Auditory brainstem responses in patients under treatment of hemodialysis

This study evaluated the effects of end stage chronic renal failure (CRF) on auditory function and changes in auditory function following a single session of hemodialysis. The experimental group included 31 patients with end-stage renal failure on chronic hemodialysis. The control group consisted of 31 healthy volunteers. The patients were examined prior to and following a session of hemodialysis. Measurements included pure tone audiometry, tympanometry and acoustic reflex measurements, auditory brainstem responses (ABR), and blood now chemistry parameters. Controls underwent the same test battery, with the exception of biochemical and hematological assessment. Prior to hemodialysis sessions, all ABR latencies except interpeak latency I-III were significantly prolonged in the experimental group. A comparison between controls and the experimental group following hemodialysis indicated that wave V absolute latency and interpeak latencies III-V and I-V were significantly prolonged in the slow repetition rate paradigm. In the fast repetition rate, absolute latencies of waves I and V and III-V interpeak latencies were prolonged in the experimental group. Comparison of ABR recordings prior to and following hemodialysis showed overall significant difference between the measures. Post hoc analysis showed a significant improvement in wave I and V latencies in the slow repetition rate and wave V latency in the fast repetition rate. This study showed that neural conduction along the auditory pathway is delayed in patients with end stage CRF as compared to healthy subjects. Dialysis sessions improve overall neural auditory function. However, patients with end stage CRF show delayed conduction even after a session of hemodialysis.     

Auditory Brainstem Responses in Patients under Treatment of Hemodialysis

This study evaluated the effects of end stage chronic renal failure (CRF) on auditory function and changes in auditory function following a single session of hemodialysis. The experimental group included 31 patients with end-stage renal failure on chronic hemodialysis. The control group consisted of 31 healthy volunteers. The patients were examined prior to and following a session of hemodialysis. Measurements included pure tone audiometry, tympanometry and acoustic reflex measurements, auditory brainstem responses (ABR), and blood now chemistry parameters. Controls underwent the same test battery, with the exception of biochemical and hematological assessment. Prior to hemodialysis sessions, all ABR latencies except interpeak latency I–III were significantly prolonged in the experimental group. A comparison between controls and the experimental group following hemodialysis indicated that wave V absolute latency and interpeak latencies III–V and I–V were significantly prolonged in the slow repetition rate paradigm. In the fast repetition rate, absolute latencies of waves I and V and III–V interpeak latencies were prolonged in the experimental group. Comparison of ABR recordings prior to and following hemodialysis showed overall significant difference between the measures. Post hoc analysis showed a significant improvement in wave I and V latencies in the slow repetition rate and wave V latency in the fast repetition rate. This study showed that neural conduction along the auditory pathway is delayed in patients with end stage CRF as compared to healthy subjects. Dialysis sessions improve overall neural auditory function. However, patients with end stage CRF show delayed conduction even after a session of hemodialysis.     

Brainstem auditory evoked responses in chronic renal failure and the effect of hemodialysis

Brainstem auditory evoked responses (BAER) were recorded in patients with chronic renal failure before commencement of chronic dialysis treatment, and in patients with end-stage renal failure on chronic hemodialysis for several years. Both groups of patients had delayed latencies of the third and fifth waves. The patients on hemodialysis revealed delayed latency of interpeak I-V as well. There was no correlation between wave latency, serum urea, creatinine, PTH or duration of chronic hemodialysis treatment. A hemodialysis session led to a slight shortening of the third wave. This study suggests that neural conduction along the brainstem in patients with chronic renal failure is delayed even before hemodialysis is started. Although 1 dialysis session may have some beneficial effect, long-term hemodialysis treatment does not seem to shorten the delay in neural conduction observed in patients with chronic renal failure.     

Effects of high-dose fentanyl anesthesia on auditory brain stem responses]

It was previously reported that high-dose (50 micrograms.kg-1) fentanyl anesthesia had no effect on auditory brainstem response (ABR). However, the effect of the dose of 100 micrograms.kg-1 of fentanyl is unknown. We examined the effects of the dose of 50 micrograms.kg-1 and 100 micrograms.kg-1 of fentanyl on ABRs in 10 patients scheduled for cardiovascular surgery. No significant change was observed immediately after infusion of 50 micrograms.kg-1 of fentanyl, but peak latencies of waves I, III and V were significantly prolonged and the amplitude of wave V was significantly decreased immediately after infusion of 100 micrograms.kg-1 of fentanyl. The interpeak latencies of I-III and I-V were not affected. Therefore, prolongations of latencies of waves III and V were due to the change of latency of wave I. These results demonstrate that high-dose (100 micrograms.kg-1) fentanyl anesthesia depresses the peripheral auditory perception but dose not depress the central conduction.     

Functional correlates of reduced central conduction velocity in diabetic subjects

In a previous publication, we presented evidence of slowed conduction speed in the central nervous systems of insulin-dependent diabetic subjects, manifest in a delay in the latency of the brainstem auditory-evoked response (BAER). In this article, we present the results of a multivariate study conducted on a larger sample of 50 insulin-dependent, adult diabetic subjects. The purpose of the study was to determine some of the functional correlates of the BAER delay; each patient received an assessment of the BAER, the late auditory-evoked potential (EP), the conduction velocities of the sural, median, and common peroneal nerves, and intellectual and emotional function, in addition to neurologic and audiologic examinations. A nondiabetic control group was matched with the diabetic group as to age and sex. The results indicated a delay in the latency of wave V, and in interpeak latencies I-III and I-V, of the BAER. The most reliable effect was on interpeak latency I-V; this suggested that the locus of the delay was in the central auditory projections, rather than in the acoustic nerve. In addition, BAER waves I, II, III, IV, and V were reduced in amplitude, as was the N1 component of the late auditory EP; the most reliable reduction in amplitude was in wave V. The effect was similar in magnitude for males and females, relative to their counterparts in the control group. The slowed BAER response appeared early in the disease and was not related to the duration of insulin treatment. It was correlated with a chronic loss of energy and the presence of sexual dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Research on the effectiveness of intermittent cervical traction therapy, using short-latency somatosensory evoked potentials

Short-latency somatosensory evoked potentials (SSEPs) were measured before and after intermittent cervical traction therapy to serve as objective indicators of therapy effectiveness. The subjects were 29 patients with myelopathy, 23 with cervical radiculopathy, 28 with cervical sprain, and 26 healthy individuals. SSEPs were recorded by stimulating the median nerve, and the negative potentials elicited from the brachial plexus (N9), neck (N11, lcN13, ucN13), and somatosensory area (N18) were measured to determine interpeak latencies and then corrected latency. As to the changes in SSEPs following traction, the N11-lcN13 and lcN13-ucN13 interpeak latencies for patients with type I and II myelopathy decreased, and the severity of myelopathy was inversely related to the degree of decrease. The ucN13-N18 interpeak latency for some patients with severe myelopathy increased. The N9-N11 and N11-lcN13 interpeak latencies for patients with cervical radiculopathy decreased, and the ucN13-N18 for patients with cervical sprain accompanied by autonomic nervous symptoms also decreased. Traction therapy might improve conduction disturbance primarily by increasing the amount of blood flow from the nerve roots to the spinal parenchyma. Received: April 16, 2001 / Accepted: November 12, 2001     

Multimodality electroneurophysiological findings in intra-axial and extra-axial lesions of the brain stem

Summary In 330 patients with a space occupying lesion of the posterior cranial fossa, the blink (BR) and masseter (MR) reflexes and brain stem auditory (BAEP) and somatosensory evoked potentials (SEP) were registered. The aim of our study was to look for electrophysiological criteria of differentiating between lesions within or outside the brain stem. The ipsilateral loss of BAEP in cerebellopontine angle tumours and the altered SEP in tumours within the brain stem turned out as frequent, almost specific findings. Prolonged ipsi- and contralateral late BR responses and prolonged MR responses, a long somatosensory central conduction time of the SEP and a prolonged wave III latency as well as a prolonged interpeak latency of the BAEP are not indicative but highly suspicious for a lesion within the brain stem. Prolonged early responses of the BR together with prolonged interpeak latencies of the BAEP are characteristic findings in cerebello-pontine angle tumours.     

Tolrestat, an aldose reductase inhibitor, prevents nerve dysfunction in conscious diabetic rats

The effect of 4 wk of streptozocin (STZ)-induced diabetes on the transmission time of the auditory-evoked brain stem response (ABR) was examined in conscious male Sprague-Dawley rats. Distal nerve transmission time of the auditory pathway (latency of peak II), which includes conduction along the 8th cranial nerve, increased in diabetic rats (n = 9) relative to nondiabetic rats (n = 17). The difference in peak II latency between diabetic and control rats was significant beginning 2 wk after the induction of diabetes (P less than .05). In contrast, 4 wk of STZ-induced diabetes had no effect on the central transmission time of the auditory pathway (interpeak latency between peaks II and IV). Oral administration of tolrestat, a structurally novel aldose reductase inhibitor (n = 8; 20 mg/kg twice daily 1 wk before and 4 wk after STZ injection), prevented the diabetes-induced increase in distal nerve transmission time. These findings indicate that experimentally induced diabetes can result in a nerve dysfunction as measured by the increased latencies of the early components of the ABR. Furthermore, because tolrestat prevents these changes in the ABR, aldose reductase and the polyol pathway are implicated in this neuropathy.     

Deterioration of auditory evoked potentials during cerebellopontine angle manipulations. An interpretation based on an experimental model in dogs

Evoked action potentials from the internal auditory meatus portion of the cochlear nerve (IAM-EAP's) and brain-stem auditory evoked potentials (BAEP's) from the vertex were simultaneously recorded during cerebellopontine angle (CPA) manipulations (retractions of the cerebellar hemisphere and the cochlear nerve) in dogs. The BAEP changes noted in these dogs were the same as those seen in patients. The IAM-EAP's showed graded deterioration related to BAEP changes. The results are as follows: Prolongation of the I-V interpeak latency of BAEP's, the most common finding during CPA manipulations, is the reflection of prolongation of the I-II interpeak latency, which is caused by conduction impairment or block of the nerve impulses between the extracranial portion of the cochlear nerve and the brain stem. The operative manipulations representing stretch or compression injury to the cochlear nerve in the CPA leads to an acute traumatic cranial nerve root lesion--a retrocochlear lesion. The obliteration of all BAEP components including wave I cannot be caused by conduction block. This is caused by occlusion of the internal auditory artery. Wave I of the BAEP's and the P1-N1 complex of the IAM-EAP's are important indicators of cochlear blood flow during surgical intervention. As possible causes of internal auditory artery obstruction, mechanical distortion of the relationship between the anterior inferior cerebellar artery (AICA) and the internal auditory artery at the junctional portion, mechanical vasospasm of the AICA-internal auditory artery complex, and ensuing no-reflow phenomena are discussed. Evoked action potentials are expected to be a useful intraoperative real-time monitor during CPA surgery that can detect rapid changes derived from cochlear artery insufficency. The real-time aspects can overcome some of the disadvantages of BAEP monitoring.     

Somatosensory evoked potentials evaluated in normal subjects and spinal cord-injured patients

Somatosensory evoked cortical potentials (SSEP's) were recorded in 27 healthy subjects using tibial and peroneal nerve stimulation with cephalic and non-cephalic references. Four major peaks were present in all recordings. Analysis of these components showed that SSEP's collected after tibial nerve stimulation with non-cephalic reference (linked earlobes) produced the most consistent clearly defined component peaks. Average latency, amplitude, and interpeak latency differences are presented for these SSEP's. Significant correlations were obtained between the height of the individual and the P1, N2, P2, and N3 latencies, and the N3-P1 interpeak latency. These results suggest that reproducible SSEP's can be obtained from tibial nerve stimulation in normal subjects using minimal numbers of stimulus presentations (28 to 64). The SSEP's from 34 patients with varying degrees of spinal cord trauma were compared with the SSEP's from normal subjects. These comparisons involved the P1, N2, P2, and N3 latencies and the interpeak latency values, as well as the amplitude values. Patients with normal sensory and motor neurological examinations could be distinguished from patients showing decreased sensory and motor findings or clinically complete lesions on the basis of peak latency and interpeak latency values. The latter two groups could not be distinguished from one another. In general, all patient groups had SSEP's of lower amplitude than did normal individuals, but the groups could not be distinguished from one another. These results indicate that SSEP's can be a useful clinical tool for differentiation of complete from incomplete spinal cord lesions, but do not invariably predict recovery of function.     

Carpal tunnel syndrome in patients on long-term haemodialysis.

The purpose of this study was to describe the pathophysiology of carpal tunnel syndrome (CTS) in patients on long-term haemodialysis. We examined 110 patients, who had been having haemodialysis for chronic renal failure and had CTS, to clarify the clinical features and electrophysiological changes in peripheral nerves. There was a significant correlation between the incidence of CTS and the duration of haemodialysis. Compared with idiopathic CTS, CTS caused by long-term haemodialysis had relatively limited postoperative improvement. Symptoms recurred postoperatively in 11 patients (19%) of those with CTS caused by long-term haemodialysis. Electrophysiological measurements of sensory nerve conduction velocity showed that it was slower in distal segments of the median nerve in patients on haemodialysis compared with normal volunteers. Nerve conduction velocity in the carpal tunnel was significantly delayed (p < 0.05) in the patients with CTS on long-term haemodialysis. N9-13 interpeak latencies were significantly longer (p < 0.05) in subjects who had had haemodialysis for at least 10 years. All the patients with advanced destructive spondyloarthropathy had longer N9-13 interpeak latency. These results suggest that CTS in patients on long-term haemodialysis has its basis in neuropathy. The clinical course of CTS in these patients is different from that of patients with idiopathic CTS, because the neuropathy involves not only the carpal tunnel region, but also the proximal part of the median nerve both diffusely and progressively.     

Effects of lumbar epidural anesthesia on brainstem auditory response

Auditory brainstem responses (ABR) are used increasingly to monitor the integrity of neural pathways in anesthetized patients. To evaluate the effect of epidural anesthesia on the central nervous system, we studied the effects of lumbar epidural anesthesia with lidocaine on the ABR in 10 patients. The seven peak latencies (waves I-VII) and amplitudes (waves I-VII) of the ABR were recorded before and 15 min after epidural anesthesia. Peak latencies of waves III, IV, V, VI, VII increased after epidural anesthesia compared with control values. Amplitude of waves II only decreased significantly following epidural anesthesia compared with control values. We further compared the interpeak latencies to investigate the brainstem transmission. Interpeak latencies (I-II, II-III, III-IV, IV-V, V-VI, VI-VII) were unchanged from the control values except waves VI-VII interval. Interpeak latencies of every second peak (II-IV, IV-VI, V-VII), of every third peak (II-V, III-VI, IV-VII), of every forth peak (I-VI, II-VII), of every fifth peak (I-VII) increased after epidural anesthesia compared with control values. The data obtained in the study demonstrated that lumbar epidural anesthesia with lidocaine prolonged the interpeak latencies of ABR. Considering that the waves of ABR are related to anatomically distinct sites in the auditory pathway (I; Acoustic nerve, II; Cochlear nucleus, III; Superior olivary complex, IV; Lateral lemniscus, V; Inferior colliculus, VI: Medial geniculate body, VII; Auditory radiation), the delay in the latencies of ABR seems to be present in the time intervals which involve more than two or three synaptic transmissions.     

CARPAL TUNNEL SYNDROME IN PATIENTS ON LONG-TERM HAEMODIALYSIS

The purpose of this study was to describe the pathophysiology of carpal tunnel syndrome (CTS) in patients on long-term haemodialysis. We examined 110 patients, who had been having haemodialysis for chronic renal failure and had CTS, to clarify the clinical features and electrophysiological changes in peripheral nerves. There was a significant correlation between the incidence of CTS and the duration of haemodialysis. Compared with idiopathic CTS, CTS caused by long-term haemodialysis had relatively limited postoperative improvement. Symptoms recurred postoperatively in 11 patients (19%) of those with CTS caused by long-term haemodialysis. Electrophysiological measurements of sensory nerve conduction velocity showed that it was slower in distal segments of the median nerve in patients on haemodialysis compared with normal volunteers. Nerve conduction velocity in the carpal tunnel was significantly delayed (p &lt; 0.05) in the patients with CTS on long-term haemodialysis. N_9-13 interpeak latencies were significantly longer (p &lt; 0.05) in subjects who had had haemodialysis for at least 10 years. All the patients with advanced destructive spondyloarthropathy had longer N_9-13 interpeak latency. These results suggest that CTS in patients on long-term haemodialysis has its basis in neuropathy. The clinical course of CTS in these patients is different from that of patients with idiopathic CTS, because the neuropathy involves not only the carpal tunnel region, but also the proximal part of the median nerve both diffusely and progressively.     

The effect of acute hypocarbia on human auditory brainstem responses

The effect of acute hypocarbia on auditory brainstem responses (ABRs) was studied in nine patients scheduled for cranioplasty under N2O/O2/fentanyl anesthesia. PaCO2 was allowed to stabilize for 15 min before ABR recordings were obtained during normocarbia [N] (PaCO2 = 40.8 +/- 1.9 mmHg), hypocarbia [H] (PaCO2 = 25.9 +/- 0.8 mmHg), and after return to normocarbia [NR]. No significant change in the absolute or interpeak latencies of waves I, III, and V was observed between during [N] and [H]. On return to normocarbia, the absolute latencies of waves I, III, and V increased slightly but significantly when compared with [N] or [H], although the interpeak latencies were unchanged. It is concluded that the latencies of ABR are unaffected directly by acute hypocarbia to a PaCO2 of 25 mmHg. The increase of absolute latencies on return to normocarbia may be explained by increased middle ear pressure with N2O and/or increased intracranial pressure.     

Length of tumor-cochlear nerve contact and hearing outcome after surgery for vestibular schwannoma

OBJECTIVES: Tumor size is likely to be a major determinant of hearing preservation after surgery for vestibular schwannoma. Findings in some large case series have not supported this concept, possibly due to variation in the technique used for tumor measurement. The authors sought to determine if the length of tumor-cochlear nerve contact was predictive of hearing outcome in adults undergoing resection of a vestibular schwannoma. METHODS: Patients who underwent a hearing-preserving approach for resection of a vestibular schwannoma at one institution by a neurosurgeon/neurotologist team between 2001 and 2005 were screened. Patients with American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) Class A or B hearing preoperatively were included. Magnetic resonance images were reviewed and used to calculate the length of tumor-cochlear nerve contact. Tumors were also measured according to AAO-HNS guidelines. RESULTS: Thirty-one patients were included, 8 (26%) of whom had hearing preservation. Univariate analysis revealed that extracanalicular length of tumor-cochlear nerve contact (p = 0.0365), preoperative hearing class (p = 0.028), I-V interpeak latency of the brainstem auditory evoked potential (p = 0.021), and the interaural I-V interpeak latency difference (p = 0.018) were predictive of hearing outcome. Multivariate analysis confirmed the predictive value of extra-canalicular length of contact and preoperative hearing class (p = 0.041 and p = 0.0235, respectively). CONCLUSIONS: Vestibular schwannomas with greater lengths of tumor-cochlear nerve contact increase a patient's risk for hearing loss after surgery with attempted hearing preservation. Involvement of the internal auditory canal produces a constant risk of hearing loss. Data from the experience of a single surgical team can be used to estimate the probability of good hearing outcome for any given patient with serviceable hearing and a vestibular schwannoma.     

Influence of dietary magnesium on the amplitude of wave V of the auditory brainstem response

Thirty-six weanling guinea pigs were fed either a low (600 ppm) or normal (3000 ppm) diet of magnesium for 8 weeks. One half of each diet group received intramuscular injections of magnesium-depleting drugs, furosemide and gentamicin. The other half were controls and received equal intramuscular injections of saline. Auditory brainstem responses were obtained from all animals before and after 8 weeks of treatment of diet and drugs to examine the effects of treatment upon hearing and auditory brainstem function. A three-way analysis of variance of dietary magnesium, by drug and by sex, showed no significant differences in auditory brainstem wave V thresholds, wave V latencies, or interpeak wave I-V latencies between the control and experimental groups. The low magnesium diet group, which received drugs, had significantly greater wave V auditory brainstem response amplitudes. Results can be explained on the basis of magnesium influencing the uptake of calcium into both the hair cells and associated brainstem pathways.     

Reduced variance of latencies in pudendal evoked potentials after normalization for body height

The value of the Somatosensory Evoked Potentials (SEP) in the assessment and detection of neurological disorders could be considerably enhanced if the normative standards of (SEP) characteristic parameters were normalized taking into account all other systematic sources of variance. The present study examines the influence of body height on the peak and interpeak latencies of the pudendal somatosensory evoked potentials. We examined the peak latency (L1) of the evoked potential recorded at the L1 vertebra and the onset latency (ON_c) of the cortical evoked potentials, after stimulation of the pudendal nerve, as a function of body height in 40 normal male subjects (age 20–40 years). Significant positive correlation was found between both (ON_c) latency and ON_c-L1 interpeak latency and body height (H). Assuming that the latter is proportional to the length of the neural pathways, the experimental data were fitted using a theoretical model representing the conduction in the sensory neuraxis as a function of body height. Using the estimated fitting functions, we normalized our data with regard to a typical value of body height. The normalized values of the aforementioned latencies reveal a significantly reduced variance, as compared to the original ones, and consequently their diagnostic importance is significantly increased. Similar procedures applied to the L1 (spinal) latencies and the latencies of the bulbocavernosus reflex (BCR) reveal no correlation with body height and this is discussed on the basis of neuroanatomical considerations. © 1995 Wiley-Liss, Inc.     

Evoked potentials following diazepam or fentanyl

The effects of fentanyl or diazepam on somatosensory, visual and brainstem auditory evoked potentials were studied in 13 healthy patients scheduled for elective surgery. Following control recordings of evoked potentials, either diazepam 20 mg or fentanyl 200 micrograms was administered intravenously. Evoked potentials were then recorded twice in the subsequent hour. No significant changes occurred in the latency or amplitude of somatosensory, visual or brainstem auditory evoked potentials. Although dose-related changes in evoked potential latencies and amplitudes have been demonstrated with both the inhalational and intravenous anaesthetics, these changes did not occur with diazepam or fentanyl used alone. An anaesthetic technique based on these two drugs would be suitable when intra-operative evoked potential monitoring is required to assess ischaemia and preservation of evoked responses.     

Effects of isoflurane and halothane on the auditory and somatosensory evoked potentials

The effects of isoflurane and halothane anaesthesia on brainstem auditory (BEAR) and somatosensory evoked potentials (SEP) were recorded in 15 patients; eight received isoflurane and seven halothane. Atropine alone was given as premedication. After induction of anaesthesia with thiopentone, it was maintained with 50% nitrous oxide in oxygen. Ventilation was controlled. Isoflurane and halothane concentrations were gradually increased to 3%. Recordings were made at 1%, 2.5% and 3%. There were statistically significant differences in the latencies of SEP and BEAR with increasing concentrations of anaesthetic. The BEAR waves significantly affected were wave V and the latency between peaks I to V (p less than 0.001); for the SEP, it was wave N20. SEP central conduction time was prolonged with both anaesthetics (p less than 0.001). The effects of isoflurane and halothane were similar. These results could not be explained by changes in central body temperature or end-tidal carbon dioxide concentration. The study showed a dose-related direct effect of both anaesthetic agents on the brainstem auditory and somatosensory evoked responses. It may be that the measurement of changes in evoked potentials could be a useful indicator of anaesthetic depth.     

Clinical study on short latency somatosensory evoked potentials for cervical myelopathy]

The purpose of this study was to examine the clinical value of S-SEP (short latency somatosensory evoked potentials) as a routine test of spinal cord function. On the basis of a preliminary study determining the optimal recording conditions in normal individuals, S-SEP measurement was carried out in patients with cervical myelopathy to examine its diagnostic value for spinal cord lesions. In these patients, the best recordings of N9, N11, and N13 were obtained from the cervical spinous processes with linked ear reference (A1 + A2). In severe myelopathy, the N11-N13 interpeak latency was prolonged. Those with impaired bladder function or decreased deep sensation showed a prolonged N9-N13 interpeak latency. In cases of C3-4 and C4-5 lesions, the N9-N13 and N9-P14 interpeak latencies were significantly more prolonged than in those with C5-6 lesions. The interpeak latencies from P14 to N9 and N11 gradually became shorter postoperatively.