Nerve conduction measurement based on lumbosacral evoked potentials

Lumbosacral evoked potentials (EP) following stimulation of the posterior tibial nerve at the ankle were recorded with surface electrodes at 5 cm intervals from the lower lumbar to the lower thoracic levels and the site of maximum amplitude was determined by monopolar and bipolar recordings in 27 normal subjects, 37 epileptics receiving anticonvulsant therapy and 22 patients with subacute myelo-optico-neuropathy (SMON). The amplitude of EP in monopolar recording with a reference on the contralateral knee was usually maximum 10 cm above the Jacoby line, which nearly corresponded to the 1st lumbar or 12th thoracic vertebral level. The entire nerve conduction velocity (ENCV) was calculated by dividing the distance from the ankle to the level of maximum amplitude by the peak latency of the N21 or P17. The latency of N21 at the level of maximum evoked potential was used for determining ENCV. The mean ENCV calculated using the peak latency N21 was 49.8 (1.97) m/sec in monopolar recording and 51.2 (2.48) m/sec in bipolar recording, and these values were considered to correspond the sensory conduction along the entire posterior tibial nerve. In epileptic patients mainly treated with anticonvulsant drugs such as phenytoin and phenobarbital, the ENCV was reduced in those treated for over 13 years and in those whose illness was poorly controlled, or large doses were necessary for seizure control. In SMON patients, a significant decrease in ENCV was found in the group under 60 years old in comparison with the normal control group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of noise sources in surface recording of spinal somatosensory evoked potentials

The poor signal-to-noise ratio associated with the acquision of evoked potentials is a well established fact. The problem is compounded if non-invasive techniques, using surface electrodes, are employed. The paper identifies several sources of noise associated with the acquisition of spinal somatosensory evoked potentials using surface electrodes. In addition, the relative contribution of these sources is determined experimentally for six spinal levels ranging from lower lumbar to upper thoracic. These data will prove useful in the design of digital signal processing schemes such as adaptive noise cancellation, where levels of uncorrelated noise severely limit system performance.     

Median nerve somatosensory evoked potentials: recording with cephalic and noncephalic references

We performed both cephalic and noncephalic reference SEP recordings with median nerve stimulation in normals and compared the results obtained from both recordings. Median nerve SEP with non cephalic reference revealed four positive and three negative potentials on scalp, while median nerve SEP with cephalic reference showed only one negative potential on scalp. We conclude that potentials originated from subcortical regions can be recorded from scalp by using noncephalic reference, which is not possible by cephalic reference and potential N20 obtained from somatosensory cortex by using cephalic reference does not present a single potential, consisting of combination of a few potentials. To differentiate these potentials, noncephalic reference must be used.     

皮节体感诱发电位各观测指标在评价腰骶神经根病损中的灵敏性

目的:探讨皮节体感诱发电位(DSEP)各指标在评估腰椎间盘突出症(LDH)的神经根损害中的作用及灵敏性.方法:测定96例有单侧下肢放射痛症状的LDH患者和50例正常人的DSEP并进行比较.结果:DSEP诊断LDH神经根病损的阳性率为84%,DSEP异常主要表现为P40波潜伏期侧间差异常(65%), DSEP波幅变异大,波幅变异系数平均高达58%.结论:DSEP能反映腰骶神经根功能状态,可用来评价LDH的神经根病损,其灵敏度高,与CT或MRI能互为补充;在有单侧下肢症状的LDH病例以P40波潜伏期的侧间差为最敏感的指标;波幅变异大,难以作为有肯定意义的指标.     

皮节体感诱发电位在诊断腰骶神经根损害中的临床研究

目的:探讨皮节体感诱发电位(DSEP)在诊断腰骶神经根受损及其严重程度中的临床应用价值.方法:将47例具有长期腰痛,伴有双侧下肢放射痛及间歇性跛行症状,经CT或MRI确诊有腰椎管狭窄(LSS)需要入院进行手术治疗的病例设为病例组.对照组为50例无腰腿痛和无中枢神经系统疾病的健康成年人.分别对两组进行双侧L4、L5、S1神经根DSEP检测.DSEP的异常诊断标准:P40波(即P1波)消失,和(或)P40波潜伏期延长超过正常均数+2.5倍标准差(>+2.5 s).结果:病例组中,P40波潜伏期明显延长91个皮节,P40波形消失103个皮节.分别将左右两侧三个皮节(L4、L5、S1)的P40潜伏期与正常对照组相对应皮节的P40潜伏期进行统计学分析,差异有显著意义(P<0.01).DSEP诊断LSS神经根其灵敏度和符合率均为95.7%.结论:DSEP能反映LSS时神经根受损及其严重程度,与CT或MRI能互为补充,作为需要进行手术的证据,具有重要的临床应用价值.     

The diagnostic value of dermatomal somatosensory evoked potentials in lumbosacral disc herniations: a critical approach

In this study, we examined scalp recorded dermatomal somatosensory evoked potentials (DSEPs) to electrical stimulation of L4, L5 and S1 dermatomes in 55 patients with proven lumbosacral radiculopathy and in 22 healthy subjects. We did not observe any significant ipsilateral intertrial variations and arithmetic mean side-to-side differences in normal subjects. As for segmental latencies, the dermatomal P40 latencies were directly correlated with height. The regression equations for L4, L5 and S1 dermatomes were as follows: (L4) y = 5.8 + 21.3 (height), (L5) y = -2.09 + 28.04 (height), (S1) y = -13.9 + 36.4 (height). Maximum side-to-side latency differences and maximum P 40 latencies were obtained by adding 2 standard deviations to the arithmetic means. The abnormal latencies for L4, L5 and S1 dermatomes were 48 msec., 52 msec., and 55 msec., respectively. The abnormal side-to-side latency difference were 3 msec. for all dermatomes. DSEPs accurately predicted the lesion only in four patients (7.2%). In 20 patients (36.3%), DSEPs correctly identified the lesion but also gave misleading information on the other levels. DSEP abnormality were on the correct level but opposite side in 5 patients (9%). The findings were normal in 11 patients (20%), and misleading in 15 patients (27.2%). We conclude that the ultimate diagnostic utility of DSEPs in lumbosacral radiculopathies is doubtful and controversial needs further investigations.     

腰骶神经根减压术中皮节体感诱发电位监测及其相关因素分析

目的:探讨腰骶神经根减压手术中皮节体感诱发电位(DSEP)监测的临床意义.方法:对46例经查体、腰椎MRI及DSEP检查证实存在单侧腰骶神经根(腰5或骶1神经根)压迫的患者,术前按照40岁为节点进行年龄分层(大龄组和低龄组)、病程分层以3个月为节点(慢程组和短程组)、失血量分层以200 ml作为节点(大量失血组和少量失血组);在术中进行受累节段双侧神经根DSEP监测,观察并记录不同时间节点(麻醉后、减压前及减压后)的P40波潜伏期、波幅的数据,计算减压前后P40波幅的改善率,分别以0.5、0为节点将其分层(明显改善组、不明显改善组和无改善组),比较上述不同因素分层后的相关指标.结果:大龄组疼痛视觉模拟评分(VAS)与Oswestry功能障碍(ODI)改善率之间,低龄组P40波幅改善率与ODI改善率、VAS与ODI改善率之间,P40波幅变化率、VAS改善率在不同病程组,病程、VAS改善率在不同P40波幅改善率组差异有显著意义(P＜0.05).结论:在应用DSEP分析腰骶神经根减压效果时,在不同患者相关因素下的P40波幅改善率具有重要的临床价值和意义.     

Specificity of auditory evoked potentials from rat hypothalamus: differential recording by lateral and ventromedial electrodes

Evoked potentials recorded from ventromedial nucleus (VMH) and lateral area (LHA) of the hypothalamus were studied in freely moving rats with respect to specificity of the components to recorded areas and to peripheral stimuli utilized. This study attempts to circumvent some methodological problems and contamination in data with respect to origin of recorded components by comparing monopolar and differential recordings made in VMH and LHA, areas accepted as being involved in food-intake behavior. Of the stable components, the complex with 15-20 ms latency was evaluated as of extra-hypothalamic origin. Meanwhile, those with 25-ms (positive) and 40-ms (negative) average peak latencies were considered as specific to recorded areas. Hypothalamic responses appeared not to be specific to stimulus modality, indicating convergence of different sensory modalities on studied areas. Hunger and satiety appeared to influence the amplitude of the specified components similarly, the study not providing evidence for the reciprocal relation stated in the dual center hypothesis between VMH and LHA.     

Multichannel recording of cardiac potentials

An inexpensive system for the simultaneous recording of 256 cardiac electrograms is described. Time division multiplexing of cardiac potentials by digital circuitry provides a single video signal which is recorded on video tape. During playback a demultiplexer reassembles the separate signals. Measured channel characteristics demonstrate a bandwidth of 170 Hz, a noise level of 0·2 mV peak-to-peak, and a crosstalk of −27·5 dB. The design has flexibility in that individual channel bandwidth can be exchanged with the total number of channels according to the dictates of signal requirements. To illustrate this flexibility a second system is described which provides 64 channels whose measured characteristics include an 880 Hz bandwidth, a noise level of 0·14 mV peak-to-peak and a crosstalk of −33 dB.     

A system for recording of auditory evoked responses.

A system for recording of evoked potentials from auditory stimulation was developed. The system consists of a PC equipped with an audio bandwidth board with analog input and output channels. The sound stimulus signal is generated in the computer, D/A converted, and via audio amplifier fed to earphones on the test subject. Auditory evoked potentials in response to sound stimuli are recorded via electrodes, amplified and filtered in an EEG recording system and fed to an A/D converter. The signal is analysed in the PC. The modular design of the program makes it a flexible system where stimulus and recording parameters can easily be modified and new applications can be added to standard clinical measurements. Three applications that are not possible with commercially available systems were developed and evaluated. a) A diagnostic procedure to verify hydrops in patients with Meniere's disease. b) Intraoperative recordings of auditory evoked potentials during neurootological surgery. c) Recording of mismatch negativity (MMN) potentials in evaluation of central auditory functions.     

Influence of recording instrumentation on the stimulus artifact tail in the surface acquisition of somatosensory evoked potentials

Surface recorded somatosensory evoked potentials (SEPs) are neural signals elicited by an external stimulus. In the case of electrically induced SEPs, the artifact generated by the stimulation process can severely distort the signal. The artifact is characterized by a large impulse followed by a slowly decaying tail. In some cases, the artifact tail often lasts well into the initiation of the SEP making the determination of absolute latency very difficult. While the literature often states that the recording instrumentation plays a part in the generation of this artifact tail, no firm evidence has ever been presented. In this work, comparisons are made between three instrumentation systems (BJT, JFET and CMOS) with differing input impedances in an attempt to quantify the effects on the artifact tail. The conclusions from this investigation show that there is no significant interaction between the input impedance of the recording instrumentation and the duration of the artifact tail. Each amplifier type produced results with no significant statistical differences. It was also found that while stimulation amplitude has a weak effect on the artifact tail, the greatest contribution to variation has an inter-subject origin. Consequently, it is concluded that the time constant of the artifact tail must originate from other sources that are subject dependent.     

K-means clustering method for auditory evoked potentials selection

Surface auditory evoked potentials are generally recorded using a headset of 32, 64 or 128 electrodes, but the quality of the responses is quite heterogeneous on the scalp surface. In some contexts, such as the analysis of auditory evoked potentials recorded in radio-frequency fields, the signal quality is essential, and it appears pertinent to consider only a limited number of electrodes. Therefore, before analysing signals influenced by radio-frequency fields, it is necessary to consider the preliminary step of selecting the channels where auditory activity is strong. This step is often realised by human visual selection and can take a considerable time. In this paper, a simple k-means clustering method is proposed, to select automatically the important channels, and the results are compared with traditional methods of selection. The method detected channels that showed a concordance rate of 86.5% with the visual selection (performed by five individuals) and gave the same final selection (only two extra electrodes in the automatic case). Moreover, the time needed for this automatic selection was 100 times less than that for the visual selection, and also human variability was avoided.