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H Sohmer

Publications and source records attributed to H Sohmer.

At least 91 records · Page 5Linked to original sources
PubMed1984

Survey of attempts to use auditory evoked potentials to obtain an audiogram. Review article.

Click stimuli have been used to elicit ABR in auditory diagnosis but the ABR response is dominated by the activity of high-frequency nerve fibres and it is therefore impossible to deduce hearing at lower frequencies from ABR to clicks. Short tone pips or filtered clicks are also inadequate since the response is still dominated by basal turn, high-frequency nerve fibres. In order to attempt to obtain an audiogram by means of ABR, various noise-masking techniques have been used to restrict the response to more specific regions along the basilar membrane. These included presenting click or filtered click stimuli together with either different high-pass noises in order to obtain a derived ABR or notched noise. Though these techniques have been tested on small groups of normal subjects, they have not been adequately clinically validated on sufficient numbers of hearing-loss patients with various audiogram shapes. When tested on patients with low-frequency hearing loss, inappropriate thresholds have been obtained indicating problems with lower frequencies. Alternatively, other types of auditory evoked responses based on less synchronous neural activity have been studied including the SN10 response and the 40 Hz-MLR. These responses have not been adequately clinically tested. In conclusion the evoked potential techniques have not been completely tested in the clinical situation and several studies have indicated problems with the evaluation of lower frequencies.

Acoustic Stimulation↗
PubMed1983

Cerebral perfusion pressure and auditory brain-stem responses in childhood CNS diseases.

Intracranial hypertension, complicating CNS diseases of childhood, reduces effective cerebral perfusion pressure (CPP) with resultant cerebral ischemia. The auditory brain-stem evoked response (ABR) is an important diagnostic tool that enables evaluation of brain-stem function and prognostication during the acute stage of the illness. We studied CPP and ABRs in 25 infants and children with CNS infection and cerebral ischemia. In all survivors, CPP could be maintained above 30 mm Hg, and the ABR remained normal or with partial pathology. In nonsurvivors, CPP could not be maintained above this level, and the ABR waves were completely absent. Long-term outcome was not correlated with the minimal CPP recorded during the disease or with examination of the ABR.

Adolescent↗
PubMed1983

Patterns of auditory nerve and brainstem-evoked responses (ABR) in different types of peripheral hearing loss.

Auditory brainstem response (ABR) recordings were made in different types of peripheral hearing loss (sensorineural, conductive, and mixed). Scatter diagrams were constructed by plotting different expressions of the hearing loss (audiometric and electrophysiologic) against the obtained wave latencies and for these two sets of variables, correlation coefficients and the parameters of the regression equation were calculated. Consideration is given to the possibility of diagnosing the type of peripheral hearing loss by correlating wave latencies and the electrophysiologic (ABR) threshold.

Adolescent↗
PubMed1983

Auditory nerve-brain stem evoked potentials in cats during manipulation of the cerebral perfusion pressure.

In order to study the effects of various degrees of cerebral ischemia on the auditory nerve-brain stem evoked potentials (BAEP), the cerebral perfusion pressure (CPP), defined as the difference between mean arterial blood pressure (MAP) and intracranial pressure (ICP), was systemically manipulated in anesthetized, paralyzed and ventilated cats. The CPP was varied by decreasing MAP, either by hemorrhage or by the infusion of a vasodilating drug, and elevating ICP by infusion of mock CSF into the cisterna magna, or by MAP depression and ICP elevation simultaneously. Even though the lower limit of adequate CPP is considered to be 40 mm Hg, the EEG became isoelectric at an average CPP of 24 mm Hg and the BAEP became isoelectric at an average CPP of 7 mm Hg. These extremely low CPP values of 7-24 mm Hg are far below the range of autoregulation of cerebral blood flow (CBF) so that the brain stem auditory pathway is still capable of generating its electrical response (BAEP) at very low CBF. This is paradoxical since these same regions of the brain have been shown to have the highest levels or regional metabolism as shown by their very high local cerebral blood flow and local glucose utilization.

Animals↗
PubMed1983

Auditory nerve-brain stem evoked potentials and EEG during severe hypoglycemia.

To investigate the effects of severe hypoglycemia on the ability of the brain to generate electrical activity, the EEG and auditory nerve-brain stem evoked potentials (ABP) were recorded before and during the development of insulin-induced hypoglycemia in rats (ABP only) and cats (ABP and EEG). No significant ABP changes were seen in rats in which the average blood glucose levels had reached 0.38 mmol/l (= 7 mg%). In cats, even though the EEG was depressed, no ABP latency changes and only slightly significant amplitude changes were seen in animals in which the average blood glucose level was 0.8 mmol/l. In both animals blood glucose levels were below 1.66 mmol/l for an average duration of 90 min. Therefore, even though it has been shown that the brain structures involved in generation of the ABP have higher metabolic rates, they seem to be resistant to deviations from homeostasis such as hypoglycemia.

Animals↗
PubMed1983

Diagnostic and prognostic value of auditory nerve brainstem evoked responses in comatose children.

The efficacy of auditory nerve brainstem evoked response (ABR) in the diagnosis and localization of brainstem lesions and its prognostic value in determining outcome were examined in 30 deeply comatose children. The ABR recordings obtained from each patient were correlated with the clinical, ancillary examinations and final outcome of these children. Clinical and ancillary examinations indicated damage to the cerebrum alone in 14 patients. In these children, ABR was found to be within normal limits. Isolated brainstem lesion was suggested by these examinations in 4 patients and their ABR recording showed absence of one or more of the brainstem response wave components or a prolonged brainstem transmission time (BTT). In 12 patients, damage to both the cerebrum and brainstem was suspected by clinical and laboratory examinations. In 8 patients, partial absence of brainstem waves or prolonged BTT was found. In 4, there was complete absence of all brainstem waves. All patients, regardless of etiology or depth of coma, with normal ABR, survived. Conversely, all children with complete absence of brainstem response waves succumbed. The prognosis of patients with partial absence of brainstem waves or prolonged BTT was variable. Some survived while others remained in a vegetative state or died. Our study demonstrates the importance of ABR in the diagnosis and localization of brainstem lesions and its value as a prognosticator of outcome in deeply comatose children.

Adolescent↗
PubMed1983

Early detection of hearing loss in infants by auditory nerve and brain stem responses.

Auditory-nerve and brain-stem-evoked responses (ABR) have been used alongside standard behavioral hearing tests for the early detection of hearing loss in infants and young children. Two comparisons are presented. The first concerns a group of 65 hearing-impaired children for whom we now have complete pure-tone and speech audiograms. There is a good correlation between the two types of hearing tests in 61 children; the lack of correlation in 4 children is discussed. The second comparison was conducted on neonates. Because ABR testing provides information which is far more accurate than behavioral testing, it is recommended for use in high-risk neonates, especially when mass behavioral screening is not feasible.

Audiometry↗
PubMed1983

Auditory nerve-brainstem evoked responses in hyperbilirubinemic neonates.

On the basis of the known predilection of the auditory brainstem pathway for bilirubin toxicity, we have examined auditory brainstem responses of neonates during the period of hyperbilirubinemia. The auditory brainstem responses of 24 infants with serum bilirubin values between 15 to 25 mg/dL were compared with the responses of 19 infants without hyperbilirubinemia, who had similar gestational and postnatal ages. Wave IV-V complex was absent in at least one recording of 10/24 jaundiced infants, whereas wave complex IV-V was consistently present in all of the 19 infants without hyperbilirubinemia (P less than .001). Jaundiced infants also had prolonged brainstem transmission time (P less than .01) which reflected increased latency at both lower and upper brainstem levels. The above changes were rapidly reversed in the majority of instances. Neonatal jaundice was associated with significant transient aberrations of auditory brainstem responses, suggestive of a transient brainstem encephalopathy. This evidence of bilirubin entry to the brain at conventionally acceptable serum concentrations raises questions about current concepts of the mechanism of transfer of bilirubin across the blood-brain barrier.

Bilirubin↗
PubMed1982

Recording of short latency vestibular evoked potentials to acceleration in rats by means of skin electrodes.

Short latency (less than 15 msec) vestibular potentials evoked by short and intense acceleration stimuli were recorded in rats by surface electrodes, using electronic filtering and with averaging techniques. The evoked potential is strongly dependent on the direction of rotation and on the angle of the head, and it disappears after labyrinthectomy or sectioning the 8th nerve. All these facts point to its vestibular origin. Although these results were obtained in rats, the importance and the significance of recording a vestibular evoked potential in man is obvious. It would lead to the possibility of objective verification of a vestibular disorder and localization of the lesion.

Animals↗
PubMed1982

Auditory nerve-brain stem potentials in man and cat under hypoxic and hypercapnic conditions.

In order to study the effects of hypoxic and hypercapnic respiratory gas mixtures on brain activity, the auditory nerve brain stem evoked potentials (ABP) were recorded in 6 human volunteers and in 12 cats while they were breathing various gas mixtures. In humans, no effect of gas mixtures containing 9-13% O2 or 7.5-10% CO2 was observed on the wave form, latency and amplitude of the ABP. The cats were exposed to up to 25% CO2 and down to 5.5% O2 or to combined hypoxic and hypercapnic gas mixtures for up to 45 min while recording ABP and monitoring CO2 and O2 in the respired gases, arterial blood gas levels, pH, arterial blood pressure, body temperature and EEG. The extremes of pH were 6.68 and 7.46. The EEG was depressed or became isoelectric during hypercapnia. In general, the wave form, amplitude and latencies of the ABP waves were not much affected by these conditions. Loss of ABP was observed only when the animal was ventilated with about 5% O2 and this was secondary to and following cardiac failure and depressed arterial blood pressure, presumably leading to brain ischaemia. Thus, even though the cortex (EEG) is depressed, the brain stem seems to be resistant to these alterations in the blood gases in spite of the relatively higher rates of metabolism reported for the brain stem auditory structures.

Adult↗
PubMed1982

Contribution of changes in click rate and intensity on diagnosis of multiple sclerosis by brainstem auditory evoked potentials.

Brainstem auditory evoked potentials (BAEPs) were recorded in 51 patients with different degrees of certainty with respect to multiple sclerosis (MS): Definite, probable and possible (McAlpine et al. 1972). Click stimuli were presented at various intensities and rates which were thought to stress the auditory pathways. The main types of abnormal BAEP traces were the absence of some of the brainstem waves (in the presence of a normal audiogram), prolonged brainstem transmission time (BTT) and abnormal amplitude ratio. In the definite MS group, average BTT was prolonged and average amplitude ratio was more than two standard deviations greater than the corresponding parameter in the normal group. The stressful manoeuvres of increasing click repetition rate and lowering click intensity increased the degree of abnormality of BAEP traces. There was no case in which the response to standard click stimuli (75 dB HL, 10 or 20 per sec) showed a normal trace while increasing the stimulus repetition rate and/or decreasing intensity showed a pathological response. The pathophysiology of BAEP traces in MS is discussed.

Adolescent↗
PubMed1982

Auditory nerve-brain stem responses (ABR) in children with developmental brain disorders and in high risk neonates.

Auditory nerve-brain stem evoked responses (ABR) have been used for many years to evaluate auditory and neurological disorders. This study is devoted to the demonstration that ABRs can also contribute to the assessment of children with developmental brain disorders, e.g. psycho-motor retardation, minimal brain dysfunction, cerebral palsy and autism. The ABR in many of these children was abnormal, providing evidence for the presence of brain damage in these children which is probably responsible for the disorder they display. Since many of these children suffered from some congenital, perinatal or neonatal insult, ABR recording was also conducted in high risk neonates and young infants. Many of these neonates and infants had abnormal ABRs and, in several, there was improvement of the ABR upon repeated testing. These findings of abnormal ABRs in children with developmental brain disorders who suffered a perinatal insult and abnormal ABRs in neonates who suffered such an insult lead to the following hypothesis: a congenital-perinatal-neonatal insult can cause, at the time of its occurrence, some form of brain damage which may be demonstrated by abnormal ABRs. The same underlying brain damage may also cause developmental brain disorders which become apparent when he is older. Therefore ABR recording during the neonatal period may contribute to the early detection of brain dysfunction in at-risk neonates and may predict the later appearance of neurological, behavioural and cognitive dysfunctions. A longitudinal experimental protocol for the testing and evaluation of this hypothesis is presented.

Brain Diseases↗
PubMed1982

Analysis of auditory brain stem response sources along the basilar membrane to low-frequency filtered clicks.

In order to complement the high-frequency auditory brain stem responses obtained in response to click acoustic stimuli, attempts have been made to elicit low-frequency responses by using low-frequency filtered clicks. The adequacy of these low-frequency stimuli was tested in patients with low-frequency hearing loss, and it was found that the electric response threshold was much better than the audiometric threshold to the center frequency of the filtered clicks. In addition, the responses to the low-frequency filtered clicks in normal subjects were very short in latency. However, when high-frequency noise was presented together with the low-frequency clicks, longer latency responses were obtained. These findings indicate that the high-frequency masking noise exposes low-frequency responses that were not otherwise apparent. Possible mechanisms and implications are discussed.

Acoustic Stimulation↗
PubMed1981

The latency of auditory nerve-brainstem responses in sensorineural hearing loss.

The use of auditory nerve-brainstem responses in differential diagnosis of hearing loss is based on several properties of these responses including response latency. The auditory nerve response latency has been shown to be prolonged in conductive hearing loss. The latency of the brainstem responses is also often prolonged in retrocochlear hearing loss. However, the effect of sensorineural hearing losses on auditory nerve response latency is not clear. Several authors report that response latency is prolonged in sensorineural loss, whereas others claim that it is unchanged. To study this, auditory nerve-brainstem responses to 75 dB HL clicks were recorded in normal-hearing subjects and in those with various degrees of high-frequency sensorineural hearing loss. In the more extreme hearing losses, the auditory nerve response could not be seen in the response trace, so the latency of the earlobe positive wave from the region of the inferior colliculus was considered as mirroring auditory nerve response latency, since the time interval between these two waves has been shown to be constant. The average latency of the more severe hearing loss group (more than 40 dB hearing loss at 4kHz) was found to be only 0.35 ms longer than that of the normal-hearing group. This value is smaller than that seen in most conductive and retrocochlear hearing losses. This result warrants continued use of prolonged auditory nerve response latency (greater than 0.35 ms) as an indicator of conductive hearing loss. Possible explanations for smaller latency prolongation than expected of the auditory nerve response in sensorineural hearing loss are discussed based on the properties of single auditory nerve fibers.

Audiometry↗
PubMed1981

Auditory nerve and brain stem responses in homozygous jaundiced Gunn rats.

In humans, functional evidence based on recording cochlear microphonic, auditory nerve, and brain stem responses has shown that the site of lesion in hearing loss following neonatal hyperbilirubinemia is the auditory nerve (with sparing of the hair cells). Structural damage to the central nervous system (CNS) including the cochlear nuclei has been demonstrated in adult, homozygous Gunn rats which develop hyperbilirubinemia shortly after birth. In an attempt to use the Gunn rat as an experimental model for bilirubin-induced CNS damage, auditory nerve and brain stem responses (ABR) were recorded in jaundiced (homozygous) and non-jaundiced (heterozygous) Gunn rats and in Sabra (Wistar) rats. All of the rats including the jaundiced Gunn rats had normal ABR and responded behaviorally to sound stimuli. These results suggest that the adult jaundiced Gunn rat retains auditory function and in this way differs from human patients in whom neonatal jaundice has lead to hearing loss. Therefore, the adult homozygous Gunn rat probably cannot serve as a model for hearing loss due to hyperbilirubinemia.

Animals↗