Technical Considerations in the Recording and Interpretation of the Brainstem Auditory Evoked Potential for Neonatal Neurologic Diagnosis

Interaural time coincidence detectors are present at birth: evidence from binaural interaction

Binaural processing of sounds in mammals is presumably initiated within the auditory nuclei of the caudal pons. The binaural difference waveform (BD) can be derived from the sum of the waveforms evoked by right monaural clicks plus left monaural clicks minus the waveform evoked by binaural clicks. In adults, the BD's first positive peak (beta) is large only for stimuli with interaural time differences (ITDs) that produce a fused acoustic percept. Humans at birth can localize and discriminate sound sources, but their head circumference is about two-thirds of an adult head. In order to test whether beta is related to head circumference, we recorded beta in human neonates as a function of ITD. Binaural clicks with ITDs ranging between 0 and 1000 micros were used to derive BD waveforms in 34 neonates. For ITD=0, beta was detectable in 56% of newborns. The incidence of beta detection then decreased as ITD increased. Only 9% of the babies had detectable beta for all ITDs. No correlation was found between the existence of beta and other properties of the monaural or binaural auditory brainstem response. The finding that for some infants beta was present for all ITDs up to 1.0 ms suggests that there is no recalibration of brainstem delay lines with head growth. Our data suggest that the brainstem auditory pathway for detecting interaural time differences in the adult is probably present at birth. Maturational factors such as increased myelination and greater firing synchrony probably improve the detectability of beta with age. The second peak in the BD waveform (delta) was highly correlated with the existence of wave VI in the binaural and monaural waveforms.

Auditory brainstem response screening for hearing loss in high risk neonates

The present paper reports the findings of a 7 year study evaluating the use of the auditory brainstem response (ABR) as the basis of a hearing screening procedure in a group of newborns at increased risk of hearing impairment. A Special Care Baby Unit (SCBU) population of 417 infants with diverse clinical backgrounds and treatment histories was tested for hearing impairment at birth using ABR audiometry. Some 332 passed the original screen at 30 dBnHL test level in both ears. Of the failure group, 18 did not survive and 32 had some degree of hearing impairment confirmed, nine of which were sensorineural in origin. An increased incidence of persistent middle ear disease was also noted in the failure group. A detailed operational analysis demonstrates that provided appropriate pass/fail criteria are adopted, the ABR technique offers excellent sensitivity and specificity for the detection of significant hearing loss in the test population. Furthermore, the study establishes that implementation of an ABR-based screening programme could reduce the average age at detection of permanent hearing loss by 7 months. A cost assessment shows that the introduction of such a targetted screening procedure could be done at a reasonable outlay.

An improved procedure for assessing ABR latency in young subjects based on a new normative data set

Auditory brainstem response (ABR) latencies in normal young and very young subjects are longer than in mature subjects. Use of adult norms in the assessment of young subjects may therefore result in the erroneous reporting of abnormalities in subjects who are in no way impaired. In this study a new normative data set was established by measuring ABR absolute and interpeak latencies in 374 subjects in different age groups with normal ABR and no risk factor for hearing impairment or neurological abnormality. Double exponential functions were fitted to a number of latency measures derived from the data and from those functions a table of correction values was computed. The variability in the measurements of the children is greater than that of the adults. Procedures are proposed which enable the assessment of abnormality of ABR latencies to be made for all subjects regardless of age.

Developmental course of brain-stem auditory evoked potentials in the first days of full term infants

Modifications of brain-stem acoustic evoked potentials (BAEPs) in the first 5 days of life of normal full-term infants are reported. BAEPs were recorded using rarefaction clicks at 70, 60, 40, 20 dB HL. Multiple linear regression analysis was performed to evaluate chronological and gestational age differences for all positive and negative peaks, interpeak latencies, amplitudes and amplitude ratios. The percentage of newborn infants with auditory threshold of 20 dB HL increased with the number of days. At all intensities the latency of PIII and PV decreased significantly between the 2nd and 3rd day, while the latency of PI decreased significantly between the 3rd and the 4th day; PIII and PV latencies decreased also between the 4th and the 5th day. The longer the period of gestation the longer was the PI latency recorded between the 2nd and 5th day after birth. The anatomical and physiological changes developing shortly after birth are probably responsible for the above findings. These changes most probably appear firstly in the cochlear and trapezoid nuclei and later on in the organ of Corti.

Intensity effect on latency and interval of human BAER

Intensity effect on wave latency and interval (IPI) in brainstem auditory evoked responses (BAER) from birth to adulthood was investigated. The L-I functions were slightly steeper in younger groups than in older groups, which was associated with age-related difference in the absolute latencies. Wave I latency in most age groups exhibited two "transitional" responses: one at 70 dB HL or, sometimes, at 60 dB HL and the other mostly at 20 dB HL. As click intensity decreased, the I-III IPI tended to decrease slightly while the III-V IPI tended to increase slightly in most age groups. Since the I-V IPI was constant at various intensities which could be attributed to a slight change in the morphology of wave III with altering intensity.

Cerebral electrical potentials evoked by balloon distention of the human esophagus

Cerebral evoked potentials provide a technique for evaluation of central nervous processing of information derived from a variety of sensory modalities. Evoked potentials associated with balloon distention of the smooth muscle esophagus were studied in 14 adult volunteers. Stimulation was applied via repeated inflation and deflation of a balloon attached to a pressure pump that cycled at 0.2 Hz. Cortical electrical responses were recorded from scalp electrodes at Cz, Cz', and Pz of the international 10-20 System for electroencephalographic recording. The recording electrodes were referenced to Fpz and averaged over a 1-s period for 100 repetitions. Latencies, amplitudes, and waveforms of the evoked potentials were compared with controls consisting of pump on/balloon detached, auditory masking, and conventional somatosensory posterior tibial nerve stimulation. Polyphasic evoked potentials were obtained in all subjects, and maximum positive deflections occurring with latencies of 202-396 ms. Maximal amplitudes ranged from 2.5-8.3 microV. Latencies and amplitudes of the evoked responses were highly reproducible in each subject with considerable variation among subjects.

CONCLUSIONS

(a) Reproducible evoked potentials with distinctive waveforms can be recorded in response to esophageal balloon distention in humans; (2) long latency of the evoked potentials suggests involvement of nonmyelinated visceral afferent pathways; (3) the evoked potentials are probably specific to mechanical stimulation rather than being nonspecific arousal responses; and (4) the results support this as a promising new method for investigation of the neurobiology of gastrointestinal sensation in humans that may help clarify pathological conditions of the irritable esophagus syndrome and esophagus-related chest pain.

Abnormal brain-stem function (brain-stem auditory evoked response) correlates with acoustic cry features in term infants with hyperbilirubinemia

We hypothesized that changes in brain-stem auditory evoked responses related to bilirubin would be associated with changes in cry because of the anatomic proximity in the brain stem of cranial nerves 8 (auditory) and 9 to 12 (vagal complex, which controls cry). Brain-stem auditory evoked responses and computerized cry analysis were used to study the concurrent effects of moderate hyperbilirubinemia on auditory function and cry. Fifty term infants were divided equally into two groups on the basis of serum bilirubin concentrations: low (less than 8 mg/dl; 136) mumol/L and moderate (10 to 20 mg/dl, 170 to 342 mumol/L). Forty-three infants had successful tracings of brain-stem auditory evoked responses recorded with a Cadwell model 5200A evoked response unit during two successive trials, and a cry recording of each infant was analyzed by computer. The moderate serum bilirubin group had an increase in percent cry phonation (p less than 0.02) and an increase in the variability of the first formant (p less than 0.04) in comparison with the low serum bilirubin group. Serum bilirubin values correlated positively with brain-stem conduction time (r = 0.36, p less than 0.01), percent phonation (r = 0.42, p less than 0.004), and variability of the first formant (r = 0.39, p less than 0.02). Percent phonation, the voiced component produced by increased neural control, correlated with the interpeak of waves latencies I to III (r = 0.32, p less than 0.03) and brain-stem conduction time (wave I to V) (r = 0.35, p less than 0.01). We conclude that hyperbilirubinemia affects adjoining areas of the brain stem that control hearing and cry production.

Auditory brain-stem evoked potentials to clicks at different presentation rates: estimating maturation of pre-term and full-term neonates

Auditory brain-stem evoked potentials ABEPs were recorded from 57 neonates ranging in gestational age between 27 and 43 weeks. Averages and standard deviations of I, III and V peak latencies, I-V, I-III and III-V inter-peak latency differences (IPLDs), for 10/sec and 55/sec clicks were calculated for each age group. An additional measure, the net effect of increasing stimulus rate (ISR), was calculated by subtracting 10/sec measures from their 55/sec counterparts. Correlations between ABEP measures and subject age were determined. The results of this study demonstrate a significant correlation between gestational age and electrophysiological measures of peripheral, as well as central, conduction: an inverse correlation between age and peak latencies as well as IPLDs. The slope of this correlation was steeper for the higher stimulus rate. The slope of 55/sec measures vs. age was the sum of the respective slopes of 10/sec measures and of ISR. The maturation of 10/sec measures may reflect white matter development, while ISR changes with gestational age represent maturation of synaptic efficacy. Thus, the maturation of 55/sec measures reflect the combined maturation of nerve conduction velocity and synaptic efficacy along the neonatal auditory nerve and brain-stem. This differential evaluation may enable more accurate determination of developmental age of neonates, with respect to total maturation as well as its constituents.

Brainstem electric-response audiometry in infants of a neonatal intensive care unit

Brainstem electric-response audiometry was used to assess the auditory function of 600 infants from a neonatal intensive care unit. Two groups of children were tested, one group as inpatients prior to discharge with a mean age at test of 39.4 weeks and one group as outpatients with a mean age at test of 55.4 weeks. Our results indicate that testing infants when they are older will reduce the incidence of failure on the initial evaluation and will reduce the identification of transient hearing losses which resolve spontaneously. Our results also indicate that a threshold of 30 dB nHL or less is probably normal and that some infants with a threshold of 40 dB nHL at first test require otological or audiological management.

The central auditory conduction at term date and three months after birth. II. Auditory brainstem response

This communication describes the results of auditory brainstem responses (ABRs) obtained in 25 healthy mature newborns with a follow-up at 3 months of age. The combination of ipsi- and contralateral recordings, the intensity series and the comparison with the composite group averages are useful for the identification of the separate ABR components. Differences between the records after right or left ear stimulation were not observed. Comparing our data with those obtained by others, we conclude that the interpeak latency differences (IPLDs) offer a more consistent measure of ABR latency values than the peak latencies measured from stimulus onset. The simultaneously recorded ABRs ipsi- and contralateral to stimulation show both at term, and at 3 months, an equal central conduction time. The ABR II-V complex shows contralaterally a significant shift compared with the ipsilateral II-V complex. The significant latency changes observed between term and at 3 months are due mainly to the latency decrease in the II-III IPLD.

The effect of neonatal hyperbilirubinemia on the auditory brainstem response

Auditory brainstem response (ABR) testing was performed on 30 babies in the Premature Baby Center of Kyoto University Hospital as soon after birth as possible. In cases of hyperbilirubinemia of more than 15.0 mg/dl, ABR testing was performed at least twice. In four babies with total bilirubin concentrations of more than 18.0 mg/dl at some point, abnormal ABRs were seen. These abnormalities normalized with a decrease in serum total bilirubin concentration in two of the four cases, but in the other two the abnormalities showed no change. The cause and significance of this difference are not known, but ABR is a simple and useful method for assessing the neurotoxic effects of bilirubin on the nervous system.

Auditory brainstem evoked response as a hearing test in infants and children: a follow up study

In recent years the auditory brainstem evoked response (BSER) has become an established aid in assessing hearing in unco-operative subjects. We have reviewed our experience with this technique in 293 infants and children aged less than 11 years. We have found that the threshold for click BSER correlates well with the average audiometric threshold in the 2-4 kHz range. We have had encouraging preliminary experience to support the claim by other workers that 500 Hz stimuli may be used to assess low tone auditory function. In interpreting results it is important to appreciate that hearing levels may fluctuate with disorders such as otitis media and occasionally in cases of meningitis. Caution is also advised in interpreting results in cases where central nervous system pathology capable of affecting auditory pathways is known to exist.

Maturation of the brain-stem auditory evoked potential in premature infants

Patterns of development and extent of variability of the brain-stem auditory evoked potential (BAEP) are described in 52 healthy premature infants and 50 normal term newborns with reliable conceptional ages. Binaural and monaural stimulation are compared. Serial studies of individual prematures are emphasized and demonstrate that the most consistent and least variable measures are the monaurally derived interpeak intervals. All the BAEP parameters studied mature including wave form, relative amplitude, peak and interpeak intervals, but there is far more variability in preterms than in term infants or adults, even when infants are carefully matched for conceptional age. As term is approached, BAEP variability decreases substantially, suggesting that near term the BAEP becomes a more reliable indicator of neurologic function. The variability of the BAEP in the normal preterm limits its usefulness in determining neurologic dysfunction in individual high risk infants. Nevertheless, the BAEP may still prove useful for defining group differences among infants and could provide an objective measure of those factors influencing neurologic development. Serial change in the BAEP is a specific parameter which we believe merits further study in premature infants as an index of neurologic maturation.