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Aims: To detect any functional abnormality in the brainstem auditory pathway in late preterm babies born of small-for-gestational age (SGA) using maximum length sequence brainstem evoked response., Study Design: The response was recorded and analyzed at term in 38 SGA (birthweight <3rd centile) babies born at 33-36 week gestation. The results were compared with 40 age-matched babies born of appropriate-for-gestational age (AGA) (birthweight >10th centile). None of the subjects had major perinatal problems., Results: All wave latencies and interpeak intervals in the SGA group were slightly longer than those in the AGA group at most click rates. Wave III latency was significantly longer than that in the AGA group at 227/s (P < 0.05), and wave V latency was at 227 and 910/s (P < 0.05 and 0.05). Of the interpeak intervals, only the I-V interval in the SGA group was significantly longer than that in the AGA group at the highest rate 910/s (P < 0.05). The amplitudes of waves I, III and V in the SGA group all tended to be smaller than those in the AGA group at all click rates 91-910/s. The wave V amplitude was significantly smaller at most click rates (227-910/s, all P < 0.05). The slopes of all wave latency-, interval-, and amplitude-rate functions were similar in SGA and AGA groups., Conclusions: There were marginal abnormalities in MLS BAER of low-risk late preterm SGA babies, suggesting a mild degree of maturational delay in the brainstem. Intrauterine growth retardation occurring in late preterm babies has a minor effect on neural maturation of the immature brainstem., (Copyright © 2015. Published by Elsevier Ireland Ltd.)

Aim: To examine the process of change in hearing threshold during the neonatal period after perinatal hypoxia-ischaemia., Methods: The threshold of brainstem auditory evoked responses (BAER) was measured serially during the first month after birth in 92 term babies who suffered hypoxia-ischaemia., Results: The mean BAER threshold in these babies was significantly increased on day 1 (ANOVA p < 0.001). The elevated threshold decreased progressively on days 3 and 5, but was still significantly higher than that in normal controls (p < 0.01). The elevation continuously decreased more slowly on days 10 and 15, and to a near normal level on day 30. Threshold elevation was seen in 31.7% of the babies on day 1, and 34.5% during the first three days. The rate of elevation decreased progressively thereafter. On day 30, 10.6% of the subjects still had increased thresholds. Moderate to severe elevation occurred mainly during the first week and severe elevation occurred predominately on day 1. Threshold elevation starting after days 3-5 is likely to be due to middle-ear disorders. As a whole, during the first month, 44.6% (41/92) of the babies studied had threshold elevation. BAER threshold was correlated weakly with the stage of hypoxic-ischaemic encephalopathy on days 1 and 3. The threshold was significantly higher in babies with severe encephalopathy than in those with mild or moderate encephalopathy during the first 3 d of life., Conclusion: Hearing threshold is elevated in about one-third of term babies after hypoxia-ischaemia. The elevated threshold decreases progressively after birth, and returns to normal by one month in most babies. The threshold correlates weakly with the severity of encephalopathy.

Aim: To clarify further the influence of intrauterine growth retardation (IUGR) on early neural development., Methods: In 30 small-for-gestational age (SGA) preterm infants at term, brainstem auditory-evoked responses (BAERs) were recorded with clicks of different repetition rates. All infants had a birthweight < 3rd centile, without any other major perinatal complications., Results: Compared with the BAER in 36 appropriate-for-gestational age (AGA) term infants, the preterm SGA infants did not show any abnormalities at 21 s(-1) clicks, except for a slight increase in wave III amplitude. At 51 s(-1) clicks, there was an increase in III-V/I-III interval ratio (ANOVA p < 0.05). At 91 s(-1), the I-III interval shortened, whereas the III-V interval and III-V/I-III interval ratio increased (all p < 0.05). Wave V amplitude tended to increase slightly at all repetition rates of clicks used, although this increase did not reach statistical significance. The III-V interval and III-V/I-III interval ratio in the preterm SGA infants at different click rates correlated inversely with occipitofrontal head circumference at the time of testing, i.e. the smaller the head the longer the III-V interval (all p < 0.01). Wave III amplitude at 21 s(-1) also correlated inversely with head circumference (p < 0.01), suggesting that the slight increase in this amplitude in the preterm SGA infants is related to their relatively small head size., Conclusion: There were no major abnormalities in the BAER up to 91 s(-1) clicks at term in preterm SGA infants. The slight increase in III-V interval at high-rate stimulation suggests a subtle degree of central neural dysfunction, which is associated with small head size following IUGR.

Unlabelled: This study examined whether high presentation rates of clicks while recording brainstem auditory evoked responses (BAER) can improve the detection of central auditory impairment in asphyxiated neonates using the BAER. The BAER was analysed at different presentation rates of clicks within the first week after birth in 38 term neonates who suffered perinatal asphyxia. At the routinely used 21 s(-1) clicks all BAER wave latencies increased significantly (ANOVA, p < 0.05-0.01). After excluding five neonates who had a significantly elevated BAER threshold, only wave V latency increased slightly (p < 0.05). The interpeak intervals of I-V and III-V also increased slightly (both p < 0.05). Similar results were found at 51 s(-1) clicks. As the clicks were increased to 91 s(-1), the III-V interval increased more significantly (p < 0.01) and the III-V/I-III interval ratio also increased significantly (p < 0.01). In particular, wave V amplitude reduced more significantly than that in normal term controls (p < 0.01). Compared with values in the controls, wave V amplitude reduced by 4.5%, 12.2% and 24.7% at 21, 51 and 91 s(-1) clicks, respectively., Conclusion: Although a moderate increase in the rate (e.g. 51 s(-1)) while recording the BAER did not improve the detection of hypoxic-ischaemic auditory impairment, a significant increase (e.g. 91 s(-1)) did, which mainly indicates an abnormal reduction in wave V amplitude.

Unlabelled: Seventy preterm babies who were born with a birthweight <1500 g were studied with brainstem auditory evoked responses (BAER) at 37-42 wk of postconceptional age. The data were compared with those of normal term neonates to determine the prevalence of hearing impairment in preterm very low birthweight (VLBW) babies when they reached term. The BAER was recorded with click stimuli at 21 s(-1). Wave I and V latencies increased significantly (ANOVA p < 0.01 and 0.001). I-V and III-V intervals also increased significantly (p < 0.05 and 0.001). Wave V amplitude and V/I amplitude ratio did not differ significantly from those in the normal term controls. Ten of the 70 VLBW babies had a significant elevation in BAER threshold (>30 dB normal hearing level). Eleven had an increase in I-V interval (>2.5 SD above the mean in the normal controls) and one had a decrease in V/I amplitude ratio (<0.45). These results suggest that 14% (10/70) of the VLBW babies had a peripheral hearing impairment and 17% (12/70) a central impairment. Three babies had both an increase in I-V interval and an elevation in BAER threshold, suggesting that 4% (3/70) had both peripheral and central impairments. Thus, the total prevalence of hearing impairment was 27% (19/70)., Conclusion: About one in four preterm VLBW babies has peripheral and/or central hearing impairment at term. VLBW and its associated unfavourable perinatal factors predispose the babies to hearing impairment.

Maximum length sequence brainstem auditory evoked response (BAER) was studied within the first week after birth in 28 term neonates who had perinatal hypoxia-ischemia, or asphyxia. In the BAER recorded using conventional averaging techniques (click rate 21/s), the only abnormality was a slight increase in III-V interval, in addition to an increase in wave latencies when including those who had an elevated threshold (t test, all p<0.05). In the maximum length sequence BAER, however, both the III-V and I-V intervals in the asphyxiated infants were significantly increased at all the 91/s, 227/s, 455/s, and particularly 910/s click rates (p<0.05-0.001). The I-III interval was also increased significantly at 455/s and 910/s click rates (both p< 0.05). Wave V amplitude was significantly reduced at all the click rates used (ANOVA, p<0.05-0.001), particularly at 910/s, which sometimes was the only abnormality indicative of brain damage. Both the amplitude ratios V/I and V/III were significantly decreased at 455/s and 910/s click rates (p<0.01 or 0.001). A general trend was that BAER abnormalities after hypoxia-ischemia became more prominent as click rate was increased. Significant abnormalities occurred mainly at very high click rates (455/s and 910/s), which can be achieved using the maximum length sequence technique but not by using conventional averaging techniques. Thus, this technique, which can be used at the cribside, appears to be a better method for the early detection of brain damage after hypoxia-ischemia than using conventional averaging techniques, enhancing the diagnostic value of the BAER.

Brainstem auditory evoked response (BAER) was studied in term neonates using maximum length sequences (MLS), which allows presentation of acoustic stimuli at much higher rate than possible with conventional averaging technique. The response waveforms, especially for waves III and V, were well defined at the click rates of 91-455/s. Wave latencies and interpeak intervals at various click rates were all significantly longer and wave V amplitude was smaller in the neonates than in the adults. As click rate was increased, wave latencies increased and amplitudes progressively reduced. The slopes of wave latency-rate functions were progressively steeper for the later waves. The slopes of both III-V and I-V interval-rate functions were significantly steeper in the neonates than in the adults, indicating greater rate-dependent changes in the central components of the neonatal MLS BAER. These rate-dependent changes in the neonatal MLS BAER are generally similar to those in neonatal conventional BAER, although there are some differences. The results indicate that the neonatal brainstem can process rapid acoustic stimulation up to 455/s, although this ability remains immature.

Brain stem auditory electrophysiology was assessed in children long after purulent meningitis by examining the central components of brain stem auditory evoked response (BAER) at different presentation rates of clicks. Children with peripheral hearing loss were excluded from this study to avoid any possible influence of the loss on the measurements of BAER central components. Of the 70 children who had recovered from meningitis 2 to 8 years earlier, 9 (12.9%) showed abnormalities in BAER central components--mainly a slight reduction of wave V amplitude, at the click presentation rate of 10/s. Of the remaining 61 children who did not show any obvious abnormalities in the BAER at 10/s, an abnormally prolonged I-V interval and a reduced amplitude of wave V were seen in 5 children (8.2%) at the click rate of 90/s. The total BAER abnormality rate was therefore 20.0% (14/70 cases). The results suggest that most children who survive purulent meningitis have a favorable outcome for the brain stem auditory pathway, with about 1 in 5 having mild dysfunction or a suboptimal outcome in the pathway.

Binaural interaction (BI) components in brain-stem auditory evoked potential (BAEP) and their changes with stimulus intensity and repetition rate were examined in human adult. Seven BI components were identified, which occurred between the latency range of 5 and 11 ms and coincided consistently with the latency range of BAEP waves IV-VII. Waves DV and DVII, occurring at the downslopes of BAEP waves V and VII, respectively, were the two most prominent and reproducible BI components. Wave DVII existed consistently at high, moderate and, in most cases, low stimulus intensities, suggesting that this component is neurogenic although acoustic cross-talk may account for a part of its waveform at high stimulus intensities. The latencies of all BI components increased as a function of decreasing stimulus intensity, while the interpeak intervals, especially DV-DVII, were essentially constant at different intensity levels. The amplitudes of BI components decreased slightly with decreasing intensity. As click repetition rate increased, BI wave latencies and interpeak intervals increased slightly and amplitudes decreased slightly. When repetition rate increased to above 20/s, BI components became poorly differentiated. Lower repetition rates, e.g. 10/s, are therefore preferred for routine derivation of the BI. The changes in the latency and amplitude of BI components with stimulus intensity and repetition rate were associated or concomitant with those of the corresponding BAEP components in monaural and binaural potentials. In view of the concomitant relationship between BI and BAEP latency, we designate BI components in association with the corresponding BAEP components.

Long-term effect of perinatal and postnatal asphyxia on the developing auditory brainstem was investigated in children, particularly those who exhibited residual neurodevelopmental deficits, by analyzing the central components of brainstem auditory evoked responses (BAER). The major abnormalities in the BAER were a reduction of wave V amplitude, followed by a decrease in V/I amplitude ratio, while abnormalities in interpeak intervals were relatively rare. These findings suggest that asphyxia could result in residual neural dysfunction of the brainstem but does not appear to exert any major long-term effect on neuronal transmission. BAER abnormalities occurred more frequently in the children with residual neurodevelopmental deficits than those without these deficits after perinatal asphyxia. The occurrence of BAER abnormalities was related to the duration as well as the degree of asphyxia. No significant difference was found in the abnormalities of the central BAER components between the children after perinatal asphyxia and those after postnatal asphyxia, suggesting that perinatal and postnatal asphyxia exerts a similar long-term effect on the developing central nervous system.

Development of human peripheral hearing from birth to 6 years was investigated by recording brainstem auditory evoked potentials (BAEPs). The threshold of BAEPs decreased rapidly during the first 3 months after birth (2.7 dB/week during the neonatal period, 2.6 dB/month at 1-3 months), after which further decrease occurred more slowly but continued through 1 year of age (0.26 dB/month at 3-12 months). A few days after birth, the threshold was 18 dB higher compared to the adults, and progressively decreased to 10, 5 and 2 dB at 1, 3 and 12 months, respectively. The latencies of waves I and V decreased as a function of age at a rate of 0.01 and 0.05 ms/week during the neonatal period, 0.02 and 0.10 ms/month at 1-3 months and 0.014 and 0.076 ms/month at 3-12 months, respectively. Adult latency value was attained by 2 and 4 years for waves I and V, respectively. These findings suggest that although the ear is reported to be almost adult-like at birth, the immaturity in neural functional properties limits auditory sensitivity during early childhood. It appears that human peripheral hearing threshold decreases rapidly through the third postnatal month and thereafter continues to improve slowly through early childhood. It is postulated that the first 3 months after birth are likely to be a critical period in postnatal development of human peripheral hearing.

Peripheral hearing was assessed by examining brainstem auditory evoked responses (BAER) in children who suffered perinatal or postnatal asphyxia, particularly in those with residual neurodevelopmental deficits, to investigate the long-term effect of asphyxia on the developing auditory sensitivity. The BAER data were collected at least 6 months after the episode of asphyxia. Of the children who suffered perinatal asphyxia, hearing loss was found more frequently in those who exhibited residual neurodevelopmental deficits (17.1%) than in those who did not (6.3%), but this difference did not reach statistical significance. This implied that the long-term effect of perinatal asphyxia on the peripheral auditory system and its effect on the central nervous system may be relatively discrete or not closely correlated. The occurrence of hearing loss did not appear to be closely related to the degree of perinatal asphyxia, although hearing loss occurred more frequently in the children after severe asphyxia compared to those after mild asphyxia. There was no evidence for permanent hearing loss in the children who survived severe, prolonged postnatal asphyxia and exhibited residual neurodevelopmental deficits. These findings suggest that a critical period of particular sensitivity to the effect of hypoxia may exist during the development of the human peripheral auditory system. This period may range from some time prenatally to some time shortly after birth, probably the third postnatal month. After that, hypoxia is unlikely to lead to permanent hearing loss.

Brainstem auditory evoked response (BAER) was recorded in children from birth to 6 years and adults to study the development of wave amplitude. The amplitudes of all BAER waves increased with age, the greatest changes occurring during early infancy. Adult values were reached at 6 months of age for wave I and 2 years for wave V. The two waves continued to increase above the adult values until the highest amplitude value was reached at 3 years for wave I and 5 years for wave V. Subsequently, the amplitudes decreased towards the values in adults. The V/I amplitude ratio, which was slightly than the adult value shortly after birth, decreased during the first year of life and reached the minimum value between 1 and 4 years. Thereafter, it increased towards the adult value. Throughout the maturational stages the ratio was smaller than in adults. The amplitude of wave V was relatively stable and its variation was much smaller than those of wave I and V/I amplitude ratio. Lower normative limits of these amplitude measures were given to provide a reference baseline for further study under the similar experimental conditions. We suggest that, in light of age-related differences of the V/I ratio, the normative criteria for the amplitude ratio should be established in relation to age. The amplitude of wave V is recommended to be useful in some clinical situations.

Development of wave latency and interpeak interval (IPI) in brainstem auditory evoked responses (BAER) from birth to adulthood was examined. Adult equivalence was reached for most wave latencies and IPIs between the ages of 9 months and 3 years. The observation of the III-V/I-III interval ratio suggests that after term data the I-III IPI decreases more than the III-V IPI. I-III, III-V and I-V IPIs shortened from the l-month old group to the 4-6 year old group by 22%, 15% and 19% respectively. The III-V/I-III interval ration may be a useful BAER measure. Normative data of various BAER measures at different ages are presented. The slope of the L-I function for wave V was slightly steeper in younger groups than in older groups (40 microseconds/dB in the 1-month old group 32 microseconds/dB in the adult group). This change which was accompanied by an age-related difference in the absolute wave latency. It is suggested that age-dependent norms should be used in evaluation of the L-I function.

Development of early (I-III) and late (III-V) brainstem conduction time (BCT) in the brainstem auditory evoked responses was examined and compared in 178 appropriate-for-gestational-age (AGA) and 24 small-for-gestational-age (SGA) children from birth to 6 years of age. In AGA children, the III-V/I-III interval ratio increased with age from birth to 2 years and remained relatively steady. This indicates that the development of the early and late BCT, or probably the lower and upper brainstem is not synchronous during early childhood, with a slightly faster development of the early BCT relative to the late BCT. In SGA children, the I-V, I-III and III-V intervals showed similar developmental trends to those in AGA children. However, the III-V/I-III ratio followed a developmental course which differed remarkably from that in AGA children. The ratio decreased slightly with age up to 2 years and was consistently smaller than in normal children after 1 year, indicating that the relative development of early and late BCT deviates from normal. This finding suggests that prenatal factors responsible for intrauterine growth retardation could alter the late or long-term development of the nervous system, resulting in sub-optimal outcome.

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.

The effect of click rate on wave amplitude of human brainstem auditory-evoked response (BAER) was examined at repetition rates of 10, 30, 50, 70 and 90 Hz in 80 healthy children aged 1 month to 6 years and in 21 adults. As repetition rate was increased from 10 to 90 Hz at 70 dB HL, the amplitudes in different age groups decreased by 33-45% (0.109-179 microV) for wave I and 25-41% (0.055-0.145 microV) for wave V. The older the children, the larger the absolute decrements of wave amplitudes with increasing repetition rate, but the relative decrements or reduction rates of wave amplitudes exhibited no systematically age-related differences. The V/I amplitude ratio tended to increase with increasing repetition rate in most age groups, suggesting that the amplitude of wave I is affected by the repetition rate slightly more than that of wave V. The patterns of the changes in wave amplitudes with repetition rate at lower intensity levels were essentially similar.

Click intensity effect (90 to 0 dB HL) on amplitude of the auditory brainstem responses (ABAR) was studied in 152 normal children from birth to 6 years and 16 adults. All age groups showed similar amplitude-intensity functions for waves I and V. Wave I amplitude exhibited a 'transitional' response at 60 dB HL intensity, whereas wave V exhibited a more gradual change. As the clicks were decreased from 90 to 60 dB HL, amplitude reduction was much more dramatic for wave I (mean 57%) than for wave V (mean 30%), and the V/I amplitude ratio more than doubled (mean 70%). At moderate intensity range, the reduction in amplitude with the decrease in intensity is only slightly more for wave I than for wave V, and the V/I ratio continued to increase, but more slowly. Wave V amplitude changed linearly with click intensity at the rate of 0.024-0.042 microV/dB for different age groups. The older the children, the larger the decrement of wave V amplitude with decreasing intensity, which was accompanied by an age-related difference in the absolute amplitude at equal click intensities. The V/I amplitude ratio increased with decreasing intensity at a rate of about 0.01/dB, showing no apparent age-related difference.

Latency and interpeak interval of the brain-stem auditory evoked potentials at different click rates were measured in 80 healthy children from birth to 6 years, and 21 adults. Clicks were presented at 10, 30, 50, 70 and 90/sec, and 70, 40 and 20 dB HL. At high stimulus intensity (70 dB SL), all latencies of waves I, III and V and the I-V, I-III and III-V intervals showed a progressive prolongation with increasing repetition rate. The latency- and the interval-rate functions were similar for all age groups but their slopes were slightly steeper in younger than in older. As click rate increased from 10/sec to 90/sec, the latencies of waves I, III and V at different age groups were prolonged by 4-10%, 9-13% and 12-15% respectively, and the intervals of I-V, I-III and III-V were prolonged by 15-16%, 8-16% and 14-24% respectively. The mean increments of wave V latency and I-V interval in different age groups were 0.404-0.575 and 0.332-0.526 msec respectively with increasing click rate from 10 to 50/sec, and 0.697-1.009 and 0.629-0.776 msec respectively with increasing click rate from 10 to 90/sec. The younger the age the larger the absolute increments for all these BAEP parameters, but the increasing rates for a BAEP measure were similar among different age groups, exhibiting no age-dependent differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Early development of brainstem auditory pathway was studied in 14 children with Down's syndrome (age range from 1 month to 3 years). The brainstem auditory evoked potentials (BAEP) during infancy was characterized by elevated threshold and poorly differentiated wave I. All children within 2 years had elevated threshold in one or both ears, suggesting a high incidence of peripheral hearing deficits. Follow-up tests showed that as age increased up to 3 years the elevated threshold gradually decreased and the differentiation of wave I improved. The I-V interpeak interval was slightly shorter and the amplitude of wave V was smaller than the normal controls, which existed continuously during follow-up studies. Our findings suggest that the development of peripheral hearing is delayed, although persistent hearing deficits cannot be excluded, and the functioning and development of the brainstem auditory pathway may also be abnormal in Down's syndrome children.