CRITICAL LEVELS OF SPINAL-CORD BLOOD-FLOW AND DURATION OF ISCHEMIA FOR THE ACUTE RECOVERY OF SEGMENTAL SPINAL-CORD RESPONSES IN CATS

A broad range of residual lumbar spinal cord blood flows assessed by l aser-Doppler flowmetry (rSCBF, 0-78%) was achieved by snare occlusion of the descending aorta and additional blood-volume reduction for 1-10 min in spinal cats (n = 30; 238 trials). The period of complete refle x suppression (delay until recovery) that revealed some correlation to duration (r = 0.72) and depth (r = -0.36) of ischemia showed comparab le durations in mono-and polysynaptic reflexes, whereas it was signifi cantly less for the cord dorsum potential (CDP). With rSCBF values >50 -60% reflexes and >45%, the CDP was rarely abolished, irrespective of the duration of ischemia. The threshold of duration for a complete los s of reflex responses was found to be similar to 1 min of ischemia. Th e influence of rSCBF and duration of ischemia on the occurrence of inc omplete recoveries of reflexes was assessed simultaneously in a logist ic regression model. Compared with periods of ischemia of 3 min, all l onger durations showed a steep risk gradient for incomplete recoveries ; an increment of 10% in rSCBF led to a risk reduction for incomplete recoveries of nearly 25%. These findings were significant (p < 0.001) and indicated that blood-flow thresholds and limits for the developmen t of neurologic deficits of the spinal cord are comparable to those of the brain, with the important difference that the bloodflow reserve o f the spinal cord is smaller.