Otoacoustic emissions and auditory assessment in infants at risk for early brain damage

The importance of early hearing screening has long been recognized, as the prognosis for the hearing impaired child is improved when the diagnosis is made as early as possible, and the intervention is begun immediately. For clinical screening of hearing impairment, the recording of otoacoustic emissions was recommended. As some risk factors for early brain damage are at the same time also risk factors for dysfunction of auditory system, we presumed that infants at risk for brain damage have hearing impairment more frequently than the rest of the population of the same age. We were interested in the role of otoacoustic emission testing during the assessment of auditory function in these infants. There were 110 infants at risk for brain damage included in the study. After thorough otorhinolaryngological examination, auditory function was estimated by recording of otoacoustic emissions, tympanometry, pure tone audiometry and, when necessary, auditory brainstem responses. Otoacoustic emissions were recorded by Madsen-Electronics Celesta 503 in an acoustically treated sound room. We registered spontaneous as well as transient and distortion product otoacoustic emissions. The neurologist formed two groups with different degrees of neurological risk. The collected results of auditory function were compared with the degree of neurological risk. For the statistical analysis, the procedure chi(2) and Fischer test were used. Spontaneous otoacoustic emission was detected in 38.2% of examinees. Evoked otoacoustic emissions were registered in 87.3% of infants. The testing had to be repeated in 32.7% of infants. We observed evoked otoacoustic emissions to be present also in a child with sensorineural hearing impairment and no auditory brainstem responses. Up to 32.7% of infants at risk for brain damage were hard of hearing. Conductive hearing loss was discovered with 25.4% of infants, and eight (7.3%) had sensorineural hearing impairment. In the group of examinees with only risk factors 3.6% had sensorineural impairment and in a group with abnormal motor development, there were 18.5% with that kind of hearing loss. Fischer test confirmed a statistically significant difference between the groups. Infants at risk for brain damage have more frequently impaired auditory function than their peers. For this reason, it is especially important to focus attention on the hearing condition when dealing with this population. Recording of evoked otoacoustic emissions is very helpful in pediatric audiometry, but any interpretation of the results should consider the possibility of auditory neuropathy.     

A comparison of auditory brain stem response and behavioral screening in high risk and normal newborn infants

A total of 345 newborn infants received a behavioral screening consistent with protocol adopted by the Joint Committee on Infant Hearing. Infants were divided into three groups consisting of 108 at-risk for hearing loss, 80 intensive care nursery graduates, and 157 normal control infants. Of the total, 315 newborns received auditory brain stem response (ABR) assessment. The results suggest that 4% of the high risk population had irreversible hearing loss to such a degree that amplification was warranted. Discussion focuses on the questionable use of behavioral screening in the newborn nursery and the application of ABR in a high risk population.     

Electrophysiologic signs of auditory distraction in elderly listeners

Brain mapping was used to investigate the ability of young and elderly female listeners to attend to /ga/ syllabic events at one ear in the presence of speech babble competition at the opposite ear. An oddball stimulus presentation paradigm was used to record the N1 and P2 components of the late auditory evoked potential (LAEP) from 19 scalp locations. With speech competition, elderly listeners exhibited significantly larger reductions in P2 amplitude than did young listeners. The competition produced no changes in N1 amplitude in either group. These findings contrast with those of an earlier study in which age-related reductions in N1 but not P2 amplitude were found when listeners attended to tones rather than speech stimuli in the presence of speech competition. These studies suggest that amplitude reductions in different LAEP components may provide electrophysiologic indices of age-related breakdowns in processing sounds in the presence of competition. Which LAEP components are affected may depend on experimental variables such as task difficulty or the nature of the stimuli (e.g., speech vs nonspeech).     

Comparative ABR profile in high risk infants

Auditory brainstem responses (ABR) were studied in 52 children upto the age of 3 months, suffering from neonatal jaundice, prematurity, pyogenic meningitis and septicemia. Absolute latency of wave I and interpeak latency I–V were found to be significantly delayed in cases of jaundice and absolute latency of wave V and interpeak latency I–V were prolonged in cases with prematurity. In cases following pyogenic meningitis absolute latency of wave V and interpeak latency of I–III, I–V were significantly delayed compared to septicemia where absolute latency I,V and interpeak latency I–V were significantly delayed (P<0.05). Maximum auditory insult was seen in cases with neonatal jaundice where 30.77% each had severe SN deafness and 30.77% had moderate degree of deafness compared to prematurity, meningitis and septicemia where 14.28, 7.69 and 25% were found to have severe SN deafness and 7.14, 38.46 and 25% had moderate deafness. Overall incidence of deafness of any kind in these factors was 44.23%.     

Reversible auditory brainstem responses screening failures in high risk neonates

This work is aimed at assessing the frequency of occurrence of reversible auditory brainstem responses (ABR) abnormalities within a targeted hearing screening program for high risk (HR) newborns. The effect of age on screening is also evaluated and some important clinical issues are highlighted. The audiological records of 1,294 HR neonates were retrospectively reviewed. All children were tested for hearing loss using ABR within a 17-year period. Initial failures were re-examined 4–6 months later. The mean age of infants who scored “pass” and “refer” at initial test, as well as the referral rates were calculated and compared. One hundred and seventy-eight infants (13.8%) demonstrated abnormal recordings at initial screening. From those who were present on re-examination, 64.2% showed complete and 15% partial recovery. Reversible abnormalities have been detected not only for conductive threshold elevation but also for sensorineural losses. Remarkably, 50% of the cases with absent waveforms or ABR threshold ≥80 dBnHL demonstrated complete recovery to normal. Statistically, higher rates of abnormal results were inversely associated with the newborn’s age at initial testing. In conclusion, reversible ABR abnormalities are common among HR infants due to temporary auditory dysfunction, secondary to external and middle ear pathology or retarded central nervous system maturation. The observed high rates of transient ABR abnormalities give rise to some practical questions regarding the implementation time of hearing screening for HR infants. Moreover, given that central nervous system maturation changes may still be in progress, the definite decision for an early cochlear implantation in this pediatric subset should be made after obtaining reliable behavioral hearing tests.     

EEG derivations providing auditory steady-state responses with high signal-to-noise ratios in infants

OBJECTIVE: To identify EEG derivations that yield high signal-to-noise ratios (SNRs) of the auditory steady-state response (ASSR) in infants aged 0 to 5 months. DESIGN: The ASSR was recorded simultaneously from 10 EEG derivations in a monopolar montage in 20 sleeping infants. Stimuli were tones of 0.5 or 2 kHz that were 100% amplitude modulated and 20% frequency modulated, presented at 65 dB SPL for 4.4 minutes in either the right or the left ear. An amplitude modulation frequency of 90 Hz (left ear) or 94 Hz (right ear) was used. From the 10 measured monopolar derivations, all 45 bipolar derivations were calculated mounting up to 55 EEG derivations. EEG derivations were selected in the preferred set if they had the largest SNRs within subjects and if they were obtained significantly more frequently across subjects than was expected by chance (Monte Carlo simulation and Wilcoxon signed ranks test). RESULTS: The preferred derivations are both mastoids ipsilateral to the stimulated ear with Cz as common reference. These derivations improved SNRs compared with each of several conventional EEG derivations (excluding the preferred derivations) between 16 and 69% (500 Hz, left ear), 9 and 132% (500 Hz, right ear), 31 and 193% (2 kHz, left ear), and 3 and 105% (2 kHz, right ear). In contrast to results reported earlier for adults, high SNRs were not found at the inion-Cz derivation in these infants. CONCLUSIONS: High SNRs were obtained in infants aged younger than 6 months if the ASSR was recorded from the mastoids ipsilateral to the ear of stimulation referenced to Cz.     

Delay in the development of the auditory pathways. A differential diagnosis in hearing impairment in young infants

BACKGROUND: Due to the increased frequency of screening tests in new-born infants, the number of subsequent examinations of very young children has increased in the Departments of Phoniatrics and Pediatric Audiology. To exclude hearing loss in young children, click stimulated brainstem evoked response audiometry (BERA) and otoacoustic emission tests are, in general, considered to be reliable methods. However, pathologic BERA thresholds and pathologic hearing reactions have been observed occasionally in young infants who show improved and even normal hearing reactions in subjective and objective hearing tests after some months. PATIENTS AND RESULTS: Our group of 14 children (ten female, four male) was initially examined by BERA at the ages of 1-7 months. Twelve children had an elevated risk of hearing loss due to complications in the pre-, peri- and postnatal period. In the BERA, no deafness was diagnosed, but in all children at least monaural pathologic BERA thresholds were observed. Subjective hearing tests confirmed hearing loss. Objective and even subjective hearing reactions improved and normalised within a few months at least monaurally. CONCLUSION: In very young infants, the possibility of a delayed maturation of the auditory pathways must be considered when a hearing loss is diagnosed. Our examples prove that young children with sensorineural hearing loss need more than one objective hearing examination during the first year of life.     

Audiometric estimation error with the ABR in high risk infants

Click ABR wave V thresholds in the first year were compared with follow-up behavioural pure-tone audiometry under earphones at age 3 to 6 years in 713 infants (yielding 1,367 ears) at risk for hearing loss. The observed accuracy of the ABR depends strongly on the precise definitions of the target disorder and the test abnormality criteria. For sensorineural hearing loss of more than 20 dB averaged at 2 kHz and 4 kHz, the click ABR provides an accurate test, with both false positive and false negative rates of less than 10%, using an ABR threshold criterion of 30 dB nHL. The false positive error rate can be at least halved by using a simple rule for wave V latency that discriminates conductive and sensorineural ABR threshold abnormalities. False negative errors may be explicable in terms of the lack of frequency specificity of the click stimulus.     

Electrophysiologic tests of the auditory apparatus and vestibular organ in Usher syndrome

Usher syndrome is a congenital autosomal dominant inherited disease characterised by hearing, balance and vision problems. The aim of the work was an evaluation of hearing and vestibular organ in the chosen group of patients with Usher syndrome diagnosed. Material consisted of 10 persons (5 males and 5 females) aged from 16 to 46 years with Usher syndrome diagnosed. All the patients have been in constant ENT and Ophthalmology Clinics' care. Complex hearing and balance organ, including posturography, as well as complex ophthalmologic examination were performed in each case. Medium or severe perceptive cochlear hearing loss, proper function of vestibular organ and slight elevation of stabilograms parameters were found in 6 cases. In 4 cases there were severe bilateral hearing loss, lack of vestibular function and considerable worsening of stabilograms parameters. In ophthalmologic examination in all the cases there was bilateral symmetrical dystrophy of the retina of various intensification. We concluded that hearing and balance organ examination in Usher syndrome can state accessory diagnostic aspect that might help to distinguish subtypes of the syndrome. In this way audiologic and otoneurologic tests could help to define prognosis of the disease in the individual cases. A necessity of close co-operation of genetics, ophthalmologists and ENT doctors as well as psychologists was stressed.     

Aided auditory steady-state responses in infants

Infants with hearing loss routinely receive hearing aids several months before reliable behavioral responses to amplified sound can be observed. This necessitates objective measures to validate hearing-aid fittings. A single report has demonstrated the use of ASSRs to determine aided thresholds in children but data in young infants is still lacking. The current study explored aided ASSR compared to unaided ASSR thresholds and subsequent behavioral thresholds in a group of six young infants with hearing loss who received hearing aids between three and six months of age. Aided ASSR thresholds were obtained in 83% of frequencies where aided behavioral thresholds were obtained, with a mean threshold difference of 13+/-13 dB. The aided ASSR-based threshold estimates were within 15 dB of behavioral thresholds in 63% of cases, indicating a moderate correlation (r = 0.55). Comparing aided and unaided ASSR measurements revealed an average functional gain of 36+/-15 dB. These results indicate that ASSRs can provide the first evidence of robust hearing aid benefit in young infants several months before behavioral responses are observed.     

Aided auditory steady-state responses in infants

Infants with hearing loss routinely receive hearing aids several months before reliable behavioral responses to amplified sound can be observed. This necessitates objective measures to validate hearing-aid fittings. A single report has demonstrated the use of ASSRs to determine aided thresholds in children but data in young infants is still lacking. The current study explored aided ASSR compared to unaided ASSR thresholds and subsequent behavioral thresholds in a group of six young infants with hearing loss who received hearing aids between three and six months of age. Aided ASSR thresholds were obtained in 83% of frequencies where aided behavioral thresholds were obtained, with a mean threshold difference of 13±13 dB. The aided ASSR-based threshold estimates were within 15 dB of behavioral thresholds in 63% of cases, indicating a moderate correlation (r = 0.55). Comparing aided and unaided ASSR measurements revealed an average functional gain of 36±15 dB. These results indicate that ASSRs can provide the first evidence of robust hearing aid benefit in young infants several months before behavioral responses are observed.     

婴幼儿单侧听神经瘤

目的：探讨婴幼儿单侧听神经病（AN）神经生理学特点。方法：对3例单侧AN患儿在采集病史和耳科检查的基础上,行系统的听力学检查,包括声阻抗、镫骨肌反射、听性脑干反应（ABR）、耳蜗微音电位（CM）、诱发耳声发射（EOAE）、中潜伏期反应（MLR）和事件相关电位（ERP）以及CT和（或）MRI及周围神经系统检查。结果：3例患儿鼓室图均呈“A”型,健耳的同侧和交叉镫骨肌反射可正常引出,而患耳的同侧和交叉镫骨肌反射未引出。3例患儿双侧EOAE有效引出,健耳的ABR正常引出,思耳的ABR未引出,但CM均正常。3例患儿双耳均记录到MLR及ERP。影像学和周围神经系统未见异常。结论：单侧AN与双侧AN有相似的神经生理学特点。对婴幼儿单侧AN的诊断应着重分析其神经生理学特点,建议联合应用EOAE、ABR、CM和影像学检查。应对AN患儿定期随访。     

Bone conduction auditory brainstem responses in infants

The contribution of air conduction auditory brainstem response (AC-ABR) testing in the paediatric population is widely accepted in clinical audiology. However, this does not allow for differentiation between conductive and sensorineural hearing loss. The purpose of this paper is to review the role of bone conduction auditory brainstem responses (BC-ABR). It is argued that despite such technical difficulties as a narrow dynamic range, masking dilemmas, stimulus artifact and low frequency underestimation of hearing loss, considerable evidence exists to suggest that BC-ABR testing provides an important contribution in the accurate assessment of hearing loss in infants. Modification of the BC-ABR protocol is discussed and the technical difficulties that may arise are addressed, permitting BC-ABR to be used as a tool in the differential diagnosis between conductive and sensorineural hearing. Two relevant case studies are presented to highlight the growing importance of appropriate management in early identification of hearing loss. It can be concluded that BC-ABR should be adopted as a routine clinical diagnostic tool.     

Recording auditory steady-state responses in young infants

OBJECTIVES: This study examined the auditory steady-state responses evoked by amplitude-modulated (AM), mixed-modulated (MM), exponentially-modulated (AM2), and frequency-modulated (FM) tones in 50 newborn infants (within 3 days of birth) and in 20 older infants (within 3-15 wk of birth). Our hypothesis was that MM and AM2 tonal stimuli would evoke larger responses than either the AM or FM tones, and that this increased size would make the responses more readily detectable. DESIGN: Multiple auditory steady-state responses were recorded to four tonal stimuli presented simultaneously to each ear at 50 dB SPL. The carrier frequencies of the stimuli were 500, 1000, 2000, and 4000 Hz and the modulation rates were between 78 and 95 Hz. Recordings lasting 12 minutes were obtained for each of the three types of modulation: 100% AM, MM (100% AM and 20% FM) and AM2. In six infants, responses to 20% FM were also recorded. RESULTS: In newborn infants, MM and AM2 stimuli produced responses that were on average 15% larger than AM stimuli. For AM, MM, and AM2 stimuli, the percentage of significant responses was 67%, 73%, 76%, respectively. Responses to FM stimuli were clearly evident in newborn infants and were about half the amplitude of the AM responses. Responses recorded in the older infants were 17% larger when evoked by MM and AM2 stimuli, rather than AM stimuli. Responses in the older infants were, on average, 32% larger and showed a higher incidence of significant responses than for infants in the first 3 days of life. For AM, MM, and AM2 stimuli, the percentage of significant responses was 82%, 82%, 84%, respectively. In both newborn and older infants, the overall percentage of significant responses was decreased by the 500 Hz results, which showed lower amplitudes and were less frequently detected than responses evoked by other frequencies. CONCLUSIONS: The responses to MM and AM2 tones were larger than those evoked by AM tones. Using these stimuli will increase the reliability and efficiency of evoked potential audiometry in infancy. Responses at 50 dB SPL are more easily detected at 3-15 wk of age than in the first few days after birth. Comprehensive frequency-specific testing of hearing using steady-state responses will likely be more accurate if postponed until after the immediate neonatal period.     

Central auditory processing assessment

As the acoustic information travels within the central auditory nervous system, the processing of the signal undergoes several levels of serial and parallel "bottom-up" processing influenced by high level cognitive "top-down" processes. Because the multiple location of the operational sites, the central auditory deficits are frequently quite subtle and need a test battery approach to be identified. Each of the four principal processes has at least to be tested: the closure task, the dichotic ability, the temporal ordering task and the binaural interaction function. The purpose of this review is to provide an overview of the psychoacoustic test procedures of identifying lesions or dysfunction's in the central auditory system.