The click-evoked oto-acoustic emission, c-EOAE, in preterm-born infants in the post conceptional age range between 30 and 68 weeks

[Cochlea development in infants with central nervous system impairment occurring as an effect of perinatal asphyxia]

Asphyxia in neonates with inadequate blood-inner ear barrier function causes damage to the inner ear included the degeneration of outer hair cells of the organ of Corti and oedematous changes in stria vascularis. The major consequences in the central nervous system (CNS) are found to be hypoxic-ischemic encephalopathy (HIE) in term newborns, peri- (PVH) or intraventricular hemorrhages (IVH) and periventricular leucomalacia (PVL) in preterm neonates.

THE AIM OF THE STUDY

was to carry out the objective assessment of the cochlea development using CEOAEs in infants with CNS impairment occurring as an effect of perinatal asphyxia, imaged during trans-fontanel ultrasonography.

MATERIAL AND METHODS

To the investigation 36 infants with HIE, IVH or PVL were included, the control group encompassed 32 born at term, health children. In all children three times otoscopic examination and CEOAEs recordings were performed: after birth, in 3rd and in 6th month of life using Otodynamics Otoacoustic Analyser ILO-88 in Quick Screen version. Perinatal anamnesis, general pediatric status, results of trans-fontanel ultrasonography and biochemical test results were taken into account in statistical analyses.

RESULTS

The mean amplitudes of CEOAEs in the first days of life were significantly reduced in InvG comparing to control babies. In half-octave frequency bandwidth analysis significant reduction of S/N Ratio at 1,5–4 kHz in InvG was observed. 3 and 6 months later the recorded responses significantly increased, they didn't reach values of CG but no statistical differences between groups were observed.

CONCLUSION

In conclusion, the outer hair cells activity in first days of life is reduced in newborns with CNS impairment and perinatal asphyxia in anamnesis comparing to health children. The maturation of the cochlea is intensive during first 3 months of life, later only subtle changes in CEOAEs are observed.

Assessment of hearing organ activity in a group of neonates with central nervous system impairment

OBJECTIVE

Hypoxic-ischemic encephalopathy, primary subarachnoid hemorrhage in term newborns as well as periventricular leukomalacia and intraventricular hemorrhage in premature newborns are the major consequences of perinatal asphyxia. Intrauterine hypoxia and labor prolongation can also affect the hearing organ in newborns causing reversible or irreversible changes in the cochlea, brainstem or cortex. The aim of the study was to carry out the objective assessment of the cochlea and hearing pathway activity using CEOAEs and ABR; to find relationships between hearing status and parameters effecting on nervous system in neonates with central nervous system impairment occurring following perinatal asphyxia.

METHODS

To the investigation 36 newborns with hypoxic-ischemic encephalopathy, periventricular leukomalacia or intraventricular hemorrhage were included. The control group encompassed 32 health newborns matched as to the age. In all newborns otoscopic examination, CEOAEs after birth and CEOAEs with ABR 3 months later were performed. Perinatal anamnesis, general pediatric status, results of trans-fontanel ultrasonography and biochemical test results were taken into account in statistical analyses.

RESULTS

The mean amplitudes of CEOAEs in the first days of life were significantly reduced in investigation group comparing to control babies. 3months later the recorded responses significantly increased but did not reach values of control group. No differences were found between latencies of waves I and II. ABR latencies of waves III, IV, V and interpeak latencies I-III, III-V, I-V were delayed in investigation group when compared to control patients. Also morphology of ABR recordings in investigation group has slightly changed. Perinatal aspyxia leading to hypercapnia, low gestational age, prolonged artificial ventilation and meningitis were the main risk factors related to disturbances in ABR recordings.

CONCLUSIONS

The combined use of CEOAEs and ABR in neonates with central nervous system impairment involvement revealed the existence of abnormalities in cochlear micromechanics and retrocochlear auditory pathway. Etiology seems to be multifactoral.

Frequency shifts with age in click-evoked otoacoustic emissions of preterm infants

A previous study [Brienesse et al. (1997). Pediatr. Res. 42, 478-483] demonstrated a positive shift with increasing postmenstrual age (PMA) in the frequencies of synchronized spontaneous otoacoustic emissions (SSOAEs) in preterm infants. We used a mixed model approach to describe a shift with PMA in the spectra of click-evoked otoacoustic emissions (CEOAEs) measured in a group of 22 preterm infants. The rate in shift in CEOAE spectral components was found to be frequency dependent, with a mean estimate of 10 Hz/week for frequencies around 2 kHz and 30 Hz/week for frequencies around 4.25 kHz. This rate decreased with increasing PMA. Because SSOAEs are often part of the CEOAE response, a comparison was made between the shifts in SSOAEs and CEOAEs in a sub-group of 16 preterm infants. The results indicate that the shifts found for both types of OAE are similar, which supports a common mechanism for this change in OAE-characteristic. At present it is not clear to what extent developmental processes in the cochlea and the middle ear can account for these frequency shifts in the spectra of CEOAEs and SSOAEs during the preterm period.

Maturation of the auditory system: 1. Transient otoacoustic emissions as an index of inner ear maturation

The transiently evoked otoacoustic emission amplitude of 42 preterm babies (84 ears; post-conceptional age [PCA] 30-36 weeks) was compared with the TEOAE amplitude of 39 full-term babies (78 ears; PCA 37-45 weeks) in order to trace the inner ear maturation characteristics. An ILO-92 otoacoustic emission recording system was used with linear clicks of 70 dB peak equivalent SPL. The results obtained indicated: (1) There was no statistically significant difference between preterm and full-term ears; (2) There was no significant difference between males and females; (3) There was a significant difference between left and right ear TEOAE amplitude; (4) The interaction of ear with age in relation to TEOAE amplitude was statistically significant; (5) Noise and stimulus parameters did not reveal any significant differences between right and left ears; (6) A positive correlation existed between birthweight and TEOAE amplitude; and (7) A negative correlation existed between aminoglycoside treatment and TEOAE amplitude. The results indicate subtle changes in TEOAE amplitude over time, showing a natural development of the inner ear function during the process of maturation.

Click-evoked otoacoustic emissions (CEOAEs) recorded from neonates under 13 hours old using conventional and maximum length sequence (MLS) stimulation

Maximum length sequence (MLS) stimulation allows click evoked otoacoustic emissions (CEOAEs) to be averaged at very high stimulation rates. This enables a faster reduction of noise contamination of the response, and has been shown to improve the signal-to-noise ratio (SNR) of CEOAEs recorded from adult subjects. This study set out to investigate whether MLS averaging can enhance the SNR of CEOAEs recorded in newborns within the first day after birth, and so improve the pass rates for OAE screening in this period, when false alarm rates are very high. CEOAEs were recorded in a neonatal ward from 57 ears in 37 newborns ranging from 6 to 13h old, using both conventional (50/s) and high rate (5000/s) MLS averaging. SNR values and pass rates were compared for responses obtained within equal recording times at both rates. MLS averaging produced an SNR improvement of up to 3.8dB, with the greatest improvement found in higher frequency bands. This SNR advantage resulted in pass rate improvement between 5% and 10%, depending on pass criterion. A significant effect of age was found on both SNR and pass rate, with newborns between 6 and 10h old showing significantly lower values than those tested between 10 and 13h after birth, as well as a much greater improvement due to MLS averaging. The findings show that MLS averaging can reduce false alarm rates by up to 15% in very young neonates in a neonatal ward setting.

Low prevalence of hearing impairment among very low birthweight infants as detected by universal neonatal hearing screening

OBJECTIVES

To (a) study the prevalence of hearing impairment in a cohort of very low birthweight (VLBW) infants and (b) evaluate the effectiveness of transient evoked otoacoustic emissions (TEOAE) as a first stage in-hospital hearing screening tool in this population.

STUDY DESIGN

The study group was a cohort of 346 VLBW infants born in 1998-2000 at The Sheba Medical Center. The prevalence of hearing impairment in the study group was compared with that of all other newborn infants participating in a universal newborn hearing screening programme during the same period. To evaluate the effectiveness of TEOAE, a control group of 1205 healthy newborns who had no known risk factors for hearing impairment was selected. The results and follow up of hearing screening for these infants were examined retrospectively.

RESULTS

Only one VLBW infant (0.3%) was diagnosed with bilateral sensory-neural hearing loss. In addition, nine infants (2.7%) were diagnosed with conductive hearing loss. Bronchopulmonary dysplasia and low Apgar score were the most significant factors for predicting the occurrence of conductive hearing loss. The percentage of VLBW infants who successfully passed the in-hospital TEOAE screening was 87.2, compared with 92.2% in the full term control group. No false negative cases were detected on follow up.

CONCLUSIONS

The study shows a low incidence of sensory-neural hearing loss in a cohort of VLBW infants and a relatively high incidence of conductive hearing loss. TEOAE screening was found to be an effective first stage in-hospital hearing screening tool in this population.

Cochlear maturation and otoacoustic emissions in preterm infants: a time–frequency approach

Click-evoked otoacoustic emissions (CEOAEs) from preterm infants were analyzed to characterize developmental changes of cochlear active mechanisms. Due to their strong time-varying properties, CEOAEs were studied with a time-frequency approach--the wavelet transform (WT). By means of the WT, CEOAEs were decomposed into 12 frequency bands, spanning the 0.25-6.25 kHz range. For each band, the root-mean-square (RMS) level and latency were studied as functions of both frequency and age. Because CEOAEs were averaged using the non-linear mode of acquisition, the developmental changes in observed in this study are related to the non-linear component (which is actually the most predominant component of the active cochlear response) of CEOAEs, the linear one being mostly canceled out by non-linear averaging. In our study, there was evidence that properties of CEOAE non-linear components are related to the post-conception age (PCA) in that the levels and latency of CEOAE frequency components changed until the age of about 38 weeks post-conception, whereas after 38 weeks, CEOAE features were very similar to those of term newborns. In particular, the CEOAE levels increased and latency decreased with age. The observed changes in CEOAE properties seem to reveal a development of cochlear active mechanisms, although contributions from outer and middle ear development cannot be excluded. Also, in agreement with previous physiological and behavioral findings, our results revealed that the development of CEOAE properties was not the same for all the frequencies, being greater for frequencies 4 kHz, and resembled the development of the cochlear partition, which proceeds from base to apex.

Emissão otoacústica evocada transitória: instrumento para detecção precoce de alterações auditivas em recém-nascidos a termo e pré-termo

Introdução: O diagnóstico e a intervenção precoces nas alterações auditivas são de fundamental importância no desenvolvimento infantil. O registro das emissões otoacústicas tem sido largamente indicado, por ser um exame rápido, de fácil aplicação. Objetivo: Os objetivos do presente estudo foram avaliar a função auditiva periférica de recém-nascidos a termo e pré-termo adequados e pequenos para a idade gestacional, por meio da pesquisa das emissões otoacústicas transitórias, identificando a prevalência de alterações auditivas nesta população; verificar a influência das variáveis idade gestacional e peso ao nascimento, assim como de tipos de tratamento, ventilação mecânica, administração de medicamentos ototóxicos e permanência em incubadora e analisar os fatores que interferem nos programas de triagem auditiva neonatal. Forma de estudo: Clínico prospectivo. Material e método: Foram avaliadas 157 crianças, sendo 43 nascidas a termo, 79 pré-termo adequadas à idade gestacional e 35 pré-termo pequenas à idade gestacional. Resultado: Observou-se que recém-nascidos prematuros falham mais nas respostas das emissões otoacústicas. A prevalência de perda auditiva condutiva na população estudada foi de 29 orelhas para 1000 e para perda auditiva neurossensorial de 16 orelhas para 1000. As crianças de peso baixo ao nascimento foram as mais difíceis de serem avaliadas. As emissões otoacústicas transitórias foram observadas a partir de 27 semanas de idade gestacional. Os tipos de tratamentos utilizados foram fatores que influenciaram negativamente nas respostas das emissões otoacústicas nos grupos de prematuros. Conclusão: O trabalho de diagnóstico precoce da perda auditiva deve ser objetivo de equipe interdisciplinar -- neonatologista, pediatra, otorrinolaringologista, fonoaudiólogo, enfermeiro e familiares -- e deve ser seguido, imediatamente, por programas de intervenção precoce.

Neonatal hearing screening with transient evoked otoacoustic emissions: a learning curve

The present paper reports on the implementation of a neonatal hearing screening programme in a private hospital in Belgium. A maternity-based neonatal hearing screening project with transient evoked otoacoustic emissions (TEOAEs) was started in 1993. The cost of the test was not covered by the public health insurance, so the parents had to pay the full cost for screening their child (approximately 30 Euro). Since 1993 the programme strategies have been changed on several occasions to improve the quality and efficacy. A retrospective analysis was performed on: (1) the test pass rate; (2) the coverage; and (3) the number of children who become 'Lost to follow-up' after failing the initial test. The data show a steady learning curve with a time course of several years. They also demonstrate that it is worthwhile and feasible to run a high-quality screening programme in a private establishment.

Development of human cochlear active mechanism asymmetry: involvement of the medial olivocochlear system?

To study the functional development of the medial olivocochlear system, transient-evoked otoacoustic emission suppression experiments were conducted in 73 ears of 38 pre-term and 11 full-term neonates. The continuous contralateral stimulation was a broad band white noise, presented at 70 dB SPL. Efferent suppression was determined by subtracting the without-contralateral stimulation condition from the with-contralateral stimulation condition. Across this population, a mean suppression effect of contralateral stimulation on transient-evoked otoacoustic emissions was found, with most of the suppression effect observed after 8 ms. The amount of suppression is linearly, positively correlated with the conceptional age. In the subgroup of bilaterally tested neonates, the suppression of transient-evoked otoacoustic emissions is similar in the right ear and the left ear in subjects whose conceptional age is less than 36 weeks and significantly higher in the right ear than in the left ear in older neonates. This last observation was seen at frequencies where transient-evoked otoacoustic emission amplitudes became higher in the right ear than in the left ear as the conceptional age increased, a finding already reported in adults. This study shows that the functional adult pattern of the medial efferent system, probably involved in the detection of signals in noise such as speech sounds, seems to appear gradually in neonates and represents one of the several arguments in favor of functional auditory lateralization in humans, with a right ear advantage.

Frequency shift of individual spontaneous otoacoustic emissions in preterm infants

In adults, spontaneous otoacoustic emissions (SOAE) have shown a considerable frequency stability. In preterm infants, however, the SOAE proved to show an apparent and consistent upward shift of frequency at increasing postconceptional age (PCA). In 25 ears of 14 preterm infants (PCA, 29.1-41.3 wk) a total of 66 SOAE frequencies were monitored, ranging from 1611 to 5774 Hz. All but one of the SOAE frequencies shifted toward higher frequency. The SOAE frequency shift rate in Hertz per week was proportionally constant relative to the SOAE frequency. The mean shift rate was 0.74 +/- 0.39%/wk. At increasing PCA, the SOAE frequency shift rate tended to slow down. A linear fit through the data predicted the SOAE frequency to stop at about 45-50-wk PCA. The frequency dependence and time course of the SOAE frequency shift strongly suggest cochlear maturation during the last period of gestation.