Studies of experimental cervical spinal cord transection. Part III: Effects of acute cervical spinal cord transection on cerebral blood flow.

Regional cerebral blood flow (CBF) was measured by the microsphere technique in anesthetized, mechanically ventilated dogs before and after cervical laminectomy in four (control group), or cervical laminectomy followed by cervical cord transection (CCT) at the C-6 level in six (experimental group). No significant differences in arterial pH, pO2 or pCO2 were observed between control and experimental dogs. Baseline values for mean arterial pressure (MAP) were also similar in the two groups, but MAP fell in all experimental dogs after CCT (p less than 0.025). At 120 minutes after CCT, three of the six dogs had an MAP greater than 60 torr (66 +/- 4 torr), and in three the MAP was greater than 50 torr (45 +/- 3 torr). Regional CBF in cortical gray matter, white matter, and medulla did not change significantly after CCT in dogs with MAP greater than 60 torr. The CBF fell significantly at 120 minutes after CCT in all regions sampled in the dogs with MAP less than 50 torr (p less than 0.025). At 30 and 120 minutes after CCT, cerebellar blood flow fell significantly in all experimental animals (p less than 0.05). These findings indicate that, despite hypotension and sympathetic denervation of cerebral vessels, CBF in cortical gray matter, white matter, and medulla is maintained at normal levels after CCT by autoregulation as long as MAP exceeds 60 torr. Decreased cerebellar blood flow in the experimental group suggests redistribution of CBF after CCT with relative preservation of flow to gray matter, white matter, and medulla. Reduced CBF in the acutely cord-injured patient with significant hypotension (MAP less than 60 torr) may stimulate or complicate coexistent head injury.