Long-term and short-term variations in amplitude and frequency of spontaneous otoacoustic emissions in pre-term infants

Characterizing spontaneous otoacoustic emissions across the human lifespan

This study characterizes 1571 archival and newly acquired spontaneous otoacoustic emissions (SOAEs) from 632 human subjects with ages ranging from premature birth through the seventh decade of life. Automated detection and Lorentzian modeling were applied to identify SOAEs and characterize SOAE features throughout the human lifespan. Results confirm higher-level, higher-frequency, and more numerous SOAEs from neonates compared to young adults. Approximately 85% of newborns have measurable SOAEs as compared to 51%-68% for young adults. Newborn SOAEs are also an average of 5 to 6 dB higher in level than those from young-adult ears. These age differences may reflect immature ear-canal acoustics and/or the pristine condition of the neonatal cochlea. In addition, newborns as a group showed broader SOAE bandwidth and increased frequency jitter, possibly due to higher intracochlear noise; additionally, 22% of newborn SOAEs had a different, non-Lorentzian spectral shape. Aging effects were also observed: 40% of elderly ears had SOAEs, and these were greatly reduced in level, likely due to lower power gain in the aging cochlea. For all ages, SOAE bandwidths decreased with frequency in a way that mirrors the frequency dependence of stimulus-frequency otoacoustic emission delays as predicted by the standing-wave model of SOAE generation.

[The hearing function in the premature infants]

The present review of the literature is focused on the morphological and functional aspects of antenatal ontogenesis of the hearing system with special reference to the peculiar features of its formation during the post-natal period in the premature infants. In this context, the results of the objective psychoacoustic investigation s are considered (including those obtained by such methods as threshold audiometry, verbal and non-verbal tests, evaluation of central auditory processing of the sound information). Also presented are the results of the objective methods of hearing investigations (acoustic impedancometry, registration of optoacoustic emission and auditory evoked potentials). The underdevelopment of the hearing system in the premature infants manifests itself as the specific functional features of all its components. Their parameters are presented with reference to dynamics of their formation. In addition, the problem of central auditory processing of the disorders that are very likely to be present in the premature infants are discussed.

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.

Frequency distribution of synchronized spontaneous otoacoustic emissions showing sex-dependent differences and asymmetry between ears in 2- to 4-day-old neonates

OBJECTIVE

The mature pattern of frequency distribution of synchronized spontaneous otoacoustic emissions (SSOAEs) has been reported to be bimodal in adults and children between 5 and 11 years of age; however, little is known about the distribution in neonates between 2 and 4 days after birth. Furthermore, overall differences in frequency distribution resulting from difference in sex and asymmetry between ears have not been carefully examined. The aim of this study is to determine the frequency distribution of SSOAEs in neonates at 2 to 4 days of age, evaluate the maturity of the pattern of distribution in this age group, and to evaluate the effects of differences in sex and asymmetry between left and right ears on the frequency distribution.

METHODS

We evaluated 224 ears in 112 newborns (59 girls, 53 boys) whose ages ranged from 2 to 4 days. The SSOAEs were measured using ILO96.

RESULTS

Most of the SSOAEs (86.5%) appeared at frequencies between 1.01 and 4.50 kHz. The overall frequency distribution of the SSOAEs showed a 'peak-valley-peak' pattern when plotted. Two peaks with maxima at 1.41-1.60 and 3.01-3.20 kHz were separated by a valley with a minimum at 2.41-2.60 kHz. Both girls and boys had approximate monomodal patterns in the distribution of SSOAEs. Significant sex-dependent differences were noted with more SSOAEs at the lower frequencies (<or=2 kHz) in boys (46.1%) than in girls (32.0%) (P<0.05) and more SSOAEs at the higher frequencies (2.51- 4.50 kHz) in girls (50.9%) than in boys (37.5%) (P<0.05). Both the right and left ears showed the 'peak-valley-peak' pattern that was similar to the overall distribution pattern. But, compared with the peaks measured in the left ears at 1.01-1.50 and 3.01-3.50 kHz, the peaks of the right ears at 1.51-2.00 and 2.51-3.00 kHz were much closer to the valley.

CONCLUSIONS

The overall distribution of frequency of SSOAEs in 2- to 4-day-old neonates had the similar mature 'peak-valley-peak' distribution pattern seen in adults. Significant sex-dependent differences of the SSOAEs frequency distributions have been found. However, only slight ear asymmetries of the SSOAEs frequency distributions can observed in this age group.

Otoacoustic emissions latency difference between full-term and preterm neonates

Transiently evoked otoacoustic emissions (TEOAEs) were recorded from full-term and preterm neonates. The responses were decomposed, by means of an adaptive approximation method, into waveforms of defined frequencies, amplitudes, latencies and time spans. Statistically significant differences in the latency values were found between the tested groups. Differences were also found in the time spans of the TEOAEs components. For the preterm neonates the contribution of long-duration components (i.e. long-time span) was higher. Those components were characterized by narrow frequency band and contrary to the short-time span components their latencies did not depend on frequency. The removal of the long-duration components, from the pool of analyzed data, decreased the latency differences between the tested groups. The results indicate that the origin of the longer latency values for preterm neonates (with a post conceptional age up to 33 weeks) in respect to full-term neonates can be attributed to the presence of long-lasting components. The correspondence, which was found between frequencies of long-duration components and the spectral peaks of spontaneous otoacoustic emissions (SOAEs), suggests that those components may be connected with SOAEs.

Clinical investigation on spontaneous otoacoustic emission (SOAE) in 447 ears

OBJECTIVES

It is known that spontaneous otoacoustic emission (SOAE) is often observed in normal hearing ears, but concrete clinical application of SOAE test has been rarely reported, compared with transiently evoked otoacoustic emission (TEOAE) and distortion product otoacoustic emission (DPOAE) tests. In addition, there have been a variety of opinions concerning laterality of SOAE, and influence of gender and hearing on SOAE. The reason for this may be that each report has the small number of subjects and lacks in statistical power. Therefore, in the present study, SOAE, TEOAE and DPOAE were measured in 447 ears of subjects at various ages with different hearing level, and statistical analysis was performed to investigate the clinical significance of SOAE.

MATERIALS AND METHODS

The subjects were 447 ears in 268 patients (268 ears in females, and 179 ears in males). The age of subjects ranged from 0 to 75 years (mean: 30.8 years), and there were 222 left and 225 right ears. The subjects of schoolchildren or older (414 ears) received pure-tone audiometry, and infants (33 ears) received auditory brain-stem response (ABR). SOAE and TEOAE were measured using ILO88 (Otodynamics, Version 4.20). DPOAE was measured using ILO92 (Otodynamics, Version 1.32).

RESULTS

Incidence of SOAE and the number of SOAE per ear were high in the subjects at age of 50 years or younger, in those with hearing level of not more than 30 dB, in the right ear, and in females. Incidence of SOAE in the whole of normal hearing ears was approximately 38%, but the ears with SOAE had almost normal hearing of not more than 30 dB.

CONCLUSIONS

SOAE is useful for objective hearing assessment. Moreover, SOAE sometimes appeared in the ears in which TEOAE or DPOAE could not be confirmed, and it might be useful for definite diagnosis of disease state to measure SOAE in addition to TEOAE or DPOAE.

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.

Automated auditory brainstem response in neonatal hearing screening

Severe congenital hearing impairment is an important handicap affecting 0.1% of apparently healthy liveborn infants and 1-2% of graduates of neonatal intensive care units. The prognosis for intellectual, emotional, language and speech development in the hearing-impaired child is improved when the diagnosis is made early and intervention is begun before the age of 6 mo. Universal screening is preferable, since about 50% of infants with hearing loss are not discovered if neonatal hearing screening is restricted to high-risk groups. The automated auditory brainstem response (AABR) screener is a dedicated hearing screening device which provides information not only about the outer/middle ear and cochlea but also about the auditory pathway up to the brainstem. AABR has an agreement with conventional auditory brainstem response up to 98%. It uses a 35 dB near hearing level click. No operator interpretation is needed and it can be used on the ward and during oxygen therapy without disturbance from ambient noise. Reported referral rates in a hospital-based screening programme at the time of discharge vary, with an average of 4%. AABR has also been used in a home-based setting, with the same results. The time necessary for screening varies with the setting, but ranges from 4 to 15 min. Initial costs range from $15 to $25 per test, which is similar to neonatal screening for metabolic diseases. In addition to individual healthcare savings, early diagnosis may lead to savings on costs of intensive speech-language intervention and educational facilities.