Effects of Progressive Hypoxia on Long Tract Neural Conduction in the Spinal Cord

: In this experiment, the vulnerability of long tract neural conduction in the spinal cord to progressive hypoxia was studied. The physiological integrity of nonsynaptic spinal cord conduction was monitored with the spinal evoked response (SER). Focal spinal cord blood flow was measured with the hydrogen clearance method. Progressive hypoxia was created by progressively increasing the amount of nitrogen in the inspired gas mixture. The SER was seen to fail only after extended periods of severe hypoxia. Multisynaptic cerebral condition monitored by the cerebral evoked response (CER) seemed more sensitive in the three animals in which both SER and CER were recorded. Spinal cord blood flow (SCBF) was not affected by progressive hypoxia until the PO2 was below 40 torr, and then the SCBF rose dramatically with further progression of the hypoxia.