Compression of the spinal nerve roots often occurs at multiple levels simultaneously; however, the basic pathophysiology of multilevel compression is poorly defined. Using a thermal diffusion technique, Takahashi et al. 11 quantitated intraneural blood flow in the uncompressed segment between two compressive balloons in the porcine cauda equina. At 10 mm Hg compression, there was a 64% reduction of total blood flow in the uncompressed segment compared with precompression values. Total ischemia occurred at pressures 10 to 20 mm Hg less than the mean arterial blood pressure. After two-level compression at 200 mm Hg for 10 minutes, there was a gradual recovery of the intraneural blood flow toward the baseline. Recovery was less rapid and less complete after 2 hours of compression. Double-level compression of the cauda equina induced blood flow impairment, not only at the sites of compression but also in the intermediate nerve segments located between two compression sites, even at very low pressures.