The effects of early and late preterm birth on brainstem and middle-latency auditory evoked responses in children with normal neurodevelopment

Altered maturation in brainstem neural conduction in very premature babies with fetal growth restriction

BACKGROUND

Using maximum length sequence brainstem auditory evoked response (MLS BAER) to study brainstem neural conduction and maturation in fetal growth restriction (FGR) babies born very prematurely and assess the effect of FGR on brainstem neural maturation.

METHODS

MLS BAER was recorded and analyzed at a mean 40 week postmenstrual age in babies born at 27-32 week gestation without other major perinatal conditions or problems. The data were compared between babies with FGR (n = 30) and age-matched babies without FGR (n = 34) to define any differences.

RESULTS

A notable difference in MLS BAER was found in interpeak intervals between the babies with FGR and those without FGR. The FGR babies manifested significantly shortened I-III interval, moderately prolonged III-V interval, and significantly decreased III-V/I-III interval ratio. The slope of the I-III interval-rate function in FGR babies was moderately decreased, relative to that in the babies without FGR.

CONCLUSION

FGR babies born very prematurely are associated with accelerated or precocial neural maturation at caudal brainstem regions, but moderately delayed maturation at rostral brainstem regions. The altered brainstem neural maturation is different from previously reported mildly delayed maturation in FGR babies born less prematurely, and may have important implication for neurodevelopmental outcome.

IMPACT

This first MLS BAER study in FGR found that brainstem neural maturation in very premature FGR babies differed from age-matched non-FGR babies. Neural maturation in very premature FGR babies is accelerated or precocial at caudal brainstem regions but moderately delayed at rostral brainstem regions. The altered maturation is different from previously reported mild delay in brainstem neural maturation in FGR babies born less prematurely. FGR exerts a major and differential effect on brainstem neural maturation in babies born very prematurely. This alteration in very premature FGR babies may have important implication for their neurodevelopment.

Postnatal abnormality in brainstem neural conduction in neonatal bronchopulmonary dysplasia survivors

OBJECTIVE

To investigate postnatal neural conduction in the auditory brainstem in neonatal bronchopulmonary dysplasia (BPD) survivors.

METHODS

Thirty-two very preterm BPD survivors were studied at 57-58 weeks of postconceptional age. Brainstem auditory-evoked response was studied using maximum length sequence. Wave latencies and intervals were analyzed in detail. The controls were 37 normal term infants and 35 very preterm non-BPD infants.

RESULTS

Compared with normal term controls, BPD survivors showed significantly shortened I-III interval but significantly prolonged III-V interval and greater III-V/I-III interval ratio. Compared with very preterm non-BPD controls, BPD survivors showed a significant shortening in waves III latency and I-III interval, moderate prolonged III-V interval, and significantly greater III-V/I-III interval ratio. These differences were generally similar at all click rates used. The slopes of latency- and interval-click rate functions in BPD survivors did not differ significantly from the two control groups.

CONCLUSIONS

Brainstem neural conduction in BPD survivors differed from normal term and age-matched non-BPD infants; neural maturation is accelerated in caudal brainstem regions but delayed in rostral regions. Neonatal BPD survivors are associated with differential maturation in neural conduction at caudal and rostral brainstem regions, which may constitute an important risk for postnatal neurodevelopment in BPD survivors.

IMPACT

We found that brainstem neural conduction at PCA 57-58 weeks in neonatal BPD survivors differs from normal term and age-matched non-BPD infants. No major differences were found between normal term and very preterm non-BPD infants in brainstem auditory conduction. Neural conduction in BPD survivors is accelerated in caudal brainstem regions but delayed in rostral regions. Neonatal BPD survivors are associated with differential maturation in neural conduction at caudal and rostral brainstem regions. The abnormality may constitute an important risk for postnatal neurodevelopment in BPD survivors.

The Correlation Between Click-Evoked Auditory Brainstem Responses and Future Behavioral Thresholds Determined Using Universal Newborn Hearing Screening

This retrospective study was undertaken to assess the correlation between click-evoked auditory brainstem responses and behavioral hearing tests. We recruited a total of 16646 infants born in Ditmanson Medical Foundation Chia-Yi Christian Hospital, Taiwan, from 2012 to 2018 for such assessment purpose. Their data including the click-evoked auditory brainstem response (ABR), referral, and diagnostic follow-up were collected. Spearman correlation method was employed to assess the relationship between ABR and pure-tone threshold. The correlation between the click-evoked ABR that met the National Health Administration standards and the click-evoked ABR derived from estimates before and after the 2.5 years of age effectively predicted the toddlers' pure-tone audiometry (PTA) thresholds at 2-4 kHz.

Brainstem auditory pathway function at four months of corrected postnatal age in preterm infants born below 30 week gestation

OBJECTIVE

Functional status of the brainstem auditory pathway was examined at four months of corrected postnatal age in infants born below 30 week gestation to assess the effect of very or extremely preterm birth on postnatal development of the pathway.

METHODS

Thirty-four preterm infants born at 24-29 week gestation (GA24-29w) were studied at four months of corrected postnatal age. Normal controls were 38 postnatal age-matched term infants. Maximum length sequence brainstem auditory evoked response (MLS BAER) were recorded and analysed with 60 dB nHL clicks.

RESULTS

Compared with term control group, GA24-29w group manifested higher BAER threshold (p < 0.05), longer MLS BAER wave latencies at all click rates 91-910/s (p < 0.01-0.001), and lower wave amplitudes at most click rates (p < 0.05-0.01). No significant differences were found between the two groups in I-V interval at any click rates. I-III interval was shorter while III-V interval was longer in GA24-29w group than in term group at higher rates (all p < 0.05). III-V/I-III interval ratio in GA24-29w group was greater at 455 and 910/s clicks (p < 0.05 and 0.01). These interval variables showed similar changes when 4 GA24-29w infants with threshold elevation were excluded.

CONCLUSIONS

At four months of corrected postnatal age, infants born below 30 week gestation manifested elevated BAER threshold, increased wave latencies, and reduced amplitude. They also manifested a small decrease in I-III interval but a small increase in III-V interval at high rates. Very or extremely preterm birth exerts a mild or moderate effect on postnatal development of the brainstem auditory pathway.

Impact of prematurity on neurodevelopment

The consequences of prematurity on brain functional development are numerous and diverse, and impact all brain functions at different levels. Prematurity occurs between 22 and 36 weeks of gestation. This period is marked by extreme dynamics in the physiologic maturation, structural, and functional processes. These different processes appear sequentially or simultaneously. They are dependent on genetic and/or environmental factors. Disturbance of these processes or of the fine-tuning between them, when caring for premature children, is likely to induce disturbances in the structural and functional development of the immature neural networks. These will appear as impairments in learning skills progress and are likely to have a lasting impact on the development of children born prematurely. The level of severity depends on the initial alteration, whether structural or functional. In this chapter, after having briefly reviewed the neurodevelopmental, structural, and functional processes, we describe, in a nonexhaustive manner, the impact of prematurity on the different brain, motor, sensory, and cognitive functions.

Newborn hearing screening at the Neonatal Intensive Care Unit and Auditory Brainstem Maturation in preterm infants

OBJECTIVES

Aim of this study is to report and discuss the results of 4 years of Newborn hearing screening (NHS) program at the Neonatal Intensive Care Unit (NICU), particularly evaluating the clinical ABR results.

METHODS

Retrospective study. NHS data from NICU newborns, admitted for ≥5 days, in the period from January 1st^, 2013 and December 31st^, 2016, were retrieved and analyzed. NHS results were classified as following: (i) "pass" when both ears for both the a-TEOAE (automated Transient-Evoked Otoacoustic Emissions) and the a-ABR (automated Auditory Brainstem Response) protocol resulted as "pass"; (ii) "fail" when one ear, at either one of the two performed tests resulted as "fail"; (iii) "missing" when the newborns were not tested with both protocols. All "fail" and "missing" newborns were retested (with both tests): in the case of a second "fail" result, a clinical ABR was performed within a period of 3 months.

RESULTS

A total of 1191 newborns were screened. From those, 1044/1191 resulted as "pass", 108/1191 as "fail", and 39/1191 as "missing". During the re-testing of these 147 newborns, 43 were assigned as "missing", 63 were assigned as "pass" (showing bilaterally a wave V identifiable within 30 dB nHL) and 25 failed the retest and/or did not present an identifiable wave V within 30 dB nHL. Among the 147 retested infants, we identified a group of 16 subjects who resulted as NHS "refer" and who, during the audiological follow-up, showed either: (i) a unilateral or bilateral wave V identifiable over 30 dB nHL, at the first clinical ABR assessment; or (ii) a bilateral wave V identifiable within 30 dB nHL, in a following clinical ABR test during the first year of life. These 16 subjects were defined to have an 'Auditory Brainstem Maturation' issue.

CONCLUSIONS

A possible "maturation" of the ABR response (and therefore of the auditory pathway) has been hypothesised in 16 out of 1191 infants (1.3%). A delay of the auditory pathway maturation in preterm babies compared to term newborns has already been suggested in the literature. A possible delay of the NHS retest could be considered, in selected cases, with significant savings in economic resources and parental anxiety.

Changes in Auditory Brainstem Response in very preterm and late preterm infants

AIM

Aim of this study was to compare the absolute and interpeak latencies of Auditory Brainstem Responses (ABR) in very preterm and late preterm infants at 1 month and 3 months of corrected age.

METHOD

ology: ABR traces were obtained from 80 preterm infants (40 very preterm and 40 late preterm) at 1 month and 3 months of corrected age in a prospective, comparative cohort study. Auditory click stimuli at 70 dBnHL and 30 dBnHL, with repetition rate of 11.1/s were used. Absolute latencies of peak I, III, V and interpeak latencies of peak I-V, I-III and III-V were analyzed and compared between preterm groups at 1 month and 3 months of corrected age. Wilcoxon Signed Ranks test was used to compare the ABR variables. Mann Whitney test was used to make inferences between groups.

RESULTS

There was a statistically significant difference in absolute latencies and interpeak latencies between very preterm and late preterm infants at 1 month of corrected age (p < 0.05). Absolute latency of peak I was similar among both groups of preterms. Absolute latencies of peak III, V and interpeak latencies I-III, III-V and I-V were prolonged in very preterm infants at 1 month of corrected age. However, these latencies were significantly reduced at 3 months of corrected age. This indicated accelerated maturation/myelination of the central auditory nervous system in very preterm infants. Absolute latencies of peak III and V and interpeak interval I-V was reduced in late preterm infants at 3 months of corrected age and this was statistically significant. This reduction in latency was considered to be a normal age dependent change.

CONCLUSION

Findings of the current study revealed that there was no deviation in the pattern of auditory maturation among preterms; it followed the typical 'caudal to rostral' form of maturation. Very preterm infants have less mature neuronal development compared with late preterm infants at 1 month of corrected age which catches up at 3 months of corrected age.

Maturation of auditory brainstem response in early term infants at 6 weeks and 9 months

BACKGROUND

Emerging evidence indicates that infants who were born between 37 and 38 weeks of gestation are at higher risk of adverse long-term neurodevelopmental outcomes. Yet little is known about the auditory neural maturation during the first year of their life.

AIM

To compare the development of auditory brainstem response in early term (ET, 37-38 weeks gestational age, GA) and full term (FT, 39-41 weeks GA) infants.

METHODS

126 infants received ABR testing at 6 weeks. 107 of them returned for the second assessment at 9 months, among which, 93 completed the ABR recordings. Comparison of the ABR variables were made depending on gestational age.

RESULTS

Analysis of covariance (ANCOVA) was used to identify the differences in ABR outcomes between two groups. After controlling for confounders, latencies for wave III, V and I-III, III-V and I-V intervals were prolonged in ET group compared with FT group at 6 weeks (all p<0.03). ABR parameters of both groups developed as the infants got older. At 9 months, ET infants remain showing the longer wave V latency and I-V interval (all p < 0.02) than FT infants.

CONCLUSION

During early postnatal life, ET has a different pattern of functional auditory brainstem development comparing with FT infants. The prolonged auditory conduction time suggests less mature of the central auditory system in ET infants before 9 months.

Auditory brainstem response in very preterm, moderately preterm and late preterm infants

BACKGROUND

Auditory brainstem response across preterm infants help in understanding difference if any in auditory maturation.

OBJECTIVE

To analyze and compare absolute and interpeak latencies of ABR in very preterm, moderate preterm and late preterm infants at term age.

METHOD

ABR traces were obtained from 148 ears of preterm infants (52 of very preterm, 44 of moderately preterm & 52 of late preterm) at term age. ABR was recorded with 11.1/s clicks at different intensity levels.

RESULTS

Absolute latencies of peak I, III, V and interpeak latencies of peak I-V, I-III and III-V were analyzed and compared between three preterm groups. One way ANOVA was used to compare ABR parameters between three groups of preterm infants and also to compare ABR parameters across various gestation ages. There were no overall differences in absolute latencies, interpeak latencies and amplitude of ABR between preterm groups and across various gestation ages (P>0.05). Pearson correlation was used to find the correlation between gestation age and ABR parameters. However, no correlation was found. ABRs were similar among preterm groups at term age which reflects that the brainstem maturation is similar among preterm groups.

CONCLUSION

Gestational age at birth does not seem to influence absolute and interpeak latencies of ABR at term age. In preterm neonates, the findings lead to suggest that maturation of auditory pathway occurs in a similar manner in preterm infants regardless of gestational age at birth. We conclude that preterm birth alone as a risk factor does not appear to have any marked effect on the development of ABR at term age.

Auditory impairment in infants with neonatal chronic lung disease is alleviated after term

AIM

Very premature infants with neonatal chronic lung disease (CLD) have been reported to have major auditory impairment at term, and we examined the outcomes in 30 infants after term age.

METHODS

Brainstem auditory evoked response (BAER) was recorded at a postconceptional age of 46-61 weeks in 13 CLD cases and 14 controls from China and 17 CLD cases and 22 controls from the UK.

RESULTS

The BAER threshold in the CLD infants was slightly higher. Clicks at the normal hearing level (60 dB) showed no significant differences between the cases and controls in the latencies of BAER waves I, III and V and the I-V interval. However, the CLD infants demonstrated marginal shortening in the I-III interval and a marginal increase in the III-V interval. The amplitudes of BAER waves in the CLD infants were all slightly smaller than the controls. At 70 and 40 dB normal hearing level, the BAER findings were similar to those obtained at 60 dB normal hearing level, with only small variations.

CONCLUSION

There were minor BAER abnormalities in the CLD infants, suggesting minor auditory impairment. The auditory impairment previously detected at the term date was later alleviated.

Early definition of type, degree and audiogram shape in childhood hearing impairment

In the context of permanent childhood hearing loss, early audiological diagnosis is a prerequisite for activation of an adequate rehabilitation program to prevent or limit the known effects that auditory deprivation determines on language development and cognitive skills in neonates. Audiological diagnosis consists schematically of three phases: identification of subjects at risk, definition of hearing loss and/or children features, verification of appropriateness of diagnosis itself and a rehabilitation programme. Strategies and methods of audiological diagnosis are well defined and include an integration of data coming from objective methods with clinical and behavioural data. Although the substantial effectiveness of procedures and a general consensus on their use and interpretation have been defined, there are several critical issues concerning the achievement of this objective, which will be discussed in this paper.

Is very early hearing assessment always reliable in selecting patients for cochlear implants? A case series study

INTRODUCTION

This study concerns a case series of 23 infants with a diagnosis of severe-to-profound hearing loss at 3 months old, who significantly improved (even reaching a normal auditory threshold) within their first year of life.

METHODS

All infants were routinely followed up with audiological tests every 2 months after being fitted with hearing aids as necessary. A reliable consistency between the various test findings (DPOAE, ABR, behavioral responses, CAEP and ECoG) clearly emerged in most cases during the follow-up, albeit at different times after birth.

RESULTS

The series of infants included 7 cases of severe prematurity, 6 of cerebral or complex syndromic malformations, 5 healthy infants, 2 with asymptomatic congenital CMV infection, and 1 case each of hyperbilirubinemia, hypoxia, and sepsis. All term-born infants showed a significant improvement over their initial hearing threshold by 6 months of age, while in most of those born prematurely the first signs of threshold amelioration occurred beyond 70 weeks of gestational age, and even beyond 85 weeks in one case.

CONCLUSIONS

Cochlear implantation (CI) should only be considered after a period of auditory stimulation and follow-up with electrophysiological and behavioral tests, and an accurate analysis of their correlation. In our opinion, CI can be performed after a period of 8 months in all term-born infants with persistent severe-to-profound hearing loss without risk of diagnostic error, whereas the follow-up for severely preterm infants should extend to at least 80 weeks of gestational age.

An acoustic gap between the NICU and womb: a potential risk for compromised neuroplasticity of the auditory system in preterm infants

The intrauterine environment allows the fetus to begin hearing low-frequency sounds in a protected fashion, ensuring initial optimal development of the peripheral and central auditory system. However, the auditory nursery provided by the womb vanishes once the preterm newborn enters the high-frequency (HF) noisy environment of the neonatal intensive care unit (NICU). The present article draws a concerning line between auditory system development and HF noise in the NICU, which we argue is not necessarily conducive to fostering this development. Overexposure to HF noise during critical periods disrupts the functional organization of auditory cortical circuits. As a result, we theorize that the ability to tune out noise and extract acoustic information in a noisy environment may be impaired, leading to increased risks for a variety of auditory, language, and attention disorders. Additionally, HF noise in the NICU often masks human speech sounds, further limiting quality exposure to linguistic stimuli. Understanding the impact of the sound environment on the developing auditory system is an important first step in meeting the developmental demands of preterm newborns undergoing intensive care.

Effects of ventilation on hearing loss in preterm neonates: Nasal continuous positive pressure does not increase the risk of hearing loss in ventilated neonates

INTRODUCTION

There is increased risk of hearing loss in preterm neonates. This risk is further increased by environmental noise exposure especially from life support equipment such as ventilation. Nasal continuous positive airway pressure (NCPAP) used for respiratory support of preterm neonates is known to be associated with prolonged exposure to high levels of noise. However, there is paucity of information on the effect of NCPAP as compared to mechanical ventilation on hearing loss among preterm neonates.

METHODS

A retrospective chart review was performed on neonates with birth weight (BW) <1500g. Association of clinical factors including the use of NCPAP and mechanical ventilation with failure of hearing screen were studied. Those who failed hearing screen were followed for 2 years to observe long term effects of NCPAP on the hearing loss.

RESULTS

Of 344 neonates included in the study, 61 failed hearing screen. Gestational age (p=0.008), BW (p=0.03), ventilation (p=0.02), intrauterine growth retardation (p=0.02), necrotizing enterocolitis (NEC) (p=0.02), apnea (p<0.001), use of vancomycin (p=0.01) and furosemide (p=0.01) were associated with failure of hearing screen. On multivariate analysis, ventilation (OR 4.56, p=0.02), apnea (OR 2.2, p<0.001) and NEC (OR 2.4, p=0.02) were predictors of failed hearing screen. As compared to those not ventilated, the odds of failing hearing screen was 4.53 (p<0.01) and 4.59 (p<0.01) for those treated with NCPAP and mechanical ventilation respectively, with there being no difference between these two ventilatory modalities. Of the 61 neonates, 42 were followed for 2 years, of which 19 had confirmed hearing loss. Among these 19 neonates, there was no difference (p=0.12) between those who were treated with NCPAP or with mechanical ventilation.

CONCLUSION

There is no increase in the hearing loss in preterm neonates treated with NCPAP as compared to mechanical ventilation despite being exposed to higher environmental noise generated by the NCPAP.

Sex and gestational age effects on auditory brainstem responses in preterm and term infants

BACKGROUND

Some studies find delayed development of the auditory brainstem in preterm infants, but others do not.

AIM

To compare auditory brainstem responses (ABRs) in healthy preterm and term infants depending on sex and gestational age (GA).

METHODS

Participants were 111 preterm (27-36weeks GA) and 92 term (37-41weeks GA) infants. ABR tests were conducted at 6weeks (corrected age if preterm).

RESULTS

There were no overall differences between term and preterm groups in ABRs. However, males showed longer latencies for waves III, V, and I-III, III-V, and I-V intervals and smaller amplitudes for wave III and V than females in both preterm and term groups (all p values≤.01). A 3-way interaction between group, sex, and GA (p<.05) showed that preterm males with later GA had longer wave I-V interval, whereas term females with later GA showed shorter wave I-V interval. Growth velocity predicted wave I-V interval in preterm infants, controlling for other factors (male: p=.07, female: p<.05).

CONCLUSION

ABRs in preterm and term infants were similar at 6weeks (corrected age if preterm), but males had less advanced ABRs than females. More rapid growth predicted less mature ABR in later GA preterm infants in this setting where they were unlikely to receive extra iron. The roles of GA, growth, and iron balance in ABR development warrant further study.

Modifications of auditory brainstem responses (ABR): observations in full-term and pre-term newborns

OBJECTIVE

In this study, we have evaluated by means of auditory brainstem responses (ABR), in a population derived from a newborn hearing screening protocol, some aspects of maturation of the auditory pathways in the first months after birth, and the possible repercussions on early treatment.

MATERIALS AND METHODS

In this retrospective study newborns were recruited through our hearing screening program, and an ABR evaluation was performed on 339 newborns, that had risk factors or had failed the screening, or both. Such population was divided in two groups for statistical analysis purposes: full-term and pre-term. The initial ABR was pathological in 70 infants.

RESULTS

We observed an improvement over time of the estimated hearing threshold in follow-up ABRs in 43 newborns (26 in the full-term group, mean improvement 27.9 dB SPL, and 17 in the pre-term group, mean improvement 34.6 dB SPL); such an improvement might be related to a maturation of the auditory pathways that was not complete at birth.

CONCLUSIONS

The auditory system might not be completely developed at birth, and might require some months to complete; hence any early clinical approach should consider the possibility of an overtreatment, and any therapeutic strategy should only be considered once the diagnosis is certain and definitive.

An initial overestimation of sensorineural hearing loss in NICU infants after failure on neonatal hearing screening

OBJECTIVE

Infants admitted to neonatal intensive care units have a higher incidence of significant congenital hearing loss. We classified audiologic diagnoses and follow-up in infants who had been admitted to our neonatal intensive care unit.

METHODS

We included all infants admitted to the neonatal intensive care unit at Sophia Children's Hospital between 2004 and 2009 who had been referred for auditory brainstem response measurement after failing neonatal hearing screening with automated auditory brainstem response. We retrospectively analyzed the results of auditory brainstem response measurement.

RESULTS

Between 2004 and 2009 3316 infants admitted to our neonatal intensive care unit had neonatal hearing screening. 103 infants failed neonatal hearing screening: 46 girls and 57 boys. After first auditory brainstem response measurement we found 18% had normal hearing or a minimal hearing loss. The remainder had a type of hearing loss, distributed as follows: 15% conductive, 32% symmetric sensorineural, 14% asymmetric sensorineural, and 21% absent auditory brainstem responses. Repeated auditory brainstem response measurement showed a shift in hearing outcome. The main difference was an improvement from symmetric sensorineural hearing loss to normal hearing. However, in a small percentage of children, the hearing deteriorated.

CONCLUSIONS

As many as 58% of infants in this high-risk population who failed the neonatal hearing screening were diagnosed with sensorineural hearing loss or absent auditory brainstem responses. An initial overestimation of sensorineural hearing loss of about 10% was seen at first auditory brainstem response measurement. This may be partially explained by a conductive component that has resolved. Finally, in a small percentage of children the hearing deteriorated.

Incidence and clinical value of prolonged I-V interval in NICU infants after failing neonatal hearing screening

Infants admitted to neonatal intensive care units (NICUs) have a higher incidence of perinatal complications and delayed maturational processes. Parameters of the auditory brainstem response (ABR) were analyzed to study the prevalence of delayed auditory maturation or neural pathology. The prevalence of prolonged I–V interval as a measure of delayed maturation and the correlation with ABR thresholds were investigated. All infants admitted to the NICU Sophia Children’s Hospital between 2004 and 2009 who had been referred for ABR measurement after failing neonatal hearing screening with automated auditory brainstem response (AABR) were included. The ABR parameters were retrospectively analyzed. Between 2004 and 2009, 103 infants were included: 46 girls and 57 boys. In 58.3% (60 infants) of our population, the I–V interval was recordable in at least one ear at first diagnostic ABR measurement. In 4.9%, the I–V interval was severely prolonged. The median ABR threshold of infants with a normal or mildly prolonged I–V interval was 50 dB. The median ABR threshold of infants with a severely prolonged I–V interval was 30 dB. In conclusion, in case both peak I and V were measurable, we found only a limited (4.9%) incidence of severely prolonged I–V interval (≥0.8 ms) in this high-risk NICU population. A mild delay in maturation is a more probable explanation than major audiologic or neural pathology, as ABR thresholds were near normal in these infants.

Relative maturation of peripheral and central regions of the human brainstem from preterm to term and the influence of preterm birth

Relative maturation of peripheral and central regions of the neonatal brainstem was studied using brainstem auditory evoked responses in 174 healthy preterm infants (gestational age 30-36 wk). From 30- to 42-wk postconceptional age (PCA), I-III and III-V intervals shortened with increasing age. It was difficult to detect any apparent differences in maturational rate between the two intervals. However, III-V/I-III interval ratio decreased with increasing age, indicating that from preterm to term III-V interval shortens more than I-III interval. During term period (37- to 42-wk PCA), I-III interval was similar to term controls, but III-V interval was significantly longer and III-V/I-III interval ratio was significantly greater than controls at 37- to 38-wk PCA and 39-40 wk PCA and was the same as controls at 41-42 wk. Therefore, from 30- to 42-wk PCA maturation of central regions of the brainstem, reflected by III-V interval, is relatively faster than peripheral regions, reflected by I-III interval which seems to be already more mature than III-V interval before 30 wk. Maturation in central regions in preterm infants is relatively delayed at early term, but "catches-up" later, whereas peripheral regions already reach normal level of maturation at early term. Preterm birth slightly delays early maturation of central brainstem regions.

A neurobiological model for the effects of early brainstem functioning on the development of behavior and emotion regulation in infants: implications for prenatal and perinatal risk

Neurobiological models propose an evolutionary, vertical-integrative perspective on emotion and behavior regulation, which postulates that regulatory functions are processed along three core brain systems: the brainstem, limbic, and cortical systems. To date, few developmental studies applied these models to research on prenatal and perinatal risk. We propose a conceptual model that incorporates three integrated levels of observations for the study of early risk: (a) brainstem-related physiological regulation of cyclic processes and sensory integration, e.g., vagal regulation, circadian rhythms; (b) emotion and attention regulation capacities that draw on the integration of brainstem and limbic systems; and (c) higher-level outcomes that draw on the intactness of brainstem and limbic networks, including socio-emotional self-regulation, inhibitory control, and cognitive processing. We discuss implications of the model for the development of regulatory capacities during the prenatal and early postnatal stages in infants born with specific perinatal risk. We underscore the importance of assessing sub-cortical and brainstem systems and the longitudinal effects of transitory brainstem dysfunction on physiological homeostasis, motivation, arousal-modulated attention, stress reactivity, and mother-infant co-regulation. The assessment of brainstem dysfunction can be conducted during hospitalization and may help detect infants at risk for the development of self-regulatory deficits at the first weeks of life.

Delayed auditory pathway maturation in the differential diagnosis of hypoacusis in young children

Auditory deficiencies have profound implications for the development of communication abilities, social exchange, and cognitive skills. Although advances in technological instrumentation have decreased the age at which it is possible to detect auditory deficits, an absence of electrophysiological or behavioral reaction to sound does not always reflect hypoacusis. The objective of this study was to evaluate the evolution of audition in a group of children referred for therapy to the CINDA Foundation (Center for Research and Information in Auditory Deficiencies) in Bogota, Colombia, with an initial diagnosis of severe to profound sensorineural hearing loss. We evaluated 25 patients younger than 2.5 years of age with a protocol which included auditory evoked potentials, behavioral responses (tonal audiometry-responses to voice and startle) and language observation. After evaluation, the children began a program of auditory stimulation with audiological follow-up for a period of 6 months to 1 year. The audiological follow-up of the children after auditory stimulation showed significant improvements in both electrophysiological and behavioral indices of their hearing levels (p<.001, one-tailed Wilcoxon exact test). We found a high percentage of children in early stages of auditory maturation with a false diagnosis of hypoacusis (32%). The absence of response may result from compromised auditory reception or processing. Thus, delayed maturation of the auditory pathway should be considered in the differential diagnosis of young children with sensorineural hearing loss.

Neurodevelopmental profile in low-risk preterm infants at 5 years of age

The goal of this study is to determine the neurodevelopmental profile of a group of low-risk preterm infants and to determine whether the potentially unfavourable outcome is due to a few infants with moderate to severe impairments or to a majority of infants with only slight impairments. In a prospective study 44 low-risk preterm infants, i.e. infants with a neonatal risk score indicating a favourable outcome, born between 25-34 weeks gestational age, and 18 healthy term infants were examined neurologically and tested neuropsychologically at 5 years of age. The more unfavourable outcome in the group of low-risk preterm infants compared with the term infants was largely attributable to a poorer outcome in 12 of the 44 low-risk preterm infants. The remaining low-risk preterm infants showed similar test scores compared with the term infants. From these results we conclude that the unfavourable neurodevelopmental outcome of low-risk preterm infants is due to moderate to severe impairment in a few low-risk preterm infants, rather than slight impairment in the majority. The low-risk preterm infants with an unfavourable outcome showed particular impairment on measures of visual-motor integration, concentration and auditory memory in combination with integrative functions.

Diagnostic and predictive value of auditory evoked responses in preterm infants: II. Auditory evoked responses

In this study, the diagnostic and predictive value of brainstem, middle latency, and cortical auditory evoked responses (BMC-AERs) obtained in the neonatal period in 81 preterm infants was assessed in relation to neurodevelopmental outcome. The preterm infants were neonatally classified according to risk category and gestational age. The BMC-AERs were analyzed with respect to detectability, latencies, and amplitudes as well as derived latency and amplitude measures. At 5 y of age the neurodevelopmental outcome was assessed from neurologic and neuropsychologic evaluations. The results showed that BMC-AER differences mainly correlated with risk category (low risk/high risk) and to some extent with degree of prematurity. In view of these findings the degree of prematurity and the effect of risk category have to be taken into account, when BMC-AERs are applied in the preterm period to predict neurodevelopmental outcome. In this study the BMC-AERs for infants with abnormal neurodevelopmental outcome were scarcely distinguishable from the BMC-AERs for infants with normal neurodevelopmental outcome. Thus far, this and previous reports have indicated that BMC-AERs in preterm infants are useful in maturational studies and with infants showing symptoms related to lesions or dysfunction of the peripheral and/or central auditory system. For predicting neurodevelopmental outcome in preterm infants, BMC-AERs are of limited clinical value.