Simultaneous laser-Doppler flowmetry of canine spinal cord and cerebral blood flow: responses to PaCO2 and blood pressure changes.

We observed the relative changes of both spinal cord blood flow (local SCBF) and local cerebral blood flow (local CBF) using independent laser-Doppler flowmeters (LDF) in 12 dogs under N2O(50%)-O2-enflurane(1.0%) anesthesia. The dorsal surface of the lumbar spinal cord and the parietal surface of the brain were partially exposed. Two fine LDF probes were placed between the exposed surfaces and the dura maters at each site. Both local SCBF and local CBF decreased simultaneously with hyperventilation and increased with hypoventilation within several seconds. The local SCBF responses to PaCO2 changes were similar in direction and degree as those of the local CBF. Autoregulation of local SCBF to arterial blood pressure (ABP) changes was abolished, though that of the local CBF was still recognized in a blunted fashion within a mean ABP range of 50 to 150 mmHg.