Inter-relationships between spinal cord blood flow, neuronal death and neurological function in rabbit spinal cord ischemia.

Following rabbit spinal cord ischemia we measured histology, neurological outcome and spinal cord blood flow to investigate relationships between these quantities over a range of ischemia durations. Rabbits underwent reversible spinal cord ischemia induced by temporary aortic artery occlusion for zero to 65 min. In one cohort, surviving spinal cord cells were counted after 4 days of reperfusion using computer image analysis (n=23). Neurological outcome (paraplegic or non-paraplegic) was assessed in another group (n=381) after 18 h of reperfusion. A third group (n=8) had spinal cord blood flow measured by radioactive tracer immediately after ischemia. Histological analysis showed fewer motor neurons and astrocytes surviving as ischemia duration increased. Following 13 min (95% confidence interval (CI), 6 to 27) of ischemia 50% of low lumbar cord motor neurons remained alive; 50% of rabbits were paraplegic following 28.4 (26.7 to 30.0) min of ischemia; 28% (17% to 48%) of low lumbar motor neurons survived at this duration; 5% of rabbits were permanently paraplegic following 13.6 (10.6 to 16.1) min of ischemia, although only 52% (30% to 87%) of lower spinal cord motor neurons survived. Low lumbar cord blood flow was reduced to 2% of flow in non-ischemic thoracic cord after 25 and 60 min of ischemia (0.52 and 0.59 ml/100 g/min, respectively). These data support a fundamental hypothesis on which experimental ischemia is based: that substantial neuronal death follows directly from reversible ischemia and leads to permanent neurological deficit.