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.
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).
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.
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.
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.
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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