Study design: An in vivo study to measure rat spinal cord blood flow in real-time at the site of compression using a newly developed device.
Objectives: To evaluate the change in thoracic spinal cord blood flow by compression force and to clarify the association between blood flow recovery and motor deficiency after a spinal cord compression injury.
Summary of background data: Until now, no real-time measurement of spinal cord blood flow at the site of compression has been conducted. In addition, it has not been clearly determined whether blood flow recovery is related to motor function after a spinal cord injury.
Methods: Our blood flow measurement system was a combination of a noncontact type laser Doppler system and a spinal cord compression device. The rat thoracic spinal cord was exposed at the 11th vertebra and spinal cord blood flow at the site of compression was continuously measured before, during, and after the compression. The functioning of the animal's hind-limbs was evaluated by the Basso, Beattie and Bresnahan scoring scale and the frequency of voluntary standing. Histologic changes such as permeability of blood-spinal cord barrier, microglia proliferation, and apoptotic cell death were examined in compressed spinal cord tissue.
Results: The spinal blood flow decreased on each increase in the compression force. After applying a 5-g weight, the blood flow decreased to <40% of the precompression level. Complete ischemia was reached using a 20-g weight. After decompression, the blood flow level in the 20-minute complete ischemia group was significantly higher than that in the 40-minute complete ischemia group. The hind-limb motor function in the 40-minute complete ischemia group was significantly less than that in the sham group (without compression), while no significant difference was observed between the 20-minute ischemia group and the sham group. In the 20-minute ischemia group, the rats whose spinal cord blood flow recovery was incomplete showed significant motor function loss compared with rats that completely recovered blood flow. Extensive breakdown of blood-spinal cord barrier integrity and the following microglia proliferation and apoptotic cell death were detected in the 40-minute complete ischemia group.
Conclusion: Duration of ischemia/compression and blood flow recovery of the spinal cord are important factors in the recovery of motor function after a spinal cord injury.