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Biomedical subjects

H Sohmer

Publications and source records attributed to H Sohmer.

144 records · Page 8Linked to original sources
PubMedDate not supplied

Cochlear, brain stem, and cortical evoked responses in nonorganic hearing loss.

After complete but inconclusive audiometric evaluation, 30 suspected cases of nonorganic hearing loss (NOHL) were referred to this laboratory for a complete battery of electric response audiometry tests (recording of cochlear, brain stem and cortical evoked responses). The chief advantages of these tests lie in their ability to more objectively confirm the presence of NOHL and to elicit the true threshold of the subject. Such tests along with psychiatric evaluation, indicate that NOHL can be subdivided into categories, examples of which are presented and discussed: malingering or conscious simulation of deafness for obvious personal gain, and psychogenic deafness in which an emotional problem (e.g., combat stress, anxiety) is unconsciously converted into a hearing problem in an escape mechanism. The basis of NOHL in some cases may be a mixture of both conscious components (malingering) and unconscious components (psychogenic). Several cases of NOHL are really nonorganic overlays or exaggeration on a small to moderate organic hearing loss. The psychogenic hearing loss seen in soldiers with combat neurosis may have originally developed as a psychogenic exaggeration of a temporary threshold shift induced by the noise of battle. Thus objective electrophysiological hearing tests and psychiatric evaluation have contributed to a better understanding of NOHL.

Adolescent↗
PubMedDate not supplied

Cochlear and brain stem responses in hearing loss following neonatal hyperbilirubinemia.

The site of lesion in hearing loss following neonatal hyperbilirubinemia is unclear. Histopathological studies have implicated the brain stem auditory nuclei while other investigations have hinted at a lesion in the cochlea. In order to clarify this issue, attempts were made to record responses from the auditory pathway in 13 patients with hearing loss following neonatal hyperbilirubinemia. The neural response from the auditory nerve was absent in 11 of the 13 patients and present only in response to high intensity stimuli in 2 patients. However, the response of the cochlear hair cells (cochlear microphonic potential) was present in 9 of the 13 patients. In most other cases of sensorineural hearing loss, with no history of hyperbilirubinemia, the hair cell response was absent. This is functional evidence for auditory nerve damage in cases of hearing loss following neonatal hyperbilirubinemia while the hair cells are spared.

Adult↗
PubMedDate not supplied

Latency of auditory nerve response in neonates one to eight hours old.

Recording the response of the auditory nerve (W1) in neonates can contribute to the diagnostic distinction between audiological-otological versus neurological pathology. If W1 latency were subject to relatively rapid shortening in the hours directly after birth, inconsistencies in the literature might be clarified. The purpose of this research was to study W1 in neonates one to eight hours old in order to determine if significant latency changes occur during this period. Auditory nerve-brainstem responses were recorded in 40 full-term neonates and in 12 normal adults. W1 latency in 1- to 3-hour-old neonates was 1.81 +/- 0.28 ms and 1.77 +/- 0.18 ms in 7- to 8-hour-old neonates. This difference was not significant. In adults, W1 latency was significantly shorter (1.36 +/- 0.06 ms). These findings indicate that auditory nerve latency is about 0.43 ms longer at birth than in the adult and that the latency does not shorten significantly during the first hours after birth.

Adult↗
PubMedDate not supplied

Short latency vestibular evoked response to acceleration stimuli recorded by skin electrodes.

Short latency vestibular evoked response to repetitive acceleration stimuli were recorded by skin electrodes in cats, using electronic filtering and averaging techniques. The evoked response is composed of six to eight waves during the first 10 ms after the stimulus. These are followed by longer latency responses which are myogenic in nature. All of these waves disappear with the animal's death and after excision of both eighth nerves. In recordings from the animal after excision of the eighth nerve on one side, the response patterns of excitation versus inhibition are demonstrated using excitatory and inhibitory acceleration stimuli. The possible generators of the evoked response are discussed in the light of the physiology of the vestibular pathways.

Animals↗
PubMedDate not supplied

Action potentials recorded with evoked potential techniques: modes and sites of generation.

Short latency evoked potentials (auditory and somatosensory) include compound action potentials which have been thought to be generated as a result of synchronous nerve impulses (volley) in the sensory pathways. The results of studies in experimental animals with intracranial electrodes or lesions and in patients with clearly localized and identified brain lesions have been interpreted as evidence that these waves are initiated at specific sites such as the neural outflows from the relevant nuclei of the respective pathways. However recordings of the auditory nerve-brain stem evoked responses (ABR) intracranially during neurosurgical procedures and considerations of the latency of the very early somatosensory evoked potentials (SEP) have cast doubt as to this suggested mode of generation of these far-field potentials and, therefore, their sites of initiation. Careful studies of SEP in humans, in vitro experiments with nerve bundles and computer simulations have shown that far-field action potentials can be initiated at sites where the propagated action potential volley passes through boundaries between volume conductor regions differing in geometry and in conductivity. These studies have provided insight into the modes of generation of SEP and ABR and their possible sites, showing that they may be more sensitive to the passive properties of the surroundings of nerve tracts rather than their functional state per se.

Action Potentials↗
PubMedDate not supplied

Multimodality (auditory, visual and somatosensory) evoked potentials in the sand rat, Psammomys obesus.

Multimodality (auditory, visual and somatosensory) evoked potentials were recorded in the sand rat (Psammomys obesus) and compared to those obtained in albino rats, under almost identical conditions. Clear responses could be obtained from each species. The evoked potentials from the sand rat were qualitatively similar in waveform, latency and amplitude to those recorded in albino rats. Since there is a strain of sand rat which develops diabetes when on standard chow and since the sand rat has adapted to the desert environment, further study should involve evoked potential recordings in sand rats during hyper- and hypothermia and in diabetic sand rats.

Animals↗
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Intermediate endocochlear potential levels induced by hypoxia.

It seems that the positive potential of the scala media (endocochlear potential [EP]) and the high potassium concentration in the endolymph are generated and maintained by an electrogenic pump. In order to study its properties, the EP was measured in cats ventilated with low oxygen gas mixtures (2.25-10%). It was found that the EP could be maintained at intermediate levels which were more or less linear functions of blood oxygen tension (25-60 mmHg), showing that the pump can operate on intermediate levels. This hypoxic preparation may contribute to the study of cochlear blood flow.

Acoustic Stimulation↗
PubMedDate not supplied

Central auditory tests and auditory nerve-brainstem evoked responses in multiple sclerosis.

In 43 multiple sclerosis (MS) patients and an equal number of age- and sex-matched normal controls, auditory nerve-brainstem evoked responses (ABR), audiometric tests, central auditory tests (CAT) and clinical-neurological examinations were conducted. The CAT included rapid alternating speech perception, masking level differences to tones and to words and lateralization based on interaural time and intensity differences. The results in the MS group on the ABR and each of the CAT differed significantly from those in the control group. The ABR results and the lateralization test results were each abnormal in 50% of the MS patients. The ABR, CAT and clinical examination results were all mutually correlated. These findings are probably related to the fact that the demyelination in MS induces a decrease in impulse velocity, to temporal dispersion and to desynchrony of impulses in groups of affected axons and to the fact that the ABR and the CAT tests chosen are dependent on synchronous impulse firing and on the precise timing of the arrival of impulses from each ear at some brain centre. These tests may therefore contribute to neurological and to audiological diagnosis.

Adolescent↗
PubMedDate not supplied

Electrocochleography during noise-induced temporary threshold shifts.

The responses of the auditory nerve and brain stem auditory nuclei were recorded non-traumatically in human subjects by means of electrocochleography before, during and after exposure to white noise intensities which produced temporary threshold shifts. The largest decrement (amplitude decrease and latency increase) was seen in the response of the auditory nerve. Large intersubject variability was seen in the effects of the noise exposure on response amplitude, latency and recovery rates.

Acoustic Stimulation↗
PubMedDate not supplied

Auditory nerve and brain stem responses to sound stimuli at various frequencies.

The responses of the auditory nerve and brain stem auditory nuclei have been recorded with ear lobe and scalp electrodes in response to unfiltered click stimuli which excite mainly high-frequency nerve fibers. In order to overcome this limitation, normal subjects and patients with hearing loss were stimulated with third-octave filtered clicks with center frequencies of 250, 500 and 1 000 Hz. Analysis of the responses suggests that these lower-frequency stimuli excite lower-frequency cochlear nerve fibers. It is concluded that low-frequency filtered clicks can be used to complement unfiltered clicks in order to obtain a more complete objective audiogram.

Acoustic Stimulation↗
PubMedDate not supplied

Comparison of earlobe and promontorium recording sites in electrocochleography.

A compound cochlear action potential can be recorded in man from the promontorium, after perforation of the tympanic membrane. This same cochlear action potential (along with the responses of the brain stem auditory nuclei) can also be recorded by means of earlobe-vertex electrodes. Recordings were made in patients with chronic perforations of the tympanic membrane from the promontorium and simultaneously from the earlobe (-vertex) in order to see if there is a difference in response threshold. As click intensity was decreased, the responses disappeared in both recordings at about the same stimulus intensity (threshold). At near-threshold click intensities, the response seen in the promontorium recording was the compound cochlear action potential while in the earlobe vertex recording, the response often seen was seen was that from the inferior colliculus. Thus, in most cases, there is no real advantage to be gained by perforating the tympanic membrane in order to record from the promontorium since an identical response threshold can be obtained using surface electrodes.

Acoustic Stimulation↗
PubMedDate not supplied

Comparison of hearing threshold determined by auditory pathway electric responses and by behavioural responses.

In order to evaluate their reliability for determing the hearing threshold, the cochlear microphonic potentials, the auditory nerve and brain stem neural evoked responses as well as the cortical evoked responses were compared with the behavioural hearing thresholds of the same subjects in the same session. The threshold for recording the cochlear microphonic potnetial was found to be appreciably higher than the behavioral threshold. The threshold for recording the auditory nerve and brain stem responses was within a few decibels of the behavioural threshold. The thresold of the cortical evoked response was several decibels higher. It is concluded that (1) the auditory nerve and brain stem neural evoked responses are the best indicators of hearing threshold; (2) the cortical evoked responses are usually comparable, and (3) all types of evoked responses are indispensable aids in the evaluation of hearing and the determination of site of lesion in the auditory system.

Audiometry↗
PubMedDate not supplied

Comparison between self-hypnosis, masking and attentiveness for alleviation of chronic tinnitus.

The efficacy of self-hypnosis (SH), masking (MA) and attentiveness to the patient's complaints (AT) in the alleviation of tinnitus was evaluated. Forty-five male patients close in age with chronic tinnitus related to acoustic trauma were assigned to three matched subgroups: SH, AT or MA. The therapeutic stimuli in the SH and MA sessions, recorded on audio cassettes, were given to the patients for use when needed. SH significantly reduced the tinnitus severity; AT partially relieved the tinnitus; MA did not have any significant effect.

Adult↗
PubMedDate not supplied

Transient evoked otoacoustic emissions in newborns in the first 48 hours after birth.

Newborns are often discharged from hospital at the age of about 48 hours. At this age, transient evoked otoacoustic emissions (TEOAEs) are not necessarily recordable in all healthy newborns. In order to determine the factors which would enable the successful recording of TEOAEs before discharge to facilitate screening for hearing, 65 fullterm newborns under 48 hours of age were tested, the youngest being 10 hours old. The ears of those neonates in whom TEOAEs could not be obtained (N = 7 neonates bilaterally, 6 unilaterally) were examined otoscopically, cleaned of vernix and retested for TEOAEs. We were thus able to record in at least one ear in all neonates tested, if the ears were clean, if they were asleep and if the testing room was quiet.

Acoustic Stimulation↗
PubMedDate not supplied

Transient evoked otoacoustic emissions in laboratory animals.

Transient evoked otoacoustic emissions (TEOAEs) are much used clinically. However, it has been difficult to record them in small laboratory animals, and experimental manipulations designed to determine the generation mechanisms of this type of emission could not be performed. After refining the technique, based on the use of short clicks and a short amplifier gain suppression period, TEOAEs were recorded using the same instrumentation and techniques in rabbits, Psammomys obesus (fat sand rats), mice, rats and guinea pigs. Distortion product emissions were also recorded. The responses in each species differed with respect to threshold, magnitude, frequency spectrum and duration (endpoint). The ability to record TEOAEs routinely in laboratory animals should now allow for further experimentation on the mechanisms of their generation, on the cochlear amplifier in general and on the comparison of TEOAEs with distortion product emissions in individual species and animals.

Acoustic Stimulation↗