Physiological mechanisms of onset adaptation and contralateral suppression of DPOAEs in the rat.

An investigation was undertaken to measure medial olivocochlear (MOC) reflexes in anesthetized rats before and after sectioning of the middle-ear muscles. Distortion product otoacoustic emission (DPOAE) magnitude and phase temporal responses were measured ipsilaterally to study MOC-mediated "DPOAE onset adaptation" and in the presence of a contralateral noise to study MOC-mediated contralateral "suppression" (terms as used by previous researchers). Distortion product otoacoustic emission onset adaptation and contralateral suppression had predictable changes in direction of magnitude and phase that were dependent on the input-output function. After sectioning of the middle-ear muscles (MEMs), DPOAE onset adaptation and contralateral suppression were greatly reduced, and there were little, if any, changes in phase. These "residual" changes were interpreted as a result of the MOC reflex. The results suggest that what appears to be DPOAE onset adaptation and contralateral suppression can be mediated primarily by MEM reflexes. When studying MOC effects on otoacoustic emissions (OAEs) using acoustic stimulation, it is necessary to make recordings over a span of stimulus levels. In addition, looking at both magnitude and phase of the OAE may help separate what is due to the MOC reflex from MEM reflex.

The New York State universal newborn hearing screening demonstration project: introduction and overview.

OBJECTIVE: To determine the feasibility of universal newborn hearing screening, including intervention of identified infants, in the state of New York. DESIGN: The New York State Department of Health issued a request for proposals that invited regional perinatal centers to apply for funding to implement universal newborn hearing screening. Hospitals were free to choose their own protocols but were to use physiologically based measures to screen infants for possible hearing loss. Criteria for passing the screening measures were common across sites. Infants failing the screening were to have diagnostic testing. Identified infants were to be followed by the state's Early Intervention Program and its associated Infant-Child Health Assessment Program. RESULTS: Seven regional perinatal centers (eight hospitals) representing the various regions of the state were funded for 3 yr to implement universal newborn hearing screening and follow-up of identified infants. Detailed data analysis was performed for inpatient, outpatient, and intervention outcome measures and for the various protocols. Most of the outcome measures were analyzed in terms of year of program operation, nursery type, and geographic region of the state. CONCLUSIONS: Universal newborn hearing screening was feasible in regional perinatal centers across the state of New York. The average ages of identification of hearing loss, hearing aid fitting, and enrollment in early intervention were less than those reported in published studies where universal newborn hearing screening was not in place.

New York State universal newborn hearing screening demonstration project: inpatient outcome measures.

OBJECTIVE: To evaluate the feasibility of universal newborn hearing screening by examining inpatient outcome measures from 8 hospitals located in geographically diverse areas of New York State over a 3-yr period. DESIGN: Funding was provided by the New York State Department of Health to implement predischarge hearing screening programs in the neonatal intensive care units (NICUs) and well-baby nurseries (WBNs) of eight hospitals. Various screening protocols including transient evoked otoacoustic emissions alone or in combination with conventional auditory brain stem response or screening auditory brain stem response were implemented by each site. Measured outcomes included rate of misses, refusals, and fails. Results were analyzed as a function of year of operation, nursery type, and geographic location. RESULTS: Six out of eight hospitals successfully implemented universal hearing screening during the first year, and the remaining 2 hospitals implemented programs during the second year of the project. Over a period of 3 yr, 69,761 newborns were screened at the eight hospitals representing 96.9% of all live births. The overall fail rate (4.04%) combined with the miss rate (2.61%) resulted in 6.63% of infants referred for outpatient follow-up. Mean data indicated that inpatient outcome measures improved with year of operation, with most individual hospitals also showing improvements. Both fail and miss rates were higher in the NICU than in the WBN and for hospitals located in New York City than in other regions of the state. CONCLUSIONS: Inpatient outcome measures of a universal newborn hearing screening project, which involved multiple centers across geographically diverse regions of New York State, were acceptable in terms of successfully screening a high percentage of live births and attaining low refer rates for outpatient screening. This study adds to the growing body of literature supporting the feasibility of screening all newborns before hospital discharge.

The New York State universal newborn hearing screening demonstration project: ages of hearing loss identification, hearing aid fitting, and enrollment in early intervention.

OBJECTIVE: To determine the ages of hearing loss identification, hearing aid fitting, and enrollment in early intervention through a multi-center, state-wide universal newborn hearing screening project. DESIGN: Universal newborn hearing screening was conducted at eight hospitals across New York State. All infants who did not bilaterally pass hearing screening before discharge were recalled for outpatient retesting. Inpatient screening and outpatient rescreening were done with transient evoked otoacoustic emissions and/or auditory brain stem response testing. Diagnostic testing was performed with age appropriate tests, auditory brain stem response and/or visual reinforcement audiometry. Infants diagnosed with permanent hearing loss were considered for hearing aids and early intervention. Ages of hearing loss identification, hearing aid fitting, and enrollment in early intervention were investigated regarding nursery type, risk status, unilateral versus bilateral hearing loss, loss type, loss severity, and state regions. RESULTS: The prevalence of infants diagnosed with permanent hearing loss was 2.0/1000 (85 of 43,311). Of the 85 infants with hearing loss, 61% were from neonatal intensive care units (NICUs) and 67% were at risk for hearing loss. Of the 36 infants fitted with hearing aids, 58% were from NICUs and 78% were at risk for hearing loss. The median age at identification and enrollment in early intervention was 3 mo. Median age at hearing aid fitting was 7.5 mo. Median ages at identification were less for infants from the well-baby nurseries (WBNs) than for the NICU infants and for infants with severe/profound than for infants with mild/moderate hearing loss, but were similar for not-at-risk and at-risk infants. Median ages at hearing aid fitting were less for well babies than for NICU infants, for not-at-risk infants than for at-risk infants, and for infants with severe/ profound hearing loss than for infants with mild/ moderate hearing loss. However, median ages at early intervention enrollment were similar for nursery types, risk status, and severity of hearing loss. CONCLUSIONS: Early ages of hearing loss identification, hearing aid fitting, and enrollment in early intervention can be achieved for infants from NICUs and WBNs and for infants at risk and not at risk for hearing loss in a large multi-center universal newborn hearing screening program.

The New York State universal newborn hearing screening demonstration project: outpatient outcome measures.

OBJECTIVE: To investigate outpatient outcome measures of a multi-center, state-wide, universal newborn hearing screening project. DESIGN: Eight hospitals participated in a 3-yr, funded project. Each hospital designed its own protocol using common criteria for judging whether an infant passed a hearing screening. Infants were tested in the hospital, and those either failing the in-hospital screening or who were not tested in the hospital (missed) were asked to return 4 to 6 wk after hospital discharge for outpatient rescreening. Those infants failing the outpatient rescreening were referred for diagnostic auditory brain stem response testing. Each hospital used its own audiological equipment and criteria to determine whether a particular infant had a hearing loss. All data were collected and analyzed for individual hospitals, as well as totaled across all hospitals. Data were analyzed in terms of year of program operation, nursery type, and geographic region. RESULTS: Seventy-two percent of infants who failed the in-hospital screening returned for outpatient testing. The percentage of in-hospital fails returning for retesting was significantly higher than the percentage of in-hospital misses returning for retesting. The percentage of infants returning for retesting increased with successive years of program operation. Some differences were noted in the percentage of infants returning for retesting among hospitals and geographic regions of the state. Some differences in outpatient outcome measures also were noted between infants originally born into the neonatal intensive care unit (NICU) and the well-baby nursery (WBN). The percentage of infants from the NICU who returned for retesting was slightly higher than that for infants from the WBN. The percentage of infants from the WBN passing the outpatient rescreening was higher than that for the NICU infants. The overall prevalence of hearing loss was 1.96/1000, with that in the NICU being 8/1000 and that in the WBN being 0.9/1000. Positive predictive value for permanent hearing loss based on inpatient screening was approximately 4% and based on outpatient rescreening was approximately 22%. CONCLUSIONS: Several outpatient outcome measures changed with successive years of program operation, suggesting that programs improve over time. Also, some outpatient outcome measures differ between NICU and WBN populations. The differences noted across regions of the state in the percentage of infants returning for outpatient retesting require further research to determine whether differences are due to demographic and/or procedural differences.

New York State universal newborn hearing screening demonstration project: effects of screening protocol on inpatient outcome measures.

OBJECTIVE: To examine differences among various test protocols on the fail rate at hospital discharge for infants in the well-baby nursery (WBN) and neonatal intensive care unit (NICU) who received hearing screening through a universal newborn hearing screening demonstration project. DESIGN: The outcomes of several screening protocols were examined. Two technologies were used: transient evoked otoacoustic emissions (TEOAEs) alone or in combination with the auditory brain stem response (ABR). The performance of test protocols in both nurseries within eight hospitals was examined over a 2- to 3-yr period. In the WBN, six hospitals used a screening protocol of TEOAE technology first followed by an ABR (automated or conventional) technology screening for newborns who referred on TEOAE screening. Two hospitals used TEOAE only in the WBN. Seven hospitals used screening protocols in the NICU that used a combination of TEOAE and ABR technologies (TEOAE technology administered first or second, before or after TEOAE, or TEOAE and ABR tests on all infants). Only one hospital used TEOAE technology exclusively for hearing screening. RESULTS: Significant differences among screening protocols were found across hospitals in the first, second, and third years of the program. The combination of TEOAE technology and ABR technology (a two-technology screening protocol) resulted in a significantly lower fail rate at hospital discharge than the use of a single-technology (TEOAE). Fail rates at discharge were twice as high using the one-technology protocol versus two-technology protocol, even when the best outcomes from program year 3 were considered exclusively. Results of two-technology versus one-technology protocols were similar in the NICU. Use of a second technology for screening TEOAE fails significantly reduced every hospital that used the protocol's fail rate at discharge. CONCLUSIONS: A two-technology screening protocol resulted in significantly lower fail rates at hospital discharge in both the WBN and NICU nurseries than use of a single-technology (TEOAE) hearing screening protocol.

Recovery of the human compound action potential following prior stimulation.

The recovery from prior stimulation of the compound action potential (CAP) was measured using a forward masking stimulus paradigm in four normal-hearing, human subjects. The CAP was recorded using a wick electrode placed on the tympanic membrane. The effects of a 4000-Hz, 97-dB SPL conditioning stimulus on CAP amplitude in response to a 4000-Hz probe were measured as a function of conditioner-probe interval for three probe levels. The normalized probe response amplitude was completely recovered to the control values at an average conditioner-probe interval of 1359 ms, similar to that observed in chinchilla (Relkin, E.M., Doucet, J.R., Sterns, A., 1995. Recovery of the compound action potential following prior stimulation: evidence for a slow component that reflects recovery of low spontaneous-rate auditory neurons, Hear. Res. 83, 183-189). The present results are interpreted as a consequence of the slow recovery of low spontaneous-rate (SR), high threshold neurons from prior stimulation (Relkin, E.M., Doucet, J.R., 1991. Recovery from prior stimulation. I: Relationship to spontaneous firing rates of primary auditory neurons. Hear. Res. 55, 215-222) and may provide indirect physiological evidence for the existence of a class of low-SR auditory neurons in humans.

Basic characteristics of click-evoked otoacoustic emissions in infants and children.

Since Kemp [J. Acoust. Soc. Am. 64, 1386-1391 (1978)] first described click-evoked otoacoustic emissions (COAEs), researchers have advocated their use as an excellent tool for diagnosing hearing loss in infants and children. However, there are few detailed reports of COAEs in this population, and those that do exist suggest that there are age-dependent differences. The purpose of the current study was to determine basic characteristics of COAEs in infants, toddlers, children, and young adults and to define any differences among age groups. An additional goal was to ensure that spontaneous otoacoustic emissions (SOAEs) did not confound any possible developmental effects. COAEs and SOAEs were measured from one ear of 223 normal-hearing subjects. COAE input/ output functions indicated that children aged less than one year have higher COAE levels than older children and adults. Children aged 1-5 yr had higher COAE levels than those aged 12-17 yr and adults. These differences were independent of level and SOAE status, but were dependent on frequency. The results of this study suggest that different clinical norms may be necessary for children aged less than 6 years.

Basic characteristics of distortion product otoacoustic emissions in infants and children.

Distortion-product otoacoustic emissions at the 2 f1-f2 frequency (DPOAEs) are being advocated as a clinical tool for diagnosis of peripheral auditory pathology. Because they can be measured quickly and noninvasively, they may be an excellent method for identifying hearing loss in infants and children. However, few studies have examined the characteristics of DPOAEs in infants and children or detailed if, and how, their responses differ from those of adults. The purpose of the current study was to determine basic characteristics of DPOAEs in infants, toddlers, children, and young adults and to define any differences among age groups. An additional goal was to ensure that the presence of spontaneous otoacoustic emissions (SOAEs) did not confound any developmental effect. DPOAE input/output (I/O) functions at seven f2 frequencies and SOAEs were measured from one ear of 196 subjects. Children aged less than 1 yr had significantly higher mean DPOAE levels than older children and adults, and children aged 1-3 yr had higher mean DPOAE levels than teens and adults. These differences were dependent on frequency but were independent of f2 level and SOAE status. At every f2 frequency, groups of individuals having SOAEs had higher mean DPOAE levels than those not having SOAEs.

COAE thresholds: 1. Effects of equal-amplitude versus subtraction methods.

Although research has demonstrated that click-evoked otoacoustic emissions (COAEs) elicited by high-level stimuli are useful for identifying hearing loss, the ability of COAEs to predict behavioral thresholds has not been adequately tested. Results of studies comparing COAE thresholds and behavioral thresholds have been equivocal, perhaps due to the need for a more rigorous approach to COAE threshold estimation. The present study was designed to address several methodological concerns in COAE threshold testing, particularly the effects of two methods of stimulus presentation on COAE testing and threshold calculation. In an attempt to make COAE threshold estimation consistent across participants, COAE threshold calculations were based on mean noise floor levels across participants. COAE and noise floor levels were measured in 15 participants using both equal-amplitude clicks and a subtraction method. Broadband COAEs were analyzed into 1/3 octave bands, so that input/output functions could be examined and COAE thresholds could be calculated for each 1/3 octave band. Comparison of the two stimulus methods indicated several differences. Mean noise floor levels for the equal-amplitude method were approximately 6 dB lower than those measured for the subtraction method across frequency. In many cases COAEs evoked using the equal-amplitude method were higher in amplitude than those evoked using the subtraction method. COAE thresholds measured using the equal-amplitude click stimuli were significantly lower than those measured using the subtraction method. The significantly higher thresholds obtained using the subtraction method may be attributed in part to the reduction of COAE amplitude by the subtraction procedure, and not merely to the higher noise level. Slopes of the input/output functions were not significantly different between the two stimulus methods. These results suggest that the equal-amplitude method is preferable for COAE threshold testing because lower noise floor and larger amplitude COAEs may be obtained in the same test time.

Click- and tone-burst-evoked otoacoustic emissions in normal-hearing and hearing-impaired ears.

Click-evoked otoacoustic emission (COAE) and tone-burst-evoked otoacoustic emission (TBOAE) input/output (I/O) functions and group latencies were measured in normal-hearing and hearing-impaired ears to determine the extent to which these two types of transient-evoked otoacoustic emissions (TEOAEs) were similar. When stimulus levels measured in 1/3 octave bands centered at 500, 1000, 2000, and 4000 Hz were similar, TBOAE and COAE I/O functions were essentially identical in regions of normal hearing. This held true in subjects who had normal hearing from 250 to 8000 Hz as well as for subjects who had normal hearing across some frequency ranges but hearing impairment across others. The high degree of correlation offers support to the view that both types of transient emissions share common generators. There were no significant differences in group delay between TBOAEs measured from normal-hearing and hearing-impaired subjects.

COAEs and SSOAEs in adults with increased age.

OBJECTIVE: The purpose of this study was to compare click-evoked otoacoustic emissions (COAEs) of subjects having similar auditory thresholds but different age ranges. It is well known that elevated hearing thresholds are common with increasing age and that deterioration of outer hair cells is often noted in cases of hearing loss due to increased age. It has also been reported that evoked otoacoustic emissions (EOAEs) decrease with increased age. However, there is still some question whether changes in EOAEs with aging are associated with the increased hearing threshold or whether there is some additional effect of aging that enfluences EOAEs. DESIGN: COAE input/output functions and synchronized spontaneous OAEs (SSOAEs) were measured in two groups of subjects having similar auditory thresholds, one ranging in age from 19 to 29 yr, the other ranging in age from 40 to 61 yr. Mixed-model ANOVAs were performed to determine whether there were any statistically significant differences in COAEs based on age group. RESULTS: There were no statistically significant differences in COAE level or COAE threshold between age groups. Significant differences in COAEs were found for subjects based on whether they had measurable SSOAEs, regardless of age. CONCLUSIONS: Age does not significantly reduce COAE level nor increase COAE threshold. Other factors, such as presence of SSOAEs and hearing loss, undoubtedly have more influence on COAEs than the factor of age.

Analysis of transient-evoked otoacoustic emissions in normal-hearing and hearing-impaired ears.

Transient-evoked otoacoustic emissions (TEOAEs) were measured in 113 normal-hearing and hearing-impaired ears to examine repeatability within a test session, which TEOAE parameter (level, TEOAE level-to-noise or reproducibility) best identified hearing loss and if the TEOAE separated into frequency-specific bands identified hearing loss in a corresponding frequency region. TEOAEs and stimulus levels were found to be very repeatable. For broadband TEOAEs, TEOAE level, TEOAE-to-noise, and % reproducibility were found to identify hearing loss equally well, based on measurement of the area underlying relative operator characteristic curves. Analysis for frequency-specific bands showed that separation of normal-hearing and hearing-impaired ears depended on frequency, with best identification at 2000 and 4000 Hz, identification at 1000 Hz slightly worse, and virtually no separation between normal-hearing and hearing-impaired ears at 500 Hz. Again, all three parameters were essentially equal in identifying hearing loss. Subjective evaluations of presence or absence of TEOAEs was highly correlated between two judges, with good agreement for TEOAEs at 1000, 2000, and 4000 Hz. The findings from this study suggest that TEOAEs will be valuable for clinical use because of their repeatability and identification of hearing-impaired ears.

Otoacoustic emissions in an adult with severe hearing loss.

The present study describes the unexpected finding of evoked otoacoustic emissions (EOAEs) from the left ear of a subject with severe-to-profound bilateral sensorineural hearing loss. No EOAEs could be measured from the right ear. To ensure that the EOAEs were not artifacts, two different instrumentation systems were used and both provided similar results. It is suggested that the subject may have a group of surviving outer hair cells in some regions of her left cochlea with corresponding inner hair cell or neural damage.

Age-dependent changes in susceptibility to ototoxic hearing loss.

Several species undergo age-dependent changes in susceptibility to noise-induced and drug-induced hearing loss. In this experiment 18-day-old mice were given 200 mg/kg kanamycin plus varying doses of bumetanide (20, 30 or 40 mg/kg). Thresholds of the scalp-recorded compound action potential of the auditory nerve indicated that diuretic doses of 30 and 40 mg/kg produced significant loss of hearing sensitivity. Thirty-eight-day-old mice were then treated with 200 mg/kg kanamycin plus 40 mg/kg bumetanide and demonstrated no loss of hearing sensitivity. These results confirm the existence of age-dependent changes in susceptibility to ototoxic hearing loss in mice. Furthermore, the treatment, consisting of two injections on the same day, offers promise as a means of defining the critical period of susceptibility in greater detail than has been possible with aminoglycosides alone.