals, the SEP persisted during aortic cross clamping. The total SCBF in the thoracic and lumbar regions of these two animals exceeded 20 ml/100 g/min after 30 minutes of ischemia and was significantly greater than the flow recorded in sheep whose evoked response disappeared. The relation between spinal cord ischemia and evoked potential alterations is discussed in detail.