Time course of brainstem pathophysiology during first month in term infants after perinatal asphyxia, revealed by MLS BAER latencies and intervals

Short-term outcome of functional integrity of the auditory brainstem in term infants who suffer perinatal asphyxia

OBJECTIVES

To assess short-term outcome of impaired functional integrity of the auditory brainstem in term infants who suffer perinatal asphyxia.

METHODS

Maximum length sequence brainstem auditory evoked response (MLS BAER) was recorded and analyzed at a mean age of 3months in term infants after perinatal asphyxia. The data were compared with age-matched normal term infants.

RESULTS

The infants after asphyxia showed an increase in the latency of MLS BAER wave III at 91, 455 and 910/s, and wave V at all click rates of 91-910/s. The interpeak intervals in the infants after asphyxia were increased at almost all click rates. The IV and I-III intervals were increased at all click rates, and the III-V interval was increased at 455 and 910/s. These increases were generally more significant at higher than at lower click rates. The amplitudes of waves I, III and V in the infants after asphyxia were reduced at all click rates. The V/I amplitude ratio was increased at 91-455/s clicks. The slope of III-V interval-rate function was abnormally increased. 17.1% of the infants after asphyxia had an abnormal increase in IV intervals.

CONCLUSIONS

MLS BAER was moderately abnormal at 3months of age in term infants after perinatal asphyxia, suggesting moderate impairment in the functional integrity of the auditory brainstem. The impairment occurs in 17.1% of the infants. Compared with that found at term, the impairment has improved, but not completely recovered.

Effect of neonatal asphyxia on the impairment of the auditory pathway by recording auditory brainstem responses in newborn piglets: a new experimentation model to study the perinatal hypoxic-ischemic damage on the auditory system

INTRODUCTION

Hypoxia-ischemia (HI) is a major perinatal problem that results in severe damage to the brain impairing the normal development of the auditory system. The purpose of the present study is to study the effect of perinatal asphyxia on the auditory pathway by recording auditory brain responses in a novel animal experimentation model in newborn piglets.

METHOD

Hypoxia-ischemia was induced to 1.3 day-old piglets by clamping 30 minutes both carotid arteries by vascular occluders and lowering the fraction of inspired oxygen. We compared the Auditory Brain Responses (ABRs) of newborn piglets exposed to acute hypoxia/ischemia (n = 6) and a control group with no such exposure (n = 10). ABRs were recorded for both ears before the start of the experiment (baseline), after 30 minutes of HI injury, and every 30 minutes during 6 h after the HI injury.

RESULTS

Auditory brain responses were altered during the hypoxic-ischemic insult but recovered 30-60 minutes later. Hypoxia/ischemia seemed to induce auditory functional damage by increasing I-V latencies and decreasing wave I, III and V amplitudes, although differences were not significant.

CONCLUSION

The described experimental model of hypoxia-ischemia in newborn piglets may be useful for studying the effect of perinatal asphyxia on the impairment of the auditory pathway.

Mild maturational delay of the brainstem at term in late preterm small-for-gestation age babies

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.

Neural conduction impairment in the auditory brainstem and the prevalence in term babies in neonatal intensive care unit

OBJECTIVE

To detect neural conduction abnormality in the auditory brainstem in term babies in the neonatal intensive care unit (NICU), determine prevalence of the abnormality, and assess if maximum length sequence (MLS) technique improves early detection of the abnormality.

METHODS

One hundred and six term babies were recruited, and studied by recording and analysing MLS brainstem auditory evoked response (BAER). Interpeak intervals were analysed in detail, which were then compared with those in normal term babies.

RESULTS

Wave V latency and I-V and III-V intervals in MLS BAER were increased in the NICU term babies at all click rates 91-910/s, particularly at 455 and 910/s (p<0.05-0.001). No major abnormalities were found in wave I and III latencies and I-III interval. The abnormal increase in I-V and III-V intervals were seen in significantly more cases at 455 and 910/s in MLS BAER than at 21/s in conventional BAER (X(2)=10.92-13.88, all p<0.01). As a whole, 38 (35.8%) of the NICU babies had abnormal III-V and/or I-V intervals in MLS BAER, which was significantly more than 13 (12.2%) in conventional BAER (X(2)=16.14, p<0.01).

CONCLUSION

There is neural conduction impairment in the auditory brainstem in NICU term babies, which occurs in one-third of these babies.

SIGNIFICANCE

Term babies in NICU are at risk of neural conduction impairment in the auditory brainstem. High click rates in MLS BAER enhance early detection of the impairment.

Changes in amplitude-integrated electroencephalograms in piglets during selective mild head cooling after hypoxia-ischemia

BACKGROUND

Amplitude-integrated electroencephalogram (aEEG) is a simplified, alternative means of monitoring cerebral function and may be more useful clinically in some situations than conventional EEG. The aim of this study is to evaluate newborn piglets as an animal model to examine the effect of selective mild head cooling (HC) on aEEG after hypoxia-ischemia (HI).

METHODS

Thirty-four piglets were randomly allocated to the following treatment groups: normothermic control group (NC, n = 7), selective HC control group (HC, n = 9), normothermic HI group (NHI, n = 9), and selective HC HI group (SHC-HI, n = 9). HI was induced by temporary occlusion of both carotid arteries and simultaneous reduction of the concentration of inspired oxygen to 6% for 30 minutes. Mild hypothermia (35°C) was induced after HI using a HC cap and was maintained for 24 hours. Changes in aEEG were monitored for 6 days after these treatments and the incidence of abnormalities analyzed. Physiological parameters were also measured during this period.

RESULTS

In the two HI groups, animals exhibited severely abnormal aEEGs [continuous low voltage (CLV), burst-suppression, or flat tracing (FT)] 20 minutes after the beginning of HI. At 2 hours, the aEEG returned to normal in most of these animals. From 12 hours to 6 days, all animals in the NHI group exhibited severely abnormal aEEGs. Fewer animals in the SHC-HI group exhibited severe abnormal aEEGs during this time period, and four out of nine (44.4%) animals had continuous normal voltage (CNV) at 6 days.

CONCLUSIONS

Selective mild HC decreases the incidence of severe abnormal aEEGs at late times after HI in newborn piglets.

Brainstem auditory electrophysiology is supressed in term neonates with hyperbilirubinemia

BACKGROUND

Whether hyperbilirubinemia suppresses electrophysiological activity of the neonatal auditory brainstem remains to be investigated.

AIM

To determine whether hyperbilirubinemia suppresses the brainstem auditory electrophysiology in term neonates.

METHODS

Maximum length sequence brainstem auditory evoked response (MLS BAER) was recorded shortly after confirming hyperbilirubinemia in 58 term neonates. Wave amplitudes of the response were analyzed in detail.

RESULTS

Compared with age-matched term controls, the neonates with hyperbilirubinemia showed a significant reduction in the amplitudes of MLS BAER waves III and particularly V at all click rates 91-910/s. The reduction tended to be more significant at higher than lower rates. Wave I amplitude was reduced at 910/s. V/I amplitude ratio was decreased at all click rates. Therefore, the amplitudes of MLS BAER, particularly later, waves were all reduced. The amplitudes of all MLS BAER waves tended to be reduced with the increase in total serum bilirubin level. All wave amplitudes were correlated with the level of total serum bilirubin at some or most click rates.

CONCLUSIONS

Brainstem auditory electrophysiology is suppressed in neonates with hyperbilirubinemia, which related to the severity of hyperbilirubinemia. Wave amplitudes are valuable BAER variables to detect functional impairment of the brainstem and auditory pathway in neonatal hyperbilirubinemia, and are recommended to be used in assessing bilirubin neurotoxicity to the neonatal brain.

Impaired function of the auditory brainstem in term neonates with hyperbilirubinemia

OBJECTIVE

We studied maximum length sequence brainstem auditory evoked response in term neonates with hyperbilirubinemia to further our understanding of hyperbilirubinemia on the neonatal auditory brainstem and to determine if maximum length sequence technique improves detection of brainstem auditory impairment due to bilirubin neurotoxicity.

METHODS

Maximum length sequence brainstem auditory evoked response was recorded and analysed shortly after confirming total serum bilirubin levels greater than 15mg/dL in fifty-seven term neonates with hyperbilirubinemia.

RESULTS

Most wave latencies and interpeak intervals in maximum length sequence brainstem auditory evoked response in the neonates with hyperbilirubinemia were correlated with the level of total serum bilirubin at some or most click rates used. Compared with age-matched normal term controls, wave V latency in these neonates was increased significantly at all 91-910/s click rates (p<0.05-0.001). The I-V and I-III interpeak intervals were also increased significantly at all these rates, and the III-V interval increased at 227-910/s clicks (p<0.05-0.001). The differences between the neonates with hyperbilirubinemia and the controls were more significant at higher than at lower click rates. The slopes of wave V latency-rate function and I-V and III-V interval-rate functions were all significantly increased. By comparison, the abnormalities in conventional BAER were less significant, with only I-III and I-V intervals were increased (both p<0.05).

CONCLUSIONS

Functional status of the auditory brainstem is impaired in neonatal hyperbilirubinemia. Maximum length sequence technique at high click rates improves detection of bilirubin neurotoxicity to the neonatal auditory brainstem, particularly for the more rostral regions.

Neural conduction abnormality in the brain stem and prevalence of the abnormality in late preterm infants with perinatal problems

Neurodevelopment in late preterm infants has recently attracted considerable interest. The prevalence of brain stem conduction abnormality remains unknown. We examined maximum length sequence brain stem auditory evoked response in 163 infants, born at 33-36 weeks gestation, who had various perinatal problems. Compared with 49 normal term infants without problems, the late preterm infants showed a significant increase in III-V and I-V interpeak intervals at all 91-910/s clicks, particularly at 455 and 910/s (p < 0.01-0.001). The I-III interval was slightly increased, without statistically significant difference from the controls at any click rates. These results suggest that neural conduction along the, mainly more central or rostral part of, auditory brain stem is abnormal in late preterm infants with perinatal problems. Of the 163 late preterm infant, the number (and percentage rate) of infants with abnormal I-V interval at 91, 227, 455, and 910/s clicks was, respectively, 11 (6.5%), 17 (10.2%), 37 (22.3%), and 31 (18.7%). The number (and percentage rate) of infants with abnormal III-V interval at these rates was, respectively, 10 (6.0%), 17 (10.2%), 28 (16.9), and 36 (21.2%). Apparently, the abnormal rates were much higher at 455 and 910/s clicks than at lower rates 91 and 227/s. In total, 42 (25.8%) infants showed abnormal I-V and/or III-V intervals.

CONCLUSION

Conduction in, mainly in the more central part, the brain stem is abnormal in late preterm infants with perinatal problems. The abnormality is more detectable at high- than at low-rate sensory stimulation. A quarter of late preterm infants with perinatal problems have brain stem conduction abnormality.

Functional impairment of the auditory pathway after perinatal asphyxia and the short-term effect of perinatal propofol anesthesia in lambs

BACKGROUND

Sensorineural hearing loss (SNHL) is a common feature in the postasphyxial syndrome in newborns. Several anesthetic drugs have been proposed to attenuate secondary neuronal injury elicited by hypoxia-ischemia. We hypothesized that propofol anesthesia reduces auditory impairment after perinatal asphyxia in comparison with isoflurane.

METHODS

Twenty-three pregnant ewes were randomized to propofol or isoflurane anesthesia and sedation. The lambs underwent in utero umbilical cord occlusion (isoflurane n = 5; propofol n = 7) and were compared with sham-treated animals (isoflurane n = 5; propofol n = 6) at a gestational age of 133 d. For 8 h after delivery by cesarean section, repeated auditory brainstem responses (ABRs) were recorded to obtain hearing thresholds, peak amplitudes, latencies, and interpeak latencies.

RESULTS

Significantly elevated mean thresholds, diminished amplitudes, and elevated latencies were observed in the asphyxia group relative to the control group through the observation period. Comparison of anesthetic treatment in the asphyxia group revealed a significantly lower elevation in threshold and less impairment in the ABR amplitudes and latencies during propofol anesthesia as compared with isoflurane anesthesia.

CONCLUSION

Our results support the hypothesis that anesthesia with propofol has a preventive effect on the functional changes to the auditory pathway in the event of perinatal asphyxia.

Amplitude reduction in brainstem auditory response in term infants under neonatal intensive care

OBJECTIVE

To examine brainstem auditory electrophysiology in term neonates under intensive care due to perinatal conditions other than hypoxia-ischemia.

METHODS

Maximum length sequence brainstem auditory evoked response was studied in term neonates in an intensive care unit. The amplitudes of wave components of the response were analysed to assess brainstem auditory electrophysiology.

RESULTS

The amplitudes of all wave components in the neonates under intensive care tended to be smaller than in those in normal term controls. Wave I amplitude was significantly reduced at all 91-910/s clicks (p < 0.05-0.01). The amplitudes of waves III and V were also reduced, respectively, at 227-910/s (all p < 0.05) and at 455 and 910/s (both p < 0.01). The amplitude reduction was slightly more significant at higher than lower click rates, but there were no significant differences in the slopes of wave I, III and V amplitude-rate functions between the neonates under intensive care and the controls.

CONCLUSIONS

Wave amplitudes of maximum length sequence brainstem auditory evoked response were reduced in term neonates under intensive care due to perinatal conditions other than hypoxia-ischemia.

SIGNIFICANCE

Brainstem auditory electrophysiology is depressed in term neonates under intensive care, possibly due to collective adverse effects of perinatal conditions. The impairment to the neonatal, particularly rostral, brainstem due to other perinatal conditions is less severe than that due to hypoxia-ischemia previously reported.

Cochlear function in 1-year-old term infants born with hypoxia-ischaemia or low Apgar scores

AIM

To examine the influence of perinatal hypoxia-ischaemia (HI) or low Apgar scores on distortion product otoacoustic emissions (DPOAEs) in infants at 1 year and detect any postnatal changes.

METHODS

Eighty-eight term infants born with perinatal HI or low Apgar scores alone were recruited at 1 year of age. The ears with type A tympanogram (normal) were studied with DPOAEs at 10 frequencies between 0.5 kHz and 10 kHz.

RESULTS

DPOAE pass rates were decreased at all frequencies 1-10 kHz, particularly 1 and 2 kHz in both infants born with HI and those with low Apgar scores (χ(2) = 3.80-15.09, P < 0.05-0.01). Overall pass rates in the two groups were also decreased (X(2) = 10.78 and 12.12, P < 0.01 and 0.01). No marked differences were found between infants born with HI and those with low Apgar score. Compared with those recorded at 1 and 6 months, DPOAE pass rates at 1 year were increased slightly in infants born with HI, but showed no marked changes in those born with low Apgar scores.

CONCLUSIONS

DPOAE pass rates, mainly at 1 and 2 kHz, were decreased at 1 year in infants born with perinatal HI and low Apgar scores, suggesting a relative poor cochlear function. Further studies are needed to ascertain the hearing acuity.

Maximum length sequence brainstem auditory evoked response in low-risk late preterm babies

OBJECTIVES

Recent research indicates that there is delayed development in the more central part of the auditory brainstem in very preterm babies. We aimed to study whether this is also the case for late preterm babies.

METHODS

The maximum length sequence brainstem auditory evoked response (MLS BAER) was used to study functional status of the auditory brainstem. Babies born at 33-36 week gestation and without any major perinatal complications were recruited. MLS BAER was recorded and analyzed at term age.

RESULTS

No significant correlation was found between most MLS BAER variables and physiological factors (gender, postconceptional age, bodyweight, and head circumference obtained at time of testing). Wave latencies and amplitudes, and I-V and I-III intervals in the preterm babies were essentially similar to those in the term controls at all click rates. However, III-V interval increased significantly at 227-910/s clicks (p<0.05-0.01). All latencies, amplitudes and intervals correlated significantly with click rates (all p<0.001). No differences were found in the slopes of MLS BAER variables-rate functions between the later preterm babies and term controls.

CONCLUSIONS

Babies born at 33-36 weeks gestation without major complications had an increased III-V interval at high-rate stimulation. This suggests that late preterm babies have a mild delay in neural conduction in the more central part of the auditory brainstem.

Differences in impaired brainstem conduction between neonatal chronic lung disease and perinatal asphyxia

OBJECTIVE

To explore any differences in impaired brainstem function between preterm infants with neonatal chronic lung disease (CLD) and term infants after perinatal asphyxia.

METHODS

Brainstem auditory evoked responses (BAERs) collected using maximum length sequence (MLS) technique were compared at term equivalent age between 43 CLD infants and 117 asphyxiated infants.

RESULTS

In both CLD and asphyxiated infants there was a significant increase in wave V latency and I-V interval in MLS BAER. CLD infants showed a significant increased III-V interval but a normal I-III interval at all click rates. However, asphyxiated infants showed a significant increase in both III-V and I-III intervals. I-III interval was shorter and III-V/I-III interval ratio was greater in CLD infants than in asphyxiated infants. The slope of I-III interval-rate function was steeper in asphyxiated infants than in CLD infants, while the slope of III-V/I-III interval ratio-rate function was the other way around.

CONCLUSIONS

CLD infants had a major increase in more central components of MLS BAER, without appreciable abnormality in more peripheral components. However, asphyxiated infants had a significant increase in both central and peripheral components.

SIGNIFICANCE

Neonatal CLD affects more central regions of the brainstem, whereas perinatal asphyxia affects both peripheral and central regions. This difference, which is likely related to the different nature of hypoxia in CLD and asphyxia, may have some significance for neuroprotective interventions for the two problems.

Impairment of perinatal hypoxia-ischemia to the preterm brainstem

Hypoxia-ischemia is a major perinatal problem that results in severe damage to the newborn brain. This study assessed functional integrity of the brainstem at term in preterm infants after perinatal hypoxia-ischemia to shed light on the influence of hypoxia-ischemia on the preterm brainstem. We recruited sixty-eight preterm infants after perinatal hypoxia-ischemia, ranging in gestation 28-35 weeks. Brainstem evoked response was studied at term age (37-42 weeks postconceptional age) with 91-910/s clicks using the maximum length sequence technique. Compared with healthy preterm infants, the preterm infants after perinatal hypoxia-ischemia showed a significant increase in I-V interval at very high rates 455 and 910/s of clicks (P<0.05, 0.05). III-V interval and III-V/I-III interval ratio also increased significantly at 455 and 910/s (P<0.05-0.01). The slope of III-V interval-rate function was significantly steeper than in the healthy preterm infants (P<0.05). Compared with normal term controls, the preterm infants after hypoxia-ischemia showed similar, but slightly more significant, abnormalities. The differences between the preterm infants after hypoxia-ischemia and the healthy preterm and term infants generally increased with increasing click rate. These results demonstrated that central components of brainstem auditory evoked response were abnormal at very high click rates in the preterm infants after perinatal hypoxia-ischemia. Click rate-dependent change in the more central part of the brainstem is also abnormal. Apparently, functional integrity of the brainstem, mainly in the more central part, is impaired. Hypoxic-ischemic damage to the preterm brainstem is unlikely to completely recover within a relatively short period after the insult, which is of clinical importance.

Brainstem auditory outcomes and correlation with neurodevelopment after perinatal asphyxia

We used brainstem auditory-evoked responses and neurodevelopmental assessment to detect abnormalities and correlations between such responses and neurodevelopmental outcomes in 78 children (aged 4-12 years) who survived perinatal asphyxia. Twenty children had brainstem auditory-evoked response abnormalities, including increased threshold, reduced wave V amplitude, decreased V/I amplitude ratio, and prolonged I-V interval. Thirty-seven exhibited neurodevelopmental deficits, including cerebral palsy and developmental delay. The remaining 41 exhibited no deficits. Brainstem auditory-evoked response abnormalities were evident in 15 of 37 (40.5%) children with neurodevelopmental deficits, but in only 5 of 41 (12.2%) with no deficits, which differed significantly (chi(2) = 8.2, P < 0.05). The sensitivity, specificity, positive predictive value, and false-negative rate of brainstem auditory-evoked responses to reflect neurodevelopmental outcomes were 40.5%, 87.8%, 75.0%, and 59.5%, respectively. These findings suggest that in children who survive perinatal asphyxia, brainstem auditory impairment occurs more frequently in those with versus those without neurodevelopmental deficits. Brainstem auditory-evoked responses display a moderate correlation with clinically determined neurodevelopmental outcomes. Despite limitations, brainstem auditory-evoked response is valuable for assessing auditory and neurodevelopmental outcomes after perinatal asphyxia.

Sustained depression of brainstem auditory electrophysiology during the first months in term infants after perinatal asphyxia

OBJECTIVE

To gain further insights into the pathophysiological processes of neuronal impairment in neonatal brainstem after perinatal asphyxia.

METHODS

Maximum-length sequence brainstem auditory-evoked response (MLS BAER) was recorded with clicks at 91, 227, 455 and 910/s on days 1, 3, 5, 7, 10, 15 and 30 after birth in 108 term infants who suffered perinatal asphyxia. Wave amplitude variables in the MLS BAER were analysed in detail at 40 dB above BAER threshold in 86 infants who had no peripheral hearing impairment.

RESULTS

On day 1 the amplitudes of MLS BAER waves I, III and V were all reduced significantly at all click rates, especially at higher ones (91-910/s, ANOVA P<0.05-0.001). On day 3 these amplitudes were reduced further. On days 5 and 7, the amplitude reduction persisted and did not show any significant further changes. On days 10 and 15 the reduced amplitudes were increased slightly. On day 30 all amplitudes were still reduced significantly (P<0.05-0.0001). During the first month, the reduction of wave amplitudes was more significant for the later MLS BAER components than for the earlier ones, and occurred most significantly at 455 and 910/s clicks. By comparison, the amplitude reduction in conventional BAER was much less significant.

CONCLUSIONS

During the first month after perinatal asphyxia the amplitudes of MLS BAER waves were reduced significantly and persistently, which was more significant at higher rates of clicks than at lower rates. The reduction is much more persistent than the increase in wave latencies and intervals we previously reported.

SIGNIFICANCE

There is sustained depression of brainstem auditory electrophysiology, indicating neuronal damage of the auditory brainstem, in infants after perinatal asphyxia. This may have important clinical implications.

The effects of electrode montage on the amplitude of wave V in the auditory brainstem response to maximum length sequence stimuli

The use of maximum length sequence (MLS) stimuli to elicit an auditory brainstem response (ABR) has been limited, in part, by the observation that these stimuli reduce ABR wave amplitudes. This study recorded ABR waveforms from 14 normally hearing adults using MLS click stimuli (maximum stimulus rate = 250 clicks per second) at stimulus levels of 70, 60, 50, 40, 30 and 20 dB nHL, with a vertical and then an ipsilateral electrode montage. The vertical electrode montage produced significantly larger (p < 0.05) wave V amplitudes, with no change in wave V latencies (p > 0.05), at all stimulus levels. This result suggests a vertical electrode montage could be used to counter some of the loss in wave V amplitude observed when using MLS stimuli.

Functional impairment of the brainstem in infants with bronchopulmonary dysplasia

OBJECTIVES

To gain new insights into the influence of bronchopulmonary dysplasia on the immature brain and to detect abnormalities, we studied the functional integrity of the brainstem in infants with bronchopulmonary dysplasia.

METHODS

Forty-one very preterm infants with bronchopulmonary dysplasia were studied at postconceptional ages of 37 to 42 weeks. Brainstem auditory evoked responses were recorded and analyzed by using the maximal length sequence technique.

RESULTS

Compared with term control subjects, wave V latency in the maximal length sequence brainstem auditory evoked response of the infants with bronchopulmonary dysplasia increased significantly at all 91 to 910 clicks per second rates. Similarly, I-V and particularly III-V interpeak intervals increased significantly. The III-V/I-III interval ratio also increased significantly at all click rates. All of these abnormalities became more significant as the click rate was increased. Compared with healthy, very preterm control subjects, all of these maximal length sequence brainstem auditory evoked response variables increased significantly at all click rates, although the differences between the 2 groups were slightly smaller than those between the infants with bronchopulmonary dysplasia and the term control subjects. The wave I and III latencies and I-III interval in the infants with bronchopulmonary dysplasia did not show any abnormalities. The slopes of the wave V latency-rate function and I-V and particularly III-V interval-rate functions for the infants with bronchopulmonary dysplasia were significantly steeper than those for both term and healthy, very preterm control subjects. The slope of the III-V/I-III interval ratio-rate function for the infants with bronchopulmonary dysplasia was also significantly steeper than those for the 2 control groups.

CONCLUSIONS

The results suggest poor myelination and synaptic function of the brainstem in infants with bronchopulmonary dysplasia, resulting in impaired functional integrity. In comparison, peripheral neural function was relatively intact.

Sub-optimal function of the auditory brainstem in term infants with transient low Apgar scores

OBJECTIVES

To assess functional integrity of the auditory brainstem in neonates with transient low Apgar scores.

METHODS

Forty-two term infants were studied with brainstem auditory evoked response (BAER) using the maximum length sequence during the first month of life. All had transient low Apgar scores but no clinical signs of hypoxic-ischaemic encephalopathy (HIE).

RESULTS

The latencies of BAER waves I and III in these infants were similar to those of age-matched normal controls at all click rates (91/s, 227/s, 455/s and 910/s) during the period studied. Wave V latency was increased at 910/s on day 1 (P<0.01), but did not differ from that in the controls on any other days. I-V interval was increased significantly at 455/s and 910/s on day 1 (P<0.01 and 0.001) and day 3 (P<0.05 and 0.01). On days 5 and 7, BAER wave latencies and intervals were similar to those in the controls. On day 30, all latencies and intervals reached the values in the controls. No abnormalities were seen in BAER wave amplitude variables on any days.

CONCLUSIONS

Neonates with transient low Apgar scores but without HIE had a significant increase in I-V interval at very high click rates on the first three days of life.

SIGNIFICANCE

Brainstem auditory function is sub-optimal during the first few days in neonates with transient low Apgar scores.

Brainstem auditory evoked response in neonatal neurology

Over the last three decades, the brainstem auditory evoked response (BAER) has been used to assess functional integrity and development of the auditory system and the brain in conditions that affect the brainstem auditory pathway. As a non-invasive objective test, BAER is particularly suitable in very young or sick infants. It is the major tool to detect hearing impairment in high-risk infants, and a component in universal hearing screening. BAER is also a valuable adjunct to detect neurological impairment in many developmental disorders and functional abnormalities in a range of neurological diseases. The maximum length sequence (MLS) technique has recently been incorporated into neonatal BAER study. Recent results indicate that the MLS has the potential to improve the diagnostic value of BAER in some clinical situations, although the wider utility of this relative new technique remains to be further explored.

Neonatal auditory function and depressed Apgar score: correlation of brainstem auditory response with Apgar score

AIM

To examine the relationship between neonatal auditory function and Apgar score in term infants with depressed Apgar scores.

METHODS

Brainstem auditory evoked response (BAER) was recorded on day 3 after birth in term infants who had Apgar scores < or = 7 at 1 and/or 5 min. Half of the infants also had Apgar scores at 10 min, with 17 < or = 7.

RESULTS

No BAER variables correlated significantly with 1-min Apgar score. However, wave III and V latencies, and I-V, I-III and III-V intervals correlated significantly and negatively with 5-min Apgar score (p < 0.05-0.01). These BAER variables were significantly longer in infants with 5-min Apgar scores < or = 7 than those > 7. Wave V latency and all intervals also correlated negatively with 10-min Apgar score (p < 0.05-0.01). Compared to normal controls, all latencies were prolonged in infants with depressed Apgar scores (all p < 0.05-0.01). All intervals were also prolonged in those with 5-min scores < or = 7 (p<0.05-0.01). Similar results were found when defining the depression of Apgar score as < or = 6.

CONCLUSION

A depressed 5- and/or 10-min Apgar score is an indicator associated with neonatal auditory, mainly central, impairment. Apgar score < or = 7 or 6 at 1 min alone is unlikely to be associated with central impairment.

Distortion product otoacoustic emissions in term infants with a low Apgar score

CONCLUSION

Term infants with a low Apgar score have cochlear impairment, mainly at the frequencies 1-3 kHz. Compared with infants with both a low Apgar score and hypoxic-ischaemic encephalopathy we reported before, the impairment is less severe.

OBJECTIVE

To detect any peripheral impairment of cochlear origin in infants with a low Apgar score.

SUBJECTS AND METHODS

Fifty-four term infants with a low Apgar score at 1 and/or 5 min but without clinical signs of hypoxic-ischaemic encephalopathy were recruited. Distortion product otoacoustic emissions (DPOAEs) were recorded with the f2 primary tone at 10 frequencies (0.5-10 kHz) on days 3-5 and 1 month after birth.

RESULTS

On days 3-5 DPOAE pass rates at most frequencies tended to be decreased, and were significant lower than those in normal term controls at 1, 2, 3, 5, 6 and 10 kHz (chi2=4.49-40.31, p<0.05-0.005). The greatest difference occurred at 1 kHz; 18.5% failed the DPOAE test and this was significantly higher than in the controls (4.3%, chi2=7.65, p<0.01). At 1 month the DPOAE pass rate at most frequencies did not show any significant improvement. The overall failure rate (14.8%) did not differ significantly from that on days 3-5.

Signal to noise ratio analysis of maximum length sequence deconvolution of overlapping evoked potentials

In this study a general formula for the signal to noise ratio (SNR) of the maximum length sequence (MLS) deconvolution averaging is developed using the frequency domain framework of the generalized continuous loop averaging deconvolution procedure [Ozdamar and Bohórquez, J. Acoust. Soc. Am. 119, 429-438 (2006)]. This formulation takes advantage of the well known equivalency of energies in the time and frequency domains (Parseval's theorem) to show that in MLS deconvolution, SNR increases with the square root of half of the number of stimuli in the sweep. This increase is less than that of conventional averaging which is the square root of the number of sweeps averaged. Unlike arbitrary stimulus sequences that can attenuate or amplify phase unlocked noise depending on the frequency characteristics, the MLS deconvolution attenuates noise in all frequencies consistently. Furthermore, MLS and its zero-padded variations present optimal attenuation of noise at all frequencies yet they present a highly jittered stimulus sequence. In real recordings of evoked potentials, the time advantage gained by noise attenuation could be lost by the signal amplitude attenuation due to neural adaptation at high stimulus rates.

Maximum length sequence BAER at term in low-risk babies born at 30-32 week gestation

Thirty babies born at 30-32 week gestation without any major perinatal problems were studied at term with brainstem auditory evoked response (BAER) to detect any abnormalities in central auditory function in low-risk very preterm babies. The BAER was recorded and analyzed at 37-42 week postconceptional age using maximum length sequence technique (MLS). The data obtained were compared with those of 38 normal term controls. Wave I and III latencies in the very preterm babies did not show any significant differences from the controls at all repetition rates of click stimuli used (91-910 s(-1)). Wave V latency and I-V interpeak interval tended to increase at all click rates, and differed significantly from the controls at the highest rate 910 s(-1) (P < 0.05). Both III-V interval and III-V/I-III interval ratio increased significantly at all click rates, particularly at 455 and 910 s(-1) (P < 0.05-0.001). On the other hand, I-III interval tended to decrease. None of wave I, III and V amplitudes showed any abnormalities. Neither did V/I nor V/III amplitude ratios. These results suggest that development of the central auditory system is slightly delayed, which can be shown by MLS BAER at very high rate-stimulation, in low-risk very preterm babies.

Signal-to-noise ratio and frequency analysis of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials

In this study, a frequency domain formulation of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials is developed and applied for the extraction of transient responses from recordings obtained at high stimulation rates. This formulation allows for a faster execution of CLAD by using fast Fourier transform algorithms. The frequency characteristics of the deconvolution filter depends exclusively on the stimulus sequence and determines whether the noncoherent noise is amplified or attenuated in different frequencies. A formula for calculating the signal-to-noise ratio (SNR) achieved by the deconvolution process is developed. The newly developed theory and the methodology is applied to the extraction of the auditory brainstem and middle latency responses using various sequences. The effects of the sequence used and the number of sweeps averaged in ongoing acquisition on SNR are examined by using single sweep recordings. The results verify the deconvolution theory and the methodology and show its limitations. Depending on the frequency characteristics of the sequence, the deconvolution process can amplify or attenuate the EEG noise. Proper selection of the stimulus sequence can increase the SNR enhancement obtained with conventional averaging.

Brainstem auditory function at term in preterm babies with and without perinatal complications

Functional integrity of the auditory brainstem was studied at term in babies born at 30-36 wk of gestation using maximum length sequence brainstem auditory evoked response (MLS BAER). Compared with normal term babies, preterm babies who had perinatal complications showed a tendency of an increase in wave V latency and I-V and III-V intervals at all 91-910/s clicks, with statistical significance at higher rates. Wave V latency and I-V interval increased significantly at 455/s and 910/s. III-V interval increased at all click rates, which was more significant at higher rates. III-V/I-III interval ratio increased at most rates. Waves III and V amplitudes reduced significantly mainly at 455/s and 910/s. In preterm babies who had no perinatal complications, there were no major MLS BAER abnormalities except an increase in III-V interval at 91-910/s. By comparison, the preterm babies with perinatal complications had a significant increase in wave V latency, I-V and III-V intervals, and III-V/I-III interval ratio at 455/s and 910/s clicks. These results suggest that although there are no major abnormalities in brainstem auditory function in preterm babies without perinatal complications, the auditory brainstem, mainly the more central part, in preterm babies with perinatal complications is impaired, which becomes more apparent at very high stimulus rates. We conclude that preterm babies with perinatal complications are at high risk of central auditory impairment.

Distortion product otoacoustic emissions in term infants after hypoxia-ischaemia

Distortion product otoacoustic emissions (DPOAEs) were recorded in 46 term infants who suffered perinatal hypoxia-ischaemia to identify which frequencies in the cochlear audiogram are susceptible to perinatal hypoxia-ischaemia. On days 3-5 after birth, the pass rates across the frequencies of the f(2 )primary tone between 1 and 10 kHz, particularly 1-5 kHz, were all lower than those in normal term controls (X(2 )= 7.27-32.30, all P <0.01). Of the 92 ears, 15 (16.3%) failed the DPOAE test, which was significantly higher than in the controls (4.3%, X(2) = 5.81, P <0.05). At 1 month, 80 ears with a type A tympanogram were re-tested. The pass rates at most frequencies, mainly 1 and 2 kHz, were slightly further decreased. Thirteen ears (16.2%) failed the DPOAE test. These results suggest that the neonatal cochlea, mainly at the frequencies 1-5 kHz, is impaired shortly after perinatal hypoxia-ischaemia and the impairment remains at 1 month.

CONCLUSION

Perinatal hypoxia-ischaemia impairs the neonatal cochlea mainly at the frequencies 1-5 kHz and the impairment detected on days 3-5 after birth is unlikely to improve in the later neonatal period. These findings may have implications for the management of hearing impairment in infants after perinatal hypoxia-ischaemia.