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

Tone-burst elicited auditory brainstem responses in full-term and pre-term infants

OBJECTIVE

To investigate the reliability of tone-burst auditory brainstem response (TB-ABR) latencies and thresholds in pre-term and full-term infants.

DESIGN

TB-ABRs to 500 Hz and 4000 Hz tone-burst stimuli were recorded at two-week intervals over the first six weeks of life in a group of full-term infants (40-46 weeks gestational age [GA]) and over ten weeks (36-46 weeks gestation) in a group of preterm infants. Linear mixed model analyses evaluated within-subject changes and the effects of the subject group, age at assessment, and stimulus frequency on ABR latency and threshold.

STUDY SAMPLE

Twenty-four infants participated. Nine were full-term (GA: 39-41 weeks) and fifteen were healthy pre-term (GA: 28-34 weeks) at birth.

RESULTS

TB-ABR wave V latencies at 70 dBnHL decreased throughout the study (p < 0.001) in pre-term babies for both test frequencies by approximately 0.5 ms. There were, however, no group or GA (at birth) effects indicating that response latency normalized in these children by the due date. Similarly, TB-ABR threshold levels in the premature group were elevated (p = 0.001) by approximately 5 dB in pre-term evaluation but were equivalent to those of full-term participants in the post-term assessment period.

CONCLUSIONS

In healthy, pre-term infants, tone-burst ABR testing is reliable from 36 weeks gestation.

Efferent Auditory Pathways Inhibition in Turner syndrome

PURPOSE

The goal of this study is to investigate the efferent auditory pathways inhibition in Turner's syndrome and to relate it to the cytogenetic profile.

METHODS

This is a cross-sectional study with a comparison group. A sample with 94 participants divided into two groups: The study group was a sample of 40 patients diagnosed with Turner's syndrome (17.6 years of age). The control group was composed of 54 volunteers (18.9 years of age), female, without syndrome. The selected individuals were submitted to efferent auditory pathways inhibition research.

RESULTS

The mean of the inhibitory effect of the efferent auditory pathway in the study group in the right ear was 0.4 dB and in the comparison group it was 1.9 dB, however in the left ear the mean of the inhibitory effect of the efferent auditory pathway was 1.4 dB in the study group and 0.8 dB in the comparison group. The inhibitory effect of the efferent auditory pathway was present in 14 individuals with monosomy and in 15 with other cytogenetic alterations.

CONCLUSIONS

In the study group, the efferent auditory pathways inhibition value was significantly higher in the left ear and significantly lower than the control group in the right ear. There was no significant difference in efferent auditory pathways inhibition of right ear and left ear between the karyotype types.

Distortion product otoacoustic emissions in very preterm infants: A longitudinal study

BACKGROUND

Very preterm infants are at a greater risk of developing neurodevelopmental impairments such as neuro-motor delays, vision and hearing deficits (Roze and Breart, 2004; Saigal and Doyle, 2008) [1,2]. The hearing difficulties in preterm infants vary depending on the co-morbid conditions. However, prematurity itself is considered as a risk factor that influence the functioning of auditory system.

AIM

The current study aims to compare the DPOAEs in very preterm infants and term infants at 1 month, 3 months and 6 months of age (corrected age in preterm infants).

METHOD

DPOAEs were recorded in 72 very preterm infants and 30 term infants at 1 month, 3 months and 6 months of age. All these infants had obtained 'pass' results in newborn hearing screening using ABR. DPOAE f2 test frequency was measured at six frequencies (1500 Hz, 2000 Hz, 3000 Hz, 4500 Hz, 6000 Hz and 8000 Hz) with primary tone stimulus intensity L1 equal to 65 dBSPL and L2 equal to 55 dBSPL with primary tone f2/f1 frequency ratio of 1.2. Otoscopic examination and tympanometry was performed prior to DPOAE testing, to ascertain normal middle ear status.

RESULTS

DPOAE amplitude did not change significantly between two groups from 1 month till 6 months of age (p > 0.05). DPOAE amplitude and noise floor in very preterm infants were not different from term infants and DPOAE amplitude did not vary significantly across f2 frequencies at various time periods.

CONCLUSION

The current study findings provided evidence that prematurity did not constitute as a factor to influence the results of DPOAE in very preterm infants who passed newborn hearing screening test. Any significant reduction in DPOAE amplitude or absence of DPOAE in very preterm infants has to be considered and monitored effectively, as it may not reflect a developmental process of cochlear function; instead it could indicate the presence of inner ear or middle ear pathology.

Efferent inhibition of otoacoustic emissions in preterm neonates

INTRODUCTION

Abnormalities in auditory function of newborns may occur not only because of preterm birth, but also from the use of medications and from diseases related to prematurity.

OBJECTIVE

To analyze the inhibitory effect from stimulation of the olivocochlear efferent system on transient evoked otoacoustic emissions in preterm neonates, comparing these data with those from full-term neonates.

METHODS

This was a prospective, cross-sectional, contemporary cohort study with 125 neonates, pooled into two groups: full-term (72 full-term neonates, 36 females and 36 males, born at 37-41 weeks of gestational age); and preterm (53 neonates, 28 males and 25 females, born at ≤36 weeks of gestational age, evaluated at the corrected gestational age of 37-41 weeks). Otoacoustic emissions were recorded using linear and nonlinear click-evoked stimuli, with and without contralateral stimulation.

RESULTS

The inhibitory effect of the efferent pathway in otoacoustic emissions was different (p=0.012) between groups, and a mean reduction of 1.48dB SPL in full-term births and of 1.02dB SPL in preterm births was observed for the non-linear click-evoked stimulus.

CONCLUSION

The results suggest a reduced inhibitory effect of the olivocochlear efferent system on otoacoustic emissions in preterm neonates.

Maturação auditiva periférica: análise das amplitudes das emissões otoacústicas produto de distorção em neonatos pré-termo e a termo

Objetivo : Comparar neonatos prematuros e a termo quanto à presença e amplitude das Emissões Otoacústicas Produto de Distorção (EOAPD), bem como caracterizá-los em relação aos indicadores de risco para perda auditiva. Métodos : Estudo realizado por análise das EOAPD (frequências de 2000, 3000, 4000, 6000 e 8000 Hz) e dos indicadores de risco para perda auditiva. Os neonatos foram agrupados segundo a idade gestacional. Os resultados foram analisados empregando-se testes ANOVA, Kruskal-Wallis e Qui-quadrado (5%). Resultados : A amostra constituiu-se de 109 neonatos (218 orelhas), com distribuição homogênea quanto ao gênero e a classificação a termo/pré-termo. Foi observado alto risco para perda auditiva em 40,4% dos lactentes. Dos indicadores de risco para deficiência auditiva, os mais frequentes foram a permanência em incubadora e internação em UTI superiores a cinco dias. As EOAPD mostraram-se presentes em 209 orelhas (95,9%). A ausência de respostas às EOAPD foi significativamente mais recorrente nos grupos com menor idade gestacional. Verificou-se aumento das amplitudes das EOAPD de acordo com o aumento da idade gestacional, exceto para a frequência de 8000 Hz na orelha esquerda. Não foi observada diferença entre orelhas e gêneros quanto à presença e amplitude das EOAPD. Conclusão : Há diferença entre os grupos pré-termo e a termo, quanto à presença e amplitude das EOAPD: maior probabilidade de falha nos grupos com menor idade gestacional e aumento (não linear) das amplitudes, conforme a idade gestacional torna-se maior. Os achados sugerem o fenômeno de maturação do sistema auditivo periférico.

Emissões otoacústicas evocadas transientes em recém-nascidos a termo e pré-termo

OBJETIVO: analisar a amplitude absoluta e nível de Response das emissões otoacústicas evocadas transientes em recém-nascidos pré-termo e a termo. MÉTODOS: participaram deste estudo 50 recém-nascidos a termo e 50 pré-termo, os quais foram submetidos à triagem auditiva neonatal por meio da pesquisa das emissões otoacústicas evocadas transientes, realizada entre 24 horas e 11 semanas de vida. Todos os recém-nascidos apresentaram presença de emissões otoacústicas evocadas por clique no teste da triagem auditiva neonatal. RESULTADOS: não houve diferença estatisticamente significante da amplitude e nível de Response entre os recém-nascidos a termo e pré-termos. Não houve correlação significante entre os fatores prematuridade, idade do recém-nascido no teste e tempo de estimulação auditiva com os resultados obtidos. CONCLUSÃO: as emissões otoacústicas evocadas transientes registradas em recém-nascidos a termos e pré-termos apresentam semelhante amplitude absoluta e nível de Response.

Emissões otoacústicas produto de distorção em normo ouvintes e em perdas auditivas neurossensoriais leve e moderada com os protocolos 65/55 dB NPS E 70/70 dB NPS

OBJETIVO: estudar comparativamente as amplitudes das emissões otoacústicas produto de distorção em indivíduos normo ouvintes, com perdas auditivas de graus leve e moderado. MÉTODOS: a amostra compôs-se de 41 indivíduos na faixa etária de 18 a 45 anos, sendo 25 do sexo feminino e 16 do sexo masculino. Foram realizadas audiometrias tonal e vocal para classificar os grupos conforme perfil audiométrico; imitanciometria para avaliar as condições da orelha média; e emissões otoacústicas produto de distorção, utilizando os protocolos L1 = 65 dB NPS e L2 = 55 dB NPS e L1=L2= 70 dB NPS. No total, foram analisadas 63 orelhas (32 orelhas direitas e 31 orelhas esquerdas). Os indivíduos selecionados foram distribuídos em três grupos distintos, sendo o primeiro grupo (G1) composto de 21 orelhas com audiometria tonal com limiares dentro da normalidade (grupo controle); o segundo grupo (G2) composto de 21 orelhas com perdas auditivas neurossensoriais de grau leve; e o terceiro grupo (G3) composto por 21 orelhas com perdas auditivas neurossensoriais de grau moderado. Os dados audiométricos foram comparados com os resultados das Emissões Otoacústicas Produto de Distorção (DPOAE). RESULTADOS: encontrou-se diminuição e ausência das amplitudes no grupo com perda auditiva de grau leve (G2) e ausência de respostas no grupo com perda auditiva de grau moderado (G3) em ambos os protocolos. CONCLUSÃO: com relação ao grau da perda auditiva, pode-se concluir que quanto maior a perda auditiva, menor o aumento da amplitude das EOAPD.