听觉诱发电位及体感诱发电位在颅脑外伤致昏迷患者的应用

严重颅脑损伤昏迷患者脑功能的监测是判断预后和指导治疗的重要手段。听觉诱发电位(BAEP)及体感诱发电位(SSEP)因其方便、无创并能连续实时监测昏迷患者相关神经传导通路电生理的变化,间接反映脑干上行激活系统、大脑皮层结构与功能的完整性,越来越成为临床对严重颅脑损伤昏迷患者预测预后和指导治疗的重要手段。本文就近年来相关研究进行综述,旨在指导临床实践。     

Brainstem auditory evoked potentials and middle latency auditory evoked potentials in young children

Measurements of brainstem auditory evoked potentials (BAEP) and middle latency auditory evoked potentials (MLAEP) are readily available neurophysiologic assessments. The generators for BAEP are believed to involve the structures of cochlear nerve, cochlear nucleus, superior olive complex, dorsal and rostral pons, and lateral lemniscus. The generators for MLAEP are assumed to be located in the subcortical area and auditory cortex. BAEP are commonly used in evaluating children with autistic and hearing disorders. However, measurement of MLAEP is rarely performed in young children. To explore the feasibility of this procedure in young children, we retrospectively reviewed our neurophysiology databank and charts for a 3-year period to identify subjects who had both BAEP and MLAEP performed. Subjects with known or identifiable central nervous system abnormalities from the history, neurologic examination and neuroimaging studies were excluded. This cohort of 93 children up to 3 years of age was divided into 10 groups based on the age at testing (upper limits of: 1 week; 1, 2, 4, 6, 8, 10 and 12 months; 2 years; and 3 years of age). Evolution of peak latency, interpeak latency and amplitude of waveforms in BAEP and MLAEP were demonstrated. We concluded that measurement of BAEP and MLAEP is feasible in children, as early as the first few months of life. The combination of both MLAEP and BAEP may increase the diagnostic sensitivity of neurophysiologic assessment of the integrity or functional status of both the peripheral (acoustic nerve) and the central (brainstem, subcortical and cortical) auditory conduction systems in young children with developmental speech and language disorders.     

Middle latency auditory evoked potentials in patients with parkinsonism

The aim of this study was to assess the middle latency auditory evoked potential (MLAEP) findings in idiopathic Parkinson's disease (IPD) and in patients who are regarded as having atypical parkinsonian disorders (AP) and to determine whether MLAEPs could contribute to the differential diagnosis of IPD and AP.MLAEPs were evaluated in 19 control subjects and in a total of 35 patients with parkinsonism, of which 27 had IPD and 8 had AP. Among IPD patients, P1 was absent in 1 nondemented patient with young-onset Parkinson's disease (YOPD) (5%) and in 2 of 7 demented (28.5%) IPD patients. In the AP group, 3 of the 7 (42.8%) nondemented patients and the one patient with dementia showed the absence of P1. The absence of P1 was found to be significantly higher in AP patients than IPD patients (p=0.0335).In conclusion, MLAEPs were found to be normal in nondemented IPD patients with only a few exceptions. The absence of P1 in nondemented patients with parkinsonian symptoms may bring the diagnosis of IPD into question. The absence of P1 could be detected in AP patients at least as often as in demented IPD patients. Thus, the measurement of MLAEPs may be a clinically useful adjunct to the clinical examination of patients with parkinsonism.     

Short latency somatosensory evoked potentials in patients with syringomyelia

Short latency somatosensory evoked potentials (SSEPs) following median nerve and posterior tibial nerve stimulation were studied in six patients with syringomyelia. Three patients had Chiari malformations, two patients experienced fracture of the spine and one patient had a cauda equina ependymoma. SSEPs following median nerve stimulation were abnormal in all patients, of which five patients showed abnormal SSEPs only in the unilateral stimulation on the side of sensory deficits. SSEPs obtained from three out of eight upper extremities which showed no disturbance of deep sensation, were abnormal, so SSEPs were able to detect subclinical abnormality indicating dorsal column dysfunction. Abnormal patterns of SSEPs were classified in three types as follows; Type 1: disappearance of P13, N16 and N18 (3 cases), Type 2: the prolonged interpeak latency P11-P13 (2 cases), and Type 3: abnormal N16 and N18 with preserving P13 (1 case with Chiari malformation). P9 and P11 were present without prolonged latencies in all cases. SSEPs following posterior tibial nerve stimulation were abnormal in two of the three tested patients. Those two patients had disturbance of deep sensations in the lower extremities. All patients underwent surgical treatment, syringo-peritoneal shunt in four patients, foramen magnum decompression with syringo-subarachnoid shunt in one patient, and total removal of an ependymoma of the cauda equina with syringotomy in one patient. Postoperative neurological improvement were found in three patients, of which two cases also showed improvement in SSEPs. On the contrary SSEPs were unchanged in two patients with posttraumatic syringomyelia, whose postoperative neurological condition was also unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Short latency visual evoked potentials in man

Contrary to auditory and somatosensory evoked potentials, surface recorded visual evoked potentials which arise in subcortical neural elements have rarely been described. Considerable disagreement exists between the reports in the literature on such visual potentials. In this study, flash stimuli were used to evoke the potentials which were recorded from the skin overlying the infra-orbital ridge, outer canthus, middle of the forehead, vertex, mastoid ipsilateral to the stimulated eye and inion, using a non-cephalic reference. The potentials were amplified in a band which was chosen to omit slow retinal and cortical potentials, and to enhance activity which might include compound neural activity. Potentials were recorded from 9 subjects (13 eyes), and for each one the effects of eye position and stimulus intensity were studied. The results indicate that the series of components recorded within the first 100 msec following photic stimulation were volume-conducted activity generated by a subset of the visual system which is activated by luminosity changes. The generators of the first 4 or 5 components seem to be situated within the retina, the subsequent components seem to be generated in the optic nerve or tracts, and the later components may be thalamo-cortical in origin. These potentials may complement pattern evoked potentials in a more accurate definition of sites of lesions along the visual pathway.     

Short latency somatosensory evoked potentials in infants

Short latency somatosensory evoked potentials (SEPs) to unilateral median nerve electrical stimulation were recorded from normal infants at birth and at 2, 4, 6, 8, 10 and 12 months of age. Three channels were recorded: Erb's point-Fz; C II (over 2nd cervical vertebra)-Fz; contralateral C' (2 cm posterior to C3 or C4)-Fz. Sweep time = 50 msec. At birth, the C II potential was seen in all infants; the Erb's point and C' potentials were seen in two-thirds. All older infants had well developed potentials at all sites. The mean latency of the Erb's point potential was stable over time. The latency of the C II potential decreased with maturation. At C', 4 components were seen, the latencies of which decreased with maturation: N1, P1, N2 and P2. The duration of N1 and P1 decreased with maturation. Standard deviations were relatively small for latencies and large for amplitudes. SEPs were adversely affected by using the 60 c/sec filter. Increasing the low frequency filter from 1 to 30 c/sec changed SEP, particularly in younger infants. Abnormal SEPs were seen in prematures surviving periventricular hemorrhage.     

Short latency somatosensory evoked potentials in patients with neurological lesions

Short latency somatosensory potentials following median nerve stimulation were recorded in patients grouped according to anatomic location of neurological lesion. Patients with cerebral lesions causing severe sensory deficit lacked a major positive wave of cortical origin that in normal subjects peaked at a mean latency of 20.5 ms. Patients with severe cervical spinal cord disease lacked all of the normal somatosensory response except for the earliest component attributed to peripheral nerve activity. Patients with brain-stem lesions showed delayed latencies of later waves and prolonged interwave latencies. However, auditory evoked potentials measured in the group with brain-stem lesions were more helpful in localization. Analysis of short latency somatosensory potentials can discriminate between peripheral nerve, spinal cord, brain-stem, and cerebral lesions. Further experience and refinement of technique of measurement should increase the value of this procedure.     

Short latency evoked potentials: new criteria for brain death?

The aim of this study was to evaluate whether the auditory brain stem responses (ABR) and short latency somatosensory potentials (SEP) from median nerve stimulation are effective tools in the confirmation of brain death. Thirty six brain dead patients were submitted to ABR and 24 to SEP in the same session. All waves of the ABR were absent in 28 (77.8 per cent) patients, while only wave I was present in the others (22.2 per cent). In SEP recordings the components later than P13 were absent in 17 (70.8 per cent) of cases; in the remaining seven patients (29.2 per cent) a N13/P13 dissociation (namely, retention of the cervical N13 and absence of the far-field P13) was found. The results suggest that SEP and ABR are reliable tools in the diagnosis of brain death and should be included in the criteria: they enable the functional status of two pathways in the brainstem to be checked, which cannot be explored by the clinical examination.     

Short latency somatosensory evoked potentials in Charcot-Marie-Tooth Disease

9 patients with Charcot-Marie-Tooth Disease (CMTD) of intermediate type (PMA type II, 10), all from the same family, presented with a significant increase of the interpeak N9-N13 latency. This increase is already present in the pre-symptomatic phase of the disease and there is no significant difference between the various patients of different ages and clinical severity, indicating that the lesions appears very early and tends to establish itself equally early. Similar behaviour is also seen in the distal conduction velocity along the sensitive fibres, while the more proximal areas seem to be relatively spared. The authors interpret these data as an expression of a distal central peripheral sensory neuropathy. In contrast, the lesion of the peripheral motor fibres, particularly in the legs, has a different and more severe pattern of evolution. Alterations in central conduction time (N13-N20) were not seen in any of the 9 patients studied.     

Short latency somatosensory evoked potentials and brain-stem auditory evoked potentials in coma due to CNS depressant drug poisoning. Preliminary observations

In patients in coma due to severe CNS depressant drug overdose the central somatosensory conduction time (CCT) after median nerve stimulation is prolonged and N20 is dispersed. Brain-stem auditory evoked potentials demonstrate delayed interpeak latencies (IPLs) I-III, III-V and I-V. This was observed in 4 out of 5 patients investigated after intake of an overdose of amitriptyline (2 cases), barbiturates, meprobamate and nitrazepam (one case each). Toxic levels of drug overdose were related to prolonged CCT and IPLs, whereas normal CCT and IPLs were found at therapeutic drug plasma levels. CCT, IPLs and dispersion of N20 decreased during the course of coma. All patients were successfully treated. It appeared that SSEP and BAEP investigations could make a distinction between a 'toxic' and a 'therapeutic' coma level in severe drug overdose. It further appeared that normalization of CCT and IPLs preceded clinical improvement.     

Intermediate and long latency SEPs in relation to clinical disability in traumatic brain injury patients

Intermediate (0-60 ms) and long latency (0-500 ms) somatosensory evoked potential (SEP) patterns were compared in terms of their relationship to degree of clinical disability in severe traumatic brain injury patients. Long latency (LL) SEP patterns correlated significantly with clinical disability as measured by the Disability Rating scale while intermediate latency (IL) SEP patterns did not. Evoked potential abnormality (EPA) scores based upon LL SEP patterns appear better able to reflect extent and severity of brain dysfunction and overall clinical condition than do IL SEP patterns for severe traumatic brain injury patients.     

Facial expressions modulate the time course of long latency auditory brain potentials

Long latency auditory brain potentials were recorded while subjects listened to bi-syllabic words spoken with an emotional expression and concurrently viewed congruent or incongruent facial expressions. Analysis of the auditory waveforms suggests the existence of a positive deflection around 240 ms post-stimulus with a clear posterior topography (the P2b component). This potential is subsequent upon the modality-specific auditory N1-P2 components and precedes the amodal N2-P3 complex. Congruent face-voice trials elicited an earlier P2b component than incongruent trials suggesting that auditory processing is delayed in the presence of an incongruent facial context. These electrophysiological results are consistent with previous behavioural studies showing an acceleration of reaction times for rating voice expressions that are part of congruent bimodal stimulus pairs. A source localisation analysis performed on the scalp EEG during the time-window corresponding to the P2b component disclosed a single dipole solution in the anterior cingulate cortex.     

Age-related changes in human middle latency auditory evoked potentials

We recorded middle latency auditory evoked potentials (MAEPs) in young (20-40 years) and elderly (60-80 years) subjects with normal hearing. The Pa component was prolonged in latency and markedly enhanced in amplitude in the elderly subjects. No changes were found in Na, or in the binaural interaction of the MAEP. Differences in Pa amplitude and latency were not due exclusively to changes in auditory thresholds, since they were not duplicated by changes in stimulus intensity, and persisted when MAEPs from selected young and old subjects were compared at similar SPL levels. The enhancement of Pa amplitude appears to reflect age-related central modifications in auditory processing.     

Age-related latency changes in the brain-stem auditory evoked potentials

The effects of age on the brain-stem auditory evoked potentials were studied on 156 healthy subjects with ages ranging from 18 to 76 years. The latencies of peaks I-VII and the interpeak latencies of I-III, III-V and I-V were consistently shorter for the female group than the male group. The females also had higher peak amplitude than the males. The effects of sex on the peak and interpeak latencies were observed in all age groups. There was a small progressive prolongation in the peak latency with increasing age, particularly peak V. Although a correlation between the age and the I-III interval was not observed, there was also a small increase with age in the interpeak latencies of III-V and I-V.     

Short latency mechanically evoked somatosensory potentials in humans.

Somatosensory potentials evoked by mechanical stimulation were recorded by surface electrodes over (1) the digital nerves in the index finger, (2) the median nerve at the wrist, (3) the median nerve near the axilla, (4) the brachial plexus, (5) the cervical cord at CII, (6) the scalp overlying the somatosensory cortex. Nerve conduction velocities varied inversely with age and ranged from 43 to 68 m/sec. Mechanically evoked potentials recorded from the electrodes overlying the digital nerves were an artifact of the finger movement. All other electrode configurations recorded potentials comparable to those evoked by electrical stimulation of nerves. These mechanically evoked potentials could prove useful in the assessment of clinical disorders of somatosensory function from receptor to cortex in man.     

Short latency somatosensory evoked potentials in children with autism

SSEP were recorded in normal volunteer, autism, MBD and MR groups in order to find electrophysiological evidence of a brain lesion. Peak latencies per 1 m body length, P1/H, P2/H and P3/H in MR, and P3/H in autism, were greater than those in normal controls. The values of interpeak latencies per 1 m body length, P1-P3/H and P2-P3/H in autism and MR, were greater than those in normal controls. These in MBD were not different from in normal controls. The cause of the increase in P1/H in MR is unknown. The increases in P1-P3/H and P2-P3/H suggest that in autism and MR there is brainstem dysfunction. It is not clear whether there is a relationship among autism, MBD and MR.     

Visual evoked potentials and long latency event-related potentials in chronic renal failure

We studied auditory event-related potentials elicited in a target detection paradigm (P300) and pattern shift visual evoked potentials (PVEPs) in 22 patients with chronic renal failure and no clinical evidence of cognitive or visual impairment. Thirteen patients were maintained on chronic hemodialysis, and 9 patients were receiving a low-protein diet. Thirty-three percent of patients receiving the low-protein diet and 58% of the dialysis patients had abnormal P300 latencies. Most patients tested had abnormal PVEP. Four hemodialysis patients had elevated serum parathyroid hormone (PTH) levels, and 9 had normal or slightly elevated values. P300 and PVEP latencies were abnormal in both groups. These observations indicate that elevated PTH levels are not solely responsible for the abnormalities in all patients. P300 and PVEP may be valuable in evaluating neuronal dysfunction in the patient with chronic renal failure.     

Effects of attention on auditory evoked middle latency potentials

The effects of attention on the auditory evoked middle latency potentials (MLPs) were examined in 23 normal subjects. Early positive-negative-positive-negative waves (about 8, 11, 15 and 18 msec peak latencies) and a late positive one (about 30 msec peak latency) were recorded from the unilateral mastoid-nose tip. The amplitudes of the early portions of MLPs to binaural 50 dB SL clicks during attention decreased as compared to those obtained when the subjects were not attending to the test stimuli. No significant difference was seen in the latency of any early wave.