Cortical Somatosensory Evoked Potentials Research Articles

P328 Not only the absence but also amplitude reduction of cortical SEPs predict ominous outcome in comatose patients after cardiac arrest

In comatose patients after cardiac arrest (CA) bilateral absence of cortical SEPs is a high reliable predictor of poor outcome but it is present in no more than 40% (1). Low amplitude pathological SEPs were found in 28.9% (2) of subjects but only few papers analysed the prognostic significance of this pattern (3–4). To evaluated prognostic value of N20-P25 amplitude of SEPs, recorded at 6–12 h after CA. Retrospectively, we analysed comatose patients after CA admitted to our hospital. SEPs were recorded at 6–12 h after CA. We determined the lowest SEP amplitude in a subject that recovery consciousness We evaluated the accuracy of SEP amplitude in predicting the “no consciousness recovery” by ROC curves. Outcome was evaluated at 6 months by GOS. One-hundred and eighteen patients were analysed. None of subjects with N20-P25 amplitude less than 1.2 mV recovered consciousness. The area under the ROC curves was 0.96 for “no consciousness recovery”. SEP amplitude threshold determined by ROC analysis was 1.21 mV. For this SEP amplitude threshold, we found a sensibility: 85.9% and specificity: 100.0%. Not only the absence but also the amplitude reduction (less than 1.2 mV) of N20-P25 is associated with no consciousness recovery with very high predictive value.

Epidermal Electrode Technology for Detecting Ultrasonic Perturbation of Sensory Brain Activity.

We aim to demonstrate the in vivo capability of a wearable sensor technology to detect localized perturbations of sensory-evoked brain activity. Cortical somatosensory evoked potentials (SSEPs) were recorded in mice via wearable, flexible epidermal electrode arrays. We then utilized the sensors to explore the effects of transcranial focused ultrasound, which noninvasively induced neural perturbation. SSEPs recorded with flexible epidermal sensors were quantified and benchmarked against those recorded with invasive epidural electrodes. We found that cortical SSEPs recorded by flexible epidermal sensors were stimulus frequency dependent. Immediately following controlled, focal ultrasound perturbation, the sensors detected significant SSEP modulation, which consisted of dynamic amplitude decreases and altered stimulus-frequency dependence. These modifications were also dependent on the ultrasound perturbation dosage. The effects were consistent with those recorded with invasive electrodes, albeit with roughly one order of magnitude lower signal-to-noise ratio. We found that flexible epidermal sensors reported multiple SSEP parameters that were sensitive to focused ultrasound. This work therefore 1) establishes that epidermal electrodes are appropriate for monitoring the integrity of major CNS functionalities through SSEP; and 2) leveraged this technology to explore ultrasound-induced neuromodulation. The sensor technology is well suited for this application because the sensor electrical properties are uninfluenced by direct exposure to ultrasound irradiation. The sensors and experimental paradigm we present involve standard, safe clinical neurological assessment methods and are thus applicable to a wide range of future translational studies in humans with any manner of health condition.

O135 Sensory evoked potentials and central motor conduction times in children with dystonia help predict outcomes from Deep Brain Stimulation (DBS)

Objectives Deep Brain Stimulation (DBS) of the Globus Pallidus Internus produces dramatic benefits in primary dystonia. Improvements in patients with secondary dystonia are smaller and vary markedly between individuals. Predictive markers are lacking. This study tests the hypothesis that Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) may predict outcome from DBS in childhood dystonia. Methods Data were obtained from 180 consecutive children with dystonia undergoing multidisciplinary assessment for DBS (mean age 10 years; range 2.5–19). CMCT to each limb was obtained using Transcranial Magnetic Stimulation and the F-wave method. Median and posterior tibial nerve SEPs were recorded over contralateral and midline centro-parietal scalp. Technically unsatisfactory data were excluded. Structural abnormalities were assessed with cranial MRI. Outcome from DBS at 1 year was assessed as percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m). Results Satisfactory CMCT data were obtained from 146 children, of whom 28 (19%) had an abnormal CMCT to at least one limb. Satisfactory cortical SEP data were obtained from 100 children, of whom 47 had at least one abnormal cortical potential. Abnormal CMCTs and SEPs were both observed more frequently in secondary than primary/primary plus dystonia (CMCT abnormal in 22% secondary versus 9% primary patients; SEP abnormal in 53% secondary vs 24% primary patients). Of children proceeding to DBS, improvement in BFMDRS-m was greater in those with normal (n = 78) than abnormal CMCT (n = 11) (Mann Whitney test p = 0.002) and was also greater in those with normal (n = 35) versus abnormal SEPs (n = 16) (Mann Whitney test p = 0.001). On sub-group analysis, the relationships between CMCT/SEPs and BFMDRS-m scores were independent of aetiology (primary versus secondary) and MRI findings (normal versus abnormal). Discussion/Conclusion CMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia and relate to DBS outcome. These markers may therefore contribute to patient selection and counselling of families about potential benefit from neuromodulation. Significance We identify neurophysiological markers that can guide the selection of patients for DBS.

S111 Brain reorganization following the use of robotic hand prosthesis in four amputees

The amputation of a hand (as of any other body part) is followed by a cascade of plastic changes on the motor and somatosensory pathways; such changes are probably contributing to the Phantom limb syndrome, a distressing situation affecting the vast majority of amputees. Although many effort, a clear explanation of the phantom syndrome is still missing and it could be considered the result of multiple contributing mechanisms acting both at peripheral and central nervous system. The typical feature of cortical plastic reorganization following limb amputations is the invasion of the “deafferented” cortex by neighbouring areas in both the primary somatosensory and the motor cortices. The degree of cortical reorganization was directly related to the magnitude of pain: the greater the remapping, the more severe the pain. On the other side, some novel evidences indicate the persistence of a certain degree of functionality of the somatosensory and motor cortices corresponding to the amputated part and recent evidences showed a correlation between the amount of functional persistence and phantom limb pain, more persistence causing more phantom limb pain. Moreover, it was recently suggested a link between this hypotheses and the aberrant peripheral activity characterized by ectopic evoked and spontaneous nerve activity. Almost all previously cited evidences are the results of non-longitudinal studies, where one or more groups of patients are analysed in a resting situation. Very few information are reported in literature explaining how plastic changes evolve during the use of prosthesis and this is particularly true considering new prototypes of bidirectional neurally hand prosthesis. These implanted neural interfaces for the peripheral nervous system have shown a remarkable potential as tools to restore the bidirectional communication between the hand prosthesis and the nerves in the residuum. In the frame of European founded projects we assessed neuroplastic changes of brain sensorimotor organization (through the assessment of cortical SEPs, MEPs, EEG source analysis, connectivity analysis and fMRI) following the use of a robotic hand during trainings of different durations (4–24 weeks) in four human amputees, providing new advancements in the understanding of the complex phenomena of phantom limb syndrome.

Effects of 12 Weeks of Chiropractic Care on Central Integration of Dual Somatosensory Input in Chronic Pain Patients: A Preliminary Study

ObjectiveThe purpose of this preliminary study was to assess whether the dual somatosensory evoked potential (SEP) technique is sensitive enough to measure changes in cortical intrinsic inhibitory interactions in patients with chronic neck or upper extremity pain and, if so, whether changes are associated with changes in pain scores. MethodsThe dual peripheral nerve stimulation SEP ratio technique was used for 6 subjects with a history of chronic neck or upper limb pain. SEPs were recorded after left or right median and ulnar nerve stimulation at the wrist. SEP ratios were calculated for the N9, N13, P14-18, N20-P25, and P22-N30 peak complexes from SEP amplitudes obtained from simultaneous median and ulnar stimulation divided by the arithmetic sum of SEPs obtained from individual stimulation of the median and ulnar nerves. Outcome measures of SEP ratios and subjects’ visual analog scale rating of pains were recorded at baseline, after a 2-week usual care control period, and after 12 weeks of multimodal chiropractic care (chiropractic spinal manipulation and 1 or more of the following: exercises, peripheral joint adjustments/manipulation, soft tissue therapy, and pain education). ResultsA significant decrease in the median and ulnar to median plus ulnar ratio and the median and ulnar amplitude for the cortical P22-N30 SEP component was observed after 12 weeks of chiropractic care, with no changes after the control period. There was a significant decrease in visual analog scale scores (both for current pain and for pain last week). ConclusionThe dual SEP ratio technique appears to be sensitive enough to measure changes in cortical intrinsic inhibitory interactions in patients with chronic neck pain. The observations in 6 subjects revealed that 12 weeks of chiropractic care improved suppression of SEPs evoked by dual upper limb nerve stimulation at the level of the motor cortex, premotor areas, and/or subcortical areas such as basal ganglia and/or thalamus. It is possible that these findings explain one of the mechanisms by which chiropractic care improves function and reduces pain for chronic pain patients.

Somatosensory Evoked Potentials in Patients with Hypoxic-Ischemic Brain Injury.

Predicting the future of patients with hypoxic-ischemic encephalopathy after successful cardiopulmonary resuscitation is often difficult. Registration of the median nerve somatosensory evoked potential (SSEP) can assist in the neurologic evaluation in these patients. In this article, the authors discuss the principles, applications, and limitations of SSEP registration in the intensive care unit, with a focus on prognostication. Registration of the SSEP is a very reliable and reproducible method, if it is performed and interpreted correctly. During SSEP recordings, great care should be taken to improve the signal-to-noise ratio. If the noise level is too high, the peripheral responses are abnormal or the response is not reproducible in a second set of stimuli; therefore, interpretation of the SSEPs cannot be done reliably. A bilaterally absent cortical SSEP response is a very reliable predictor of poor neurologic outcome in patients with HIE. It has a high specificity, but a low sensitivity, indicating that present cortical responses are a weak predictor of a good recovery. Further research is being done to increase the sensitivity. Somatosensory evoked potentials can be used in a multimodal approach for prognostication of outcome.

Analysis of the tremor in juvenile myoclonic epilepsy

PurposeWe aimed to investigate juvenile myoclonic epilepsy (JME) patients complaining of tremor unrelated to valproate (VPA) treatment and evaluate if there were differences between JME patients with and without tremor and essential tremor (ET) patients to exclude comorbidity. MethodsFifteen JME cases with the complaint of tremor, 14 JME patients without tremor, 14 patients with ET and 14 healthy subjects (HS) were included. Regularity, frequency and amplitude of the tremor and superimposed myoclonia were assessed by accelerometric analysis. Cortical SEPs evoked by the stimulation of the median nerve were recorded bilaterally. Clinical and neurophysiologic features were statistically compared between the groups. FindingsAmplitude of postural tremor of the left hand was significantly increased in the ET group compared to JME patients with tremor, but there were no differences regarding to frequency. Strikingly, there were superimposed irregular, low-amplitude inconstant myoclonic jerks located to distal part of the fingers in JME group with tremor. Initial frequency of myoclonic seizures was also significantly higher in this group compared to JME patients without tremor but this difference disappeared after treatment. The group of JME with tremor had the highest N20-P25 and P25-N35 amplitudes, followed by JME without tremor, ET and HS, respectively. ConclusionTremulous hand movements in JME resembled ET, but their amplitude was lower and characterized with accompanying irregular myoclonic jerks. The presence of tremor in JME patients should be taken into consideration to create more homogeneous groups in genetic and pathophysiological studies of JME.

Effect of early evaluation of CSEP and DNEP on spinal cord ischemic injury: an experimental study

Objective To investigate the effect of early evaluation of cortical somatosensory evoked potentials(CSEP)and desending neurogenic motor evoked potentials(DNEP)in spinal cord ischemic injury by observing the early change characteristics of CSEP and DNEP of spinal cord ischemia in rabbits. Methods To establish a rabbit model with different degree of permanent spinal cord ischemic injury through the ligation of different levels of lumbar arteries. The rabbits were divided into 5 groups(ligation of the left renal artery and the different levels of lumbar arteries between arterial bifurcations respectively, including 1 to 5-artery group). After modeling, CSEP and DNEP were continuously recorded for 60 min. After 2 days, the samples of ischemic central area were selected for HE staining. The motor function score Tarlov criteria were used to assess the motor function. The relationship between the amplitude variation of CESP and DNEP and the motor function after ligation were analyzed. Results There were statistical significance in the percentages of the CSEP amplitude and preoperative baseline amplitude between the 4- and 5-artery groups compared with before ligation(P 0.05). There were statistical differences in the percentages of the DNEP amplitude and preoperative baseline amplitude among the 3-, 4- and 5 artery groups compared with before ligation(all P 0.05). Compare with before ligation, there were statistical significances in the motor function 2 days after ligation between the 4- and 5-artery group(all P 0.05). The amplitude variation of CSEP and DNEP was positively correlated with the motor function 2 days after ligation of blood vessels(r=0.97, P<0.001; r=0.95, P<0.001). Conclusions Both CSEP and DNEP can predict the motor function after spinal cord injury. DNEP is more sensitive to spinal cord ischemic injury and is more specific to motor function. It can find ischemic injury in the early spinal cord ischemia. Key words: Spinal cord ischemia; Evoked potentials, somatosensory; Evoked potentials, motor; Rabbits

SEP Montage Variability Comparison during Intraoperative Neurophysiologic Monitoring

Intraoperative monitoring is performed to provide real-time assessment of the neural structures that can be at risk during spinal surgery. Somatosensory evoked potentials (SEPs) are the most commonly used modality for intraoperative monitoring. SEP stability can be affected by many factors during the surgery. This study is a prospective review of SEP recordings obtained during intraoperative monitoring of instrumented spinal surgeries that were performed for chronic underlying neurologic and neuromuscular conditions, such as scoliosis, myelopathy, and spinal stenosis. We analyzed multiple montages at the baseline, and then followed their development throughout the procedure. Our intention was to examine the stability of the SEP recordings throughout the surgical procedure on multiple montages of cortical SEP recordings, with the goal of identifying the appropriate combination of the least number of montages that gives the highest yield of monitorable surgeries. Our study shows that it is necessary to have multiple montages for SEP recordings, as it reduces the number of non-monitorable cases, improves IOM reliability, and therefore could reduce false positives warnings to the surgeons. Out of all the typical montages available for use, our study has shown that the recording montage Cz-C4/Cz-C3 (Cz-Cc) is the most reliable and stable throughout the procedure and should be the preferred montage followed throughout the surgery.

Evaluation of Electrophysiological Effects of Melatonin and Alpha Lipoic Acid in Rats with Streptozotocine Induced Diabetic Neuropathy

Neuropathy is a common complication of diabetes mellitus and is closely related to quality of life. There are many studies in which biological ingredients, such as alpha lipoic acid (ALA), that may inhibit or reduce the generation of diabetic neuropathy were investigated. Another biological agent that may reduce the generation of diabetic neuropathy is melatonin and there are a few studies that investigate the effects of melatonin on diabetic neuropathy. In this study we aimed to examine the effect of melatonin on experimentally induced diabetic neuropathy by comparing it with both ALA and control groups. We included 24 male Wistar rats. Tibial motor nerve conduction and cortical tibial nerve somatosensory evoked potentials (SEP) studies were performed before and after diabetes mellitus (DM) for all rats. Rats were divided into 3 (ALA, melatonin and control) groups. After 2 weeks of treatment period, tibial motor nerve conduction and cortical tibial SEP studies were repeated. Our data showed that ALA significantly increased nerve conduction velocity and amplitude in rats with diabetic neuropathy (p=0,001; p=0,002). Also, melatonin significantly increased nerve conduction velocity and amplitude in rats with diabetic neuropathy (p=0.002; p=0.002). There was no significant difference between the electrophysiological effects of ALA and melatonin. Besides, neither ALA nor melatonin did significantly affect P1 and N1 latency values on cortical tibial nerve SEP studies. Our study is the study in which both tibial nerve conduction and cortical tibial SEP studies were performed to compare effects of ALA and melatonin on experimental diabetic neuropathy. Lack of significant difference on cortical tibial SEP study would be attributed to the involvement of other central nervous system pathways which do not include ALA or melatonin in the pathogenesis. RESULTS of ALA group are important by means of giving objective evidences for results of biochemical studies about the role of ALA in the pathogenesis of diabetic neuropathy. However, there is not enough information about the effect of melatonin in the pathogenesis of diabetic neuropathy. Consequently, results of our study may anticipate further biochemical and clinic studies which investigate the about the role of melatonin in diabetic neuropathy.

A model of acute central cervical spinal cord injury syndrome combined with chronic injury in goats.

To develop a large animal model for acute central cervical spinal cord injury syndrome (ACCSCIS. Twenty-four adult male goats were randomized into four groups including group A with acute compression injury, group B with anterior chronic compression, group C as the test group that received anterior chronic compression by screw and acute compression by posterior balloon insertion, and group D as normal controls that received sham surgery. Neurological function (modified Tarlov motor function), CT, MRI, cortical somatosensory evoked potentials (CSEP), and pathological analysis were evaluated. The data were analyzed statistically. The motor function of the goats in group C was significantly lower than other groups. CSEP before spinal cord compression showed a stable pattern. Spinal cord compression resulted in a gradual decrement in the peak latency and significant increment in the peak amplitude. Cervical spinal canal occupying ratio was significantly lower in group C than the other groups. MRI revealed focal low signal in T1 weighted images and focal high signal in T2 weighted images in group C. Pathological analysis showed more severe lesions in the gray matter than that in the white matter in group C. The model well simulated the pathogenesis and resembled the clinical characteristics of ACCSCIS. This model seems to have the potential to contribute to the development of effective therapies for ACCSCIS.

Alterations in oropharyngeal sensory evoked potentials (PSEP) with Parkinson’s disease

Movement of a food bolus from the oral cavity into the oropharynx activates pharyngeal sensory mechanoreceptors. Using electroencephalography, somatosensory cortical-evoked potentials resulting from oropharyngeal mechanical stimulation (PSEP) have been studied in young healthy individuals. However, limited information is known about changes in processing of oropharyngeal afferent signals with Parkinson’s disease (PD). To determine if sensory changes occurred with a mechanical stimulus (air-puff) to the oropharynx, two stimuli (S1-first; S2-s) were delivered 500ms apart. Seven healthy older adults (HOA; 3 male and 4 female; 72.2±6.9 years of age), and thirteen persons diagnosed with idiopathic Parkinson’s disease (PD; 11 male and 2 female; 67.2±8.9 years of age) participated. Results demonstrated PSEP P1, N1, and P2 component peaks were identified in all participants, and the N2 peak was present in 17/20 participants. Additionally, the PD participants had a decreased N2 latency and gated the P1, P2, and N2 responses (S2/S1 under 0.6). Compared to the HOAs, the PD participants had greater evidence of gating the P1 and N2 component peaks. These results suggest that persons with PD experience changes in sensory processing of mechanical stimulation of the pharynx to a greater degree than age-matched controls. In conclusion, the altered processing of sensory feedback from the pharynx may contribute to disordered swallow in patients with PD.

Expression of praxis induction on cortical excitability in juvenile myoclonic epilepsy.

This study aimed to evaluate the effects of praxis induction on sensorimotor cortical and transcallosal excitability in juvenile myoclonic epilepsy (JME). A total of 36 subjects (18-62years) were included. The JME group was screened by video-electroencephalography neuropsychological protocol and divided into JME without praxis induction [JME-WI (n=12)], JME with praxis-induced seizures or epileptiform discharges [JME-PI (n=10)], and healthy controls (n=14). Motor and somatosensory cortical excitability and transcallosal pathways were evaluated through single-pulse transcranial magnetic stimulation (sTMS) and somatosensory evoked potentials (SEPs). Motor and transcallosal excitabilities tested with sTMS were not different in the motor-dominant or non-dominant hemisphere among groups. Significant differences were found in cortical SEP amplitudes in the P27 component of the non-dominant hemisphere (p=0.03, Cohen's d=0.98), N35 in the dominant hemisphere (p=0.04, Cohen's d=0.96), and P27-35 interpeak amplitude in both somatosensory cortices of the JME-PI group (p=0.03, Cohen's d=0.96; p=0.02, Cohen's d=1.05) when compared with healthy controls. Giant SEPs were observed in two (16.7%) and five (50%) patients of the JME-WI and JME-PI groups, respectively. Cortical latencies did not reveal differences. Praxis induction was associated with enhanced excitability in the somatosensory cortex of JME patients. These findings may help clarifying the less favorable therapeutic response in the JME-PI group and indicate identifying praxis induction as an important determinant in differentiating between JME patients.

84. A proposal of early neonatal sep classification as prognostic predictor in hypoxic ischemic encephalopathy

Aim of this study is to evaluate the relationships between a new classification of somatosensory-evoked-potentials in cascade (SEPs-C) with simultaneous video-electroencephalogram (VEEG) obtained by 1-h integrated neurophysyiological monitoring (1 h-IMNA) and clinical assessment by Sarnat–Sarnat (SS), Cerebral arteries Resistance-Index (RI) using pulsed-Doppler and Magnetic Resonance Imaging (MRI) as early predictors of a 1-year outcome in Hypoxic-ischemic-encephalopathy (HIE). 1 h-IMNA of VEEG and SEPs (bilateral median nerve stimulation) were assessed in 8 (4M-4F) asphyxiated term-infants within 1 and 4 weeks from birth. In all infants SS, RI and MRI were early performed. 1 h-IMNA and RI were also assessed in 20 healthy term-infants, as control-group. Trend of SEPs-C was evaluated in relation to behavioural-states during the VEEG-recording (wakefulness, quiet/active sleep). In control-group SEPs-C were present and modulated. In the 8 asphyxiated infants were identified 4 cortical SEPs’ patterns: bilateral absence/pathological-alteration (A–A), monolateral absence/pathological alteration (A–N), hypovoltated/non-modulated (h/nm), normal (NN) in agreement with RI and MRI. The recognize of SEPs-C pattern during 1 h-IMNA, considering hypovoltage and/or modulation in relation to behavioural-state, especially if concording with RI and MRI’s patterns, could implement the early prognostic-value to identify the moderate asphyxiated newborns. This proposal of neonatal SEPs’classification and its relations with IR and RMI call for further studies as early predictors of HIE, especially if mild.

87. Median nerve SEPs predict motor outcome in neonatal ipossic-ischemic encephalopathy treated with hypothermia

The role of SEPs in motor prognosis of hypoxic–ischemic neonatal encephalopathy has been evaluated in pre-hypothermia era (Suppiej, 2010) but their role in babies treated with hypothermia has not been studied yet. We investigated motor outcome at 12 months of age in 38 children who suffered from hypoxic–ischemic neonatal encephalopathy and were treated with hypothermia at the NICU of the Paediatric University Hospital of Padua. All performed median nerve SEPs in the neonatal period, traces were scored as bilaterally present (group1) or as bilaterally/unilaterally absent (group2) cortical N20 response. At follow up 4/38 children had the diagnosis of cerebral palsy (all of them had bilaterally absent cortical SEP). Of the remaining 34, 7 had abnormal (

ID 253 – Good functional outcome after prolonged postanoxic coma and myoclonic status epilepsy

Objective Present the possibility of a reasonable neurological recovery in early onset myoclonic status epilepsy (MSE) and prolonged postanoxic coma (PC). Methods A 43-year-old woman suffered a severe respiratory failure due to an anaphylactic reaction during anaesthetic induction before surgery. She required an urgent tracheostomy and remained in PC with reactive pupils and corneal reflexes, but with no withdrawal reaction to painful stimuli. Over the next hour she showed diffuse myoclonic jerks refractory to different antiepileptic drugs, midazolam and propofol. The EEG pattern revealed diffuse epileptiform discharges suggestive of MSE. Therapeutic hypothermia was induced, as was a barbituric coma using tiopental. Results PC and MSE persisted after suppression of the barbituric coma. The MRI was normal and repeated EEG confirmed MSE with stimulus-induced discharges. Cortical somatosensory evoked potentials (CSEP) were preserved and a second barbituric coma was induced. 48 days later the patient regained consciousness and was able to interact, being discharged on day 90. Conclusions Even in the event of an unfavourable initial prognosis, preserved brainstem reflexes, CSEP and EEG reactivity indicate the requirement for an intensive treatment of postanoxic status epilepsy. Key message Despite early onset of MSE and prolonged PC a global evaluation is necessary before establishing an accurate prognosis.

Hindlimb dysfunction character in response to spinal cord ischemia/reperfusion in rabbits

Objective To investigate the effect of spinal cord ischemia/reperfusion injury on hindlimb dysfunction in rabbits. Methods Twenty-eight health adult rabbits were distributed into normal control group (n=4) and model group (n=24) according to the random number table. The model of spinal cord ischemia/reperfusion injury was established by selective occlusion of lumbar arteries. The model group were submitted to ischemia for 30 min (Group Ⅰ), 60 min (Group Ⅱ) and 90 min (Group Ⅲ) before the reperfusion with 8 rabbits each. Jacobs score, Reuters score and Rivlin inclined plane test were used to evaluate the hindlimb function in each Group at days 1, 3 and 7 after reperfusion. Changes in nerve conduction function in each group were observed using the cortical somatosensory evoked potential (CSEP). Results At days 1, 3 and 7, the paraplegia rates in group Ⅰ were 50%, 38% and 38% respectively, in Group Ⅱ were 75%, 88% and 100%, and in Group Ⅲ were all 100%. Paraplegia rate differed significantly among the three groups at 1 d and 3 d (P 0.05). With the prolongation of reperfusion, the Reuters score in Group Ⅰ dropped but not differed from that in control group (P>0.05); the Reuters score in Groups Ⅱ and Ⅲ increased and differed from that the control group (P 0.05). Critical angle and obstacle rate of the inclined plane in control group were (68.4± 3.0)° and 0%. One day after reperfusion, critical angles of the inclined plane in Groups Ⅰ, Ⅱ and Ⅲ were (58.8±4.1)°, (38.5±2.8)° and (29.8±1.8)°, and the obstacle rates were (14.5±0.9)%, (43.6±2.4)% and (56.0±2.9)%. There were significant differences compared to control group (P 0.05). Latencies of CSEP N1 and P1 waves in Group Ⅱ [(33.1±1.8)ms and (58.6±4.0)ms] were longer than these in control group [(23.7±0.5)ms and (48.1±4.1)ms]and group Ⅰ [(26.2±0.7)ms and (50.2±4.2)ms] (P 0.05). While the CSEP wave disappeared in Group Ⅲ. Conclusions Severity of spinal cord inschemia/reperfusion injury is related to the duration of ischemia. Hindlimb dysfunction caused by ischemia/reperfusion injury is characterized mainly by spastic paraplegia. Key words: Spinal cord ischemia; Reperfusion injury; Dysfunction

Abstract 18713: Quantification of Cortical Recovery After Cardiac Arrest With Continuous Somatosensory Evoked Potentials

Objective: Reliable early prognostication of neurologic recovery in comatose cardiac arrest (CA) survivors remains a major clinical challenge. We hypothesized that continuous somatosensory evoked potentials (SSEP) in the immediate post-CA period could enable early quantification of cortical recovery. Methods: Pigs were instrumented for hemodynamic and SSEP monitoring. For SSEP, stimulation was applied to the right median nerve and electrodes in the brachial plexus and scalp acquired recordings. The primary cortical signal was the N20. Animals were then subjected to ventricular fibrillation CA that was left untreated for up to 4 minutes and followed by advanced cardiac life support until return of spontaneous circulation (ROSC). SSEP monitoring started before CA and continued after ROSC until SSEPs were unchanged for 60 minutes. Results: Six experiments were performed. In all animals, peripheral, subcortical, and cortical SSEPs were acquired prior to CA, demonstrating morphology similar to that of humans. Cortical potentials completely disappeared during CA. Average arrest duration was 6.9 ± 3.0 min. After ROSC, the N20 signal returned but with variable recovery rate and amplitude. The final N20 amplitude inversely trended with total duration of arrest (Figure 1). The N20 amplitude recovery over time took a logarithmic shape and ranged from 5 to 180 minutes to reach maximum (Figure 2). Conclusions: Continuous SSEP monitoring allows for quantification of cortical recovery within hours of short duration CA in a porcine model. The maximum N20 amplitude and rate of increase may be useful tools for quantifying recovery of cortical function in comatose cardiac arrest survivors.

Comparison of the Wake-up Test and Combined TES-MEP and CSEP Monitoring in Spinal Surgery

A retrospective clinical analysis. The aim of this study was to compare the effectiveness of the wake-up test with that of combined monitoring of transcranial electrical stimulation motor evoked potentials (TES-MEP) and cortical somatosensory evoked potentials (CSEP) in spinal surgery. TES-MEP/CSEP combined monitoring is being increasingly recognized as the ideal approach to detect spinal neurophysiological compromise during spinal surgery; however, as a result the merit of the wake-up test is now in doubt. TES-MEP/CSEP combined monitoring was performed simultaneously in 426 patients who underwent spinal surgery at our department, and wake-up tests were conducted on 23 patients because of positive neurophysiological monitoring results with uncertain causes or persistent positive monitoring findings after all potential causes had been resolved. Preoperative and postoperative neurological examinations were performed as the gold standard to detect irreversible spinal function compromise. All data were collected to compare the efficiency of TES-MEP/CSEP combined monitoring with that of the wake-up test. Positive results of TES-MEP/CSEP combined monitoring were recorded in 64 cases. Among them, the positive monitoring findings agreed with the results of the neurological examination in 51 cases, and the monitoring results did not match that of neurological examination in 13 cases. No false-negative result was observed. The sensitivity of TES-MEP/CSEP monitoring was 100%, the specificity was 96.5%, and the Youden index was 0.965. Wake-up tests were conducted in 23 cases. In 8 patients the positive monitoring findings completely matched the postoperative neurological examination results. In contrast, in the other 15 cases with negative neurophysiological monitoring results, only 9 patients retained intact neurological function and 6 patients suffered compromised neurological function. The sensitivity of the wake-up test was 57.1%, the specificity was 100%, and the Youden index was 0.571. Combined TES-MEP and CSEP monitoring, with its high sensitivity and specificity, is an effective method for monitoring spinal function during surgery and should be the preferred choice. The wake-up test is a useful complementary method for monitoring because of its high specificity.

Facilitation of cutaneous inputs during the planning phase of gait initiation.

It has been shown that during the planning of a voluntary movement the transmission of cutaneous afferent inputs to the somatosensory cortex is attenuated shortly before the motor output as well as during movement execution. However, it is not known whether the sensory suppression observed during the planning phase (i.e., before any movement execution) is a systemic phenomenon or whether it is dependent on movement context. For example, movements such as step initiation are controlled based on information received from cutaneous receptors in the feet. Because afferent information emerging from these receptors is critical for movement initiation, we hypothesized that suppression of these inputs may not occur during the planning phase prior to gait initiation. To examine this hypothesis we measured the cortical response to somatosensory stimulation during the planning phase of step initiation and during movement execution. Sensitivity to cutaneous stimulation was assessed by measuring the amplitude of the cortical somatosensory-evoked potential (SEP, over the Cz electrode) following electrical stimulations of the plantar sole of one foot. Two stimulations were provided during the planning phase of a step movement and two stimulations during movement execution. It was found that the P50-N80 SEP was facilitated in the early planning phase (-700 ms before motor execution) compared with when participants remained still (control standing task). This mechanism might contribute to an enhanced perception of cutaneous input leading to a more accurate setting of the forces to be exerted onto the ground to shift the body's weight toward the supporting side prior to foot-off.