Brainstem Auditory Evoked Responses Latencies Research Articles

Brainstem auditory evoked responses in newly diagnosed untreated hypothyroid females

Background: Hypothyroidism stands as a prevalent endocrine disorder, affecting females more than males. Among the array of otolaryngological manifestations linked with thyroid dysfunctions, sensorineural hearing loss emerges as the most frequently encountered issue. Evoked potentials serve as valuable tools extensively utilized in studying brain disturbances. Among these evoked potentials, Brainstem Auditory Evoked Response (BAER) stands out as one of the methods employed for assessing the pathology within the brainstem auditory pathway. Aims and Objectives: The aim of the study is to evaluate the auditory sensory process in the brainstem using BAERs in newly diagnosed untreated hypothyroid individuals. Materials and Methods: Forty newly diagnosed untreated hypothyroid females of 20–50 years were taken as cases and forty age-matched females were considered controls. The hypothyroidism was diagnosed by estimating the serum levels of free T3 (fT3), free T4 (fT4), and thyroid-stimulating hormone. After getting informed written consent, the absolute latencies and interpeak latencies of BAER were recorded using NeuroPerfect EMG 2000 system with installed BAER in the research laboratory, Department of Physiology, Coimbatore Medical College, Coimbatore, and the data were analyzed by student unpaired t-test. Results: The absolute latencies I, III, V and interpeak latencies I- III, III- V, I – V were significantly prolonged in newly diagnosed untreated hypothyroid females (P < 0.0001) and also there was a direct correlation between thyroid profile changes and the BAER latencies. Conclusion: The results of the present study suggest that hypothyroidism impacts the auditory pathway diffusely and early identification of auditory pathway involvement in thyroid hormone deficiency can be achieved using BAER. Prolonged BAER latencies observed in newly diagnosed untreated hypothyroid females are attributed to defective myelination of neural pathways and diminished cerebral metabolism. Hence, integrating BAER recordings into screening protocols could enhance the accuracy and early assessment of neurological involvement in hypothyroid females.

Evaluation of visual evoked potentials and brain-stem auditory evoked response in patients of chronic kidney disease.

Chronic kidney disease (CKD) is associated with functional changes in the central nervous system (CNS) which, in the initial stages do not manifest clinically. Early involvement of the CNS can be identified by the assessment of the electrocortical activity. Visual evoked potential (VEP) and brain-stem auditory evoked response (BAER) are useful tests for the early diagnosis of CNS involvement in CKD and are more sensitive compared to electroencephalography. One hundred adult CKD patients (stage 3-5 and 5D) and 50 controls were included in the study. Clinical and biochemical parameters were assessed and all the patients and controls underwent VEP and BAER evaluation. Evaluation of the VEP showed prolonged latencies of all the three peaks (N75, P100, and N145) compared to controls. Furthermore, all the absolute and interpeak BAER latencies for the CKD patients were similarly prolonged compared to controls. CNS dysfunction is common in CKD patients. The electrophysiological tests of VEP and BAER can be used for the early diagnosis of these disorders, even in the sub-clinical stages, thus allowing for their better management.

Evaluation of central vestibular syndrome in dogs using brainstem auditory evoked responses recorded with surface electrodes

ABSTRACT The present study aimed to analyse the wave morphology, amplitude, latency, and intervals of the brainstem auditory evoked responses (BAERs) in dogs with central vestibular syndrome (CVS) recorded with surface electrodes. Ten dogs with CVS were examined by mono- and binaural stimulation, using the Neuropack electrodiagnostic system, with stimulus intensities of 90 dBSPL. BAERs examinations revealed morphological changes of waves I, II, III, and V and decreased amplitudes of all waves in 7/10 dogs. P values obtained were = 0.014 for wave I amplitude, 0.031 for II, and III and 0.032 for V. Comparing the latencies of waves I, II, III, and V generated by right and left monoaural stimulation in dogs with CVS, we did not observe significant differences (P>0.05). No statistical differences were observed for BAERs latencies of the waves recorded after binaural and monaural stimulation (left or right). As far as we know, this is the first study of BAERs using surface electrodes, obtained from dogs with CVS.

Brainstem Auditory Evoked Responses in Children Living at High Altitude in the Andes Mountains

This neurophysiological study compared brainstem auditory evoked responses (BAER) in children living at high elevations (2800 to 3000 meters) in the Andes Mountains of Ecuador with a reference group of children living at sea level in the U.S. BAER absolute latencies of waves I through V; interpeak latencies I-III, III-V, and I-V; amplitudes of waves I and V; and the V/I amplitude ratio were measured by scalp electrodes at acoustic click stimulus rates of 10 and 50 pulses per second (pps). Statistical analysis showed that the high-altitude group had significantly longer absolute and interpeak BAER latencies than the sea-level reference group at both the 10 and 50 pps stimulus rates for most wave peaks. The amplitudes of waves I and V were significantly reduced for the high-altitude group at 10 and 50 pps, suggesting blood O2 saturation effects. The BAER of children in the high-altitude group suggested physiological anomalies in auditory neural conduction and summation compared with the sea-level group. The results further suggest that small physiological effects of altitude on BAER, especially at elevations near 3000 meters and higher, should be taken into consideration in the evaluation of brainstem auditory function.

Association of hemoglobin levels and brainstem auditory evoked responses in lead-exposed children

ObjectivesDecreased blood hemoglobin (HbB) levels and anemia have been associated with abnormal brainstem auditory evoked responses (BAER). Lead (Pb) exposure has also been associated with anemia and aberrant BAER. This study investigated the relationship between HbB level and BAER wave latency and amplitude in Pb-exposed Andean children. Design and methodsSixty-six children aged 2 to 15years (mean age: 9.1; SD: 3.3) living in Pb-contaminated villages were screened for HbB levels, blood Pb (PbB) levels and BAER latencies and amplitudes. ResultsThe mean HbB level observed in the study group was 11.9g/dL (SD: 1.4; range: 8.6–14.8g/dL). The mean HbB level corrected for altitude was 10.3g/dL (SD: 1.4; range: 6.9–13.1g/dL), and suggestive of anemia. The mean PbB level was 49.3μg/dL (SD: 30.1; range: 4.4–119.1μg/dL) and indicative of Pb poisoning. Spearman rho correlation analyses revealed significant associations between the BAER absolute latencies and HbB level, indicating that as the HbB level decreased, the BAER wave latency increased. Children with low HbB levels (≤11g/dL) showed significantly prolonged absolute latencies of waves I, II, III, IV and V compared to the children with normal HbB levels. Although a significant relationship between HbB and BAER waves was observed, no significant associations between PbB level and BAER parameters were found. ConclusionLow hemoglobin levels may diminish auditory sensory-neural function, and is therefore an important variable to consider when assessing BAER in children with anemia and/or Pb exposure.

The effects of aggressive vs. conservative phototherapy on the brainstem auditory evoked responses of extremely-low-birth-weight infants

This study was a two-center, stratified, parallel-group randomized trial comparing the effects of aggressive vs. conservative phototherapy on brainstem auditory evoked response (BAER) latencies in infants with extremely low birth weight (ELBW, ≤ 1,000 g). BAER latencies of 751-1,000 g birth-weight infants were shorter by 0.37 ms (95% confidence interval (CI) = 0.02, 0.73) for wave V, 0.39 ms (0.08, 0.70) for wave III, and 0.33 ms (0.01, 0.65) for wave I after aggressive phototherapy at one center. Interwave intervals did not differ significantly. Similar nonsignificant trends were recorded for 501-750 g birth-weight infants. At the other participating center, no significant differences were recorded, cautioning against overgeneralizing these results. The effects of bilirubin on the auditory pathway in ELBW infants depend on a complex interaction of bilirubin exposure, newborn characteristics, and clinical management. Aggressive phototherapy was initiated sooner and continued at lower bilirubin levels than conservative phototherapy. A total of 174 ELBW infants were enrolled in the study; 111 infants were successfully tested at 35 weeks postmenstrual age (PMA); 57 died; and 6 were not successfully tested.

Changes in Brainstem Auditory Evoked Response Latencies in Term Neonates With Hyperbilirubinemia

Ninety term neonates with hyperbilirubinemia were studied with brainstem auditory evoked response to clarify the ototoxic effect of hyperbilirubinemia, and detect any differences in ototoxic effect between different levels of total serum bilirubin. The response threshold in these neonates was significantly elevated (P < 0.001). All wave latencies and I-V interval increased significantly (P < 0.05-0.0001), and correlated weakly with total serum bilirubin (r = 0.24-0.28, all P < 0.05). Twenty-five neonates (28%) had abnormal responses, including 14 (16%) with elevated thresholds or increased wave I latency, suggesting peripheral auditory impairment, and 16 (18%) with increased I-V interval, suggesting central auditory impairment. Wave V latency and I-V interval were longer in neonates with total serum bilirubin of <20 mg/dL than in those with bilirubin 11-15 mg/dL (P < 0.05). However, there were no significant differences in response variables between neonates with total serum bilirubin 11-15 mg/dL and those with bilirubin 16-20 mg/dL, and between neonates with bilirubin 16-20 mg/dL and those with bilirubin >20 mg/dL. Thus, although the acute ototoxic effect of hyperbilirubinemia tends to be more significant at a higher rather than lower level of total serum bilirubin, auditory impairment does not increase closely with the increase in bilirubin.

Ventral surgical approach to the caudal brain stem in dogs.

To develop a safe neurosurgical procedure that accessed the ventral pons and medulla of the dog primarily for the removal of brain stem neoplasms. In vivo study. A cadaver study was performed on mesocephalic dog heads to develop a neurosurgical approach to the ventral brain stem. Based on this study, an approach to the ventral brain stem was developed by basioccipital craniectomy. This procedure was performed on 4 young neurologically normal Beagle dogs to assess morbidity and mortality associated with the procedure. Morbidity was evaluated by subjective criteria, daily complete neurologic examinations, comparison of preoperative and postoperative brain stem auditory evoked response (BAER) tests, and postmortem examinations. Three dogs developed a transient cough but were neurologically normal after surgery. One dog was euthanatized within 12 hours of surgery because of severe postoperative morbidity associated with basilar artery disruption due to improper development of the craniectomy. Prolongations of postoperative BAER latencies were observed in 2 dogs but did not appear to be associated with clinical deficits or histopathologic changes in the brain stem. Minimal histopathologic changes were observed except in the dog with basilar artery disruption. Results of this study indicate that, although technically challenging, this procedure can be performed with minimal morbidity. The main indication for this procedure is surgical reduction or biopsy of ventrally located brain stem neoplasms in dogs. The major disadvantage is anatomic restrictions that prevent access to laterally oriented ventral brain stem masses.

Longer brainstem auditory evoked response latencies of individuals with fragile X syndrome related to sedation

Brainstem auditory evoked response latencies were studies in 75 males (13 with fragile X syndrome, 18 with mental retardation due to other causes, and 44 with no disability). Latency values were obtained for each ear for the positive deflections of waves I (P1), III (P3), and V (P5). Some individuals with mental retardation required sedation. Contrary to previous report, latencies obtained for individuals with fragile X did not differ from those obtained for persons without mental retardation. Persons receiving sedation, whether or not their retardation was due to fragile X, had longer latencies for wave P5 than persons who did not receive sedation. This effect of sedation may also explain the previously reported increased latencies for persons with fragile X.

Prenatal and perinatal lead exposures alter acoustic cry parameters of neonate.

We performed acoustic analyses on cries elicited from a subset of healthy babies born to the Mexico City Prospective Lead Study at 2 days (n = 75), 15 days (n = 176), and 30 days (n = 166). Lead was measured in maternal blood every 8 weeks during pregnancy from week 12 to delivery and in umbilical cord (1-38 micrograms/dL, 0.05-1.84 mumol/L). Percent nasalization and number of cries decreased in babies born to mothers with higher lead levels in the last two trimesters while median fundamental frequency increased in babies born to mothers with higher lead at 12 weeks of pregnancy, and with higher cord lead in multiple regression analysis. Decreased percent nasalization was related to increased brainstem auditory evoked response latencies and interpeak intervals in a subset of the sample. The results suggest an effect of gestational exposure to lead on apparatus innervated by cranial nerves and/or lead effect on cry mediated by lead-altered auditory function. Altered baby cry and auditory function associated with lead might contribute to developmental delays by affecting early communication between caretaker and baby.

Magnetic resonance imaging assessment of brainstem distortion associated with a supratentorial mass.

Quantitative measurements of brainstem distortion and neural dysfunction were obtained in 25 cases of chronic subdural haematoma. The horizontal and rotational brainstem displacements were measured on axial and coronal MRI in all patients pre-operatively, and brainstem auditory evoked responses (BAERs) were obtained in 11 cases. Logarithmic relationships were noted on both horizontal and rotational displacements of the brainstem and cerebrum. The type of shift changed in the rostro-caudal direction. In the axial plane, the cerebral hemisphere shifts and rotates, the midbrain shifts laterally with no rotation, and the pons shifts minimally but rotates moderately. In the coronal plane, the marked rotation of the cerebral hemisphere and moderate rotation of the brainstem result in midbrain kinking, suggesting a downward displacement of the midbrain. The prolongation of BAER latencies and central conduction times correlated with septum shift. The results of peak-V latency indicated that brainstem rotation in the coronal plane reflects upper brainstem dysfunction most closely. This study presents objective measurements of brainstem displacement shown on MRI, and clarifies the relationships between anatomical and physiological changes in the brainstem that are associated with supratentorial lesions.

Brainstem auditory evoked responses (BAERs) during the menstrual cycle in women with and without premenstrual syndrome

Brainstem auditory evoked responses (BAERs) were recorded at three menstrual cycle phases (menstrual, late follicular, and late luteal) in a sample of healthy control women ( n = 21) and in a sample of women ( n = 30) diagnosed as suffering from Late Luteal Phase Dysphoric Disorder (LLPDD). The latter were divided on the basis of retrospective and prospective self-ratings into moderate (PMS+) and severe (PMS++) symptom groups. Results showed (1) no change in BAER latencies at different phases of the menstrual cycle; (2) increased BAER latencies for wave III in women with moderate PMS symptoms compared with healthy controls; (3) increased BAER latencies for waves III and V in women with severe PMS symptoms compared with healthy controls. These results raise the possibility of brainstem dysfunction in PMS women, and support the idea of a neurobiological predisposition to this order.

Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). I: Effects of click level, rate, and polarity.

Three experiments evaluating the effects of various stimulus manipulations on the click-evoked gerbil brain-stem auditory-evoked response (BAER) are reported. In experiment 1, click polarity and level were covaried. With increasing click level, there is a parallel decrease in the latency of the first five BAER peaks (i-v) and an increase in BAER peak amplitudes. Mean wave i amplitude was greater for rarefaction than condensation clicks at high click levels; mean wave v amplitude was greater for condensation clicks at higher click levels. Experiment 2 covaried click rate and polarity. The latency of the BAER peaks increased with increasing click repetition rate. This rate-dependent latency increase was greater for the later BAER peaks, resulting in an increase in the i-v interval with increasing click rate. As rate increased, the amplitudes of waves i and v decreased monotonically, whereas the amplitudes of waves ii-iv were largely uninfluenced by click rate. As in experiment 1, mean wave i amplitude was greater for rarefaction clicks, whereas mean wave v amplitude was greater for condensation clicks. The magnitude of these polarity dependencies on waves i and v amplitude decreased with increasing click rate. Experiment 3 evaluated the effects of click polarity on BAERs to high-intensity (100 dB pSPL) clicks presented at a rate of 10 Hz. In eight of ten gerbils evaluated, wave i amplitude was greater to rarefaction clicks, and, in all ten animals, wave v amplitude was greater to condensation clicks. The effects of click level and rate on BAER peak amplitudes, latencies, and interwave intervals are reminiscent of stimulus dependencies reported for the human BAER. The effects of click polarity on the amplitudes of waves i and v of the gerbil BAER have also been reported for the human BAER.

Cerebral blood flow and evoked potentials during Cushing response in sheep.

We determined how alterations in systemic hemodynamics, characteristic of the Cushing response, are related to changes in cerebral blood flow (CBF), cerebral metabolic rate of O2 (CMRO2), and brain electrical conductive function, as assessed by somatosensory-evoked potentials (SEP) and brain stem auditory-evoked responses (BAER). In three groups of eight pentobarbital-anesthetized sheep, intracranial pressure was gradually elevated to within 50, 25, or 0 mmHg of base-line mean arterial pressure and then held constant for 40 min by intraventricular infusion of mock cerebrospinal fluid. Microsphere-determined CBF fell when cerebral perfusion pressure was less than 50 mmHg. CMRO2 fell when CBF fell greater than 30-40%. Mean aortic pressure and cardiac output increased when CBF fell greater than 40%, i.e., at approximately the level at which CMRO2 fell. Furthermore, the magnitude of the increase in arterial pressure and cardiac output correlated with the reduction of CMRO2. SEP latency did not increase unless CBF fell greater than 55-65%, corresponding to a 20-30% reduction of CMRO2. Increased latency of BAER wave V was associated with a fall in midbrain blood flow of greater than 65-70%. Thus increase in SEP and BAER latencies required reductions of flow greater than those required to elicit a systemic response. This demonstrates that there is a range of intracranial pressure over which the increase in arterial pressure preserves sufficient CBF to sustain minimal electrical conductive function. The best predictor of the onset and magnitude of the Cushing response in adult sheep is the decrease in CMRO2.

Effects of Enflurane on Brainstem Auditory Evoked Responses in Humans

The effects of enflurane anesthesia on brainstem auditory evoked responses (BAERs) was determined in 10 patients with normal hearing undergoing various surgical procedures. Arterial blood pressure, body temperature, and arterial Pco2 were controlled during the 2- to 5-hour recording sessions. End-tidal enflurane concentrations were continuously recorded on a chemetron Medspect II mass spectrometer in three subjects. BAERs were obtained by, and recorded on a Nicolet CA 1000, from C2 with reference to A1 or !2, with a 2000 click-averaging for each measurement. Enflurane administered at clinical concentrations (0.5% to 3%) produced a consistent changes in BAER latencies. The waves significantly affected (p less than 0.01) were waves III, IV, and V and interpeak latency I-V. The magnitude of theses changes was related to the concentration of enflurane and was magnified by temporarily decreasing the Paco2. These findings confirm similar data obtained in animals which have shown the same effects at doses that can produce generalized seizure activity. BAER analysis shows that changes predominate at the pons and midbrain levels and affect the brain stem conduction time, which likely reflects the action of enflurane on the activity of the reticular activating system.

Age and sex differences in the human auditory brainstem response.

Age and sex differences in the brainstem auditory evoked response (BAER) were investigated in older (60 to 79 yrs), middle-aged (40 to 59 years), and young (20 to 39 yrs) individuals. Within each age group the number of males (N = 10) and females (N = 10) were divided equally. Scalp potentials were recorded from the vertex to clicks presented at 60, 70, and 80 dB(SL) for stimulus rates of 5, 10, and 15 clicks/sec. Results indicated that older adults had longer latencies at Wave III than either middle-aged or young adults. Age effects were also found for Waves I, II, and IV but were restricted to the lowest intensity and were more evident in older males than females. Significant sex effects showed that the females in each group had shorter Wave IV and V latencies than males. The results suggest that age affects neural propagation at the level of the olivary complex (Wave III) and that BAER latencies are also influenced by the sex of the individual.

A Study of Frequency Specificity of the Auditory Fast Responses

In order to establish the application of action potentials (AP) of the cochlear nerve and brain stem auditory evoked response (BSR) in clinical audiology, the frequency specificity of them was studied using the special masking techniques.The change of AP and BSR latencies and amplitudes of white noise evoked responses were observed using the high and low pass filtered masking noise. Secondaly the band stop (reject) noise was produced during the tone pip stimuli by the frequency selective masking.According to the first examination, AP responses depended on the frequency range of cochlear partitions higher than 2kHz, while those responsive for BSR extended to a octave lower range.It is considered that the latencies of responses are dependent to the most basal part of the cochlear partition, which is stimulated when the stimulus conditions are held constant. The amplitudes of AP are decided by the length of the stimulated cochlear partition, when the stimlus conditions areheld constant and the lower frequency bands of masking are changed.The following results were obtained from the second examination. The thresholds of responses were 5dB above subjective ones to the 4kHz and 81kHz tone pip stimuli.On the other hand AP and BSR thresholds to the 2kHz tone pips were 20dB and 15dB above subjective threshold respectively. The AP responses were not obtained and BSR were unstable to the the tone pips at 1kHz.The intensity-latency curves of AP and BSR were shifted in parallel with the frequency from high to low.It is concluded that the effective frequency of the tone pips were 4kHz or higher for AP, and 2kHz or higher for BSR in clinical application. The frequency selective masking of the band stop noise is necessary for us to obtain the responses from more restricted part of the cochlear partition.