Haruo Takano

Motor evoked potential monitoring during upper cervical spine surgery.

Motor evoked potential (MEP) produced by transcranlal electrical stimulation was recorded from an epldural electrode In 20 consecutive patients during upper cervical spine surgery. In 5 patients, transient attenuation to approximately 50% followed by complete recovery was observed, and no neurologic deficit was noted. One patient had complete loss of MEP and was left a respiratory quadriplegic. In 2 cases, MEP amplitudes increased after tumor extirpation and remarkable remissions were observed. The MEP correlated with clinical outcomes and was a useful monitoring technique for upper cervical spine surgery, free of complication. In cat experiments designed to analyze conducting pathways, the maximal amplitude of the initial spike of MEP existed In the ventromedlal spinal cord, which contains the extrapyramidal tracts. Motor evoked potential was proven to reflect motor function based on the spinal cord compression study.

Redundant Nerve Roots in Patients with Degenerative Lumbar Spinal Stenosis

Extensive fundamental and clinical investigations have been performed concerning redundant nerve roots (RNR) and the pathogenesis of cauda equina claudication (CEC) in degenerative lumbar canal stenosis (DLCS). These investigations consisted of (1) anatomic observations on RNR in 117 fixed cadaveric specimens, (2) myelographic study in 117 patients with or without DLCS, (3) operative observation on neural elements with special reference to the cauda equina in 56 DLCS patients (including a postoperative follow-up), and (4) electrophysiologic tests using spinal cord action potential recording under walking load preoperatively and intraoperative measurement of nerve conduction velocity of RNR. The RNR have neuronal losses resulting from a longer duration stenosis that suggests a sort of friction neuritis. Complicated factors contribute to the pathogenesis of CEC and the development of root gripping, such as the magnitude of RNR, the extent of the stenosis, a narrowed sac, age-dependent axial shortening of the spinal canal, and dynamic or postural factors. In cases with severe RNR, satisfactory operative results can be obtained only after thorough decompression with dural incision.

Intracortical facilitation and inhibition after paired magnetic stimulation in humans under anesthesia

The evoked spinal cord potential (ESCP) and the evoked compound muscle action potential (ECMAP) after paired transcranial magnetic stimulation were recorded simultaneously in eight subjects undergoing spine surgery. The ESCP was composed of a short-latency initial wave (D-wave) followed by later waves (I-waves). The mean conduction velocity of each wave was approximately 60 m/s. The interstimulus interval (ISI) affected the amplitude of both ESCP and ECMAP; the amplitude was inhibited at short ISIs (2 ms and 5 ms), was facilitated at ISI of 10 ms, and was inhibited again at longer ISIs (50 ms, 100 ms and 200 ms). The changes in later I-waves were prominent compared to the stable D-wave. These results suggest that transcranial magnetic stimulation alters the excitability of the motor cortex by affecting synaptic transmission in corticomotor (CM) neurons. The inhibition of the motor cortex at longer ISIs may contribute to a silent period following transcranial magnetic stimulation.

Magnetic-evoked compound muscle action potential neuromonitoring in spine surgery

Study Design. Muscle action potentials elicited by paired transcranial magnetic stimulation were recorded during spine surgery in 34 patients. Anesthesia was based on ketamine and fentanyl. Objectives. To evaluate the optimal anesthetic regimen to be used for transcranial magnetic stimulation, and to determine the clinical import of magnetic evoked compound muscle action potentials. Summary of Background Data. Muscle action potential by transcranial magnetic stimulation has been difficult to record under general anesthesia. Ketamine is known to not suppress the muscle responses, although no conclusive clinical study has been reported. Methods. Paired transcranial magnetic stimulation was delivered as muscle action potentials were recorded from the limb musculature. Results. Neuromonitoring was reliable in 55% of total cases and in 82% of the recent cases after reducing fentanyl dosage. Paired magnetic stimulation was an excellent facililtation technique for reliable monitoring. At higher dosages, fentanyl and ketamine decreased the reproducibility of the responses. Conclusions. Magnetic-evoked compound muscle action potential neuromonitoring is a sensitive and selective motor pathway monitoring method that covers the entire motor pathway, including the white and gray matter of the spinal cord. Ketamine-based anesthesia is a good choice for this purpose.

Monitoring for spinal cord ischemia by use of the evoked spinal cord potentials during aortic aneurysm surgery

PURPOSE This clinical study was to evaluate changes of evoked spinal cord potentials (ESCPs) elicited by direct spinal cord stimulation and to determine their relation to spinal cord ischemia during aortic aneurysm surgery. METHODS We monitored descending ESCPs from the thoracic spinal cord and lumbar enlargement after cervical spinal cord stimulation (thoracic descending ESCP and lumbar descending ESCP), and segmental ESCP at lumbar enlargement elicited by bilateral tibial nerve stimulation in 22 aortic aneurysm surgical operations. RESULTS ESCP changes were classified into three types: (1) decrease of amplitude in lumbar descending ESCP and segmental ESCP; (2) decrease of amplitude in segmental ESCP alone; (3) decrease of amplitude in all ESCPs. The late negative waves of both lumbar descending ESCP and segmental ESCP were more sensitive than other components of ESCPs. Postoperative paraplegia occurred in the two cases that showed persistent diminution of amplitude in the late negative waves. Segmental ESCP was less reliable than lumbar descending ESCP, because it depended entirely on the adequate perfusion of the lower extremities. CONCLUSIONS Lumbar descending ESCP was the best method for the spinal cord ischemia during aortic aneurysm surgery. Spinal cord ischemia could be detected by diminution in the amplitude of the late negative wave of lumbar descending ESCP. The recovery amplitude of the late negative wave after declamping correlated with the neurologic outcome.

Changes of evoked action potentials and histology of the spinal cord, and hind limb dysfunction in spinal cord ischemia of cats.

The electrophysiological, neurological, and neuropathological correlates of the spinal cord ischemia induced by the aortic cross-clamping of cats were studied with the goal of developing the reliable evoked spinal cord potentials (ESCPs) for the monitoring of spinal cord ischemia. The five types of ESCPs were elicited as follows; descending ESCPs recorded from the L2 and L5 vertebral levels, vertex motor evoked potential from the L2 vertebral level, ascending ESCP from the T1 vertebral level, and segmental ESCP after sciatic nerve stimulation. The late negative waves of both descending ESCP from L5 and segmental ESCP were susceptible to ischemia. The descending ESCP from L5 was not influenced by peripheral nerve ischemia or reflected ischemia in the whole spinal cord. Therefore, the late negative wave of the descending ESCP from L5 served as the most reliable index for spinal cord ischemia. When aortic clamping was continued for > or = 30 min after the disappearance of the late negative wave of descending ESCP from L5, the amplitude recovery of this wave decreased to 25%, resulting in paraplegia. Histologically, the posterior horn of the gray matter in the lumbar enlargement was the most vulnerable to ischemia.

Vibrational damper for cables of the Tsurumi Tsubasa Bridge

Abstract The Tsurumi Tsubasa Bridge, one of the main bridges in the Metropolitan Expressway Bay-shore route, is a 1020m long, single plane, 3-span continuous cable-stayed bridge with a 510 m center span. For the cables of this bridge, a new countermeasure, the combined use of highly damping rubber (HDR) and dampers, was adopted to reduce wind-induced vibrations and additional stress caused by live load. This countermeasure can make the installation position of dampers lower from the deck level than the conventional method using combination of rubber and dampers. Therefore it is superior in terms of ease of installation and maintenance, and design. Its effectiveness was confirmed in vibration tests and field observations.

Effects of coil orientation and magnetic field shield on transcranial magnetic stimulation in cats.

To obtain suitable stimulus conditions for transcranial magnetic stimulation, the evoked compound muscle action potential (ECMAP), evoked spinal cord potential (ESCP), and magnetic and electric fields were analyzed in cats with and without the use of a magnetic field shield. Cats were stimulated using a figure 8 magnetic coil placed on the cranium above the motor cortex. The maximum ECMAP amplitude was recorded when the electric current in the coil was in the mediolateral direction, regardless of whether a magnetic shield with a 5 × 5 cm window was used. ECMAP and ESCP thresholds were reduced when magnetic shielding was in place. Due to the edge effect, the strengths of the magnetic and electric fields were highest in the brainstem area, which is an inhomogeneous volume conductor of the cats cranium. A large induced electric field directed caudally elicited ECMAP and ESCP responses effectively when a magnetic shield with a 5 × 5 cm window was in place.

Effects of systemic or spinal cord cooling on conductive spinal evoked potentials

To elucidate the mechanism of alterations of spinal evoked potentials after hypothermia, the effects of systemic and local cooling on conductive spinal evoked potentials were studied in cats. Conductive spinal evoked potentials were recorded from the L1 epidural space after epidural stimulation at the T4 level and during concomitant reduction of body temperature followed by rewarming. On local cooling and rewarming of the stimulating area or the recording area, conductive spinal evoked potentials changes were also analyzed. Systemic cooling provoked an increase in latency, duration, and amplitude as the body temperature decreased. Evoked potentials were not changed by the local cooling of the stimulating area. Thus, the evoked potentials changes of the spinal cord suggest that spinal cord cooling does not influence the stimulus threshold, but may affect the interaction between the amplitude change and the duration in individual spike potentials, and produces changes in temporal dispersion.

Origins and Conducting Pathways of Motor Evoked Potentials Elicited by Transcranial (Vertex-Hard Palate) Stimulation in Cats

Spinal cord evoked potentials were elicited in cats by transcranial electrical stimulation with electrodes on the vertex and hard palate. Vertex motor evoked potentials (V-MEP) were also recorded. An extracellular microelectrode recording technique was then used to analyze the results by isopotential mapping. The relationship between the distribution of field potentials and the stimulation polarity was studied using the field potential distribution of the V-MEP in the lower thoracic spinal cord that had been represented on the isopotential maps. The first negative wave of the V-MEP showed maximal amplitude distribution in the anterior funiculus, which corresponds to the extrapyramidal tracts. This pattern was seen with both stimulation polarity arrangements: 1) stimulation with the cathode at the vertex and the anode at the hard palate, and 2) stimulation with the anode at the vertex and the cathode at the hard palate. When the cathode was at the vertex, the stimulation threshold was lower, and the response had higher amplitude than when the anode was at the vertex. Recording V-MEPs elicited by vertex cathode stimulation could provide an excellent method of monitoring the extrapyramidal tracts in cats.