Brainstem auditory evoked potential combined with high resolution cranial base CT can optimize the diagnosis of auditory nerve injury / 中华创伤杂志(英文版)

PURPOSE@#Auditory nerve injury is one of the most common nerve injury complications of skull base fractures. However, there is currently a lack of auxiliary examination methods for its direct diagnosis. The purpose of this study was to find a more efficient and accurate means of diagnosis for auditory nerve injury.@*METHODS@#Through retrospectively analyzing the results of brainstem auditory evoked potential (BAEP) and high-resolution CT (HRCT) in 37 patients with hearing impairment following trauma from January 1, 2018 to July 31, 2020, the role of the two inspection methods in the diagnosis of auditory nerve injury was studied. Inclusion criteria were patient had a clear history of trauma and unilateral hearing impairment after trauma; while exclusion criteria were: (1) severe patient with a Glasgow coma scale score ≤5 because these patients were classified as severe head injury and admitted to the intensive care unit, (2) patient in the subacute stage admitted 72 h after trauma, and (3) patient with prior hearing impairment before trauma. According to Goodman's classification of hearing impairment, the patients were divided into low/medium/severe injury groups. In addition, patients were divided into HRCT-positive and negative groups for further investigation with their BAEP results. The positive rates of BEAP for each group were observed, and the results were analyzed by Chi-square test (p < 0.05, regarded as statistical difference).@*RESULTS@#A total of 37 patients were included, including 21 males and 16 females. All of them were hospitalized patients with GCS score of 6-15 at the time of admission. The BAEP positive rate in the medium and severe injury group was 100%, which was significantly higher than that in the low injury group (27.27%) (p < 0.01). The rate of BEAP positivity was significantly higher in the HRCT-positive group (20/30, 66.7%) than in the HRCT-negative group (1/7, 14.3%) (p < 0.05). Twenty patients (54.05%) were both positive for BEAP and HRCT test, and considered to have auditory nerve damage. Six patients (16.22%) were both negative for BEAP and HRCT test, and 10 patients (27.03%) were BAEP-negative but HRCT-positive: all the 16 patients were considered as non-neurological injury. The rest 1 case (2.70%) was BAEP-positive but HRCT-negative, which we speculate may have auditory nerve concussion.@*CONCLUSION@#By way of BAEP combining with skull base HRCT, we may improve the accuracy of the diagnosis of auditory nerve injury. Such a diagnostic strategy may be beneficial to guiding treatment plans and evaluating prognosis.

Alterações retrococleares na esclerose sistêmica: relato de casos / Retrocochlear impairments in systemic sclerosis: a case report study

RESUMO Objetivo Relatar três casos de pacientes portadores de Esclerose Sistêmica e que apresentaram alterações retrococleares. Método Trata-se de um estudo de relato de casos de três indivíduos com esclerose sistêmica e alteração retrococlear, acompanhados em um serviço de reumatologia. Todos os pacientes realizaram o Potencial Evocado Auditivo de Tronco Encefálico e, quando necessário, nova audiometria. Resultados Todos os indivíduos apresentaram perda auditiva do tipo sensorioneural. Não foi identificado na avaliação audiológica básica qualquer resultado que sugerisse alteração retrococlear, porém o PEATE apresentou-se alterado. Conclusão Pode-se concluir que o estudo revela alterações retrococleares nesta população, ocorrendo tanto nas latências absolutas quanto no intervalo interpico. E, neste contexto, reumatologistas e fonoaudiólogos, ao acompanharem pacientes com esclerose sistêmica, devem estar atentos para a possibilidade da ocorrência dessa alteração nessa população. Revela também, a necessidade de estudos epidemiológicos sobre o tema.

ABSTRACT Purpose To report three cases of patients with Systemic Sclerosis (SSc) and retrocochlear impairments. Methods This is a case report of three individuals with SSc and retrocochlear impairments assisted at a rheumatology outpatient clinic. All individuals underwent Brainstem Auditory Evoked Potential (BAEP) and, when necessary, audiometry. Results All three individuals presented sensorineural hearing loss. Although no retrocochlear impairment was identified in the basic audiologic evaluation, the BAEP results were altered. Conclusion Retrocochlear impairments were present in the individuals under study, both in the absolute latencies and interpeak interval, thereby demanding the attention of rheumatologists and speech-language pathologists to such changes during the monitoring of SSc patients. The results also show a need for epidemiological studies on the theme.

Application of neurophysiological monitoring and microsurgical technique in acoustic neurinoma resection / 中华显微外科杂志

Objective To investigate the application of neurophysiological monitoring and microsurgi-eal technique in acoustic neurinoma resection, exploring the significance of neurophysiological monitoring in facial and auditory nerve reservation of acoustic neuronma microsurgery. Methods Accompanied with EMG and BAEP nerve monitoring, 113 patients harboring acoustic neuroma were treated surgically by the subocipi-tal retrosigmoid approach for reserving facial and auditory nerve. The facial nerve was stimulated to evaluate its function during late-operation. Postoperative facial and auditory nerve function were valuated in all the postop-erative following up. Results All of them were treated microsurgically via the suboccipitai retrosigmoid ap-proach. Total tumors resection was achieved in 102 cases (90.3%), subtotal resection in 6 cases(5.3%) and partial resection in 5 case (4.4%). The facial nerve was preserved anatomically in 98 cases (86.7%), the functional valuation of facial nerve according to the House-Brakman (H-B) postoperatively: 86 cases (76.1%) in class Ⅰ -Ⅱ , 12 cases(lO.6%) in class Ⅲ-Ⅳ and 15 cases (13.3%) in class Ⅴ-Ⅵ. The acoustic nerve was preserved anatomically in 40 cases (35.4%). It denoted the good function of facial nerve responsing sensi-tively to electrostimulation ≤ 4mA at the end of operation. Conclusion Assisted with the intraoperative electrophysiological monitoring techniques, it would be greatly facilitate the preservation of facial and auditory nerve in acoustic neuroma resection. Simultaneously, it would valuate the functional convalescence by late-op-erative electrostimulation in the postoperation.

Analysis of Results of Brainstem Auditory Evoked Potential In 79 Cases of Language-Impaired Children / 医学研究杂志

Objective To study the change and its application of the brain stem auditory evoked potentials (BAEP) in language -impaired children. Methods We used evoked potentials Denmark Wedy Keypoint device to analysis the BAEP test results of the 79 cases of children in our hospital from August 2006 to December 2008. Rsults The total rate of BAEP abnormalities in children was 64.6% , of which 15.7% for one of the bilateral BAEP wave disappeared, 11.8% for the unilateral BAEP wave disappeared with the other side of the wave being abnormal BAEP,and 72.5% for the wave latency (PL) and wave interphase (IPL) abnomal. Conclusion BAEP is a sim-ple, noninvasive, threshold stability, results reliable and reproducible method of examination. For language -impaired children of hearing damage and abnormal neural pathway ,it can provide valuable objective indicators.

Influence of Acupuncture on Cephalic Acupuncture Points Region Over the Brain-stem Evoked Potential of Patients Suffering Insufficient Blood-Supply of Vertebral Basilar Artery / 中国中医药信息杂志

Objective From the angle of electrophysiology, go further into the mechanism of action of acupuncture treatment to the insufficient blood-supply of vertebral basilar artery and at the same time, make a comparison of the effects between the acupuncture on cephalic meridian points and zonation cephalic acupuncture. Methods Through the contrast before and after adopting the self-acupuncture on the testees of 28 cases (including healthy persons of seven cases and TIA patients of 21 cases), observe the change of immediate effect of all waves latent period values of BAEP. Results The BAEP wave latent period of healthy persons (exclusive of I wave of auditory fainting region) assumes a relative delay within the physiological range and by comparison between points and region, the delay of V-wave Baihui point is evidently higher than that of auditory fainting region. However, the latent period of all waves of TIA patients is relatively moved up, especially there are evident differences before and after the I-wave acupuncture is carried out. Viewing from the comparison between points and region, there is no significant difference. Conclusion The function of acupuncture lies in the adjustment of antagonistic body state and it is most effective under the pathological state. Acupuncture will play the main role of excitation to the auditory nerve conduction of BAEP of TIA patients (from cochlea to midbrain) and the influence over the peripheral nerves is more sensitive than over the center ones. Although points and region have their own relative specificities, there is no significant difference between them.

The Relativity Study of BAEP and BEAM/EEG in Newborn Hypoxia-Ischemic Encephalopathy / 医学研究杂志

Objective Study the special value of the brainstem auditory evoked potential(BAEP)and Brain Geography Diagram(BEAM/EEG)for diagnosis of Newborn HypoxicIschemic Encephalopathy(HIE),the correlation between BAEP,BEAM/EEG and HIG,and the relation with HIE linger effect,so as to evaluate clinical curative effect,find out the best treatment time,lower the occurrence of linger effect.Methods the BEAM/EEG and BAEP were detected synehronously by adopting 16 traots of BEAM/EEG and BAEP instruments for HIE before treatment,at thirtieth day,the third Month,the sixth Month,the twelfth Month and the twenty-fourth Month respectively.Results The BAEP,BEAM/EEG have special diagnostic value on nerve cell function recovery,examination of recovery period in particalar.The research discovers the both are not synehronous in recovery period,the BAEP recovers is later than BEAM/EEG;for heavy degree HIE,BAEP recovering is slow with bad therapy effect,BAEP index sign is more sensitive to BEAM/EEG to assess linger effect.Conclusions Simple BEAM/EEG damaye indicates the brain cortex iniury only,so the prognosis is good;while BAEP damage suggestes the patiemts have brain stem nerve cell injury simultaneously,with bad prognosis for the heavy degree abnormality.in combination with BAEP and BEAM/EEG in clinical practiae,investigation of recovery degree of HIE herve cells by kinds of electric physiology angles it would have important value to perfect the treatment of HIE.

Study on The Effects of Chronic Renal Failure on Hearing and Its Mechanism / 浙江中医药大学学报

[Objective]To observe the effects of chronic renal failure (CRF)on hearing and investigate its mechanism.[Methods] Twenty-nine male wistar rats were randomly divided into four groups:Ⅰthe normal rats as control for 12 days (n=6); Ⅱrats given adenine(ig) for 12 days (n=8); Ⅲthe normal rats as control for 24 days (n=6);Ⅳ rats given adenine(ig) for 24 days(n=9). The rat model of CRF was produced by being perfused of adenine [300mg/kg]for 12d and 24d. Brain-stem auditory evoked potential(BAEP) was utilized to evaluate the auditory function and renal tissue morphology was observed; Serum sampling was used to determine the content of Cr, BuN. The expression of NOSⅡin the cochlear was measured by immunohistochemical technique.[Results] After adenine given for 12d or 24d, the Cr and BuN were in significant higher level than that in control group. The BAEP thresholds were gradually higher than that in control group, the BAEP delitescence prolonged. Light microscopic observation of renal tissue showed that the degree of fibrosis was gradually higher. Data of immune histochemistry about the cochlear tissue showed that the expressions of NOSⅡ were feebly positive in the cochlear vassal texture, inner-outer hairy cell and helical-ganglion cell, and following functional damage of the kidney, their expressions reinforced gradually, amongst which strongest expression was vassal texture, the next helical-ganglion cell, the last inner-outer hairy cell.[Conclusion]CRF can result in deafness. It is likely concerned with toxic effects of the metabolizable substance, the metabolizable dysfunction of the electrolyte, shortage of trace elements, etc. One of the important mechanisms of the effects of CRF on hearing is the toxic damage of NO to cochlea.

The Role of Brainstem Auditory Evoked Potential in the Diagnosis of Cerebral Concussion / 医学研究杂志

Objective To observe the change of brainstem auditory evoked potential(BAEP)of cerebral concussion patients.Methods The results of BAEP of 60 patients with cerebral concussion were analyzed and were compared with the results of CT test.Results Among the results of 60 cases of cerebral concussion,the abnormal rate of BAEP was 83%;the abnormal rate of CT test results was 21%.Conclusion BAEP is of great value in the early diagnosis of cerebral concussion and in the efficient evaluation of the function of brain stem.

Comparison of BAEPs in three different kinds of brainstem disorders / 中华物理医学与康复杂志

Objective To compare the brainstem auditory evoked potential (BAEP) in patients with different kinds of brainstem disorders, so as to offer a significative electrophysiological means for diagnosis and differential diagnosis of different kinds of brainstem disorders. Methods BAEP was recorded from 80 cases of vertebrobasilar arterial insufficiency, 56 cases of acoustic neuroma and 47 cases of chronic cerebellar degeneration and compared with that from 50 healthy people. Results The abnormal rates of the three different case groups were 73.75%, 94.61%, 89.36%, respectively. Each group of patients demonstrated their own characteristics with regard to the BAEP. Conclusion Each of the three brainstem disorders has its own characteristics with BAEP.

Effects of Early Intervention on Functional Outcome and NGF in Brain of Rats with Brain Damage / 中国心理卫生杂志

Objective: To explore the effects of early intervention on functional outcome and the repair mechanisms in rats with hypoxic-ischemic brain damage (HIBD). Methods: A HIBD rat model was established by ligating either uterine vessel of one pregnant horn. The way of intervention was the neonatal handling and enriched environment. One trial passive avoidance response, brainstem auditory evoked potential (BAEP) and NGF levels in the brain were used as assessment index. Results:(1) In the one trial passive avoidance response test, the medial step-through latency (STL) of intervention group (n=18) was much longer than that of non-intervention group (n=15) (P

The Application of BAEP ln Neonates with Hyperbilirubinemia / 中国医师杂志

2 weeks ) were screened by BAEP. Results Hearing-ability of 11 children(11/23,47.8%) was abnormal,one month later hearing-ability of 2 children was abnormal, and there months later hearing-ability of only 1 child was abnormal. Conclusion Hyperbilirubinemia may cause hearing-ability damage in neonates and BAEP is one of effective audiometric means.

Diagnostic value of SPECT,TCD and BAEP to vertebral-basilar artery ischemia vertigo / 临床神经病学杂志

Objective To investigate the diagnostic value of SPECT,TCD and BAEP to vertebral basilar artery ischemia vertigo Methods 100 cases of vertebral basilar artery ischemia vertigo were inspected by SPECT,BAEP and TCD All the results were analyzed and compared Results Among 100 cases, it shows that the diagnostic rate of SPECT is 80 percent,BAEP is 58 3 percent and TCD is 78 percent Conclusion SPECT is found having the highest diagnostic rate,it sensitively and accurately reflects the position of cerebral ischemia Although BAEP having the lowest diagnostic rate, it can still effectively shows Brain Stem Ischemia Comparing with SPECT and BAEP, TCD is simple and convenient to carry out It sensitively reflects the conditions of cerebral vessel and cerebral blood stream,but it is insensitive to make sure the position Therefore, three of them offer the valuable,external and diagnostic proof to vertebral basilar artery ischemia vertigo,and they can have a role of inter reinforce

Determination of Follow-up Time of Abnormal Brainstem Auditory Evoked Potential in Infancy

OBJECTIVE: To determine optimal follow-up time of BAEP for the infants with abnormal BAEP at the initial screening test. METHOD: Control group consisted of 85 infants with normal BAEP and experimental group consisted of 41 infants with abnormal BAEP at the first examination but normalized on regular follow-up examinations. Gestational age (correctional age), intrauterine period, birth weight, delivery method, presence of perinatal asphyxia, Apgar score after 1 minute, the highest serum bilirubin level, and the results of cranial ultrasonography were recorded. The above parameters, peak and interpeak latencies of BAEP were compared between both groups. RESULTS: Lower correctional age at the first BAEP, shorter intrauterine period, and lower birth weight were noted in experimental group (p<0.001). The average correctional age when BAEP had normalized in experimental group was 45.0+/-5.8 weeks, which was much later than 40.2+/-2.8 weeks in control group (p<0.001). 90.2% of infants among experimental group revealed normalized BAEP within 48 weeks, and 95.1% within 51 weeks according to correctional age, or within 12 weeks after initial examination. CONCLUSION: We recommend that BAEP should be rechecked after 48 weeks by correctional age for the high risk infants who were abnormal with initial screening BAEP.

Electrophysiologic Neuromonitoring Changes during Tumor Surgery in Cerebellopontine Angle

BACKGROUND: Intraoperative neurophysiologic monitoring(INM) is well known to be useful method to reduce intraoperative complications during tumor surgery in cerebellopontine angle(CPA). We investigated the changes of INM during the surgery. It might be helpful to keep one's eyes on which monitoring modalities are reluctant to change during the operation. METHODS: We included 49 subjects who had undergone CPA tumor surgery under INM. Their pathology was as follows; vestibular schwannoma in 37, other cranial nerve schwannoma in 3, meningioma in 5 , cyst in 2. The modalities of monitoring were short latency auditory evoked potentials(AEP), somatosensory evoked potentials(SEP) , facial and trigeminal nerve EMG(EMG). Stimulation of SEP was on left or right median, posterior tibial nerves. We studied the frequency of abnormal INM changes and the factors affecting it. RESULTS: The subjects who had abnormal changes in at least one monitoring modality were 19(38.8.%). AEP changes were in 6.1%, SEP in 12.2% and EMG in 24.5%. The AEP monitoring had no potentials from II through V wave in 28 subjects(57.1%). SEP monitoring had improvement in 2 subjects and aggravation in 6, especially involved in median nerve SEP. Tonic EMG activities were observed in 3 facial muscles of 3 subjects, 2 of 4, 1 of 5. Regarding the pathology of tumor, meningioma had much more changed INM than vestibular schwannoma. The volume of tumor was bigger in abnormal INM group than normal group although it is not statistically significant. Also abnormal SEP and EMG group had bigger mass than normal group. CONCLUSIONS: INM has frequent electrophysiologic changes during tumor surgery in CPA. Especially EMG can be changed the most frequently. The larger tumor are, the more frequently abnormal changes in INM of CPA tumor surgery are.

The Significance of the EEG, Brainstem Auditory Evoked Potential ( BAEP ) and Brain Ultrasonographic Findings of Asphyxiated Newboms on the Neurological Outcome

PURPOSE: The objective of this study was to analyze the relationship between the electrophysiological studies(EEG and BAEP) and brain ultrasonography and the prognosis of the newborn infants with asphyxia. METHODS: Clinical records, including electrophysiological findings of EEG and BAEP and brain ultrasonography, of 29 term infants with neonatal asphyxia, who had been admitted to the Pediatric Department of Chosun University Hospital between January 1994 and June 1997 were reviewed retrospectively. RESULTS: Out of the 29 cases that returned for follow up, 23 cases were neurodevelopmentally normal, but 6 cases showed delayed development on the Korean Denver Developmental Scale Test(KDDST). Of 19 cases with abnormal EEG findings, 5 showed delayed developrnent on the KDDST(P>0.05). Follow up EEG was performed in 10 cases', 8 of them were normalized, and two remained abnormal without delayed development on the KDDST. Of 8 cases with abnormal brain ultrasonographic findings, 5 showed delayed development on the KDDST(P0.05). Follow up BAEP was performed in 8 cases, and all cases were normal. CONCLUSION: These results suggest that abnormal findings of EEG and BAEP in the asphyxiated term newborn were reversible, but abnormal brain ultrasonographic findings, especially intracranial hemorrhage, were significantly correlated with delayed development.

Clinical Application of BAEP Changes in Patients with Brainstem Lesion

Recently, brainstem auditory evoked potentials(BAEP;s) have been employed in many clinical situation as a sensitive electro-physiological parameter to assess the central auditory pathway and, indirectly, the integrity of brainstem functions. In this study, the author has recorded BAEP's in 17 patients with brainstem lesion who were admitted to the Department of neurosurgery, Kyung Hee University Hospital and analyses the abnormalities related with site of lesion by clinical signs and CT scan, and outcome and clinical course. The results are as followings: 1) In the patients suspected brainstem lesions, abnormalities of BAEP's, particularly BTT(brainstem transmission time) are very sensitive indicator to the diagnosis of brainstem lesions. 2) Abnormalities of BAEP's are useful in localizing the site of lesions within brainstem. 3) The patients with bilateral pathological BAEP's clearly have a poor prognosis compared with those with unilateral pathological BAEP's and the patients with flat wave form have the higher possibility of poor prognosis than those with prologation of latency or abnormal wave form. 4) There are significant correlation between changes of follow-up BAEP's and clinical course.

The Findings of Brainstem Auditory Evoked Pontential(BAEP) and Somatosensory Evoked Potential(SSEP) in Head Injury

There were 84 cases of brainstem auditory evoked potential(BAEP) and 90 cases of somatosensory evoked potential(SSEP) from the 124 cases of head injury. The studies were performed within the first three days after head injury in most cases and after ten days in emergency operative cases. The results of BAEP and SSEP studies recorded from 67 normal volunteers were used as a control group. The latency, amplitude and wave pattern of the evoked potential were examined and a peak or interpeak latency were considered abnormal when it exceeded the corresponding mean(2SD found in the control group. The wave patterns were arranged in BAEP as grade I:all waves were normal; grade II: waves I, II, III were abnormal;grade III:waves IV, V, VI were abnormal;grade IV:all waves were abnormal. In SSEP as grade I:all waves were normal;grade II:N13 wave was abnormal;grade III:N19wave was abnormal;grade IV:all waves were abnormal. The abnormal findings by percentage were:47.6% in latency of BAEP, 68.9% in latency of SSEP, 49.4% in wave pattern of BAEP and 87.8% in wave pattern of SSEP. The BAEP was superior to SSEP in correlation to clinical parameters including GCS, duration of coma, basal cisterns in initial brain CT scan and Glasgow outcome scale(GOS). As a BAEP criterion, the wave V latency and the BCT(III-V interpeak latency) and as a SSEP criterion, the central conduction time(N19-N13) were more correlated to duration of coma and GOS. The appearance of the basal cisterns on initial brain CT is significantly correlated with wave V and BCT of BAEP only. Grade I and II were reliable predictors of a good prognosis. Therefore, we concluded that BAEP and SSEP are adjunctively diagnostic tests for determining the outcome of head injuried patients.

Clinical Evaluation of Evoked Potentials in Cerebrovascular Diseases

With 4-Channel Nicolet-CA 1000 clinical averager, somatosensory evoked potentials(SSEP) and brainstem auditory evoked potentials(BAEP) were studied in 40 patients with intracerebral hematoma and 40 patients with cerebral infarction. SSEP was more sensitive response in putamen(20/23) or thalamic(6/7) hemorrhage and infarction of middle cerebral artery territory(13/28). in contrast BAEP was high percentage in abnormality in brainstem or cerebellar lesion. Cortical wave(N18) was usually not traceable in large size of hematoma or having midline shift in brain CT scan. There was close correlation between the severity of motor weakness and abnormality of SSEP. The best neurological outcome was found in the patients of P24 wave formation. In our results, SSEP and BAEP seemed to be very useful for evaluation of stroke patients.

Correlation of Evoked Potentials and Regional Cerebral Blood Flow in SAH Patients with Vasospasm

With 4 channel Nicolet-CA 1000 clinical averager and 133 Xenon inhalation method, somatosensory evoked potentials (SSEP), brainstem auditory evoked potentials (BAEP) and regional cerebral blood flow (r-CBF) were studied in 30 patients with ruptured cerebral aneurysms. 8 out of 30 patients had abnormal SSEP, 11 out of 30 patients had abnormal BAEP and 4 out of 14 patients had decreased r-CBF. The SSEP was abnormal in 6 out of 10 patients with severe vasospasm but in only 2 out of 20 patients without vasospasm or with mild and moderate spasm. The BAEP was abnormal in 5 out of 10 patients with severe vasospasm but 6 out of 20 patients without spasm or with mild and moderate spasm. Regional CBF was decreased in 3 out of 4 patients with severe vasospasm but only 1 out of 10 patients without spasm or with mild and moderate spasm. Abnormal SSEP, BAEP & decreased r-CBF in patients with severe vasospasm indicated a poor prognosis. We got the results as follows ; 1) Abnormal SSEP, BAEP and decreased r-CBF are correlated with severity of vasospasm in SAH patients. 2) Abnormal SSEP and BAEP correlated with the clinical status. 3) Brain stem transmission time (BTT) is less sensitive than central conduction time (CCT) as indicator of vasospasm.

Evoked Potentials in Brain Death

With 4 Channel Nocolet-CA 1000 clinical averager, somatosensory evoked potentials(SSEP), brainstem auditory evoked potentials(BAEP) and visual evoked potentials(VEP) were studied in 23 patients who fulfilled the clinical criteria for brain death. The results were as follows : 1) In SSEP, all patients had identifiable Erb's point wave and 11 out of 23 patients(48%) had cervical portion wave, but none of these patients had identifiable cortical portion wave. 2) In BAEP, 19 out of 23 patients(83%) had no identifiable BAEP waveforms, including wave I, and 4 patients(17%) had only wave I. 3) In VEP, 15 out of 23 patients(65%) had no identifiable VEP waveforms and 8 patients(35%) had short latency-low amplitude wave with no any of the longer latency components of central system origin.