Abstract: The scientific workshop, organized under the 6th European Framework Programme, the Marie Curie Host Fellowship for the Transfer of Knowledge "NoiseHear" Project, by the Nofer Institute of Occupational Medicine (Åódź, Poland, 15-16 November 2006), gathered world specialists in noise, chemicals, and ototoxicity, including hearing researchers, toxicologists, otolaryngologists, audiologists and occupational health physicians.The workshop examined the evidence and the links between isolated exposure to organic solvents, combined exposure to noise and solvents, and effects on the auditory system. Its main purpose was to review the key scientific evidence to gather the necessary knowledge for developing adequate occupational health policies. This paper summarizes the workshop sessions and subsequent discussions.
Abstract: OBJECTIVE: This study evaluated efferent medial olivocochlear (MOC) function in patients with multiple sclerosis (MS). Various afferent auditory abnormalities have been described in MS, but there is a paucity of data on efferent function. The brain stem is a site of predilection for MS plaques and the efferent MOC pathway may be affected at this level. METHODS: The study included 30 patients who had normal hearing. According to MRI findings, they were divided into two groups: those with an identifiable brain stem lesion (n = 10) and those with MS lesions in other parts of the central nervous system but without demonstrable MS plaques in the brain stem (n = 20). MOC function was evaluated by the olivocochlear suppression test, using transient evoked otoacoustic emissions. All subjects underwent standard auditory tests, including pure-tone audiometry and recording of auditory brain stem evoked responses. Twenty-two healthy subjects with normal hearing, matched for age and gender, served as a reference group for the auditory data. RESULTS: The results showed that 66.6% of all patients had reduced MOC function, particularly those (90%) with identified lesions of the brain stem on MRI. Furthermore, abnormal MOC function was found in 55% patients without evidence of a brain stem lesion on MRI. CONCLUSIONS: This study provides the evidence for a deficit of efferent auditory function in the majority of patients with MS. Taking into consideration the possible roles of the MOC system in processing of auditory information, abnormal MOC suppression in patients with MS may explain a variety of auditory presentations that are currently largely overlooked. This study also highlights the diagnostic value of the MOC suppression test as a site-of-lesion diagnostic test in MS and in identifying subtle brain stem lesions undetected by MRI, suggesting that subtle brain stem lesions may exist and that the MOC suppression test is sufficiently sensitive to detect them. Accordingly, the MOC suppression test may provide a tool for an early diagnosis of MS.
Abstract: Audiological testing, interviews and exposure measurements were used to collect data on the health effects of styrene exposures in 313 workers from fiberglass and metal-product manufacturing plants and a mail terminal. The audiological test battery included pure-tone audiometry, distortion product otoacoustic emissions (DPOAE), psychoacoustic modulation transfer function, interrupted speech, speech recognition in noise and cortical response audiometry (CRA). Workers exposed to noise and styrene had significantly poorer pure-tone thresholds in the high-frequency range (3 to 8 kHz) than the controls, noise-exposed workers and those listed in a Swedish age-specific database. Even though abnormalities were noted on DPOAE and CRA testing, the interrupted speech and speech recognition in noise tests were the more sensitive tests for styrene effects. Further research is needed on the underlying mechanisms to understand the effects of styrene and on audiological test batteries to detect changes in populations exposed to solvents.
Abstract: Industrial hearing loss has generally been associated with noise exposure, but there is a growing awareness that industrial solvents can have an adverse effect on the auditory and vestibular systems in man. Both animal experiments and human studies point to an ototoxic effect of industrial solvents, as well as some central auditory and vestibular disturbances. This review examines the research from the last four decades in an attempt to get an overview of the available evidence. Research shows that industrial solvents are ototoxic in rats. The majority of the solvents studied cause a loss of auditory sensitivity in the mid-frequencies in rats, affecting outer hair cells in the order OHC 3 > OHC 2 > OHC 1 . Inner hair cells are generally unaffected. Spiral ganglion cells are most vulnerable to trichloroethylene. Simultaneous exposure to solvents and noise results in a synergistic effect; the pattern of trauma mirrors that due to solvent exposure rather than noise, but is more enhanced. There is a critical level when synergy occurs. The effects of solvents on the vestibular system are neurotoxic and influence the vestibulo-oculomotor system in both animals and humans; humans also present with problems in postural sway. There is a strong suggestion from human studies that solvents are ototoxic in man, but findings show that both the peripheral and central auditory pathways can be affected. Hearing losses can be in the high frequency region or can affect a wider range of frequencies. Hearing loss and balance disturbances can occur at levels below permitted levels of exposure. The synergistic effect of combined exposure to solvents and noise has also been noted in humans, resulting in greater hearing losses than would be expected from exposure to noise and solvents alone. The findings from both human and animal studies indicate that exposure to industrial solvents or to industrial solvents and noise can have an adverse effect on hearing and balance. The implications for industry and hearing conservation are far reaching.
Abstract: Aircraft maintenance workers are exposed to a mixture of solvents in the presence of intermittent noise. For this study these workers exposed to solvent mix and noise, were compared with mill workers exposed to noise alone, printed circuit board operatives exposed to solvents alone and those exposed to none who acted as controls. Tympanometry, acoustic reflex thresholds, transient and distortion product otoacoustic emissions, auditory brainstem potentials, nystagmography and posturography were examined. There was a significant effect on pure tone thresholds for both noise and solvents+noise. The distortion product otoacoustic emissions declined with frequency and exhibited lower DP amplitude with noise compared to solvents and noise group. The transient emissions showed a similar effect. Over 32% of subjects with solvent and noise exposure had abnormalities of the auditory brainstem responses in terms of interwave interval prolongation. The mean acoustic reflex thresholds showed a pattern of differences which differentiate noise from solvent and noise groups. The contralateral pathway appears to be differentially affected by solvent exposure. 32% of subjects in the solvents and noise group had an abnormal posturographic finding. In the solvents and noise group 74% had abnormalities of saccades, 56% of pursuit and 45% of optokinetic nystagmus.
Abstract: Different scientific groups have studied and continue to study the health impacts of physical and chemical agents in the environment. In most cases, every study group has considered the health effect as being solely due to the air pollutant(s) under investigation, for example air pollution without due regard for the simultaneous presence of noise pollution whereas both have an impact on the cardiovascular system. Or in the case of noise studies the contribution of solvent, asphyxiant or metal exposures has not been considered, which can have an impact on hearing impairment. One can, therefore, question the stringency of the available evidence of epidemiological studies in both fields to warrant the consideration of air pollutants as confounding or aggravating factors in studies of specific effects due to noise (and vice versa). In this paper we weigh the existing evidence on the association of noise and air pollutant exposure and associated health impacts. In forthcoming publications, the authors will consider the influence of other factors, which can confound noise studies but are currently not included in the analysis.
Abstract: Solvents are commonly used in many industries and therefore exposure to multiple solvents is a common occupational hazard. A myriad of peripheral and central nervous system toxic effects can be produced by both acute and chronic low level exposures. Dizziness is often an early symptom of solvent exposure but has only in recent times been investigated specifically. The indications from the studies reviewed are that vestibular disturbances are common in workers exposed to solvents and dose-response relationships need to be established for early detection of vestibulo-toxicity.
Abstract: Exposure to multiple physical and chemical agents is common in occupational environments but workplace hazards and occupational safety criteria for combined exposures is lacking. NoiseChem is an European Commission research project examining the effects of exposure to noise and chemicals on hearing and balance. Partners in Sweden, Finland, France, Denmark, UK and Poland with expert guidance from partners in USA will examine workers and study the mechanisms of action in animals to determine the levels of risk associated with joint exposure to noise and solvents. This paper briefly outlines the project details.
Abstract: A disadvantage of magnetic resonance imaging (MRI) is the high level of noise produced (peaking between 122 dB and 131 dB). We used otoacoustic emissions (OAEs) as a method to quantify the effect of MRI-generated noise on the cochlea. OAEs were measured in 16 patients before and after MRI and in 16 controls. OAEs decreased in patients after MRI, but the controls, who were not exposed to MRI noise, showed no decrease over the same period. The change in OAEs shows a clear effect of MRI noise on cochlear function, despite use of earplugs. The importance of correctly fitted earplugs cannot be underestimated.
Abstract: Exposure to multiple physical and chemical agents is common in occupational environments but workplace hazards and occupational safety criteria for combined exposures are lacking. NoiseChem is an European Commission research project examining the effects of exposure to noise and chemicals on hearing and balance. Partners in Sweden, Finland, France, Denmark, UK and Poland with expert guidance from partners in the USA will examine workers and study the mechanisms of action in animals to determine the levels of risk associated with joint exposure to noise and solvents. This paper briefly outlines the project details.
Abstract: Noise exposure is the most common cause for the generation of tinnitus. This study evaluated the variability of spontaneous emissions in industrial workers exposed to noise and reporting the presence of tinnitus in comparison with those exposed to noise but without tinnitus. The assumption being that exposure to noise leads to some instability within the cochlea, which alters the spontaneous emission activity. Thus those experiencing tinnitus may show greater variability than those without tinnitus. 198 mill workers in Poland exposed to noise levels between 85-95dBA for a mean of 12+/-6.6 years, 104 of whom had reported the presence tinnitus and 94 without tinnitus were evaluated for otoscopy, audiometry and otoacoustic emissions. The tests were repeated between 5-10 days in most subjects to check for variability. There were significant differences in the mean age, pure tone average, transient emissions amplitude and variability between groups with and without tinnitus. There were no significant differences between sessions for these measures in either group. Those with tinnitus had poorer thresholds by an average of around 15dB, and reduced TOAE of around 2.6dB compared with those without tinnitus. There are a number of factors such as age, pure tone thresholds and tinntius, which may be responsible for the reduction in emissions. For the purposes of examining SOAE stability, all SOAE peaks were classed as stable if SOAE frequency in the two sessions remained unchanged and variable if SOAE peaks were present in both sessions but shifted in frequency or present in one sessions and absent in the other. SOAE were present in 73.1% of tinnitus group and in 50% of non-tinnitus group. Of these 92% of the tinnitus group had present and variable SOAE whereas 48.9% of the non-tinnitus group did. Thus the positive predictive value was calculated at 65% for those with variable SOAE having tinnitus and significantly higher at 86% negative predictive value for those with stable SOAE having no tinntus. The likelihood ratio of tinnitus being present given that SOAE are present and variable is 1.87 and is significantly reduced for no tinnitus given that SOAE are present and stable at 0.156. This study has clearly demonstrated that the incidence of spontaneous emissions is higher in noise-exposed workers than previously observed and the stability from week to week is significantly lower in those with subjective tinnitus.
Abstract: Noise exposure is the most common cause of tinnitus. Noise induced permanent tinnitus (NIPT) can derive from occupational noise exposure, leisure noise or acoustic trauma. In general NIPT is high - pitched and tonal. The most common observed frequency of tinnitus on pitch matching is the same as the worst frequency for hearing. The sensation level of NIPT is usually low and sometimes negative. There is no correlation of significance between the discomfort caused by NIPT and audiometric findings. In occupational NIPT the interval between the start of noisy work and the appearance of tinnitus is long (many years) but with leisure noise and acoustic trauma the interval between exposure and tinnitus is frequently very short (immediate). It is a problem that the incidence of musically induced tinnitus is increasingly more common. It is also a much greater handicap for a young individual to suffer from tinnitus than from a small high tone hearing loss. Much more attention needs to be given to improve these matters. The treatment of NIPT is not different from tinnitus treatment in general.
Abstract: The difference between the legal assessment of the disability associated with noise induced hearing loss and that experienced by the worker has not as yet been successfully resolved. Legal assessment is driven by financial consideration rather than the rehabilitation needs of the subject. The aim of this paper is to present this problem and consider the formulae currently used in the UK and Poland in the assessment of noise induced hearing disability.
Abstract: Otoacoustic emissions have been shown to be extremely useful in screening for hearing impairment in babies. This review considers the current evidence available with regard to the role of otoacoustic emissions in the screening for noise induced cochlear damage. A number of studies indicate that otoacoustic emissions provide an indication of cochlear damage prior to any change in the pure tone audiometric threshold. There is also some evidence that the medial efferent system evaluation using contralateral sound activated suppression of emissions indicates dysfunction after noise exposure. Increased variability of spontaneous emissions has also been shown to be associated with the presence of tinnitus in various aetiologies.
Abstract: Tinnitus is frequently accompanied by noise-induced hearing losses, and perhaps as it is assumed--particularly with those arising from exposure to impulsive types of noise. In order to explain it and to estimate a prevalence of tinnitus in the industrial, impulse noise workers the group of 261 drop-forge operators exposed to impulses with peak levels of 135 dB versus 169 age-matched controls was subjected to otological and audiometric examination, and then the complaints for tinnitus in both groups have been analysed. The prevalence of tinnitus, highest in operators with longer exposure duration (> 10 years) was found in 184 individuals (70.4%) versus 6 (3.5%) in controls. The findings closely corresponded with the degree of impulse noise-induced hearing loss. As the maximum audiometric notch was mostly localised at 6 kHz and rarely at 4 kHz, consequently the approximate pitch of the tinnitus was related to the frequencies where hearing was most affected. It is concluded that impulse noise-induced tinnitus may be sometimes more severe in its effects than is hearing loss, thus it creates an additional reason for strict hearing conservation programmes.
Abstract: Otoacoustic emissions and contra-lateral sound activated efferent suppression of emissions were examined to determine whether they provide any early indication of auditory damage from exposure to noise. Three groups were studied: noise exposed workers (n=50, mean age 42 years), patients with Meniere's disease (n=24, mean age 48 years) and normal subjects (n=24, mean age 41 years). All subjects underwent routine pure tone audiometry, tympanometry and otoacoustic emission testing. As a number of studies have shown that with hearing threshold better than 30 dB HL, emissions are almost always present and are generally absent with hearing loss greater than 30 dB HL, subjects in this study were sub grouped into these two categories in order to examine the incidence of emissions. Absence of emissions in subjects with mean hearing thresholds better than 30 dB HL varied from 0% in normal controls, 8% in patients with Meniere's disease and a significantly high 56% in noise exposed workers despite similar mean hearing thresholds for all groups. The mean transient emission levels for the noise exposed workers was significantly lower than the controls and Meniere's groups. This study clearly indicates that in the noise-exposed group there is sub clinical and sub audiometric damage to the outer hair cells responsible for generation of otoacoustic emissions. Of those with normal otoacoustic emissions, the efferent suppression was absent in 60% of noise exposed workers but in only 3.8% of control subjects implying that the efferent control may also be affected in a significant proportion despite normal hearing thresholds and emissions.
Abstract: OBJECTIVE: Tinnitus may be caused by a lesion or dysfunction at any level of the auditory system. This study explores cochlear mechanics using otoacoustic emissions in patients with tinnitus after head injury, in whom there seems to be evidence to support dysfunction within the CNS. METHODS: The study included 20 patients with tinnitus and other auditory symptoms, such as hyperacusis and difficulty in listening in background noise, after head injury, in the presence of an "intact" auditory periphery (normal or near normal audiometric thresholds). They were compared with 20 normal subjects and 12 subjects with head injury, but without tinnitus, who had similar audiometric thresholds. In all subjects otoacoustic emissions, including transient click-evoked (TEOAEs) and spontaneous otoacoustic emissions (SOAEs), were recorded, and a test of efferent medial olivocochlear suppression, consisting of recording of TEOAEs under contralateral stimulation, was performed. RESULTS: A significantly higher prevalence of SOAEs (100%), higher TEOAE response amplitudes, and reduced medial olivocochlear suppression in patients with tinnitus in comparison with subjects without tinnitus have been found. CONCLUSION: These findings have been interpreted to be an extracochlear phenomenon, in which the reduction in central efferent suppression of cochlear mechanics, leading to an increase in cochlear amplifier gain, was subsequent to head injury. Auditory symptoms in these patients seemed to constitute the "disinhibition syndrome".
Abstract: The suppression of transiently evoked otoacoustic emissions by contralateral sound stimulation is thought to occur as a result of the action of the efferent pathway from the superior olivary complex to the cochlea via the medial olivo-cochlear neurons. The purpose of this study was to determine the time taken for this pathway to activate the suppressive mechanism in response to contralateral sound in normal human subjects. The time for onset of suppression was found to be between 7 and 20 ms.
Abstract: Auditory brainstem potential components II and V are delayed in the contralateral recording in comparison with that ipsilateral to the stimulus. Wave III is recorded earlier contralaterally. The effect of increasing stimulus repetition rate on the ipsilateral/contralateral latency differences in these components was examined. There is a progressive increase in latency from Wave I to Wave V ipsilaterally with an increase in stimulus rate; however, contralaterally there is no further increase in latency after Wave III. At 40 Hz stimulus rate, therefore, the ipsi/contra difference in the latency of Wave V disappears, suggesting that there is a differential effect of peripheral and central adaptation on the ipsilateral and contralateral auditory pathways.
Abstract: Hearing impairment can be the cause of significant disability and handicap. This medico-legal case demonstrates the need for accurate assessment of both the severity and type of hearing loss if the best clinical management is to be provided. In particular, the case identifies the critical role of additional, objective auditory testing when pure tone audiometry, which depends on the subjective response of the individual, is inconsistent or indicates severe hearing impairment.
Abstract: Evoked otoacoustic emissions (EOAE) are active mechanical responses from the cochlea which provide information about the integrity of the preneural cochlear receptor mechanisms. It may be hypothesised, therefore, that if a hearing impairment is neural in origin, normal EOAEs may be obtained from the cochlea, which, although dissociated, is functioning normally. This study examined the status of the cochlea with EOAE in patients with cochlear (Meniere's disease) and neural (surgically proven acoustic neuroma) disease. In patients with presumed cochlear lesions, no emissions were present with mean hearing worse than 40 dB across a frequency range of 0.5 to 4 kHz. Similarly, an EOAE was not present in any of the 26 acoustic neuroma patients studied when the average (0.5 to 4 kHz) hearing was greater than 40 dB. We conclude that dissociation of the cochlea in patients with acoustic neuroma appears to be rare and, in fact, cochlear involvement occurs in most cases. Possible mechanisms responsible for the effect on the cochlea in this group include degenerative changes due to chronic partial obstruction of the blood supply by the tumour, biochemical alterations in the inner ear fluids, loss of efferent control of active mechanical tuning, and hair cell degeneration secondary to neuronal loss in the eighth nerve.
Abstract: The effects of contralateral acoustic stimulation on evoked otoacoustic emissions (OAE) were examined in three subject groups in order that the impact of efferent olivocochlear bundle section (as a consequence of vestibular neurectomy) could be compared with normal findings, and with a control surgical population. Results demonstrated that the inhibitory effect of contralateral noise on OAE amplitude was absent from the cochlea with severed efferent fibers. These findings appear to be independent of acoustic reflex activity, as suppression was absent despite normal reflexes. Inter-aural suppression of emissions recorded from the patients' intact cochleae act as a control and show a clear reduction in amplitude during contralateral stimulation in a frequency specific pattern consistent with normal findings. Patients who had undergone a similar surgical approach for vascular decompression of the VIIIth nerve without vestibular nerve section, were studied in order to assess the impact of retrolabyrinthine surgery on inter-aural suppression. Inhibition of OAE amplitude was maintained in all control cases in both the operated and intact sides, and was consistent with suppression observed in normal subjects, suggesting that the surgical procedures had not disturbed inter-aural suppression of otoacoustic emissions. It is concluded that the olivocochlear efferent system, when activated by low level contralateral acoustic stimulation, has an inhibitory role in controlling the cellular mechanisms responsible for the generation of otoacoustic emissions in humans. OAE techniques in conjunction with contralateral acoustic stimulation may thus prove to be of value in providing a rapid and non-invasive clinical test of efferent function and offer a means of investigating the functional significance of the efferent auditory system in humans.
Abstract: Transiently evoked otoacoustic emissions can be suppressed with simultaneous contralateral sound stimulation. This is considered to be effected via the efferent pathway from the superior olivary complex (SOC) to the contralateral cochlea. This study examined this effect in patients with extrinsic and intrinsic lesions of the brainstem which may affect the efferent pathway either within the vestibular nerve which carries the efferent bundle to the cochlea or within the brainstem at the level of the SOC. Suppression is reduced or absent in these patients and the site and size of the lesion determines whether the suppression is affected unilaterally or bilaterally. Lesions affecting the auditory afferent pathway without significant alteration in hearing appear to affect the efferent pathway too.
Abstract: This study demonstrates that, following unilateral vestibular neurectomy, the inhibitory effect of contralateral acoustic stimulation on evoked otoacoustic emissions is absent. The patient acts as her own control in that the unoperated side shows normal suppression of otoacoustic emission amplitude with contralateral acoustic stimulation. The lack of interaural suppression of otoacoustic emissions on the sectioned side, in the presence of normal acoustic reflex threshold levels, provides evidence that observed phenomena are not merely a function of middle ear reflex activity. It is concluded that the lack of inhibition in the operated ear is due to the sectioning of the olivocochlear bundle within the inferior vestibular nerve, removing the efferent control of the receptor cells. Otoacoustic emissions recorded during contralateral acoustic stimulation may thus provide a rapid, non-invasive means of investigating the functional of the efferent auditory system.
Abstract: This study examines the acoustic reflex threshold criteria, derived from a large group of patients with cochlear hearing loss proposed by Cohen & Prasher (1992), in order to evaluate their effectiveness in differentiating between cochlear and retro-cochlear lesions. This criterion was tested on 63 patients with surgically confirmed cerebello-pontine angle (CPA) lesions. The false results obtained with this and other criteria were compared. The best balance between the false positive and negative results in the cochlear and retrocochlear group is provided by the criterion of any two adjacent test frequencies (proposed in the companion paper) having an upper limit of 105 dB for hearing below 60 dB and 110 dB for hearing over 60 dB. This study has also singled out the interaural difference criterion as the best diagnostic indicator with the lowest false results with only 1 false negative from 63 CPA cases and 3 false positive cases from 61 cochlear lesions with hearing thresholds over 55 dB.
Abstract: In this study several methods of defining the relationship between the magnitude of cochlear hearing loss and the acoustic reflex threshold (ART) levels were examined, with a view to defining the appropriate upper limits of ART that would ease clinical applicability and reduce the false positive rate. The 90th percentile, two standard deviations (SD) from the mean, the regression method and an empirical method based on the scatter plots of the ART at each activator frequency were all applied to the results of 99 patients with cochlear and/or peripheral vestibular pathology. The upper limits of ART defined on the basis of the scatter plots provided the most appropriate upper limits for different ranges of hearing loss, with relatively few false positives. A clinical criterion based on the ART levels at adjacent frequencies is proposed, which further reduces the false positive rate and could also prove effective in the differential diagnosis of cochlear from retro-cochlear lesions.
Abstract: Event-related potentials and reaction time measures to auditory discrimination tasks of graded difficulty were used to separate cognitive from motor processing time in 27 patients with newly diagnosed, previously untreated Parkinson's disease and later on optimal levodopa treatment. Before treatment event-related potential P3 and task performance were normal but the reaction time was prolonged compared with age matched controls. After treatment P3 latency was significantly prolonged and the reaction time reduced suggesting a dopamine induced dissociation between cognitive and motor processing. In early Parkinson's disease cognitive processing time remains normal but the motor processing time is prolonged. Dopamine replacement is followed by significantly reduced motor processing time despite increased cognitive processing time. Motor processing may reflect the dopamine status of the putamen whereas dopaminergic over-stimulation of other regions may adversely affect cognitive processing in patients treated with levodopa.
Abstract: An unusual case is presented of a patient with an acoustic neuroma, in whom the responses recorded with the usual derivation of ipsilateral recording and stimulation resulted in a normal response, whereas that derived contralaterally was abnormal. The patient was also reported to have a normal magnetic resonance scan although the tomograms revealed a widening of the internal auditory meatus and subsequent histology confirmed a schwannoma. Postoperatively the hearing was preserved and the brainstem responses showed a typical 'acoustic picture' with a delay of Waves III and V both ipsi and contralaterally. Subsequent testing showed an improvement in the latency of Wave V. Certain hypotheses are advanced regarding the mechanism involved in the latency differences observed between ipsi- and contralateral recordings, but the significance of abnormal prolongation of the latencies of certain components occurring independently in the contralateral response remains obscure. However, this patient's example clearly shows its value in clinical testing.
Abstract: Myalgic Encephalomyelitis (ME) is a form of post viral fatigue syndrome resulting in myalgia and fluctuating fatiguability. Symptoms reflecting central nervous system dysfunction are common and include muscle weakness, headache, sensory disturbances, poor short term memory and impairment of concentration. In view of the fact that sensory and cognitive disturbances are experienced by many patients objective evidence was sought with multi-modality sensory evoked potentials and auditory event-related cognitive potentials in a group of ME patients both with and without the enteroviral antigen, VP1 test positive. The auditory brainstem, median nerve somatosensory and pattern reversal checkerboard visual potentials were normal for all 37 patients tested. In contrast to the sensory potentials significant differences in the mean latencies of the cognitive potential N2 and P3 were found. Reaction times were also significantly prolonged but the performance in terms of error was not significantly affected. No significant difference emerged in any of the parameters for the VP1 test. P3 was abnormal in latency or amplitude in 36% of the VP1 positive patients for the frequency discrimination task and 48% for the more difficult duration discrimination task. The abnormalities indicate attentional deficits in some patients and slower speed of information processing in others. The prolonged latencies observed in these patients have not been observed in patients with depression in many other studies.
Abstract: Bilateral sensorineural hearing loss may introduce grossly dissimilar cochlear distortion at the two ears, causing abnormal demands to be made upon the cortical analytical centres which normally receive congruent information. As a result, the prescription of binaural hearing aids may be a handicap rather than a help. In order to explore this possibility, 10 normal subjects were presented with simulated, dissimilar cochlear distortion at the two ears. Discrimination scores with binaural presentation were poorer than the best monaural score and there were clear indications that in the former, subjects selectively attended to one ear and neglected the other. In contrast, binaural presentation of the same simulated distortion resulted in a significant improvement, compared with the monaural discrimination score. Inability of the cortex to contend with discongruent speech input from the two ears may be a factor contributing to the rejection of binaural hearing aids in some individuals.
Abstract: Acoustic reflex thresholds (ART) and auditory brainstem responses (ABR) were measured in 69 patients referred to the Neuro-otological clinic on the suspicion of a retrocochlear lesion. The pure-tone selection criterion was an average hearing loss of less than 60 dB at 0.5, 1, 2, and 4 kHz, with no thresholds exceeding 70 dB and only one threshold exceeding 60 dB. Both tests proved independently to be most effective in the diagnosis of cerebello-pontine angle (CPA) tumours and to a lesser extent for brainstem lesions. The ABR was positive in 100% of CPA group and 90% in the brainstem group compared with 93% and 70% respectively for the ART. The combination of the two tests provides patterns of abnormality which are more disease specific. In the CPA cases the most common and consistent patterns of abnormality were the unilateral delay of Wave V or III and V of the ABR associated with a vertical ART pattern indicative of an abnormality of the ipsi and contralateral reflexes on stimulating the affected side. Intrinsic brainstem lesions most commonly resulted in bilateral ABR abnormalities combined with the full-house ART pattern indicative of bilateral abnormalities of both ipsi and contralateral reflexes.
Abstract: 22 patients with unilateral acoustic neuromas were assessed audiometrically pre- and post-operatively. A high proportion (36%) were found to have a hearing loss of 10 dB or more (6 frequency average) in the contralateral ear in the post-operative period. The evidence points to a cochlear site of the loss, and serial audiograms suggest that the hearing deteriorates in the immediate post-operative period. Follow-up audiometry at three months or more showed that the hearing recovered to pre-operative levels. The possible mechanism of the hearing loss is discussed.
Abstract: We have monitored the electrocochleogram (ECochG) of 24 patients, using a transtympanic electrode, during acoustic neuroma excision. All patients had unilateral tumours with good preoperative hearing and complete excision was achieved in each case. Of the 24 patients, seven retained some hearing, however, a further two patients had normal ECochG waveforms at the end of operation but were nevertheless deaf. Thus, there is not an invariable correlation between immediate preservation of the ECochG and hearing. As expected, tumour size was important in hearing preservation. Five of seven patients with tumours less than 1.5 cm in diameter retained some hearing after operation, whereas 15 of 17 patients with tumours greater than 1.5 cm in diameter were deaf.
Abstract: Intraoperative electrocochleographic monitoring has been used in an attempt to protect cochlear nerve function during acoustic neuroma excision. One patient is presented with an apparently intact cochlear nerve and waves N1 and N2 preserved at the end of surgery, but no hearing on subsequent testing. Fifteen months after operation, cochlear microphonics and the summating potential were still present, but N1 and N2 had disappeared. There had been no improvement in her hearing and there were no consistent brainstem auditory evoked potentials on the affected side. A possible explanation for these findings is given.
Abstract: Intra-operative electrocochleography (ECochG) was used in an attempt to monitor the action potential of the cochlear nerve during acoustic neuroma surgery in 14 patients with useful pre-operative hearing. Five patients had ECochG potentials preserved and yet only three could hear when tested audiometrically later. Of those losing the potentials intra-operatively all were subsequently deaf and the pattern of waveform loss allowed determination of the probable cause of hearing loss. Complete excision of the tumour was achieved in each case regardless of the ultimate effect on the AP as it was not felt justified to risk subsequent recurrence. In common with other studies one of the best prognostic factors for these preservation of hearing was found to be the size of the tumour.
Abstract: Fourteen patients with hereditary motor and sensory neuropathy (HMSN), 12 of Type I and 2 of Type II, were assessed for auditory dysfunction. Five patients complained of hearing loss and all had pure-tone audiograms outside the normal range, while one patient who did not complain of hearing impairment also had an abnormal pure-tone audiogram. Assessment of loudness function, speech audiometry and brainstem auditory evoked potentials (BAEP) suggested that the hearing loss was the result of VIII nerve dysfunction, a conclusion supported by the abnormality of the electrocochleogram (ECochG) in one patient.
Abstract: Audiometric investigations and electrophysiologic recordings of cochlear and brain-stem auditory evoked potentials (BAEPs) were performed in 13 patients to elucidate further the type of hearing disorders in Ramsay Hunt syndrome. Transtympanic electrocochleography showed no enhancement of summating potential and did not suggest secondary endolymphatic hydrops. The recording of BAEPs was clearly abnormal in several of the 13 patients. The striking feature of the abnormalities in these patients was the prolongation of the latencies of waves III and V with the preservation of wave I, which clearly suggests retrocochlear involvement. In all the patients tested, abnormalities of the BAEPs were present only on the affected side. It is possible, on the basis of BAEP findings, to suggest that in Ramsay Hunt syndrome both cochlear and retrocochlear involvement may occur.
Abstract: Peak latency variation and the temporal interrelationships of the auditory event-related potential were investigated in 12 normal adults (ages 28-42). Measures of variation were based on both conventional averages and single trials. Estimates of N1, P2, N2 and P3 latencies were made on a trial-by-trial basis to target stimuli recorded from Fz, Cz and Pz scalp locations. Results showed that single-trial latency variability of the auditory ERP differed both among the various components and between subjects. Larger standard deviations were measured for the later N2 and P3 components than the earlier N1 and P2 components. Regression analyses between various component latencies indicated a strong covarying relationship between N2 and P3, with N2 accounting for up to 61% of the variance of P3 latency at Pz. Earlier N1 and P2 components added little to the overall prediction of either P3 or N2. For the other components, P2 accounted for 9-16% of the variance of N2, while N1 accounted for approximately 1% of the variance of N2; N1 accounted for 8-10% of the latency variation of P2. The correlations between single-trial peak latencies and RTs were positive but of low magnitude. The highest correlations between peak latency and RT were found for N2 (r = 0.33) and P3 (r = 0.24). The low correlations between the single-trial latencies of N1 and P3 suggest that the processes reflected by these components are independent and support a distinction between the earlier and the later components of the ERP. The close temporal coupling between N2 and P3 suggests that N2 may reflect cognitive properties in common to P3 in stimulus evaluation processes.
Abstract: Brain stem potentials from three groups of patients, namely those with pure progressive autonomic failure, Parkinson's disease and multisystem atrophy with progressive autonomic failure (Shy-Drager syndrome) were compared with each other and a group of normal subjects. In virtually all the patients with multisystem atrophy with progressive autonomic failure the brain stem potentials were abnormal in contrast to normal findings with Parkinson's disease. The closely associated group of patients with progressive autonomic failure alone also revealed no abnormalities of the BAEP. This separation of the two groups, Parkinson's disease and progressive autonomic failure from multisystem atrophy with progressive autonomic failure is important clinically as multiple system atrophy of the Shy-Drager type has extra-pyramidal features closely resembling Parkinsonism or a late onset cerebellar degeneration. From the abnormalities of the brain stem response in multisystem atrophy with progressive autonomic failure, it is clear that some disruption of the auditory pathway occurs in the ponto-medullary region as in nearly all patients there is a significant delay or reduction in the amplitude of components of the response generated beyond this region. The most likely area involved is the superior olivary complex.
Abstract: The neuro-otological findings are described in 3 unrelated patients who had xeroderma pigmentosum. All had impaired hearing. Routine audiometric assessment suggested that the hearing loss was of cochlear origin; brainstem evoked potentials in 2 patients and electrocochleography in 1 support this conclusion. Two adult patients had a supranuclear ophthalmoplegia. Vestibular function was mildly deranged and visual suppression of the vestibulo-ocular reflex impaired.
Abstract: The effect of contralateral white noise stimulation on ipsilaterally presented click evoked brain stem potentials was examined. Continuous contralateral white noise does not influence the brain stem response components but pulsed white noise simultaneously presented with the clicks produced a central masking effect which was observed as an amplitude reduction confined to Wave V. Our findings confirm those of Zwislocki (1971) that pulsed noise is a more effective central masker than continuous noise. A computer addition of the responses to pulsed white noise and clicks recorded independently revealed no reduction in Wave V amplitude but the response to the two stimuli presented simultaneously showed a specific reduction in Wave V amplitude. No change in the latency of Wave V was observed to suggest any 'cross-over' masking of the click stimulus. Patients with total unilateral deafness did not exhibit this phenomenon. The effect of a time delay of the masker to one ear in relation to the click presented to the other ear reduced the amplitude of Wave V less than when the two stimuli were presented simultaneously. The reduction in the amplitude, being specific to Wave V, suggests that the effect is central and that the particular locus for this aspect of central masking is at the level of the inferior colliculus.
Abstract: Ten patients with an accepted diagnosis of Friedreich's ataxia have been examined neuro-otologically, and oculomotor, vestibular and auditory function assessed. Brainstem auditory evoked potentials (BAEPs) were also recorded. A high incidence of various eye movement disorders was noted. Some of these were indicative of cerebellar dysfunction. Reduced vestibular function and impaired hearing were common to most of the patients. BAEPs were also abnormal in the majority; reasons underlying these abnormalities are discussed. Neuro-otologically, the patients did not constitute an homogeneous group. The findings cast doubt upon the accuracy and validity of the currently accepted criteria for the diagnosis and classification of the spinocerebellar degenerations.
Abstract: Transtympanic electrocochleography (ECoG) was performed on 32 normal ears, 40 ears affected by hair cell damage without any evidence of endolymphatic hydrops (sensory damage) and 44 ears affected by established Menière's disease. The amplitude of the summating potential (SP) and the amplitude of the action potential (AP) were measured at a click stimulus intensity level of 100 dB HL. The SP amplitude was expressed as a percentage of the AP amplitude. In normal ears, the mean SP/AP ratio was 25% (range 10%-63%). In sensory damage, the SP/AP ratio was 13% (range 0%-29%), and in Menière's ears, the SP/AP ratio was 51% (range 29%-89%). In this series, an SP/AP ratio of 29% provided a diagnostic dividing mark between the sensory damage and Menière's-affected ears. Although this precise division was probably fortuitous, it does suggest that ECoG is a useful tool in the differential diagnosis of these two types of cochlear disorders.
Abstract: Different means of identifying the presence of cerebello-pontine angle (CPA) tumours using brainstem auditory-evoked potentials (BAEP) were evaluated. The results from 33 ears affected by tumours were compared with BAEP from 50 normal ears and 23 ears affected by Menière's disease. Measurement of inter-aural latency differences correctly identified 97% of tumours from the normal group, but only 81% of tumours from the Menière group. Comparison of different interwave interval measures showed that the NI to NV interval was the best criterion and correctly identified 90% of the tumours from both the normal and the Menière groups. The use of transtympanic electrocochleography (ECochG) is discussed. Used alone, ECochG was of limited value in detecting CPA tumours except in five out of nine deaf ears where no BAEP were recorded but 'disconnection' action potentials were encountered. By combining BAEP and ECochG, the NI to NV interval could be identified with certainty. Combined BAEP and ECochG recordings were only undertaken when NI was unclear on BAEP recordings or when the ECochG was indicated clinically for the identification of endolymphatic hydrops. In this series, the combined use of BAEP and ECochG resulted in a tumour detection rate of 100% with a false positive rate of zero. The BAEP from the unaffected ear recorded from the ipsilateral and contralateral sides were compared. Significant NI to NV delay was noted, especially on recording from the contralateral side, when there was distortion of the brainstem due to a large tumour. The article concludes with an appendix of six illustrative case reports.
Abstract: Brainstem auditory evoked potential (BAEP) amplitude is modified according to whether or not the stimulus is applied monaurally or binaurally. In normal subjects, wave V amplitude increases by an average of 68.7% upon changing stimulation from monaural to binaural. From earlier studies there is evidence that brainstem potential amplitude is reduced in patients with multiple sclerosis (MS) but none to suggest that binaural stimulation results in increased amplitude. This study evaluated the extent of binaural summation of BAEPs in patients with MS. In a large majority of patients with MS who have no hearing deficit, BAEPs showed no increase in wave V amplitude on binaural stimulation. This finding is in contrast to the normal group and thus has diagnostic importance. Measurements of binaural summation therefore might usefully be applied to the clinical assessment of disease progression, or lack of it, in individual patients.
Abstract: With binaural stimulation the two specific parameters that can modify the neural responses substantially are the intensity differences and the time of arrival of the stimulus at the two ears; these events on electrophysiological evidence, being mediated at the superior olivary complex and at the inferior colliculus, the origins of Waves III and V respectively. Comparison of the brainstem auditory-evoked potentials to monaural stimulation with that due to binaural stimulation reveals a significant increase only in the amplitude of Wave V. The amount of increase is reduced from 68.7% with equal intensities at the two ears to 44% with a 10-dB interaural intensity difference. With a 20-dB interaural intensity difference the amplitude of Wave V reverts to that due to monaural stimulation. The 68.7% greater amplitude for Wave V was not due to effective increase in loudness sensation on binaural stimulation (which is equivalent to a monaural increase in intensity of 3 dB) but to binaural summation. In contrast to Wave V, Wave III decreased in amplitude below that resulting from monaural stimulation with intensity differences of 10 and 20 dB at the two ears. This supports the suggestion of inhibitory processes at that level of the brainstem. As only Wave V shows binaural summation the region of inferior colliculus is suggested as the site for the occurrence of this phenomenon. Binaural interaction can also be demonstrated within a limited range with intensity differences at the two ears.
Abstract: Electrode placement is an important consideration in the recording of a large-amplitude stable response. In this study, brain stem auditory-evoked potentials (BAEP) were obtained from subjects and patients under two electrode configurations, namely 'vertex-mastoid' and 'mastoid-mastoid'. The BAEP waveforms to ipsilateral, contralateral and binaural stimulation were examined for their phase relation with respect to stimulation. In the mastoid-mastoid recording mode, a complete polarity reversal was shown upon changing stimulation from the ipsilateral (with respect to the active input) to the contralateral ear. On simultaneous binaural stimulation, the response was shown to summate to zero. This observation has led to the objective assessment of asymmetry of hearing. Several patients exhibiting recruitment were tested under the mastoid-mastoid recording configuration with binaural stimulation. The results show that a summated 'null' response only occurs at an intensity level where loudness equality is attained at the two ears and recruitment is complete. Applied in this way the technique has promising application in the determination of the presence or absence of recruitment and hence in the differential diagnosis of cochlear and retrocochlear lesions.
Abstract: A tone burst with a fast rise time elicits a large-amplitude cortical response which reduces markedly as rise time is increased. This effect is not observed with white-noise bursts. It is suggested that where changes in rise time affect the spectral content of the stimulus, a change in response amplitude is encountered. The increase in the latency of the response with increase in rise time is found to be the same for both tone and noise bursts, hence independent of spectral composition.
Abstract: A number of electrical potentials can be recorded from the human scalp following acoustic stimulation. The potentials which occur within 10 msec of the stimulus onset have been termed the brain stem auditory evoked potentials (BAEPs). Latency appears to be the most stable measure and in consequence knowledge of the exact limits of normal latency of each wave is important. In this study the effects of ipsilateral and contralateral stimulation on BAEP latencies have been investigated in 23 normal subjects. The exact limits of normal latency of each wave have been established. It has been shown that significant latency differences exist between ipsilateral and contralateral stimulation. Possible hypotheses are put forward to explain the findings which demonstrate that different neural pathways are followed by ipsilateral and contralateral stimuli and that their respective responses can be investigated separately in man using BAEP recordings.
Abstract: As the latency of these responses is the most stable measure in normal subjects, the present study examines the latency of the BAEP wave forms in multiple sclerosis (MS) with a view to comparing a monaural stimulation with binaural. In previous studies binaural stimulation has been used to detect MS in clinically 'definite' cases. In this study both clinically definite and possible MS cases were examined and it was shown that in the clinically definite MS category the detection rate improved from 70% to 90% with ipsilateral/contralateral stimulation. In the possible multiple sclerosis group the detection rate was negligible with binaural stimulation compared to 67% with monaural stimulation. Both inter-wave latency and the repeatability of the response in the different groups are discussed in detail.
Abstract: This volume covers a large number of applications, such as silencers, lined ducts, acoustic materials,source characterization, acoustical design of vehicle cabs, ships, space..
