The repeat reliability of somatosensory evoked potentials

The test-immediate-retest reliability of latency and amplitude values of cervical and cortical somatosensory evoked potentials (SEP) to median nerve stimulation was assessed in 86 normal subjects aged 15 to 71 years. In addition to the stability of data between repeat trials within one test session the standard errors of measurement and the interpretable differences for SEP measures were calculated according to measurement theory. The study revealed retest correlations rtt greater than 0.80 for all latency measures of the cervical and cortical SEPs and all cortical amplitude parameters. The highest stability was found for the latency measures of the cervical components P10, N11, N13, the cortical components P16 and N20 and for the amplitude N20/P25.     

Variations in the configuration of somatosensory evoked potentials following stimulation of the median nerve

The variants of waveform patterns of cervical and cortical somatosensory evoked potentials to median nerve stimulation at the wrist were analysed in 86 normal subjects aged 15 to 71 years. In cervical SEP recordings the components N13, N14 and the trough-shaped variant of P17 showed the highest short-term stability. Immediate changes of the amplitude proportions of subcomponents within the potential, i.e. a lack of uniformity in waveforms, have to be considered normal. Significant associations were found between the occurrence of components N14 and an arm length of more than 68 cm and between the appearance of a plateau configuration of P17 and an age of at least 40 years. Considering definite criteria the latency of P17 can be used as an additional reliable parameter. In cortical SEP recordings the combination of an initial V-shaped pattern and a following bifid W-configuration appeared as the most frequent waveform profile. All parts of the potential but the positive waves of the primary complex revealed a high intraindividual stability.     

Incidence of identification and configuration variants of the NSEP signal in relation to the recording site and measuring moment

The component evaluation of the spinal and cortical recorded SEP-signals of thirty healthy volunteers after stimulation of the median nerve at the wrist gave information about variation of waveforms and frequency of peak identification with respect to the position of the active electrode and the repetition of the SEP recording. Basically one can distinguish three main groups of NSEP waveforms (Fig. 1). Firstly the "classical form" (i.e. N11 in the ascending part, N13 at the highest peak of the NSEP main component and N14 in the descending part of the curve). Secondly the "plateau-form" and thirdly the "polypeak form" (i.e. many peaks of the same amplitude). The latter two configurations were seen in more than a third of the evaluated NSEP maincomponents. Neither the position of the active electrode (C2 and C7) nor repetition of the SEP recording were found to have significant influence on the waveform. The position of the active electrode influenced the number of identificable peaks: the early components (N9 and N11) were more often recognisable when the recording was made over the lower neckregion (C7), N14 when the recording was made over the upper neckregion (C2). N13 was always identificable in both electrode positions. The repetition of the SEP recordings immediately after the first run is helpful if there was difficulty in identifying the peaks. The normal values of the SEP latency of the spinal and cortical recorded signals were evaluated taking above mentioned criteria into account.     

Effect of body size, arm length, sex and temperature on somatosensory evoked potential latency

Beside the technical factors different biological factors contribute to the variability of the somatosensoric evoked potentials. In 30 volunteers the dependence of the latency of the spinal components N9, N13 (recorded at C7), of the cortical component N20 and of the interpeak interval N13-N20 from the body size and length of the arm was investigated. A significant dependence at the 1% level (p less than 0.001) was found for the latencies of N9, N13 and N20, whereas the interpeak interval N13-N20 was significant at the 5% level (p less than 0.05). Similarly in 20 further volunteers a significant dependence of the components N1, P1, N2, P2 and N3 from the body size at the 1% (p less than 0.001) after distal stimulation of the tibial nerve was observed. Using a covariance analysis it could be shown, that even after a body size correction, in females shorter latencies occur than in males. Furtheron we studied the effect of the temperature on the SSEP-latencies, by heating the upper and lower extremity stepwise from 31 degrees C to 37 degrees C using an infrared (DISA-Regler-System) lamp. As no significant dependence could be observed, we believe that the effect of temperature on latencies is so small, that in usual conditions no correction is needed. On the contrary a correction with body size or arm length is necessary, to avoid wrong positive or negative results.     

Value of somatosensory evoked potentials in thoraco- brachial outlet syndrome

INTRODUCTION: Brachial plexus involvement in symptoms of thoracic outlet syndrome (TOS) is often difficult to assess from clinical data. Conventional EMG and nerve conduction studies (NCS) do not seem reliable to all authors. For this reason, our investigations of this syndrome were complemented by study of somatosensory evoked potentials (SEP) in order to compare the results of these different techniques. PATIENTS AND METHODS: Ten patients were studied, all of whom had prominent vascular symptoms which led to their consulting a vascular surgeon. Only one had hand wasting without hypoesthesia. None had cervical rib or cervical spine anomaly. In all cases, diagnosis was confirmed by arteriography or phlebography. Operations were decided on clinical data and results of vascular investigations. Patients were tested with conventional motor and sensitive NCS F-wave studies. Needle EMG was performed in abductor pollicis brevis, first dorsal interosseus or abductor digitiminimi. Their SEP were performed as for controls. Ten controls were studied whose SEP were obtained at Erb's point (N9) and C2 cervical spine level (N13) after percutaneous stimulation of median and ulnar nerves at the wrist on both sides. The criterion of abnormality was the mean of controls + 2.5 SD for latencies. Amplitude was considered as low when it was less than 50% of the contralateral one. RESULTS: For 2 patients EMG, NCS and SEP were abnormal. One had hand wasting and denervation in hand muscles as well as slowed median and ulnar sensory conduction with low amplitude responses. SEP at Erb's point were slightly delayed after ulnar stimulation. No cervical response was obtained after ulnar stimulation. The second one had normal responses at Erb's point but delayed responses at the cervical level. In addition, N13 amplitude after ulnar stimulation was low. Four patients had normal EMG, NCS and SEP. Two patients had normal EMG and NCS, but their SEP was questionable since latencies were normal, even though amplitude was low after median and ulnar stimulation. This was not considered this to be abnormal since it was bilateral. For the remaining 2 patients (F.1), EMG and NCS and Erb's point SEP were normal, but C2 median and ulnar responses were delayed in one case and C2 ulnar response amplitude was very low on one side only in the other. In conclusion, SEP were abnormal for 4 patients out of 10 but gave more information than conventional EMG and NCS for only 2 patients. SEP abnormalities prevailed after ulnar stimulation.     

Effect of hypothermia on median nerve somatosensory evoked potentials

Median nerve sornatosensory evoked potentials (SEP) were monitored in ten patients undergoing cardiac surgery with hypothermic cardiopulmonary bypass (CPB). Anesthesia was induced and maintained with sufentanil, oxygen, and pancuronium. Esophageal, nasopharyngeal, rectal, and blood temperatures were continuously monitored. SEPs were recorded before induction of anesthesia, after induction, and during cooling and rewarming on CPB. There was a strong negative correlation between SEP latencies and temperature (except rectal) (r = −.91, P < .001), for cortical latency and esophageal temperature. A decrease in esophageal temperature of 1°C resulted in an increase in SEP latency of 1 ms. There was also a weak positive correlation between evoked potential amplitude and temperature (r = .19) for cortical amplitude and esophageal temperature.     

Intraoperative somatosensory evoked potentials as a prognostic factor of neurologic state after carotid endarterectomy

Somatosensory evoked cervical and cortical potentials (SEP) were analyzed under general anesthesia in 106 patients undergoing carotid endarterectomy. Cortical electrical silence occurred in 5 patients without an inlying shunt; all developed a new neurologic deficit postoperatively. Analysis of the SEP in these patients revealed progredient cerebral ischemia as indicated by an increase in central conduction time (CCT) and a decrease in amplitude of the primary cortical response N20P25 resulting in a complete loss of cortical SEP later on during the clamping period. In 6 patients the insertion of a shunt restored the deteriorated SEP, these patients and those with unchanged SEP after carotid clamping showed an uneventful postoperative recovery. Taking the presence or absence of N20P25 as the sole parameter, the sensitivity of this technique was 83%, specificity 99% and predictability 83%. A normal range for CCT and amplitude of N20P25 during anesthesia and criteria for shunt insertion were developed. The presented monitoring regimen appears to be rational and is based on current concepts of cerebrovascular physiology and pathophysiology.     

电生理指标联合应用在颅内巨大动脉瘤手术中的作用

目的研究躯体感觉诱发电位(SEP)、脑电图、脑干听觉诱发电位(BAEP)联合应用在颅内巨大动脉瘤手术治疗中的影响及临床意义。方法分别对23例颅内巨大动脉瘤患者进行手术直接夹闭或动脉瘤孤立加旁路移植手术,同时行SEP、脑电图和BAEP实时监测,观察手术操作对其的影响。结果 23例患者行颅内巨大动脉瘤手术操作时,均不同程度引起SEP、脑电图和BAEP的变化。其中SEP的N20、P25潜伏期延长3～5 ms,波幅较术前降低50%;BAEP的Ⅰ、Ⅲ、Ⅴ波潜伏期延长0.7～1.0 ms,Ⅰ～Ⅲ、Ⅲ～Ⅴ波峰间期及Ⅰ、Ⅴ波幅电位较术前降低30%～50%以上。结论术中动态监测SEP、脑电图和BAEP的电位变化,可以提示颈动脉阻断后的脑灌注状态,对调整手术时间及手术方式具有重要的指导意义。     

乳果糖治疗亚临床肝性脑病的临床研究

目的 前瞻性对比乳果糖长、短程治疗对亚临床肝性脑病(SHE)的效果及其对SHE病程的影响。方法 经智力测验(数字连接试验和数字符号试验之一异常)诊断的SHE 64例随机分入对照组(21例)、短程组(21例)和长程组(22例),后2组分别服乳果糖达8周和24周。治疗前以及治疗后每间隔8周行血氨、智力测验和体感诱发电位(SEP)等检查,共随访24周。结果 每组各有20例完成追踪。与对照组和治疗前相比,长程组血氨和智力测验显著改善(P＜0．05—0．01)且SEP的N50波潜伏期稳定不变,短程组治疗到第8周也有改善(P＜0．05),但停药后又逐渐恶化。对照组的血氨、智力测验和N50波潜伏期逐渐恶化,在16周时后2项与治疗前差异有显著性(P＜0．05—0．01);而长程组血氨持续降低,其肝性脑病(HE)患病率(5％)显著低于短程组(30％)和对照组(40％)(P＜0．05)。结论 乳果糖维持治疗能够降低血氨、改善智力测验结果并可能防止SEP的恶化,最终降低HE的患病率。     

Determination of neurophysiological parameters of the aging CNS. I. Evoked potentials (author's transl)]

Somatosensory (SEP) and visual (VEP) evoked potentials were studied in 65 healthy subjects who ranged in age from 62-91 years and in 48 normal persons aged 18-38 years. The amplitudes and latencies of the different components of the evoked potentials were measured. The transmission of evoked potentials from the specific response area into different regions of the ipsi- and contralateral hemisphere were studied. The findings can be summarized as follows: The latencies of the SEP and VEP of aged subjects are significantly prolonged. The increase in latency is relatively slight for the first components, progressively higher for the following components. The amplitudes of the different components of the SEP and VEP are significantly increased in aged subjects. The modifications of the SEP-latencies and of the VEP-amplitudes are more important over the dominant hemisphere. In young subjects the SE are confirmed to the centro-parietal region. In aged persons the SEP spreads over the whole hemisphere. The hypothesis that the aging process involves the synaptic transmitter mechanisms at the cortical level is discussed in relation to the involvement of the latencies. The increase in amplitude of the evoked potentials could be explained by assuming that the inhibition - an essential property of the cortex - decreases during the aging process.     

SEP monitoring during clonidine therapy of alcohol delirium]

In 12 patients with developing alcohol withdrawal syndrome after abdomino-thoracic surgical procedures who were treated with Clonidine, short latency somatosensory evoked potentials were recorded. Clonidine leads to a good sedation, anxiolysis and moderated the psychotic symptoms. However, there was no significant correlation between the Clonidine medication and the SEP results over the time of drug administration concerning the primary cortical response N20 and the following N20/P25 wave. Therefore, the short-latency SEP-recording cannot provide a reliable monitoring of the good sedative effect of Clonidine in alcoholic withdrawal. The SEP responses after Clonidine are like those of morphine and are thought to have a similar central mode of action.     

Selective shunting based on somatosensory evoked potential monitoring during carotid endarterectomy

Somatosensory Evoked Potentials (SEPs), to median nerve stimulation, were continuously monitored in 58 patients undergoing carotid endarterectomy A first group of patients was shunted routinely; in a second group the shunt was selectively applied when inadequacy of collateral circulation was suspected based on stump pressure values and SEP changes. Both amplitude and latency modifications of SEPs occurred during surgery; however no post-operative neurological deficit was seen unless there was a complete flattening of cortical waves, even a transitory one. Inadequate collateral circulation and embolic ischemia affected SEPs differently. While the latter produced a disappearance of all cortical waves, the former led first to a progressive flattening of later cortical waves and then of N20 as well. For values of stump pressure ranging between 20 and 50 mmHg SEPs were unchanged in some patients and altered in others. These findings may explain the controversies existing about the usefulness of stump pressure for predicting tolerance to carotid clamping.     

Topography of early cortical median nerve somatosensory evoked potentials: results for routine use of the method]

The results from a topographic analysis of the early median nerve SEPs allowed to design a method for recording and analysing the SEPs in the routine laboratory. The detailed analysis of the topography of 50 normal subjects revealed: 1. An inter- and intraindividual variability of the location of the maximal amplitudes, 2. A significantly longer latency of the cortical potentials after left side stimulation, 3. A significantly higher amplitude of N20 after left side stimulation and 4. A significantly higher amplitude of the later potentials P25 and N30 after right side stimulation. It was shown that a 4-channel recording from the neck at C7 with a Fz-reference as well as from stimulus contralateral F3, CP3 and P3 or F4, CP4 and P4 with an stimulus contralateral earlobe reference provides all necessary parameters in comparison to an 20-channel recording. The definition of normal values has to take into account these results. Absolute maximum values were taken instead of the standard deviation because all amplitude values were proven to be not distributed normally. In 7 out of 30 MCA-stroke patients pathological SEP amplitudes were obtained using the 4-channel montage, whereas the 1-channel recording from CP3 and CP4 with a Fz-reference revealed normal amplitudes.     

Hyperthermia after cardiac arrest is associated with an unfavorable neurologic outcome

BACKGROUND: Moderate elevation of brain temperature, when present during or after ischemia, may markedly worsen the resulting injury. OBJECTIVE: To evaluate the impact of body temperature on neurologic outcome after successful cardiopulmonary resuscitation. METHODS: In patients who experienced a witnessed cardiac arrest of presumed cardiac cause, the temperature was recorded on admission to the emergency department and after 2, 4, 6, 12, 18, 24, 36, and 48 hours. The lowest temperature within 4 hours and the highest temperature during the first 48 hours after restoration of spontaneous circulation were recorded and correlated to the best-achieved cerebral performance categories' score within 6 months. RESULTS: Over 43 months, of 698 patients, 151 were included. The median age was 60 years (interquartile range, 53-69 years); the estimated median no-flow duration was 5 minutes (interquartile range, 0-10 minutes), and the estimated median low-flow duration was 14.5 minutes (interquartile range, 3-25 minutes). Forty-two patients (28%) underwent bystander-administered basic life support. Within 6 months, 74 patients (49%) had a favorable functional neurologic recovery, and a total of 86 patients (57%) survived until 6 months after the event. The temperature on admission showed no statistically significant difference (P =.39). Patients with a favorable neurologic recovery showed a higher lowest temperature within 4 hours (35.8 degrees C [35.0 degrees C-36.1 degrees C] vs 35.2 degrees C [34.5 degrees C-35.7 degrees C]; P =.002) and a lower highest temperature during the first 48 hours after restoration of spontaneous circulation (37.7 degrees C [36.9 degrees C-38.6 degrees C] vs 38.3 degrees C [37.8 degrees C-38.9 degrees C]; P<.001) (data are given as the median [interquartile range]). For each degree Celsius higher than 37 degrees C, the risk of an unfavorable neurologic recovery increases, with an odds ratio of 2.26 (95% confidence interval, 1.24-4.12). CONCLUSION: Hyperthermia is a potential factor for an unfavorable functional neurologic recovery after successful cardiopulmonary resuscitation.     

Clinical utility of somatosensory evoked potentials in diabetes mellitus

The posterior tibial nerve and median nerve somatosensory evoked potentials (PTN-SEPs and MN-SEPs) were investigated in 34 patients with diabetes mellitus (DM). We measured the latency of the first positive cortical potential (the cortical P37) of PTN-SEPs and that of the first negative cortical potential (the cortical N18) and Erb's potential of MN-SEPs. In 18 patients (52.9%), the cortical P37 latency was more than 3 SD longer than normal in the tibial nerve. There were positive correlations between the latency of cortical P37 and the duration of DM and the motor nerve conduction velocity of the posterior tibial nerve. Sensory action potentials of the posterior tibial nerve were not detectable in 21 patients, though cortical P37 potential was unambiguously recorded by stimulating the posterior tibial nerve even in those subjects. Diabetic retinopathy and nephropathy also tended to rise with increasing latency of cortical P37. The latency of cortical P37 is an important parameter in assessing diabetic neuropathy.     

Subcortical somatosensory evoked potentials in patients with hepatic encephalopathy caused by severe acute hepatitis

We studied the median nerve stimulated somatosensory evoked potentials (SEP) of 23 patients with hepatic encephalopathy (HE) resulting from severe acute hepatitis and 22 healthy volunteers. Ten patients who improved and survived more than 60 days were classified as Group 1 and the remaining 13 patients who died shortly after the SEP studies were classified as Group 2. The mean N9-N13 interpeak latencies (IPL) were not different among control and two patient groups. The mean N13-N20 IPL of Group 2 was significantly prolonged when compared with normal controls (P < 0.001) and Group 1 (P < 0.001). Five of the six patients with abnormal N13-N20 IPL died of hepatic failure within 24 h after SEP testing. The occurrence of abnormal subcortical conduction together with cortical dysfunction suggested that brain damage in terminal hepatic encephalopathy was diffuse. The presentation of abnormal prolongation of N13–N20 IPL of SEP during the course of severe acute hepatitis indicated a poor prognosis. Peripheral somatosensory conduction is unaffected even in terminal HE.     

脑白质疏松症患者的脑诱发电位研究

目的 探讨脑白质疏松症(Leukoaraiosis，LA)患者脑诱发电位改变的特点及其对LA的诊断价值。方法对40例脑白质疏松症合并脑梗死(LA CI)患者及40例单纯脑白质疏松症患者进行体感诱发电位(sEP)，脑干诱发电位(BAEP)及视觉诱发电位(VEP)检查，并与40名同年龄组健康人对照。结果LA CI组患者SEP、BAEP及VEP异常率分别为80％、63％及60％。SEP各波潜伏期、BAEP除Ⅰ波外各波潜伏期及波间期、VEP的P100波潜伏期和对照组相比差异均有显著性意义。而单纯LA组患者SEP、BAEP及VEP异常率分别为35％、30％及45％，SEP仅P15及％波潜伏期、VEP的P100波潜伏期和对照组相比差异有显著性意义。而BAEP和对照组相比，差异无显著性意义。结论SEP、BAEP及VEP联合检查，可反映LA患者皮层、皮层下及脑干功能的损害，并对判断LA患者白质疏松范围，LA严重程度有一定的意义。     

Spinal and subcortical somatosensory evoked potentials: a comparison with the localization of spinal, medullary and pontine lesions and in brain death

The spinal and subcortical median nerve SEPs were recorded in 65 patients with lesions of the cervical cord, medulla oblongata, pons and in brain death. A recording technique including cephalic, non-cephalic and anterior neck referenced leads was used. The location of the lesions corresponded to different types of SEP alterations: Cervical extramedullary lesions compressing the spinal cord corresponded to a prolonged P9-P14 interpeak latency. Cervical intramedullary lesions corresponded to the loss of N13, normally generated in the spinal interneurons. Vascular lesions of the medulla oblongata (Wallenberg's syndrome) showed normal SEPs. Space occupying medulla oblongata lesions corresponded to reduction in amplitude or loss of P14. Pontine lesions showed normal spinal and subcortical SEPs. In brain death P14 showed a graduate decrease in amplitude or alternatively vanished abruptly. The spinal and subcortical SEPs provide a good tool for testing the function of the lemniscal pathways and the spinal interneurons.     

The cervical somatosensory evoked potential in lesions of the cortical efferents

Cervical and cortical somatosensory evoked potentials to median nerve stimulation were analysed in 20 patients with unilateral central paresis of the arm. Neither the configuration nor the latency and amplitude measures of the neck potential did reveal any association with pathological alterations of cortical efferents or with abnormal cortically evoked responses. Thus, also in this population the evaluation of cervical potentials can be done according to the known criteria.