Y.M. Visco

The maturation of the central auditory conduction in preterm infants until three months post term. II: The auditory brainstem responses (ABRs)

Auditory cortical evoked responses (ACRs) were recorded in 65 preterm infants, at least on 3 occasions in 48 of them. The infants were divided into 5 groups according to their gestational age (GA). The recording sessions were performed at 8 conceptional age (CA) levels, defined as the gestational age added to the chronological age. The last recordings were obtained at 50-52 weeks CA. The ACRs were analyzed for the primary complex containing middle latency components (MLR) and the secondary complex, containing the slow late components. The ACR records first appear at about 25 weeks CA, initiating the premature stage followed by a transitional stage around term date and the gradual development into the mature stage, achieved at 50-52 weeks CA. The detectability rate of the various components generally increased with increasing conceptional age, for some of the components, especially N2p and N2, this rate achieved a value of about 80%. The degree of prematurity did not influence appreciably the development of the ACR. The waveforms, and to a lesser extent the latency and amplitude values, are strongly age dependent. Remarkable topographic differences between the ACR parameter latency and more importantly amplitude values are found between the derivations from the vertex and the central temporal areas, supporting the theory of different generation sites for the ACR components. The premature and mature ACR appeared relatively insensitive to changes in the states of vigilance. The ACR in premature infants are useful in developmental studies with respect to the central audition in premature infants and might contribute in the clinical assessment on the quality of the premature central auditory system.

The effect of preterm birth on brainstem, middle latency and cortical auditory evoked responses (BMC AERs)

Recent studies on the maturation of auditory brainstem evoked responses (ABRs) present conflicting results, whereas only sparse reports exist with respect to the maturation of middle latency auditory evoked responses (MLRs) and auditory cortical evoked responses (ACRs). The present study reports the effect of preterm birth on the maturation of auditory evoked responses in low risk preterm infants (27-34 weeks conceptional age). The ABRs indicate a consistent trend towards longer latencies for all individual ABR components and towards longer interpeak latencies in preterm infants. The MLR shows longer latencies for early component P0 in preterm infants. The ACRs show a remarkable difference between preterm and term infants. At 40 weeks CA the latencies of ACR components Na and P2 are significantly longer in term infants, whereas at 52 weeks CA the latencies of the same ACR components are shorter in term infants. The results support the hypothesis that retarded myelination of the central auditory pathway is partially responsible for differences found between preterm infants and term infants with respect to late ABR components and early MLR component P0. Furthermore, mild conductive hearing loss in preterm infants may also play its role. A more complex mechanism is implicated to account for the findings noted with respect to MLR component Na and ACR components Na and P2.

The maturation of auditory cortical evoked responses between (preterm) birth and 14 years of age

In this study we report on the maturation of the auditory cortical evoked response (ACR) waveform between (preterm) birth and 14 years of age. From the results it can be concluded that the ACR waveform morphology shows substantial age-dependent changes until the age of 14 years. Two transitional periods could be recognized. The first between 36 and 41 weeks conceptional age; the second between 4 and 6 years of age. The adult waveform complex is achieved between 14 and 16 years of age. Further research is needed to determine whether these transitional periods in the maturation of ACRs correspond with important functional changes of the central auditory system.

The maturation of the central auditory conduction in preterm infants until three months post term. IV. Composite group averages of the cortical auditory evoked responses (ACRs).

Composite group averages were constructed from cortical auditory evoked responses (ACRs), which are recorded sequentially at maximally 8 conceptional age levels in 5 groups of 49 preterm infants, with additional inclusion of the records of 16 prematures obtained at different conceptional age levels. The group averages for the 5 gestational age groups showed replicable waveforms at all conceptional age (CA) levels reflecting the intragroup stability of the ACR complex. From the earliest age levels, from 25 weeks CA on, ACR group averages can be obtained, containing relative low voltage fast waves and high voltage slow waves. The most outstanding developmental changes in the ACR complex are the waveform changes. Until about 36 weeks CA a premature waveform is found, followed by a transitional phase with low voltage noisy records. Finally the adult waveform is found in the measurements at three months after term date. The latency values of the group averages are determined by the waveform changes. Persistent amplitude differences are found for the slow late waves between the vertex and the central temporal derivations.

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

In preterm and term infants, brainstem and middle latency auditory evoked responses (ABR and MLR) were obtained at 40 and 52 weeks conceptional age (CA) and at 5 years of age. A neurological and neuropsychological evaluation was performed at 5 years of age. To study the effect of preterm birth on the maturation of the ABR and MLR, the preterm infants were divided into early and late preterm groups. Only children with a normal neurodevelopmental outcome at 5 years of age were entered into the study. For ABR, the late preterm group showed significantly longer mean latencies IIc, III, V, and Vc when compared with the term group at 52 weeks CA. There was a trend to longer ABR latencies I in the early preterm group compared with the term group. At 52 weeks CA, the late preterm group showed longer mean interpeak latencies III-I and V-I when compared with the term as well as the early preterm group. At 5 years, the late preterm group showed significantly longer mean ABR latencies IIc and III when compared to the early preterm group. For MLR, the early preterm group showed significantly longer mean latencies of MLR component PO when compared with the term group at 40 weeks CA. At 52 weeks, the late preterm group also had longer mean MLR latencies P0 than the term group. At 5 years of age, the term group showed higher mean peak-to-peak amplitudes Na-P0 than the early as well as the late preterm group. To a large extent, the ABR results support the hypothesis that middle ear effusions in combination with retarded myelination of the central auditory pathway are responsible for the ABR differences found between term and preterm infants with a normal neurodevelopmental outcome at 5 years of age. The longer latencies and interpeak latencies found in late preterm infants when compared with early preterm infants might be explained by an augmented vulnerability of the auditory pathway between 30 and 34 weeks CA. The MLR differences found between term and preterm infants might be explained by a difference in the maturation of primary and nonprimary MLR components.

The maturation of the central auditory conduction in preteram infants until three months post term. III. The middle latency auditory evoked response (MLR)

Middle latency auditory evoked responses (MLRs) were recorded in 64 premature infants; serially in 54 of them. The last recording sessions occurred at 50-52 weeks conceptional age (CA), defined as the gestational age (GA) added to the chronological age. The MLRs were analyzed for the components PO, Na and Pa, and the interpeak latency difference (IPLD) Na-PO. The detectability rate of PO and Na reached 80-90% at about 30 weeks CA. Pa reached the highest rate of about 60% at 52 weeks CA. The degree of prematurity did not result in clear differences with respect to the parameter values. Also, the side of stimulation did not influence the MLR parameter values. The latency values of the MLR components are strongly age dependent. Topographic differences were found between the sides ipsi- and contralateral to stimulation. They are, however, different for PO, Na and Pa. The influence of the state of vigilance on the parameter values could generally only be established at CA levels of about 32 and 52 weeks CA. The amplitude values at 52 weeks CA are especially sensitive for sleep or awake state. The particular pattern of age dependency of the different components and their topographic differences are consistent with a differential generation of bilateral nature. The early appearance of the response supports the generation of an early functioning subcortical structure in the auditory pathway.

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.

Evoked potentials in children with chronic renal failure, treated conservatively or by continuous ambulatory peritoneal dialysis

Children with chronic renal failure (CRF) show developmental, intellectual and motor disturbances. It is questionable if an early start of renal replacement therapy may prevent or delay these disturbances. We studied the neurological and intellectual development of children <5 years suffering from CRF (creatinine clearance <20% of normal) prospectively, over a period of 3 years. As part of the neurological study, brainstem auditory evoked potentials (BAEP) and somatosensory evoked potentials (SSEP) were recorded. Measurements were performed in a group of 22 children every 6 months. In 18 of these children CRF was present from birth. Sufficient data were available for analysis in 19 (BAEP) and 22 (SSEP), respectively. A delay of peak I of BAEP gave indications for peripheral conduction disturbances, possibly due to cochlear dysfunction. Brainstem conduction was normal. There were no differences between the children treated conservatively (n = 9) and those treated with continuous ambulatory peritoneal dialysis (CAPD) (n = 10). In children <2.5 years SSEP showed a delayed thalamocortical conduction, which was not observed in older children. This might indicate a delayed myelination in young children with CRF. No differences were found between the children treated conservatively (n = 10) and those treated with CAPD (n = 12).

The maturation of the central auditory conduction in preterm infants until three months post term. I. Composite group averages of brainstem (ABR) and middle latency (MLR) auditory evoked responses

Brainstem (ABR) and middle latency (MLR) auditory evoked responses were obtained sequentially in 49 preterm infants until three months post term date. In addition, the records of 16 preterm infants, obtained at different conceptional age levels, were included. The recording of these responses was performed successively in one procedure, together with auditory cortical evoked responses. The infants were divided into 5 groups according to their gestational age, i.e. the term at birth. Composite group averages were determined, showing the group stable components of the 5 gestational age groups at 8 different conceptional age levels, i.e. term at the time of the recording. The intra group stable components could thus be determined for further study of developmental trends in the responses. The group averages also serve as a reference in the visual analysis of the individual records. The averaged ABRs showed that with increasing conceptional age increasingly better identifiable waveforms were obtained. These were particularly outstanding for peaks I and V ipsilateral to stimulation, and peaks IIc and Vc contralateral to stimulation. This enabled the measurement of the central conduction times. The MLRs were especially remarkable for their latency changes which occurred in peak PO and the troughs Na and Nb. The results indicated that the conduction of the subcortical auditory afferent signals can be measured successfully in groups of very premature infants with ABRs and MLRs.

Diagnostic and predictive value of auditory evoked responses in preterm infants : I. Patient characteristics and long-term neurodevelopmental outcome

The diagnostic and predictive value of brainstem, middle latency, and cortical auditory evoked responses, obtained in the neonatal period, in 81 preterm infants was assessed in relation to neurodevelopmental outcome. Eighteen healthy term infants served as a control group. In this report the patient characteristics and neurodevelopmental outcome are presented. The preterm infants were neonatally classified according to risk category and gestational age. At 5 y of age the neurodevelopmental outcome was assessed based on neurologic and neuropsychologic evaluations. The neuropsychologic test results showed the highest IQ scores in term infants, intermediate IQ scores in low risk preterm infants, and lowest IQ scores in high risk preterm infants. The intermediate IQ scores in the low risk preterm group were due to significantly lower test scores in a small subgroup of low risk preterm infants. In a post hoc analysis 12 low risk preterm infants with an unfavorable outcome could be identified. The neuropsychologic test results of the remaining low risk infants showed no clear differences compared with the term infants. The results suggest that the unfavorable outcome of the low risk preterm group as a whole is due to moderate to severe impairment of the few, rather than slight impairment of the majority.