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We induced ischemia and stretching by retraction of the spinal cord after laminectomy in 12 anesthetized mongrel adult cats, recorded spinal motor evoked potential (SpMEP) and spinal somatosensory evoked potential (SpSSEP) and determined the spinal cord blood flow (SCBF). The results showed a correlation between progressive deterioration of the function and a decrease in SCBF. Comparing the abnormal findings of both the peak and interpeak latencies in evoked potentials, useful data were more frequently obtained using SpSSEP than SpMEP. Factors involved in their deteriorations seem to be a moderate ischemia by compression, and a stretching by the retraction of the spinal cord. From these results, we conclude that SCBF and SpSSEP are important for monitoring the impulse propagation during retraction of the cervical cord.

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We attempted to examine intracranial pressure (ICP) noninvasively using probes receiving interference echoes of ultrasound from thin layers between the skull and the surface of the cerebrum. The reception of echo through bone flaps less than 5-mm thick was good. Normal adults (4) and patients (4) were examined by attaching ultrasound probes to the frontotemporal scalp. Recordings were performed during rest, Valsalva maneuver, hyperventilation, and pumping of a shunt-flushing device. Ultrasound recordings of ICP were compared with those of the scalp using two different time windows. The effect of scalp vessels on the ultrasound recordings of ICP was evaluated. The waves from a pressure transducer and the ultrasound probe were similar. This method was found to be useful for ICP recording.