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Ear & Hearing:
doi: 10.1097/AUD.0b013e31829d5158
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Pediatric Applications of Wideband Acoustic Immittance Measures

Hunter, Lisa L.1; Prieve, Beth A.2; Kei, Joseph3; Sanford, Chris A.4

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1Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, USA; 2Department of Communication Sciences and Disorders, Syracuse University, Syracuse, New York, New York, USA. 3Hearing Research Unit for Children, School of Health and Rehabilitation Sciences, University of Queensland, Queensland, Australia; and 4Department of Communication Sciences and Disorders, Idaho State University, Pocatello, Idaho, USA.

ACKNOWLEDGMENTS: The authors declare no conflict of interest.

Address for correspondence: Lisa L. Hunter, Cincinnati Children's Hospital, Cincinnati, OH 45229, USA. E-mail: lisa.hunter@cchmc.org

Received February 02, 2013

Accepted May 19, 2013

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INTRODUCTION

Screening and diagnosis of hearing problems in the pediatric population demands a high degree of clinical test performance for detection of middle ear problems. All audiologic tests are affected by conductive hearing loss (CHL), because auditory signals are conducted through the outer and middle ear to produce a behavioral, physiologic, or electrophysiologic response. In particular, otoacoustic emissions (OAEs) are highly affected by middle ear problems, and while screening auditory brainstem responses (ABRs) appear to be less affected, air conduction thresholds for diagnostic ABR can be elevated in the presence of middle ear effusion (MEE). Pediatric audiologists therefore need sensitive, specific, and user-friendly screening and diagnostic tools that permit better interpretation of middle ear status at all ages. Traditional, single-frequency tympanometry and acoustic reflex tests have been limited in several respects, particularly in newborns and young infants. Standard single-frequency tympanometry has poor sensitivity to MEE in newborns, and to assess higher frequencies, individual probe tones are required, which is time consuming. Standard acoustic reflex tests have poor sensitivity and specificity, and have a risk of iatrogenic hearing loss due to the need for high stimulus levels (Hunter et al. 1999).

A more recently developed measure of outer and middle ear status uses a carefully calibrated probe to record middle ear responses to broadband signals. Many different physical properties can be measured using this technique, which will be referred to as wideband acoustic immittance (WAI) in this article. WAI is a catch-all term that includes physical measures known as reflectance, absorbance, and the underlying phase and magnitude quantities expressed in impedance (Za) or admittance (Ya) terms (see Rosowski et al., this issue, pp. 9S–16S). Wideband tests can be conducted at ambient pressure, or with pressurization as in tympanometry, and can also be used to evoke and measure acoustic reflexes. WAI tests provide important information about middle ear function by measuring how the middle ear receives, absorbs, and transmits sound energy across a wide range of frequencies. WAI may provide improved diagnostic capability over single-frequency tympanometry in pediatric clinical populations.

Studies of WAI have demonstrated useful applications in identifying ears with middle ear disorders or CHL (Piskorski et al. 1999; Feeney et al. 2003; Keefe & Simmons 2003; Hunter et al. 2008a; Shahnaz et al. 2009; Beers et al. 2010; Ellison et al. 2012; Keefe et al. 2012; Prieve et al. 2013). In distinguishing ears with middle ear dysfunction from healthy ears, results between the two or more defined groups are often compared. Developmental normative data, information about test–retest reliability, and clinical performance studies in specific disorders are needed to determine the clinical utility of wideband measures. Analysis of the effect size between defined disorder groups is also needed to determine how the test performs for diagnostic purposes. This article will focus on results in middle ear disorders, while normal characteristics are covered by Kei et al. (this issue, pp. 17S–26S).

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Middle Ear Assessment Issues in Newborns, Infants, andChildren

At birth, the middle ear cavity may be filled with amniotic fluid, and may also contain mesenchyme, meconium, exudates, blood, desquamated epithelial cells, hair, keratinized cells, inflammatory cells, mucosal infiltrate, and reactive polyps (Palva et al. 1999).

Aeration of the middle ear normally occurs during the first 48 hr after birth (Piza et al. 1989). The ear canal and middle ear are immature and undergo continued development postnatally, especially during the first 6 months after birth (see Kei et al., this issue, pp. 17S–26S, for further discussion).

Measures of middle ear dysfunction are essential for audiological diagnosis of hearing loss (American Speech-Language-Hearing Association 2004; Joint Committee on Infant Hearing 2007). It is possible that middle ear measures could be routinely incorporated into screening protocols. Although Universal Newborn Hearing Screening Programs (UNHS) are designed to detect permanent sensorineural or CHL, debris in the ear canal and outer ear canal collapse can affect screening results. These problems can be managed by good screening techniques and careful probe insertion. More problematic are temporary middle ear issues such as middle ear fluid (amniotic fluid at birth), mesenchyme, or meconium that does not resolve within the first few hours after birth. These fluids and materials may take days or even weeks to clear (Roberts et al. 1995) and have been shown to affect OAE and ABR recordings and pass rates. In this article, studies of WAI will be described in newborns, infants, and children with defined conditions to assess the current status of these measures for screening and diagnostic purposes.

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WAI at Ambient Pressure

Wideband measures have been studied developmentally from the newborn period to adulthood. They provide a physiologic, objective measure that can assist in the screening and diagnosis of middle ear status and have the potential to provide improved accuracy of middle ear disorders as compared with traditional single-frequency tympanometry. The majority of research to date has studied reflectance (/R2/), or absorbance (1−/R2/) in newborns and infants as related to NHS and diagnosis programs. Studies have varied in population characteristics, sample size, and measurement parameters. Because reflectance and absorbance are directly related, it is possible to consider these as essentially equivalent measurements for the purpose of this review. We reviewed published studies of WAI in populations that had newborn screening reported, as well as studies in pediatric populations with middle ear conditions diagnosed by standard tests.

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Studies in Newborn Populations

The first study to report ambient pressure WAI in neonates was by Keefe and colleagues (2000), from a large multisite study of NHS methods. Wideband admittance (Y) and reflectance (R2) were obtained at four test sites in the United States in newborns cared for in well-baby nurseries without risk factors for hearing loss, newborns cared for in well-baby nurseries having at least one risk factor for hearing loss, and graduates of neonatal intensive care units. Approximately 13% of the Y and R2 responses showed evidence of inadequate probe seal in the ear canal, based on large negative ear-canal volumes at low frequencies. After excluding these outliers and controlling for conceptional age effects, some risk factors accounted for the greatest variance in the Y and R2 responses (listed in rank order); cleft lip and palate, aminoglycoside therapy, low birth weight, history of ventilation, and low Appearance, Pulse, Grimace, Activity, Respiration (APGAR) scores. In separate analyses, Y and R2 responses varied in the first few days after birth. An analysis showed that the use of a test criterion to assess the quality of probe seal may help control the false-positive rate in OAE testing.

Ambient and wideband tympanometry data from a large number of newborns cared for in a well-baby nursery were reported by Sanford et al. (2009). Ambient absorbance data for ears that referred on distortion product otoacoustic emissions (DPOAEs) are shown compared with ears that passed DPOAEs in Figure 1. Tympanometry using a 1 kHz probe tone was also obtained. WAI was performed using the research system developed by Liu et al. (2008). Wideband tympanometric, ambient absorbance, and 1 kHz tympanometry tests were performed immediately after the infant’s first DPOAE test (day 1), in 455 infant ears (375 passed and 80 referred). Of the 80 infants referred on day 1, 67 infants were evaluated again after repeated DPOAE screening the next day (day 2). On the first test day, the median ambient absorbance obtained from the 375 ears that passed the DPOAE test varied between 0.32 and 0.65 across the frequency range of 0.25 to 8 kHz. In contrast, the median ambient absorbance obtained from the 80 referred ears was significantly lower overall—ranging from 0 to 0.38. The largest difference in absorbance between the DPOAE-Pass and DPOAE-Refer ears occurred between 1.4 and 2.5 kHz. Similarly, the ambient wideband admittance magnitude was larger for DPOAE-Pass ears than for DPOAE-Refer ears, with the best separation between 1 and 2 kHz. On the contrary, mixed results with the ambient wideband admittance phase measure occurred with the admittance phase smaller in the DPOAE-Refer group for frequencies from 0.75 to 1 kHz and larger for 2.5 to 4.5 kHz. Based on the ambient absorbance results obtained on day 1 and day 2, Sanford et al. suggested that the transient sound conduction effects, presumed to have been a contributing factor that led to an initial refer on day 1, had begun to resolve by day 2. Using clinical decision theory to classify ears that passed or referred on DPOAE screening as the gold standard, it was observed that ambient absorbance produced higher accuracy of predicting DPOAE screening outcomes than wideband tympanometry and traditional, single-frequency tympanometry. Ears that passed DPOAE screening had higher energy absorbance compared with those that referred DPOAE, as shown in Figure 1, indicating that infants that passed the DPOAE UNHS had a more acoustically efficient conductive pathway. Sanford et al. suggested that it may be feasible to consider implementing WAI measurements in conjunction with UNHS programs.

Fig. 1.
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A second study of ambient wideband reflectance in a large number of healthy newborns in comparison to DPOAE NHS results and tympanometry using a 1 kHz probe tone was reported by Hunter et al. (2010). The WAI measures were obtained using the Mimosa Hear-ID system and tympanometry was performed using the GN Otometrics Otoflex system (see data in Fig. 2). The study population included White, Hispanic, and Asian newborns, totaling 324 infants at two test sites). Clinical decision theory was also employed in this study, using “Reflectance Area Indices” integrated over various frequency ranges between 1 and 8 kHz. Normative ranges and test performance for prediction of hearing screening status were used to perform receiver operating characteristic (ROC) curve analyses (a measurement of test performance), which showed that reflectance in the frequency ranges around 2 kHz provides the best prediction of referring on DPOAE screening, as shown in Figure 2. Prediction of DPOAE status was significantly better for wideband reflectance than for than 1 kHz tympanometry. The areas under the (AUROC) curve were 0.72, 0.82, and 0.90 for 1 kHz tympanometry, 1 kHz reflectance, and 2 kHz reflectance, respectively. There were no significant relationships between reflectance and sex, ear, tone versus chirp stimulus or geographic site. In addition, birth type (vaginal versus C-section) and birth weight did not correlate to wideband reflectance. The median reflectance obtained from the distortion product (DP)-pass group varied between 0.3 and 0.55 across the frequencies from 1 to 6 kHz. The DP-refer group had higher median reflectance values than that of the DP-pass group, indicating poorer middle ear transmission in the DP-refer group. However, the two reflectance distributions overlapped, introducing a region of uncertainty. An important finding from this study was that reflectance decreased significantly with age during the first 4 days after birth, which in turn, translated into higher DP-pass rates with age during this neonatal period. The association between reflectance and DP-pass rate is consistent with the hypothesis that middle ear differences in the “screening refer” ears were due to positive pressure, amniotic fluid, and mesenchyme in the middle ear. As these differences resolve after birth, corresponding improvement in absorption of energy by the middle ear is seen. Hunter et al. recommended that newborns with high reflectance from 1–5 to 3 kHz be rescreened within a few hours to a few days, because most middle ear problems are transient and resolve spontaneously. If reflectance and OAE tests are not passed at the end of the screening protocol, referral to an otologist for ear examination was recommended along with audiologic diagnostic testing. Immediate referral to an audiologist for diagnostic hearing testing was recommended for newborns with normal reflectance and a refer result for the OAE screen; these test outcomes would be an indication of increased risk for permanent hearing loss. A recent study (Prieve et al. 2013) evaluated the effectiveness of tympanometry and ambient reflectance in detecting CHL in young infants against the gold standard of ABR. Type of hearing loss was determined using ABR with air- and bone-conducted tone bursts in 60 infant ears (median age 10 weeks); 43 ears had normal hearing (NH) and 17 had CHL. Tympanometry was measured using probe-tone frequencies of 226, 678, and 1000 Hz. Static admittance (Ya) measured with 678 and 1000 Hz probe tones was significantly different between ears with CHL and ears with NH, as shown in Figure 3. Classification of tympanograms using a 1000 Hz probe tone was significantly different between ears with CHL and NH. Neither tympanometry classification nor static admittance was significantly different between ears identified with CHL and NH using a 226 Hz probe tone. Wideband reflectance was significantly higher in the frequency bands 0.8 to 2.5 kHz and in the frequency band centered at 6.3 kHz in infants with CHL. Effect sizes (Cohen’s d) were greater than 2 for several reflectance frequency bands and Ya measured with 1000 Hz probe tones. The results were similar for calculations of Ya and subcomponents susceptance (B) and conductance (G) tympanograms. Positive likelihood ratios (LRs+) for reflectance ranged between 8.1 and 38; for Ya at 1000 Hz, LR+ ranged between 12.5 and 32. Conclusions of this study were that CHL in young infants can be detected well with ambient or tympanometric reflectance or conventional tympanometry using probe frequencies of 678 and 1000 Hz, but not of 226 Hz.

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Fig. 3.
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In summary, these studies of wideband reflectance and absorbance in ears that referred on newborn screening are in general agreement for both the magnitude and shape of the function across a wide frequency range and for the effect of increased reflectance associated with abnormal DPOAE screening. While an earlier study (Keefe et al. 2000) showed less reflectance in the low frequencies, these differences were most likely due to probe or probe seal differences. High sensitivity and specificity for prediction of newborn screening outcomes has been consistent and significantly better for WAI than for 1 kHz tympanometry. A limitation of these studies is the lack of a validated, gold standard hearing test to confirm presence of CHL as the cause for reflectance or absorbance differences. Although the presence of OAEs is a good indication of a normal cochlear function as well as a normal middle ear condition, it cannot completely rule out the absence of effusion or abnormal pressure in the middle ear (Driscoll et al. 2000). Use of a more objective gold standard such as myringotomy raises ethical issues and is not feasible for referred NHS cases due to risk of sedation and surgery in the neonate without symptoms of acute otitis media (OM). One study has incorporated the gold standard of air and bone conduction ABR to more clearly assess the clinical effectiveness of WAI to identify the presence and severity of the conductive component in newborns and young infants who refer on NHS (Prieve et al. 2013). More such studies are needed with larger samples of conductive and sensorineural hearing loss, and incorporation of tympanometric WAI to determine whether it improves upon ambient WAI measures.

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Studies in Infant Populations

A number of studies have investigated WAI measures in infants; infants in this context are defined as children who are 1 month to 1 year of age. In the infant age group, WAI measures have a primary application in providing diagnostic follow-up information for infants who have been referred from Newborn Screening Programs.

Vander Werff et al. (2007) compared reflectance for infants who referred on OAE screening with those that passed. While the primary purpose of the study was to determine test–retest reliability of wideband reflectance measures in infants and adults, this study provided data on infants who referred on newborn screening and were seen for diagnostic testing. As in the newborn period, infants who failed OAE screening had significantly higher reflectance in the range from 0.63 to 2 kHz than infants who passed an OAE screening, and the diagnostic group showed less variability than infants being screened for hearing. Although conclusions are limited by the fact that the true status of the middle ear and cochlea were not known for the infants in this study, this result may indicate that a number of these infants failed an OAE screening due to transient or permanent middle ear dysfunction, which was detected by wideband reflectance.

Hunter et al. (2008b) reported ambient reflectance and absorbance for normal and “poor status” ears in infants and children 3 days to 47 months of age, using the Mimosa Acoustics Hear-ID instrument (Champaign, IL). Infants and children were enrolled from a well-child pediatric clinic (n = 97), with comparisons of age, gender, middle ear status, and stimulus type (broadband chirp and sine wave). Children with poor status ears were diagnosed with an algorithm that included otoscopy performed by a pediatrician, 226 Hz and 1000 Hz tympanometry, and DPOAE. Results were reported separately for infants below 6 months of age (n= 33) and those aged 6 to 47 months (n = 66). No significant age effect for reflectance was found except at 6 kHz. However, significantly higher reflectance was found for ears with poor ear status, specifically for those with otitis media with effusion. Smaller, but nonsignificant differences in reflectance were found for ears with positive and negative tympanometric peak pressure. Multivariate analysis of variance showed no significant effect of stimulus type (sine wave versus broadband chirp), ear, or sex. This study did not directly compare test performance of tympanometry and reflectance for diagnosis of the poor status ears.

Werner et al. (2010) studied WAI using the research system developed by Keefe et al. (2000) in 458 infants aged 2 to 9 months and in 210 adults. Wideband reactance (X), resistance (R), and reflectance were measured in 3rd-octave bands from 0.25 to 8 kHz. Results agreed well with previous reports using the same test system in studies with fewer subjects, and documented age-related change in these measures during infancy and between infancy and adulthood, as discussed by Kei (this issue, pp. 17S–26S). While the primary purpose of the study was normative, infants whose 226 Hz tympanograms indicated reduced peak admittance (types A and B) had significantly greater resistance and reactance magnitude as measured by WAI than those with normal peak admittance (types A and C).

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Children

Several studies have examined reflectance in children over 1 year of age. A few studies of WAI have reported data from children with defined middle ear pathologies or hearing loss. The first such study was reported by Margolis et al. (2000) in a prospective cohort study of children with chronic OM treated with tympanostomy tubes. This study included children aged 9 to 16 years, with chronic OM histories, normal 226 Hz tympanograms, no air–bone gaps, and no otoscopic evidence of active OM at the time of testing. Subjects with OM were divided into two groups, one referred to as “Better Hearing” in the extended high-frequency (EHF) range (8 to 20 kHz) and one referred to as “Worse Hearing” in the EHF range. The OM groups were compared with an age-matched, healthy control group that included participants who had no more than five documented episodes of OM and no more than two in any 1-year period. Middle ear impedance and reflectance were measured with the experimental system developed by Keefe et al. (1993) over the frequency range 0.25 to 10 kHz. The Worse Hearing OM group had slightly poorer hearing in the conventional audiometric frequency range and significantly poorer hearing in the EHF range compared with the other two groups. Middle ear impedance differences among groups were confined to low frequencies (<2 kHz). The control group had significantly higher negative reactance than the two OM groups. There were no significant group differences in impedance or reflectance in the high frequencies (2 to 10 kHz). Middle ear impedance and reflectance differences did not account for the EHF hearing losses observed in children with OM histories, thus supporting the hypothesis that OM-related EHF hearing losses are cochlear in origin. This study demonstrated use of WAI in distinguishing the cause of high-frequency hearing loss as conductive or sensorineural.

Keefe and Simmons (2003) investigated ambient and tympanometric WAI measures and 226 Hz tympanometry to predict CHL in children. Wideband responses were objectively classified using moment analyses. Comparing measures at a fixed specificity of 0.90, sensitivities were lowest for peak-compensated static acoustic admittance at 226 Hz (sensitivity = 28%), intermediate for ambient-pressure absorbance (sensitivity = 72%), and highest for pressurized absorbance (sensitivity = 94%). Pressurized absorbance was accurate at predicting CHL with an AUROC curve of 0.95.

Beers et al. (2010) studied energy reflectance in 64 children (average age = 6.34 years) with diagnosed middle ear conditions compared with 78 children without middle ear conditions (average age = 6.15 years). In some cases, MEE was diagnosed by a pediatric otolaryngologist using pneumatic otoscopy and video otomicroscopy, while others were classified based on audiological test battery results (e.g., elevated air conduction thresholds, flat low- and high-frequency tympanograms, and absent transient-evoked OAEs). Subjects had air and bone conduction thresholds measured at 0.5, 1, 2, and 4 kHz, and test results were required to have a good reliability rating. In addition to elevated air conduction thresholds, absent OAEs, and abnormal impedance results, bone conduction thresholds confirmed that the hearing loss was entirely conductive in nature. The diagnosis of middle ear pathology was confirmed based on pneumatic otoscopy and video otomicroscopy conducted by a pediatric otolaryngologist. Video otomicroscopy was later independently reviewed by an otologist to confirm the original diagnosis of MEE. Reflectance was significantly higher among four middle ear conditions (normal, mild negative middle ear pressure, severe negative middle ear pressure, and MEE). The overall test performance of reflectance and tympanometry (226 Hz probe tone) in identifying MEE was evaluated using ROC curve analyses. The reflectance in the 1.25 kHz band had the best test performance (sensitivity of 96% and specificity of 95%) and was selected for further analysis. AUROC curves were higher than 0.90 for reflectance across a number of frequency bands between 800 and 5000 Hz. Compared with traditional tympanometry, for example, static admittance at 226 Hz probe-tone frequency, reflectance results had significantly better test performance in distinguishing between healthy ears and ears with MEE.

Ellison et al. (2012) compared accuracy of WAI in a group of 44 children (53 ears; median age = 1.3 years) with surgically confirmed otitis media with effusion with an age-matched control group of 44 children (59 ears; median age, 1.2 years) who had normal pneumatic otoscopic findings and no history of ear disease or middle ear surgery. An otolaryngologist judged whether MEE was present or absent and rated tympanic membrane (TM) mobility via pneumatic otoscopy. Absorbance was compared with pneumatic otoscopy classifications of TM mobility. Absorbance was reduced in ears with MEE compared with ears from the control group. Absorbance and admittance magnitude were the best univariate predictors of MEE, but a predictor combining absorbance, admittance magnitude, and phase was the most accurate overall. Absorbance varied systematically with TM mobility based on data from pneumatic otoscopy. Ellison and colleagues concluded that absorbance is sensitive to middle ear stiffness and MEE, and WAI predictions of MEE in young children are as accurate as those reported for methods recommended by clinical guidelines (Otitis Media with Effusion 2004).

A diagnostic framework shown in Figure 4, which includes WAI within the pediatric audiology cross-check framework, is helpful to consider how wideband tests, that is, tympanometry and acoustic reflexes, can be combined with OAE and ABR tests to provide a powerful and highly specific means to diagnose type of hearing loss when behavioral audiometry is not possible due to developmental level of the infant. While an individual test on its own does not provide as much diagnostically useful information as does the combination of tests, the test battery can be used to diagnose type, degree, and laterality of hearing loss. Within this framework, ABR should be replaced or validated with behavioral audiometry whenever the child is able to provide reliable behavioral responses.

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Two studies have reported WAI in infants and children with middle ear problems associated with craniofacial anomalies. Hunter et al. (2008a) studied children with cleft lip and palate, who had not been treated with myringotomy or tubes. WAI was compared with 226 and 1000 Hz tympanometry, and gold standard pneumatic otoscopy performed by an otolaryngologist for prediction of abnormal DPOAEs. Results showed that reflectance had the highest level of agreement (88%) with DPOAE compared with 226 and 1000 Hz tympanometry or pneumatic otoscopy.

Kaf (2011) studied WAI in 14 young children with Down’s syndrome and an age-, sex-, and ear-matched control group (age range of 2.5 to 5 years; N = 19 ears per group); all children had normal 226 Hz tympanograms. Despite the presence of normal tympanometric findings in both groups, results revealed that reflectance fell outside the control group’s 5th to 95th percentile range in 63% of the children with Down’s syndrome. In addition, the mean reflectance of the Down’s syndrome group was significantly lower than that of the control at 5.7 to 8 kHz.

One meta-analysis has been reported for WAI measures and detection of pathology in infants and children (Sanford et al. 2012). A systematic review of the literature with rigorous controls for study quality and use of surgical or otoscopic gold standard diagnosis yielded 10 studies of participants with otosclerosis or OM. Two of these studies investigated 1000 Hz tympanometry, seven examined multifrequency tympanometry (MFT), and two addressed wideband reflectance. Positive LRs+ were predominately uninformative for MFT and were mixed for 1000 Hz tympanometry, while LR+ values for reflectance ranged from diagnostically suggestive to informative. Negative LR− for 1000 Hz tympanometry and reflectance were at least diagnostically suggestive, while LR− values for MFT were mixed with half considered clinically uninformative and half considered diagnostically suggestive.

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SUMMARY

Current State of Knowledge

WAI tests have several positive characteristics that address needs for pediatric middle ear assessment. Maturational effects of the outer ear canal, which limit diagnostic accuracy of traditional tympanometry, are also present in the WAI data and are consistent with age-related anatomical changes in the developing outer and middle ear. Thus, WAI age-graded norms are essential to the successful clinical application of WAI measures, especially in the period from newborn to 1 year of age.

Ambient-pressure responses can be acquired in a few seconds, and studies thus far demonstrate good retest reliability, as discussed by Voss et al. (this issue, pp. 60S–64S). Careful monitoring of probe fit and acquisition of data while infants are in a quiet state appears to be critical for obtaining reliable WAI results. Wideband responses are highly sensitive to whether the probe is fully sealed in the ear canal, thus a real-time acoustic test of probe fit is needed to ensure adequate probe placement.

WAI shows potential use in screening protocols, as several studies have demonstrated significantly higher reflected energy in the mid-frequency range for infants who failed OAE screening than for those who passed OAE screening. Specifically, ears that refer on NHS have less absorbance above 1 kHz than ears that pass NHS. Ambient-pressure reflectance or absorbance may have sufficient accuracy to use in some hearing-screening applications, whereas pressurized recordings provide additional accuracy that may be appropriate for hearing-diagnostic applications. Wideband absorbance responses provide information on middle ear status that varies over the neonatal age range and is sensitive to middle ear status. Thus, a WAI-based test has good potential for use in neonatal screening tests for hearing loss.

WAI tests also show promise for diagnostic applications in infants and children. Lower absorbance has been shown for ears with CHL diagnosed by ABR testing. CHL in young infants can be detected well with WAI or tympanometry, using probe frequencies of 678 and 1000 Hz. Wideband absorbance can accurately identify CHL in newborns and infants. In addition, WAI is sensitive to MEE, and appears to be more accurate than 1000 Hz tympanometry, at least in some studies.

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Gaps in Literature and Future Research Directions

In NHS programs, WAI can assist in interpretation of failed hearing-screening results. Conclusions are limited because the true status of the middle ear and cochlea are not known for newborns and infants in studies that use OAE or tympanometry as the gold standard. However, infants who fail OAE screening appear to have results consistent with transient or permanent middle ear dysfunction, which is detected by WAI.

In infants and children, likelihood values for detection of MEE through surgical or otoscopic examination or CHL by WAI are high and similar, if not better, than results determined with tympanometry. Although results are promising, limited evidence from different types of pathologies in sufficient clinical populations restricts the conclusions that can be drawn regarding the diagnostic accuracy of WAI in infants and children. Additional investigations using stronger gold standards with more clearly defined pathologies are needed to determine which tools can most accurately predict middle ear status. Use of test-performance analyses, including sensitivity, specificity, ROC analyses, and effect sizes for ears with stronger reference standards are needed in future studies to advance our understanding of the diagnostic utility of WAI measures. Because the data available for analysis of ambient WAI contain a wealth of data points across the dimensions of frequency and absorption (or several other aspects of middle ear transfer of energy), as well as across the third dimension of ear-canal air pressure when tested tympanometrically, sophisticated analysis approaches are needed to determine those aspects of WAI that are most diagnostically relevant. Such aspects may be dependent on developmental changes and type of pathology. In infants and children, the most prevalent condition, OME, is the one that has received the most research thus far. Children with congenital middle ear anomalies, and older children and adolescents with pathologies such as cholesteatoma, ossicular erosion, and fixation are more rare, but would yield important diagnostic information if children with defined ear pathologies are included in future studies.

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