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Biomedical subjects

O Ozdamar

Publications and source records attributed to O Ozdamar.

At least 37 records · Page 2Linked to original sources
PubMed1986

Binaural interaction in the auditory middle latency response of the guinea pig.

Binaural interaction in the guinea pig middle latency response (MLR) was studied using two stimulus paradigms: binaural click stimuli and monaural click stimuli with contralateral white noise. During monaural click stimulation, the MLR is largest in amplitude over the contralateral temporal lobe. Binaural click stimulation reduces the amplitude of this response. Monaurally evoked click responses are also altered by the presentation of continuous white noise in the contralateral ear. The addition of white noise results in an increase in amplitude particularly of components A (12 msec) and B (17 msec). These alterations in response amplitude are specific to the MLR with no change occurring in the auditory brain-stem response (ABR). These findings appear to reflect interaction between the generators of middle latency response.

Acoustic Stimulation↗
PubMed1984

Auditory brain-stem responses in hydrocephalic patients.

Auditory brain-stem response (ABR) was measured in 40 patients (80 ears) with confirmed hydrocephalus. Eighty-eight percent of these patients showed some form of ABR abnormality. Responses indicative of brain-stem dysfunction consisted of prolonged I-V interwave latency (38%), reduced V/I amplitude ratio (33%), and abnormalities in wave-shape of components III (27%) and V (53%). In addition, 70% of the patients had elevated ABR thresholds; 45% had responses in excess of 20 dB HL and the remaining 25% had no ABR activity. The etiology of the hydrocephalus, head circumference and brain-stem symptoms were not associated with particular ABR abnormalities. Communicating hydrocephalus correlated significantly with both prolonged I-V conduction time and absence of ABR activity, compared with non-communicating hydrocephalus. Four of the 9 patients retested showed ABR improvement on follow-up; one patient showed deterioration. The results were compared to our prior studies of ABR in 60 post-meningitic patients and in 100 severely neurologically impaired institutionalized children in whom the incidence of intrinsic brainstem abnormalities was one-third and two-thirds that of the hydrocephalic group, respectively. The results of this study suggest that ABR can be used to document clinically unsuspected brain-stem pathology that may accompany hydrocephalus. Auditory brain-stem dysfunction is likely to complicate the assessment of hearing sensitivity in hydrocephalic patients.

Adult↗
PubMed1984

Absent auditory brain stem response: peripheral hearing loss or brain stem dysfunction?

Interpretation of auditory brain stem response (ABR) findings can be problematic in cases where waves III and V are absent. Such findings can be attributed to profound hearing loss, brain stem neuropathology, or both. Over a 3-year period, 48 patients with no known brain stem damage and on whom audiologic data were available were found to have no response by ABR or absent waves III and V. Severe to profound hearing loss was documented in 38 cases, audiometric data were equivocal in 3 cases, and 7 patients showed pure tone sensitivity ranging from normal hearing to moderate impairment. Thus 15% had better hearing sensitivity than might have been expected from their ABR findings. Each of these patients also exhibited abnormal acoustic reflex findings. We report the electrophysiological (ABR, MLR, acoustic reflex), medical (history, neurological, EEG, CT scan) and behavioral (audiometric, speech and language, learning disabilities, psychological) data which characterize this group of patients.

Acoustic Impedance Tests↗
PubMed1983

Auditory brainstem response in infants recovering from bacterial meningitis. Neurologic assessment.

Auditory brainstem response (ABR) was used to assess possible brainstem damage in 60 patients recovering from bacterial meningitis. Clear evidence of brainstem abnormalities was evident in 10% of the patients tested. Another 15% had ABRs classified as borderline normal. We evaluated various clinical and demographic factors to determine their predictive value with regard to neurologic abnormalities. Brainstem involvement was most likely when meningitis was complicated by seizures, hydrocephalus, nerve palsies (not including the eighth nerve), and a hemoglobin level of less than 11 g/dL, and when pretreatment symptoms persisted for longer than three days. Instances of partial and complete reversibility of brainstem damage were documented, indicating that reorganization of brainstem structures persisted after patients were discharged from the hospital.

Bacterial Infections↗
PubMed1983

Auditory brainstem responses in infants recovering from bacterial meningitis. Audiologic evaluation.

Auditory brainstem response (ABR) was used to assess possible hearing loss in 60 patients recovering from bacterial meningitis. The ABR results were consistent with either unilateral or bilateral hearing loss in 35% of the cases tested. Of these, 15% were conductive-type hearing loss. Twelve percent had sensorineural hearing losses and normal brainstem function. The remaining 8% had elevated ABR thresholds coincident with findings suggestive of neuropathology of the auditory brainstem pathways. A case of reversible sensorineural hearing loss was documented. Various clinical and demographic factors were examined to determine their predictive value with regard to hearing loss. As expected, otitis media occurred significantly with conductive hearing loss. Type of pathogen (Streptococcus pneumoniae) and hospitalization greater than two weeks were significantly correlated with sensorineural hearing loss. As meningitis typically affects young children who are difficult to test with conventional audiometry, ABR provides an effective means of testing hearing in this population.

Bacterial Infections↗
PubMed1983

Follow-up of infants screened by auditory brainstem response in the neonatal intensive care unit.

Auditory brainstem response screening at 40 and 60 dB was conducted in 100 infants in the neonatal intensive care unit to determine initial failure rate and prevalence of abnormality on follow-up. Of our NICU population, 20% failed one or both of the screening levels: 9% failed at 60 dB in both ears, and 11% failed at 40 dB in one or both ears. On follow-up, half of the 60 dB failure group were found to have sensorineural or conductive impairment and represent the 2% to 4% prevalence of serious otologic-audiologic problems generally found in an NICU population. Subsequent improvement (reversal) of the retest ABR records of the remaining infants in the 60 dB failure group was thought to be related to neural changes in the brainstem associated with recovery from hypoxic episodes. A transient or reversible conductive deficit appeared to account for the majority of failures at 40 dB. We recommend the screening protocol be expanded to include threshold and latency measures in infants who fail the initial screening. The transient nature of many ABR abnormalities makes postdischarge ABR, otologic, audiologic, and neurologic examinations mandatory before any inferences are made about hearing loss or neurodevelopmental disorders.

Brain Stem↗
PubMed1983

Auditory middle-latency responses in humans.

Middle-latency responses (MLR) in humans were studied using an unconventional recording technique with wide bandpass filters. Such filtering permitted simultaneous recording of the auditory brain stem response (ABR) thus facilitating comparisons between the two responses. Effects of sedation (chloral hydrate and diazepam), stimulus-related properties and the coronal distribution of MLRs were examined. Mild sedatives did not appear to affect either MLRs or ABRs. MLRs differed from ABRs in their stimulus-related properties, implying that the neuronal mechanisms underlying their generation are not the same. The amplitude of the MLR component, Pa, was largest at the vertex and symmetrically distributed over the temporal lobes. MLR components Na and Pa and ABR wave V were reliably obtained in all subjects at moderate and high stimulus intensities. At low stimulus levels, however, the detectability of wave V was more robust than the middle-latency components. Thus ABR appears to be the test of choice when hearing sensitivity is in question. MLRs are likely to be most clinically useful in patients with neurological or central auditory processing disorders.

Adolescent↗
PubMed1982

Auditory brain stem and middle latency responses in a patient with cortical deafness.

Auditory brain stem (ABR) and middle latency responses (MLR) were recorded in a patient with bilateral temporal lobe lesions. Audiological and higher cortical functions were assessed using conventional behavioral methods. Roentgenological findings were presented for localizing the lesions. Initially the patient showed no behavioral response to sound. Subsequently the patient reported inconsistent awareness of environmental sounds and pure tone sensitivity was impaired to a severe degree. Higher cortical function was essentially intact and the patient was not aphasic. ABR and acoustic reflex findings were consistent with normal functioning of the auditory periphery and brain stem pathways. MLR component Pa was absent bilaterally. These findings suggest that MLR component is bilaterally generated in the temporal lobes. Auditory cortex appears to play a role in auditory sensitivity in humans.

Adult↗
PubMed1982

Auditory middle latency responses (MLRs) in patients with cortical lesions.

Auditory middle latency response (MLRs) and auditory brain stem responses (ABRs) were simultaneously recorded in 24 patients with cortical lesions primarily affecting the temporal lobes. Site of lesion was documented by computerized tomography (CT) scan and behavioral profiles assessing language and other higher cortical functions were obtained. In patients with normal ABRs and either left or right hemisphere lesions, MLR components Na and Pa obtained at the vertex were of normal shape and latency. Exceptions to this occurred in 2 patients: one with bilateral temporal lobe lesions, the second with an infraventricular left temporal lobe lesion extending into the thalamic radiations. Although Na and Pa shape and latency were for the most part unaltered, Pa amplitude tended to cluster at the low end and below normal values. MLR recorded in the coronal plate showed Pa amplitude to be attenuated or absent over the damaged temporal lobe relative to the vertex or the intact hemisphere. This finding contrasts with data from normal subjects where Pa amplitude is largest at the vertex and essentially symmetrical about the temporal lobes. Patients showing an atypical amplitude distribution tended to have lesions involving auditory cortex and adjacent white matter projections. No obvious correlations between MLR abnormalities and behavioral findings regarding receptive and expressive language processes were found. Pa appears to be affected by temporal lobe lesions involving auditory cortex and thalamic projections. Our findings support the hypothesis that Pa is bilaterally generated by two symmetrical, vertically oriented dipole sources located about the temporal lobes.

Acoustic Stimulation↗
PubMed1981

Auditory brain stem response (ABR) in unilateral hearing loss.

Auditory brain stem responses (ABRs) wee reported with two groups of patients with confirmed and suspected unilateral hearing loss. Evidence of acoustic crossover in click stimuli when the difference in click thresholds for the two ears exceeds approximately 60 db is presented. In such a circumstance, the ABR presumably elicited from the test ear can, in fact, be a reflection of a crossover response from the non-test ear. In clinical practice, appropriate contralateral ear masking should be employed when ABR audiometry is carried out with infants and adults with suspected unilateral hearing loss.

Adult↗
PubMed1978

Behavioral, compound action potential, and single unit thresholds: relationship in normal and abnormal ears.

Comparisons were made for two species (chinchilla and mongolian gerbil) among mean behavioral audiogram, mean just detectable action potential (AP) responses to tone bursts, and single-fiber response thresholds at the characteristic frequency, averaged in one-octave bands. In normal animals and in a group of Kayamycin-treated chinchillas, these mean measures appear to have a well-ordered relationship. Unit and AP thresholds are within 10 dB from one another throughout the frequency range. Behavioral thresholds are usually 15--20 dB more sensitive, but the three curves are roughly parallel except at the highest frequencies, where the behavioral threshold begins to increase approximately one-half octave above the physiological ones. Individual examples for four gerbils and four chinchillas having hair cell losses due to Kanamycin intoxication reinforce the notion based on mean data that in most cases AP thresholds can serve to predict the behavioral threshold configuration.

Action Potentials↗
PubMedDate not supplied

Measurement of signal and noise characteristics in ongoing auditory brainstem response averaging.

Although diagnostic testing with auditory evoked potentials (EPs) has become routine, quantitative measurements of signal and noise are still lacking. In this study, current signal, power, noise power, and signal-to-noise ratio (SNR) estimation formulas are reviewed and applied to auditory brainstem response averaging. Single-sweep responses to individual sound stimuli are recorded and estimation formulas are evaluated during off-line averaging under various sound level and noise conditions. The results show that the quality of the averaged EP can be quantitatively assessed by the continuous display of the SNR and residual noise estimates during the averaging process. This method also allows the study of different types of averaging techniques to improve EP response acquisition.

Evoked Potentials, Auditory, Brain Stem↗
PubMedDate not supplied

Auditory middle latency responses in the guinea pig.

Auditory middle latency responses (latencies 6 to 50 msec in guinea pigs) were recorded from eight awake, restrained guinea pigs. Before recording, screw electrodes were implanted in the skull in a coronal plane in line with the bregma. Another electrode, which served to monitor auditory brainstem responses, was placed 1 cm posterior to the bregma. All electrodes were referenced to a lead positioned 2 cm anterior to the bregma. During the recording session, click stimuli of various repetition rates and intensity levels were delivered monaurally in a closed sound system. Auditory brainstem responses were monitored to ensure normal functioning of the peripheral auditory system. Responses from electrodes at the midline and over the temporal area ipsilateral to the stimulus ear were greatly attenuated or absent. From an electrode over the temporal area contralateral to the stimulus ear, two positive peaks occurred at latencies of approximately 12 and 27 msec. A negative trough was identified at approximately 17 msec. Latency and amplitude functions for this waveform were determined for various stimulus levels. Response amplitude increased as stimulus repetition rate was decreased. Anesthesia greatly altered waveform structure and prolonged peak latencies. These effects were more marked at stimulus repetition rates faster than 10/sec than at slower rates. Properties of the guinea pig middle latency response are compared with those previously reported for cats and humans.

Animals↗
PubMedDate not supplied

Auditory brainstem responses (ABR) with suspected deaf-blind children.

Auditory brainstem response (ABR) results with 82 severely developmentally delayed infants and children suspected of being both deaf and blind are reported. Of the 79 children on whom acceptable ABR data were obtained, 34 or 43.0% had ABR thresholds in the normal-hearing range; 16 or 20.3% in the mild-to-moderate loss range; and 3 or 3.8% in the severe loss category. Twenty-six or 32.9% produced no ABR to clicks at a maximum intensity of 90 bB HL. On the basis of established audiological and neurological diagnostic criteria, 3 children showed neurological abnormality by ABR. We conclude that the hearing status of a high percentage of otherwise untestable children can be determined by ABR, that a significant number of infants and children who appear deaf are in fact not hearing impaired, and that the occurrence of brainstem neuropathology in this population is limited.

Abnormalities, Multiple↗
PubMedDate not supplied

Adaptive Wiener filtering for improved acquisition of distortion product otoacoustic emissions.

An innovative acoustic noise canceling method using adaptive Wiener filtering (AWF) was developed for improved acquisition of distortion product otoacoustic emissions (DPOAEs). The system used one microphone placed in the test ear for the primary signal. Noise reference signals were obtained from three different sources: (a) pre-stimulus response from the test ear microphone, (b) post-stimulus response from a microphone placed near the head of the subject and (c) post-stimulus response obtained from a microphone placed in the subject's nontest ear. In order to improve spectral estimation, block averaging of a different number of single sweep responses was used. DPOAE data were obtained from 11 ears of healthy newborns in a well-baby nursery of a hospital under typical noise conditions. Simultaneously obtained recordings from all three microphones were digitized, stored and processed off-line to evaluate the effects of AWF with respect to DPOAE detection and signal-to-noise ratio (SNR) improvement. Results show that compared to standard DPOAE processing, AWF improved signal detection and improved SNR.

Algorithms↗
PubMedDate not supplied

Three cases of hereditary deafness possibly due to brainstem lesions.

In this report, 3 cases of deafness resulting from possibly autosomal recessive disorders affecting the brainstem with no other pathologies or health problems are presented. The common characteristics of these patients are the presence of an unknown functional lesion in the brainstem as documented by the auditory brainstem response testing. Radiological, behavioral and physiological test results are presented for the first time to support a hereditary deafness symptom that might arise from interfamily marriages.

Acoustic Impedance Tests↗