Identification of neonatal hearing impairment: ear-canal measurements of acoustic admittance and reflectance in neonates

Predictive Accuracy of Wideband Absorbance under Various Pressure Conditions in Identifying Infants with a Conductive Hearing Loss

OBJECTIVE

 The objectives of the study were to (i) evaluate the effectiveness of wideband absorbance (WBA) at ambient pressure (WBAamb), tympanic peak pressure (WBATPP), and 0 daPa (WBA0) to identify conductive hearing loss (CHL) in infants and (ii) compare the sensitivity and specificity of the three WBA tests with that of high-frequency tympanometry (HFT) and transient-evoked otoacoustic emissions (TEOAE).

METHOD

 A total of 31 ears with hearing thresholds no greater than 20 dB HL (reference group from 20 infants [mean age: 3.1 weeks]) and 47 ears with CHL from 31 infants (mean age: 3.4 weeks) were included in the study. Hearing threshold was determined using air-conduction tone-burst auditory brainstem response (TB-ABR) test, whereas CHL was determined using both air- and bone-conduction TB-ABR tests. HFT with a 1000-Hz probe tone, TEOAE, and WBA tests were conducted on all participants.

RESULTS

 WBAamb, WBATPP, and WBA0 of the CHL group were significantly lower than that of the reference group across a wide frequency range. Area under the receiver operating characteristic (AROC) curve for detecting CHL varied from 0.51 to 0.9 depending on the frequency. The highest AROC was obtained at 1.25 kHz for WBAamb (0.79), at 1.5 kHz for WBATPP (0.9) and at 1 kHz for WBA0 (0.80). The sensitivity and specificity were 0.98 and 0.45, respectively for HFT, and 1.0 and 0.6, respectively for TEOAE. In comparison, the WBA test had slightly lower sensitivity but higher specificity than the HFT and TEOAE tests.

CONCLUSION

 WBATPP at 1.5 kHz can identify CHL in infants as good as, if not more accurately than, WBAamb or WBA0. WBATPP test had good balance of high sensitivity and specificity compared with HFT and TEOAE. The three WBA tests are useful tools for identifying CHL in infants under 6 weeks of age.

The influence of tympanic-membrane orientation on acoustic ear-canal quantities: A finite-element analysis

Assuming plane waves, ear-canal acoustic quantities, collectively known as wideband acoustic immittance (WAI), are frequently used in research and in the clinic to assess the conductive status of the middle ear. Secondary applications include compensating for the ear-canal acoustics when delivering stimuli to the ear and measuring otoacoustic emissions. However, the ear canal is inherently non-uniform and terminated at an oblique angle by the conical-shaped tympanic membrane (TM), thus potentially confounding the ability of WAI quantities in characterizing the middle-ear status. This paper studies the isolated possible confounding effects of TM orientation and shape on characterizing the middle ear using WAI in human ears. That is, the non-uniform geometry of the ear canal is not considered except for that resulting from the TM orientation and shape. This is achieved using finite-element models of uniform ear canals terminated by both lumped-element and finite-element middle-ear models. In addition, the effects on stimulation and reverse-transmission quantities are investigated, including the physical significance of quantities seeking to approximate the sound pressure at the TM. The results show a relatively small effect of the TM orientation on WAI quantities, except for a distinct delay above 10 kHz, further affecting some stimulation and reverse-transmission quantities.

A reference for ear-canal absorbance based on semi-anechoic waveguides

Wideband acoustic immittance (WAI), in particular, ear-canal absorbance, is a useful clinical tool for assessing the middle-ear status and diagnosing conductive hearing disorders. However, little evidence documents the measurement accuracy of WAI in human ears, and, because its clinical adoption is still in its infancy, no international standards exist to define appropriate requirements for commercial instrumentation. A challenge from a standardization point of view is the lack of an absorbance reference, i.e., an acoustic load similar to the adult ear canal with a known absorbance. This paper explores various approaches to providing such an acoustic load to quantify WAI measurement accuracy. The approaches considered here include standardized and inexpensive occluded-ear simulators, and a family of semi-anechoic waveguides with different step discontinuities in cross-sectional area. These semi-anechoic waveguides could be included in a future WAI standard. In addition, a means of monitoring the stability of WAI calibrations over time is proposed, utilizing a single inexpensive occluded-ear simulator.

Use of Wideband Acoustic Immittance in Neonates and Infants

With widespread agreement on the importance of early identification of hearing loss, universal newborn hearing screening (UNHS) has become the standard of care in several countries. Despite advancements in screening technology, UNHS and early hearing detection and intervention programs continue to be burdened by high referral rates of false-positive cases due to temporary obstruction of sound in the outer/middle ear at birth. A sensitive adjunct test of middle ear at the time of screening would aid in the interpretation of screening outcomes, minimize unnecessary rescreens, and prioritize referral to diagnostic assessment for infants with permanent congenital hearing loss. Determination of middle ear status is also an important aspect of diagnostic assessment in infants. Standard single-frequency tympanometry used to determine middle ear status in infants is neither efficient nor accurate in newborns and young infants. A growing body of research has demonstrated the utility of wideband acoustic immittance (WAI) testing in both screening and diagnostic settings. Wideband power absorbance (WBA), a WAI measure, has been shown to be more sensitive than tympanometry in the assessment of outer/middle ear function in newborns. Furthermore, age-graded norms also support successful application of WBA in young infants. Despite its merits, uptake of this technology is low among pediatric audiologists and hearing screening health workers. This report describes normative data, methods for assessment and interpretation of WBA, test-retest variations, and other factors pertinent to clinical use of WAI in newborns and infants. Clinical cases illustrate the use of WAI testing in newborn and infant hearing assessment.

The effects of cochlear implantation on middle ear function: A prospective study

OBJECTIVES

Although sound conduction mechanisms may influence by cochlear implantation (CI), it is not very clear whether, how, and to what extent these mechanisms may be influenced the pediatric population. Wideband tympanometry (WBT) is a sensitive tool to evaluate alternations in the middle ear mechanics in a wide frequency range. The current study aimed to explore CI's impacts on sound conduction across the middle ear cavity using WBT in pediatrics.

METHODS

In a prospective design, 35 unilaterally implanted children (<24 months of age) with normal temporal bone anatomy were included in this study. Traditional tympanometry (226-Hz) and WBT measures were compared for each child in the implanted and non-implanted ears preoperatively and three months postoperatively.

RESULTS

No significant changes in the "static acoustic admittance" and "peak pressure" parameters were observed between the pre-CI and post-CI conditions in the implanted and non-implanted ears in the 226-Hz tympanometry test. Wideband absorbance recordings before CI surgery exhibited a double-peaked pattern over a frequency range of 250 to 8000 Hz. The pre- and postoperative acoustic energy absorbance comparisons indicated a significantly reduced mid-frequency (1260 to 3175 Hz) and high-frequency (5040 to 8000 Hz) absorbance in the implanted ears. However, our results indicated no significant differences in sound absorbance between the pre- and postoperative conditions in non-implanted ears.

CONCLUSION

Our findings suggested that WBT is a more sensitive method than traditional tympanometry for monitoring the mechanical status of the middle ear after cochlear implantation in pediatrics. Cochlear implantation in young children can significantly reduce mid- and high-frequency acoustic absorbance measured by WBT.

A reciprocity method for validating acoustic ear-probe source calibrations

Measurements of wideband acoustic immittance (WAI) rely on the calibration of an ear probe to obtain its acoustic source parameters. The clinical use of WAI and instruments offering the functionality are steadily growing, however, no international standard exists to ensure a certain reliability of the hardware and methods underlying such measurements. This paper describes a reciprocity method that can evaluate the accuracy of and identify errors in ear-probe source calibrations. By placing the ear probes of two calibrated WAI instruments face-to-face at opposite ends of a short waveguide, the source parameters of each ear probe can be measured using the opposite calibrated ear probe. The calibrated and measured source parameters of each ear probe can then be compared directly, and the influence of possible calibration errors on WAI measurements may be approximated. In various exemplary ear-probe calibrations presented here, the reciprocity method accurately identifies errors that would otherwise remain undetected and result in measurement errors in real ears. The method is likely unsuitable for routine calibration of WAI instruments but may be considered for conformance testing as part of a potential future WAI standard.

Wideband absorbance for the assessment of pressure equalizing tubes patency in children

OBJECTIVES

To analyze the feasibility of using wideband absorbance to verify the patency of pressure equalizing tubes (PETs) in clinical practice and to present the response pattern of this measure for ears with patent PET.

METHODS

This observational case-control type study evaluated 48 ears of 30 children with severe or profound hearing loss, aged 10-44 months, of both sexes. The subjects were subdivided into two groups: 24 ears with Sheppard type PET (experimental group - EG) and 24 ears with normal middle ear (control group - CG), paired with the EG, according to age, sex, and ear evaluated. To obtain the wideband absorbance, a Middle-Ear Power Analyzer, version 5.0 (Mimosa Acoustics), was used, and absorbance values for pure tone and chirp stimuli were analyzed.

RESULTS

There was no influence of ear (right or left) on the measurements obtained. The EG showed higher absorbance values at low frequencies. Although the two stimuli made it possible to identify the difference in acoustic transfer function between the groups studied, compared to pure tone, the chirp stimulus allowed identification of differences in a higher number of frequencies.

CONCLUSIONS

Ears with a patent PET present an acoustic transfer pattern that differs from that obtained for normal middle ears, with a higher absorbance at low frequencies. Both pure tone and chirp stimuli can be used to identify such differences, nevertheless, the use of chirp stimulus is recommended, since it allows differentiation over a wider frequency range.

A systematic study on effects of calibration-waveguide geometry and least-squares formulation on ear-probe source calibrations

Measuring ear-canal absorbance and compensating for effects of the ear-canal acoustics on otoacoustic-emission measurements using an ear probe rely on accurately determining its acoustic source parameters. Using pressure measurements made in several rigid waveguides and models of their input impedances, a conventional calibration method estimates the ear-probe Thévenin-equivalent source parameters via a least-squares fit to an over-determined system of equations. Such a calibration procedure involves critical considerations on the geometry and number of utilized calibration waveguides. This paper studies the effects of calibration-waveguide geometry on achieving accurate ear-probe calibrations and measurements by systematically varying the lengths, length ratios, radii, and number of waveguides. For calibration-waveguide lengths in the range of 10-60 mm, accurate calibrations were generally obtained with absorbance measurement errors of approximately 0.02. Longer waveguides resulted in calibration errors, mainly due to coincident resonance frequencies among waveguides in the presence of mismatches between their assumed and actual geometries. The accuracy of calibrations was independent of the calibration-waveguide radius, except for an increased sensitivity of wider waveguides to noise. Finally, it is demonstrated how reformulating the over-determined system of equations to return the least-squares reflectance source parameters substantially reduces calibration and measurement errors.

Wideband Tympanometry Findings in School-aged Children: Effects of Age, Gender, Ear Laterality, and Ethnicity

OBJECTIVES

Wideband tympanometry (WBT) measures middle-ear function across a range of frequencies (250 to 8000 Hz) while the ear-canal pressure is varied from +200 to -300 daPa. WBT is a suitable test to evaluate middle-ear function in children, but there is a lack of age-, ear-, gender-, or ethnicity-specific data throughout the literature. The purpose of this study was to investigate the effects of age, ear laterality, gender, and ethnicity on the WBT data retrieved from children aged 4 to 13 years determined to have normal middle-ear function.

DESIGN

Data were collected cross-sectionally from 924 children aged 4 to 13 years who passed a test battery consisting of 226-Hz tympanometry, ipsilateral acoustic stapedial reflexes, and pure-tone screening, and without significant history of middle-ear dysfunction. Participants were grouped according to their age: 4 to 6 years, 7 to 9 years, 10 to 13 years. Wideband absorbance values were extracted at 0 daPa (WBA0) and tympanometric peak pressure (WBATPP).

RESULTS

The effects of age, frequency, and pressure (WBA0 versus WBATPP) were statistically significant. There were significant differences between WBA0 and WBATPP for all age groups such that WBA0 had lower absorbance at low frequencies (250 to 1600 Hz) and greater absorbance at mid to high frequencies (2500 to 8000 Hz). Statistically significant effects of age were present for WBA0 and WBATPP such that absorbance generally increased with age from 250 to 1250 Hz and decreased with age from 2000 to 5000 Hz. There were no significant main effects of gender, ear, or ethnicity.

CONCLUSIONS

Gender-, ear-, and ethnicity-specific clinical WBA0 and WBATPP norms are not required for diagnostic purposes; however, age-specific norms may be necessary. Age-related changes in middle-ear function were observed across WBA0 and WBATPP. The data presented in this study are a suitable clinical reference for evaluating the outer- and middle-ear function of school-aged children.

On causality and aural impulse responses synthesized using the inverse discrete Fourier transform

Causality is a fundamental property of physical systems and dictates that a time impulse response characterizing any causal system must be one-sided. However, when synthesized using the inverse discrete Fourier transform (IDFT) of a corresponding band-limited numerical frequency transfer function, several papers have reported two-sided IDFT impulse responses of ear-canal reflectance and ear-probe source parameters. Judging from the literature on ear-canal reflectance, the significance and source of these seemingly non-physical negative-time components appear largely unclear. This paper summarizes and clarifies different sources of negative-time components through ideal and practical examples and illustrates the implications of constraining aural IDFT impulse responses to be one-sided. Two-sided IDFT impulse responses, derived from frequency-domain measurements of physical systems, normally occur due to the two-sided properties of the discrete Fourier transform. Still, reflectance IDFT impulse responses may serve a number of practical and diagnostic purposes.

Refining Measurements of Power Absorbance in Newborns: Probe Fit and Intrasubject Variability

OBJECTIVES

Because unresolved debris in the ear canal or middle ear of newborns may produce high false positive rates on hearing screening tests, it has been suggested that an outer/middle ear measure can be included at the time of hearing screening. A potential measure is power absorbance (absorbance), which indicates the proportion of power in a broadband acoustic stimulus that is absorbed through the outer/middle ear. Although absorbance is sensitive to outer/middle dysfunction at birth, there is large variability that limits its accuracy. Acoustic leaks caused by poor probe fitting further exacerbate this issue. The objectives of this work were to: (1) develop criteria to indicate whether a change in absorbance occurs in association with probe fit; (2) describe the variability in absorbance due to poor fitting; and (3) evaluate test-retest variability with probe reinsertions, excluding poor fits.

DESIGN

An observational cross-sectional design was used to evaluate changes in absorbance due to probe fit and probe reinsertion. Repeated measurements were recorded in 50 newborns (98 ears) who passed TEOAE screenings and were <48 hours of age. One absorbance measurement was chosen as the baseline that served as a best-fit reference in each ear. Changes in absorbance, called absorbance probe-fit Δ, were calculated relative to the baseline in each ear. Correlations were assessed between the absorbance probe-fit Δ and low-frequency absorbance, impedance magnitude, impedance phase, and equivalent volume, to determine which measures predicted poor fits. Criteria were derived from the strongest of these correlations and their performance was analyzed. Next, measurements with poor/leaky fits were identified, and the changes in absorbance that they introduced were analyzed. Excluding the poor fits, test-retest differences in absorbance, called reinsertion Δ, were determined. Variability was assessed using the SDs associated with absorbance, absorbance probe-fit Δ, and reinsertion Δ.

RESULTS

Based on the analysis of 12 moderate-strong correlations, the following criteria were adopted to identify measurements with poor fits: (1) impedance phase-based criterion (500 to 1000 Hz) > -0.11 cycles and (2) absorbance-based criterion (250 to 1000 Hz) > 0.58. Poor-fit measurements introduced statistically significant increases in absorbance up to 0.1 for 1000 to 6000 Hz, and up to 0.4 for frequencies <1000 Hz. Reinsertion Δ were ≤0.02, and were significant for 500 to 5000 Hz. The SDs of absorbance probe-fit Δ were greatest and similar to overall absorbance SD in the low frequencies. Separately, the SDs of reinsertion Δ were also greatest and similar to low-frequency absorbance SD.

CONCLUSIONS

Poor probe fits introduced the greatest inflation in absorbance for frequencies < 500 Hz, and a smaller but significant inflation for higher frequencies, consistent with controlled experiments on acoustic leaks in adults. Importantly, inflation of absorbance in diagnostically sensitive 1000 to 2000 Hz may impact its clinical performance. Test-retest with probe reinsertion contributed significantly to absorbance variability, especially in the low frequencies, consistent with reports in adults, even though changes were smaller than those associated with poor probe fit. The results indicate that variability in absorbance was reduced by minimizing acoustic leaks. Pending further validation, the probe-fit criteria developed in this work can be recommended to ensure proper probe fit.

Validation of a Bilateral Simultaneous Computer-Based Tympanometer

Purpose This study aimed to investigate the accuracy of bilateral simultaneous tympanometric measurements using a tympanometer with two pneumatic systems inside circumaural ear cups. Method Fifty-two adults (104 ears), with a mean age of 32 years (SD = 12.39, range: 18-60 years) were included in this study. A within-subject repeated-measures design was used to compare tympanometric measurements yielded with the investigational device in unilateral and bilateral simultaneous conditions compared with an industry-standard tympanometer. Results No significant bias (p > .05) was found between the mean of the differences of tympanometric measurements yielded by the two devices, except for a significant bias (p < .05) of the mean of the differences for ear canal volume measurements (0.05 cm³). The Bland-Altman plots showed overall good agreement between the tympanometric measurements between the two instruments. In all 104 ears, the tympanogram types of the KUDUwave TMP were compared with the reference device. The results were highly comparable with a sensitivity and specificity of 100% (95% CI [86.8%, 100%]) and 92.3% (95% CI [84.0%, 97.1%]), respectively. Conclusions The investigational device is a suitable instrument for unilateral or bilateral simultaneous tympanometric measurements in adults and demonstrates the potential of decentralized and accessible tympanometry services.

Reproducing ear-canal reflectance using two measurement techniques in adult ears

Clinical diagnostic applications of ear-canal reflectance have been researched extensively in the literature, however, the measurement uncertainty associated with the conventional measurement technique using an insert ear probe is unknown in human ear canals. Ear-canal reflectance measured using an ear probe is affected by multiple sources of error, including incorrect estimates of the ear-canal cross-sectional area and oblique ear-probe insertions. In this paper, ear-canal reflectance measurements are reproduced in an occluded-ear simulator and in 54 adult ear canals using two different measurement techniques: a conventional ear probe and a two-microphone probe that enables the separation of reverse- and forward-propagating plane waves. The two-microphone probe is inserted directly into test subjects' ear canals, and the two-microphone method is distinguished by not requiring the ear-canal cross-sectional area to calculate the ear-canal reflectance. The results show a reasonable agreement between the two measurement techniques. The paper further examines the influence of oblique ear-probe insertions and the compensation for such oblique insertions, which results in an improved agreement between the two measurement techniques.

Diagnosing Conductive Dysfunction in Infants Using Wideband Acoustic Immittance: Validation and Development of Predictive Models

Purpose The aims of this study were (a) to validate the wideband acoustic immittance (WAI) model developed by Myers et al. (2018a) in a new sample of neonates and (b) to develop a prediction model for diagnosing middle ear dysfunction in infants aged 6-18 months using wideband absorbance, controlling for the effect of age. Method Tympanometry, distortion product otoacoustic emissions, and WAI were measured in 124 neonates and longitudinally in 357 infants at 6, 12, and 18 months of age. Results of tympanometry and distortion product otoacoustic emissions were used to assess middle ear function of each infant. For the first study, results from the neonates were applied to the diagnostic WAI model developed by Myers et al. (2018a). For the second study, a prediction model was developed using results from the 6- to 18-month-old infants. Results from 1 ear of infants in each age group (6, 12, and 18 months) were used to develop the model. The amount of bias (overfitting) was estimated with bootstrap resampling and by applying the model to the opposite ears (the test sample). Performance was assessed using measures of discrimination (c-index) and calibration (calibration curves). Results For the validation study, the Myers et al. (2018a) model was well calibrated and had a c-index of 0.837 when applied to a new sample of neonates. Although this was lower than the apparent performance c-index of 0.876 reported by Myers et al., it was close to the bias-corrected estimate of 0.845. The model developed for 6- to 18-month-old infants had satisfactory calibration and apparent, bias-corrected, and test sample c-index of 0.884, 0.867, and 0.887, respectively. Conclusions The validated and developed models may be clinically useful, and further research validating, updating, and assessing the clinical impact of the models is warranted.

On the calculation of reflectance in non-uniform ear canals

Ear-canal reflectance is useful for quantifying the conductive status of the middle ear because it can be measured non-invasively at a distance from the tympanic membrane. Deriving the ear-canal reflectance requires decomposing the total acoustic pressure into its forward- and reverse-propagating components. This decomposition is conveniently achieved using formulas that involve the input and characteristic impedances of the ear canal. The characteristic impedance is defined as the ratio of sound pressure to volume flow of a propagating wave and, for uniform waveguides, the plane-wave characteristic impedance is a real-valued constant. However, in non-uniform waveguides, the characteristic impedances are complex-valued quantities, depend on the direction of propagation, and more accurately characterize a propagating wave in a non-uniform ear canal. In this paper, relevant properties of the plane-wave and spherical-wave characteristic impedances are reviewed. In addition, the utility of the plane-wave and spherical-wave reflectances in representing the reflection occurring due to the middle ear, calibrating stimulus levels, and characterizing the emitted pressure in simulated non-uniform ear canals is investigated and compared.

A comparison of ear-canal-reflectance measurement methods in an ear simulator

Ear-canal reflectance has been researched extensively for diagnosing conductive hearing disorders and compensating for the ear-canal acoustics in non-invasive measurements of the auditory system. Little emphasis, however, has been placed on assessing measurement accuracy and variability. In this paper, a number of ear-canal-reflectance measurement methods reported in the literature are utilized and compared. Measurement variation seems to arise chiefly from three factors: the residual ear-canal length, the ear-probe insertion angle, and the measurement frequency bandwidth. Calculation of the ear-canal reflectance from the measured ear-canal impedance requires estimating the ear-canal characteristic impedance in situ. The variability in ear-canal estimated characteristic impedance and reflectance due to these principal factors is assessed in an idealized controlled setup using a uniform occluded-ear simulator. In addition, the influence of this measurement variability on reflectance-based methods for calibrating stimulus levels is evaluated and, by operating the condenser microphone of the occluded-ear simulator as an electro-static speaker, the variability in estimating the emitted pressure from the ear is determined. The various measurement methods differ widely in their robustness to variations in the three principal factors influencing the accuracy and variability of ear-canal reflectance.

Longitudinal Development of Wideband Absorbance and Admittance Through Infancy

Purpose The aim of this article was to study the normal longitudinal development of wideband absorbance and admittance measures through infancy. Method Two hundred one infants who passed the newborn hearing screen (automated auditory brainstem response) were tested at birth and then followed up at approximately 6, 12, and 18 months of age. Most infants were of either White (86%) or Asian (11%) descent. At each test session, infants passed tympanometry and distortion product otoacoustic emission tests. High-frequency (1000-Hz) tympanometry was used at birth and 6 months of age, and low-frequency (226-Hz) tympanometry was used at 12 and 18 months of age. Wideband pressure reflectance was also measured at each session and analyzed in terms of absorbance, admittance at the probe tip, and admittance normalized for differences in ear canal area. Multilevel hierarchical models were fitted to the absorbance and admittance data to investigate for effects of age, ear side, gender, ethnicity, and frequency. Results There were considerable age effects on wideband absorbance and admittance measurements over the first 18 months of life. The most dramatic changes occurred between birth and 6 months of age, and there were significant differences between all age groups in the 3000- to 4000-Hz region. There were significant ethnicity effects that were substantial for certain combinations of ethnicity, age, and frequency (e.g., absorbance at 6000 Hz at 12 months of age). Conclusion There are large developmental effects on wideband absorbance and admittance measures through infancy. For absorbance, we recommend separate reference data be used at birth, 6 months of age, and 12-18 months of age. For admittance (both normalized and at the probe tip), we advise using separate normative regions for each age group (neonates and 6, 12, and 18 months).

Compensating for oblique ear-probe insertions in ear-canal reflectance measurements

Measurements of the ear-canal reflectance using an ear probe require estimating the characteristic impedance of the ear canal in situ. However, an oblique insertion of the ear probe into a uniform waveguide prevents accurately estimating its characteristic impedance using existing time-domain methods. This is caused by the non-uniformity immediately in front of the ear probe when inserted at an oblique angle, resembling a short horn loading, and introduces errors into the ear-canal reflectance. This paper gives an overview of the influence of oblique ear-probe insertions and shows how they can be detected and quantified by estimating the characteristic impedance using multiple truncation frequencies, i.e., limiting the utilized frequency range. Additionally, a method is proposed to compensate for the effects on reflectance of an oblique ear-probe insertion into a uniform waveguide. The incident impedance of the horn loading is estimated, i.e., were the uniform waveguide anechoic, which replaces the characteristic impedance when calculating reflectance. The method can compensate for an oblique ear-probe insertion into a uniform occluded-ear simulator and decrease the dependency of reflectance on insertion depth in an ear canal. However, more research is required to further assess the method in ear canals.

Optimizing Clinical Interpretation of Distortion Product Otoacoustic Emissions in Infants

OBJECTIVES

The purpose of this study was to analyze distortion product otoacoustic emission (DPOAE) level and signal to noise ratio in a group of infants from birth to 4 months of age to optimize prediction of hearing status. DPOAEs from infants with normal hearing (NH) and hearing loss (HL) were used to predict the presence of conductive HL (CHL), sensorineural HL (SNHL), and mixed HL (MHL). Wideband ambient absorbance was also measured and compared among the HL types.

DESIGN

This is a prospective, longitudinal study of 279 infants with verified NH and HL, including conductive, sensorineural, and mixed types that were enrolled from a well-baby nursery and two neonatal intensive care units in Cincinnati, Ohio. At approximately 1 month of age, DPOAEs (1-8 kHz), wideband absorbance (0.25-8 kHz), and air and bone conduction diagnostic tone burst auditory brainstem response (0.5-4 kHz) thresholds were measured. Hearing status was verified at approximately 9 months of age with visual reinforcement audiometry (0.5-4 kHz). Auditory brainstem response air conduction thresholds were used to assign infants to an NH or HL group, and the efficacy of DPOAE data to classify ears as NH or HL was analyzed using receiver operating characteristic (ROC) curves. Two summary statistics of the ROC curve were calculated: the area under the ROC curve and the point of symmetry on the curve at which the sensitivity and specificity were equal. DPOAE level and signal to noise ratio cutoff values were defined at each frequency as the symmetry point on their respective ROC curve, and DPOAE results were combined across frequency in a multifrequency analysis to predict the presence of HL.

RESULTS

Single-frequency test performance of DPOAEs was best at mid to high frequencies (3-8 kHz) with intermediate performance at 1.5 and 2 kHz and chance performance at 1 kHz. Infants with a conductive component to their HL (CHL and MHL combined) displayed significantly lower ambient absorbance values than the NH group. No differences in ambient absorbance were found between the NH and SNHL groups. Multifrequency analysis resulted in the best prediction of HL for the SNHL/MHL group with poorer sensitivity values when infants with CHL were included.

CONCLUSIONS

Clinical interpretation of DPOAEs in infants can be improved by using age-appropriate normative ranges and optimized cutoff values. DPOAE interpretation is most predictive at higher F2 test frequencies in young infants (2-8 kHz) due to poor test performance at 1 to 1.5 kHz. Multifrequency rules can be used to improve sensitivity while balancing specificity. Last, a sensitive middle ear measure such as wideband absorbance should be included in the test battery to assess possibility of a conductive component to the HL.

Normative Wideband Acoustic Immittance Measurements in Caucasian and Aboriginal Children

Purpose The aims of this study were to develop normative data for wideband acoustic immittance (WAI) measures in Caucasian and Australian Aboriginal children and compare absorbance measured at 0 daPa (WBA0) and tympanometric peak pressure (TPP; WBATPP) between the 2 groups of children. Additional WAI measures included resonance frequency, equivalent ear canal volume, TPP, admittance magnitude (YM), and phase angle (YA). Method A total of 171 ears from 171 Caucasian children and 87 ears from 87 Aboriginal children who passed a test battery consisting of 226-Hz tympanometry, transient evoked otoacoustic emissions, and pure tone audiometry were included in the study. WAI measures were obtained under pressurized conditions using wideband tympanometry. Data for WBA0, WBATPP, YM, and YA were averaged in one-third octave frequencies from 0.25 to 8 kHz. Results There was no significant ear effect on all of the 7 measures for both groups of children. Similarly, there was no significant gender effect on all measures except for WBATPP in Aboriginal children. Aboriginal boys had significantly higher WBATPP than girls at 1.5 and 2 kHz. A significant effect of ethnicity was also noted for WBATPP at 3, 4, and 8 kHz, with Caucasian children demonstrating higher WBATPP than Aboriginal children. However, the effect size and observed power of the analyses were small for both effects. Conclusion This study developed normative data for 7 WAI measures, namely, WBA0, WBATPP, TPP, Veq, RF, YM, and YA, for Caucasian and Aboriginal children. In view of the high similarity of the normative data between Caucasian and Aboriginal children, it was concluded that separate ethnic-specific norms are not required for diagnostic purposes.

Wideband acoustic absorbance in children with Down syndrome

INTRODUCTION

Tympanometry is currently the most frequently used tool for assessing the status of the middle ear, commonly assessed using a single 226Hz tone. However, the use of the Acoustic Immittance Measures with a wideband stimulus is a promising high-resolution evaluation, especially in individuals known to have middle ear alterations, such as Down syndrome patients.

OBJECTIVE

The aim of this study was to analyze the acoustic absorbance measurements in children with Down syndrome.

METHODS

Cross-sectional study, approved by the institution's ethics committee. Data were collected from 30 children, with a mean age of 8.4 years, 15 with Down syndrome (DS-study group) and 15 children with typical development and no hearing complaints (control group). Energy absorbance was measured at frequencies of 226-8000Hz at ambient pressure and at peak pressure as a function of frequency using TITAN equipment. Statistical analysis was performed using the established level of statistical significance of 5%.

RESULTS

With the 226Hz probe tone, 30 ears of the control group and 22 of the study group exhibited Type A tympanograms, whereas Type B was observed in eight children in the study group. The mean acoustic absorbance ratio of the study group was lower than that of the control group at frequencies centered at 2520Hz (p=0.008) for those with normal tympanometry results, and 226-4000Hz (p<0.03) for those with a Type B tympanometry curve.

CONCLUSION

The low energy absorption in the presence of normal tympanograms in children with Down syndrome may suggest middle ear abnormalities.

Acoustic Reflex Testing in Neonatal Hearing Screening and Subsequent Audiological Evaluation

PURPOSE

The aims of the study were to examine the acoustic reflex screening and threshold in healthy neonates and those at risk of hearing loss and to determine the effect of birth weight and gestational age on acoustic stapedial reflex (ASR).

METHOD

We assessed 18 healthy neonates (Group I) and 16 with at least 1 risk factor for hearing loss (Group II); all of them passed the transient evoked otoacoustic emission test that assessed neonatal hearing. The test battery included an acoustic reflex screening with activators of 0.5, 1, 2, and 4 kHz and broadband noise and an acoustic reflex threshold test with all of them, except for the broadband noise activator.

RESULTS

In the evaluated neonates, the main risk factors were the gestational age at birth and a low birth weight; hence, these were further analyzed. The lower the gestational age at birth and birth weight, the less likely that an acoustic reflex would be elicited by pure-tone activators. This effect was significant at the frequencies of 0.5, 1, and 2 kHz for gestational age at birth and at the frequencies of 1 and 2 kHz for birth weight. When the broadband noise stimulus was used, a response was elicited in all neonates in both groups. When the pure-tone stimulus was used, the Group II showed the highest acoustic reflex thresholds and the highest percentage of cases with an absent ASR. The ASR threshold varied from 50 to 100 dB HL in both groups. Group II presented higher mean ASR thresholds than Group I, this difference being significant at frequencies of 1, 2, and 4 kHz.

CONCLUSIONS

Birth weight and gestational age at birth were related to the elicitation of the acoustic reflex. Neonates with these risk factors for hearing impairment were less likely to exhibit the acoustic reflex and had higher thresholds.

Quantifying undesired parallel components in Thévenin-equivalent acoustic source parameters

The calibration of an ear probe to determine its Thévenin-equivalent acoustic source parameters facilitates the measurement of ear-canal impedance and reflectance. Existing calibration error metrics, used to evaluate the quality of a calibration, are unable to reveal undesired parallel components in the source parameters. Such parallel components can result from, e.g., a leak in the ear tip or improperly accounting for evanescent modes, and introduce errors into subsequent measurements of impedance and reflectance. This paper proposes a set of additional error metrics that are capable of detecting such parallel components by examining the causality of the source admittance in the frequency domain and estimating the source pressure in the time domain. The proposed and existing error metrics are applied to four different calibrations using two existing calibration methods, representing typical use cases and introducing deliberate parallel components. The results demonstrate the capability of the proposed error metrics in identifying various undesired components in the source parameters that might otherwise go undetected.

Current audiological diagnostics

Today's audiological functional diagnostics is based on a variety of hearing tests, whose large number takes account of the variety of malfunctions of a complex sensory organ system and the necessity to examine it in a differentiated manner and at any age of life. The objective is to identify nature and origin of the hearing loss and to quantify its extent as far as necessary to dispose of the information needed to initiate the adequate medical (conservative or operational) treatment or the provision with technical hearing aids or prostheses. Moreover, audiometry provides the basis for the assessment of impairment and handicap as well as for the calculation of the degree of disability. In the present overview, the current state of the method inventory available for practical use is described, starting from basic diagnostics over to complex special techniques. The presentation is systematically grouped in subjective procedures, based on psychoacoustic exploration, and objective methods, based on physical measurements: preliminary hearing tests, pure tone threshold, suprathreshold processing of sound intensity, directional hearing, speech understanding in quiet and in noise, dichotic hearing, tympanogram, acoustic reflex, otoacoustic emissions and auditory evoked potentials. Apart from a few still existing gaps, this method inventory covers the whole spectrum of all clinically relevant functional deficits of the auditory system.

Compensating for evanescent modes and estimating characteristic impedance in waveguide acoustic impedance measurements

The ear-canal acoustic impedance and reflectance are useful for assessing conductive hearing disorders and calibrating stimulus levels in situ. However, such probe-based measurements are affected by errors due to the presence of evanescent modes and incorrect estimates or assumptions regarding characteristic impedance. This paper proposes a method to compensate for evanescent modes in measurements of acoustic impedance, reflectance, and sound pressure in waveguides, as well as estimating the characteristic impedance immediately in front of the probe. This is achieved by adjusting the characteristic impedance and subtracting an acoustic inertance from the measured impedance such that the non-causality in the reflectance is minimized in the frequency domain using the Hilbert transform. The method is thus capable of estimating plane-wave quantities of the sought-for parameters by supplying only an arbitrary initial value for the characteristic impedance. From a comparison with a simulated waveguide, it is shown that this method can accurately estimate these quantities in a waveguide that is uniform at the position of the probe. Finally, it is demonstrated how evanescent modes, characteristic impedance, and the proposed methodology can affect the measured acoustic impedance and reflectance of an occluded-ear simulator.

Incorporating evanescent modes and flow losses into reference impedances in acoustic Thévenin calibration

This paper proposes an alternative approach to acoustic Thévenin calibration of an ear probe. An existing methodology derives the Thévenin-equivalent source parameters from the measured probe pressures in a number of short waveguides by solving an overdetermined system of equations. This existing methodology is affected by errors caused by evanescent modes when the waveguide model lengths are estimated. These errors introduce a parallel acoustic compliance into the source parameters. The proposed methodology takes into account evanescent modes and flow losses in the transition between the probe tube and waveguides during calibration. This is achieved by positioning the probe tube, without an ear tip, flush with the input plane in waveguides of well-defined dimensions and utilizing the physical rather than estimated lengths to calculate the analytical waveguide models. Terms that model evanescent modes and flow losses are added to the plane-wave impedance and adjusted to minimize the calibration error. It is shown that this method can reduce the calibration error across a wide frequency range and remove the parallel compliance from the source parameters. This approach leads to an independence of the source parameters on the calibration waveguide radius, though subsequent impedance measurements are still affected by evanescent modes.

The Effect of Ethnicity on Wideband Absorbance of Neonates with Healthy Middle Ear Functions in Malaysia: A Preliminary Study

BACKGROUND AND OBJECTIVES

Although ethnicity effect on wideband absorbance (WBA) findings was evident for adults, its effect on neonates has not been established yet. This study aimed to investigate the influence of ethnicity on WBA measured at 0 daPa from neonates with healthy middle ear functions.

SUBJECTS AND METHODS

Participants were 99 normal, healthy, full-term newborn babies with chronological age between 11 and 128 hours of age (mean=46.73, standard deviation=26.36). A cross-sectional study design was used to measure WBA at 16 one-third octave frequency points from 99 neonates comprising of three ethnic groups: Malays (n=58), Chinese (n=13) and Indians (n=28). A total of 165 ears (83.3%) that passed a battery of tests involving distortion product otoacoustic emissions, 1 kHz tympanometry and acoustic stapedial reflex were further tested using WBA. Moreover, body size measurements were recorded from each participant.

RESULTS

The Malays and Indians neonates showed almost identical WBA response across the frequency range while the Chinese babies showed lower absorbance values between 1.25 kHz and 5 kHz. However, the differences observed in WBA between the three ethnic groups were not statistically significant (p=0.23). Additionally, there were no statistically significant difference in birth weight, height and head circumference among the three ethnic groups.

CONCLUSIONS

This study showed that Malays, Chinese and Indians neonates were not significantly different in their WBA responses. In conclusion, to apply for the ethnic-specific norms is not warranted when testing neonates from population constitute of these three ethnicities.

Pressurized Wideband Absorbance Findings in Healthy Neonates: A Preliminary Study

PURPOSE

The present study aimed to establish normative data for wideband absorbance (WBA) measured at tympanometric peak pressure (TPP) and 0 daPa and to assess the test-retest reliability of both measurements in healthy neonates.

METHOD

Participants of this cross-sectional study included 99 full-term neonates (165 ears) with mean chronological age of 46.7 hrs (SD = 26.3 hrs). Of the 99 neonates, 58 were Malay, 28 were Indian, and 13 were Chinese. The neonates who passed high-frequency (1 kHz) tympanometry, acoustic stapedial reflex, and distortion product otoacoustic emission screening tests were assessed using a pressurized WBA test (wideband tympanometry). To reduce the number of measurement points, the WBA responses were averaged to 16 one-third octave frequency bands from 0.25 to 8 kHz. A mixed-model analysis of variance was applied to the data to investigate the effects of frequency, ear, gender, and ethnicity on WBA. The analysis of variance was also used to compare between WBA measured at TPP and 0 daPa. An interclass correlation coefficient test was applied at each of the 16 frequency bands to measure the test-retest reliability of WBA at TPP and 0 daPa.

RESULTS

Both WBA measurements at TPP and 0 daPa exhibited a multipeaked pattern with 2 maxima at 1.25-1.6 kHz and 6.3 kHz and 2 minima at 0.5 and 4 kHz. The mean WBA measured at TPP was significantly higher than that measured at 0 daPa at 0.25, 0.4, 0.5, 1.25, and 1.6 kHz only. A normative data set was developed for absorbance at TPP and at 0 daPa. There was no significant effect of ethnicity, gender, and ear on both measurements of WBA. The test-retest reliability of WBA at TPP and 0 daPa was high with the interclass correlation coefficient ranging from 0.77 to 0.97 across the frequencies.

CONCLUSIONS

Normative data of WBA measured at TPP and 0 daPa for neonates were provided in the present study. Although WBA at TPP was slightly higher than the WBA measured at 0 daPa at some frequencies below 2 kHz, the WBA patterns of the 2 measurements were nearly identical. Moreover, the test-retest reliability of both WBA measurements was high.

Wideband acoustic immittance for assessing middle ear functioning for preterm neonates in the neonatal intensive care unit

BACKGROUND

The primary aim of newborn hearing screening is to detect permanent hearing loss. Because otoacoustic emissions (OAEs) and automated auditory brainstem response (AABR) are sensitive to hearing loss, they are often used as screening tools. On the other hand, false-positive results are most often because of transient outer- and middle ear conditions. Wideband acoustic immittance (WAI), which includes physical measures known as reflectance and absorbance, has shown potential for accurate assessment of middle ear function in young infants.

OBJECTIVE

The main objective of this study was to determine the feasibility of WAI as a diagnostic tool for assessing middle ear functioning in preterm neonates in the neonatal intensive care unit (NICU) designed for premature and ill neonates. A further objective was to indicate the difference between the reflectance values of tones and click stimuli.

METHOD

Fifty-six at-risk neonates (30 male and 26 female), with a mean age at testing of 35.6 weeks (range: 32-37 weeks) and a standard deviation of 1.6 from three private hospitals, who passed both the distortion product otoacoustic emission (DPOAE) and AABR tests, were evaluated prior to discharge from the NICU. Neonates who presented with abnormal DPOAE and AABR results were excluded from the study. WAI was measured by using chirp and tone stimuli. In addition to reflectance, the reflectance area index (RAI) values were calculated.

RESULTS

Both tone and chirp stimuli indicated high-power reflectance values below a frequency of 1.5 kHz. Median reflectance reached a minimum of 0.67 at 1 kHz - 2 kHz but increased to 0.7 below 1 kHz and 0.72 above 2 kHz for the tone stimuli. For chirp stimuli, the median reflectance reached a minimum of 0.51 at 1 kHz - 2 kHz but increased to 0.68 below 1 kHz and decreased to 0.5 above 2 kHz. A comparison between the present study and previous studies on WAI indicated a substantial variability across all frequency ranges.

CONCLUSION

These WAI measurements conducted on at-risk preterm NICU neonates (mean age at testing: 35.6 weeks, range: 32-37 weeks) identified WAI patterns not previously reported in the literature. High reflective values were obtained across all frequency ranges. The age of the neonates when tested might have influenced the results. The neonates included in the present study were very young preterm neonates compared to the ages of neonates in previous studies. WAI measured in at-risk preterm neonates in the NICU was variable with environmental and internal noise influences. Transient conditions affecting the sound-conduction pathway might have influenced the results. Additional research is required to investigate WAI testing in ears with and without middle ear dysfunction. The findings of the current study imply that in preterm neonates it was not possible to determine the feasibility of WAI as a diagnostic tool to differentiate between ears with and without middle ear pathology.

Normative Study of Wideband Acoustic Immittance Measures in Newborn Infants

OBJECTIVE

The purpose of this study was to describe normative aspects of wideband acoustic immittance (WAI) measures obtained from healthy White neonates.

METHOD

In this cross-sectional study, wideband absorbance (WBA), admittance magnitude, and admittance phase were measured under ambient pressure condition in 326 ears from 203 neonates (M age = 45.9 hr) who passed a battery of tests, including automated auditory brainstem response, high-frequency tympanometry, and distortion product otoacoustic emissions.

RESULTS

Normative WBA data were in agreement with most previous studies. Normative data for both WBA and admittance magnitude revealed double-peaked patterns with the 1st peak at 1.25-2 kHz and the 2nd peak at 5-8 kHz, while normative admittance phase data showed 2 peaks at 0.8 and 4 kHz. There were no significant differences between ears or gender for the 3 WAI measures. Standard deviations for all 3 measures were highest at frequencies above 4 kHz.

CONCLUSIONS

The 3 WAI measures between 1 kHz and 4 kHz may provide the most stable response of the outer and middle ear. WAI measures at frequencies above 4 kHz were more variable. The normative data established in the present study may serve as a reference for evaluating outer and middle ear function in neonates.

Acoustic absorbance measurements in neonates exposed to smoking during pregnancy

OBJECTIVE

To analyze acoustic absorbance using wideband tympanometry in neonates exposed to passive smoking during pregnancy.

METHOD

A study comprising 54 neonates in the control group (CG - unexposed) and 19 in the study group (SG - exposed) was carried out. Subjects were submitted to the wideband tympanometry test and subsequent analysis of absorbance of 17 frequencies.

RESULT

Low frequencies had a lower level of absorbance compared to high frequencies for both ambient and peak pressures, with no difference between the groups.

CONCLUSION

No effect of passive smoking on acoustic absorbance measurements in neonates was observed.

Sweep frequency impedance measures in young infants: developmental characteristics from birth to 6 months

OBJECTIVE

International Journal of Audiology To study the developmental characteristics of sweep frequency impedance (SFI) measures in healthy infants from birth to 6 months.

DESIGN

All infants were assessed using high-frequency tympanometry (HFT), distortion product otoacoustic emission (DPOAE) and SFI tests. SFI measures consisted of measurement of resonance frequency (RF) and mobility (ΔSPL) of the outer and middle ear. A mixed model analysis of variance was applied to the SFI data to examine the effect of age on RF and ΔSPL.

STUDY SAMPLE

Study included 117 ears from 83 infants of different age groups from birth to 6 months.

RESULTS

The mean RF of the outer ear increased from 279 Hz at birth to 545 Hz at 4 months, whereas mean ΔSPL of the outer ear decreased from 7.9 dB at birth to 3.7 dB at 4 months of age. In contrast, the mean RF and ΔSPL of the middle ear did not change significantly with age up to 6 months.

CONCLUSIONS

Developmental characteristics should be considered when evaluating the function of the outer and middle ear of young infants (≤6 months) using the SFI. The preliminary normative SFI data established in this study may be used to assist with the evaluation.

The calibration of a prototype occluded ear simulator designed for neonatal hearing assessment applications

An innovative family of ear simulators has been conceived for the calibration and traceability of audiometric equipment. Each device within the family has been designed for a particular key age group, covering neonates through to adults. The age-specific ear simulators are intended to improve the quality of hearing assessment measurements for all test subject age groups, and will be proposed as the next generation of standardised ear simulators for audiometric applications. The family of ear simulators shares a common design and modeling approach, and the first prototype devices for neonatal applications have been manufactured. The objectives of this study were to develop calibration methods, verify conformance to the design goals, demonstrate that the device is capable of being calibrated reliably, and show that its performance is ultimately suitable for international standardisation and eventual adoption into clinical practices. Four national measurement institutes took part in a round-robin calibration comparison and an analysis of the results showed that these objectives were achieved.

Wideband reflectance measurements in newborns: Relationship to otoscopic findings

OBJECTIVES

Newborn hearing screening includes testing with otoacoustic emissions and the auditory brainstem response. Unfortunately, both tests are affected by the presence of material in the ear canal and middle ear such as vernix, meconium, and amniotic fluid. The objective of this study was to determine to what extent occlusion of the ear canal as seen on otoscopy affects wideband energy reflectance measurements in newborns. A secondary objective was to obtain additional normative wideband reflectance data in newborns.

METHODS

Newborns from a well-baby nursery were enrolled. Wideband energy reflectance measurements and otoscopy were done immediately after the hearing screening. Occlusion of the ear canal as seen on otoscopy was described on a scale of 0-100%.

RESULTS

A total of 156 babies were enrolled (mean age = 25 hours). A statistically significant difference in the reflectance at ambient pressure was found between the 0-70% and 80-100% occlusion groups. There was no significant difference in reflectance between the right and the left ears. The median reflectance pattern generally followed that of previous studies but in certain frequency regions the present reflectance values were higher.

CONCLUSION

A significant increase in reflectance occurs when 70%-80% of the ear-canal diameter is occluded. Taking otoscopy findings into account may improve the interpretation of reflectance measurements. However, further studies are required to better establish the relationship between canal occlusion and reflectance.

Effects of ear canal static pressure on the dynamic behaviour of outer and middle ear in newborns

OBJECTIVE

The present study investigated the effect of ear canal pressure on the dynamic behaviour of the outer and middle ear in newborns with and without a conductive condition using the sweep frequency impedance (SFI) technology.

METHODS

A test battery consisting of automated auditory brainstem response (AABR), transient evoked otoacoustic emission (TEOAE) and 1000-Hz tympanometry (HFT) was performed on 122 ears of 86 healthy newborns and 10 ears of 10 newborns with a conductive condition (failed TEOAE and HFT). The dynamic behaviour of the outer and middle ear, when the pressure applied to the ear canal was varied from 200 to -200daPa, was evaluated in terms of the sound pressure level (SPL) in the ear canal, resonance frequency (RF) and displacement (ΔSPL).

RESULTS

Application of either a positive or negative static pressure to the ear canal of healthy newborns increased the resonance frequency of the outer (RF1) and middle ear (RF2), but decreased the displacements of the outer (ΔSPL1) and middle ear (ΔSPL2). Positive static pressures resulted in lower SPL while negative static pressures resulted in higher SPL than that at ambient pressure (0daPa). At -200daPa, more than 90% of ears showed signs of collapsed ear canal. The dynamic behaviour under various positive and negative static pressures for newborn ears with a conductive condition indicated similar pattern of SPL, RF1 and ΔSPL1 responses for the outer ear as per healthy ears, but abnormal responses for the middle ear.

CONCLUSIONS

While both positive and negative pressures applied to the ear canal have the same effect of stiffening the outer and middle ear, negative pressure of up to -200daPa resulted in more than 90% of ears with a collapsed ear canal. The results of the present study do not only offer useful clinical information for differentiating healthy ears from ears with a conductive condition, but also provide information on the maturation aspects of the outer and middle ear in newborns.

Longitudinal development of wideband reflectance tympanometry in normal and at-risk infants

PURPOSE

The goals of this study were to measure normal characteristics of ambient and tympanometric wideband acoustic reflectance, which was parameterized by absorbance and group delay, in newborns cared for in well-baby and Neonatal Intensive Care Unit (NICU) nurseries, and to characterize the normal development of reflectance over the first year after birth in a group of infants with clinically normal hearing status followed longitudinally from birth to one year of age.

METHODS

Infants were recruited from a well-baby and NICU nursery, passed newborn otoacoustic emissions (OAE) and automated auditory brainstem response (ABR) tests as well as follow-up diagnostic ABR and audiometry. They were tested longitudinally for up to one year using a wideband middle ear acoustic test battery consisting of tympanometry and ambient-pressure tests. Results were analyzed for ambient reflectance across frequency and tympanometric reflectance across frequency and pressure.

RESULTS

Wideband absorbance and group delay showed large effects of age in the first 6 months. Immature absorbance and group delay patterns were apparent in the low frequencies at birth and one month, but changed substantially to a more adult-like pattern by age 6 months for both ambient and tympanometric variables. Area and length of the ear canal estimated acoustically increased up to age 1 year. Effects of race (African American and others compared to Caucasian) were found in combination with age effects. Mean and confidence intervals are provided for use as a normative longitudinal database for newborns and infants up to one year of age, for both well-baby and NICU infants.

Reflectance measurement validation using acoustic horns

Variability in wideband acoustic reflectance (and absorbance) measurements adversely affects the clinical utility of reflectance for diagnosis of middle-ear disorders. A reflectance standard would encourage consistency across different measurement systems and help identify calibration related issues. Theoretical equations exist for the reflectance of finite-length exponential, conical, and parabolic acoustic horns. Reflectance measurements were repeatedly made in each of these three horn shapes and the results were compared to the corresponding theoretical reflectance. A method is described of adjusting acoustic impedance measurements to compensate for spreading of the wave front that propagates from the small diameter sound port of the probe to the larger diameter of the acoustic cavity. Agreement between measured and theoretical reflectance was less than 1 dB at most frequencies in the range from 0.2 to 10 kHz. Pearson correlation coefficients were greater than 0.95 between measured and theoretical time-domain reflectance within the flare region of the horns. The agreement suggests that the distributed reflectance of acoustic horns may be useful for validating reflectance measurements made in human ear canals; however, refinements to reflectance measurement methods may still be needed.

Power reflectance testing in newborns and infants

Introduction

Auditory screening in newborns allows for detection of hearing problems early in life. However, middle ear diseases can make the diagnosis more difficult.

Objective

To evaluate the power reflectance test as an indicator of the middle ear disease and to compare it to tympanometry.

Methods

Case study evaluating 105 newborns and infants who participated in the audiology screening in 2013. The following exams were performed: transient otoacoustic emissions, power reflectance, and tympanometry.

Results

In the optoacoustic emission evaluation, approximately 95% of the subjects passed the test. The specificity of power reflectance in all frequencies studied ranged from 75.3% to 95.9%, and that of tympanometry at 1000 Hz ranged from 83% to 87.2%; there was agreement among these exams.

Conclusion

The outcome of power reflectance tests at 2000 Hz and 3000 Hz showed a correlation with tympanometry and otoacoustic emissions, and these were the most appropriate frequencies to determine middle ear disease through power reflectance measurement. It was also observed that values of power reflectance above reference levels suggested the presence of fluid in the middle ear, and thus a conductive hearing loss.

Air-leak effects on ear-canal acoustic absorbance

OBJECTIVE

Accurate ear-canal acoustic measurements, such as wideband acoustic admittance, absorbance, and otoacoustic emissions, require that the measurement probe be tightly sealed in the ear canal. Air leaks can compromise the validity of the measurements, interfere with calibrations, and increase variability. There are no established procedures for determining the presence of air leaks or criteria for what size leak would affect the accuracy of ear-canal acoustic measurements. The purpose of this study was to determine ways to quantify the effects of air leaks and to develop objective criteria to detect their presence.

DESIGN

Air leaks were simulated by modifying the foam tips that are used with the measurement probe through insertion of thin plastic tubing. To analyze the effect of air leaks, acoustic measurements were taken with both modified and unmodified foam tips in brass-tube cavities and human ear canals. Measurements were initially made in cavities to determine the range of critical leaks. Subsequently, data were collected in ears of 21 adults with normal hearing and normal middle-ear function. Four acoustic metrics were used for predicting the presence of air leaks and for quantifying these leaks: (1) low-frequency admittance phase (averaged over 0.1-0.2 kHz), (2) low-frequency absorbance, (3) the ratio of compliance volume to physical volume (CV/PV), and (4) the air-leak resonance frequency. The outcome variable in this analysis was the absorbance change (Δabsorbance), which was calculated in eight frequency bands.

RESULTS

The trends were similar for both the brass cavities and the ear canals. ΔAbsorbance generally increased with air-leak size and was largest for the lower frequency bands (0.1-0.2 and 0.2-0.5 kHz). Air-leak effects were observed in frequencies up to 10 kHz, but their effects above 1 kHz were unpredictable. These high-frequency air leaks were larger in brass cavities than in ear canals. Each of the four predictor variables exhibited consistent dependence on air-leak size. Low-frequency admittance phase and CV/PV decreased, while low-frequency absorbance and the air-leak resonance frequency increased.

CONCLUSION

The effect of air leaks can be significant when their equivalent diameter exceeds 0.01 in. The observed effects were greatest at low frequencies where air leaks caused absorbance to increase. Recommended criteria for detecting air leaks include the following: when the frequency range of interest extends as low as 0.1 kHz, low-frequency absorbance should be ≤0.20 and low-frequency admittance phase ≥61 degrees. For frequency ranges as low as 0.2 kHz, low-frequency absorbance should be ≤0.29 and low-frequency admittance phase ≥44 degrees.

Effect of contralateral stimulation on acoustic reflectance measurements

Introduction

Acoustic reflectance is an important tool in the assessment of middle ear afflictions, and the method is considered advantageous in relation to tympanometry. There has been a growing interest in the study of contralateral acoustic stimulation and its effect on the activation of the efferent auditory pathway. Studies have shown that the introduction of simultaneous stimulation in the contralateral ear generates alterations in auditory response patterns.

Objective

To investigate the influence of contralateral stimulation on acoustic reflectance measurements.

Methods

Case study of 30 subjects with normal hearing, of both genders, aged 18–30 years. The test and retest acoustic reflectance was conducted in the frequency range 200–6000 Hz. The procedure was repeated with the simultaneous presence of contralateral white noise at 30 dBNS.

Results

The analysis of the conditions of test, retest, and test with contralateral noise showed statistical difference at the frequency of 2 kHz (p = 0.011 and p = 0.002 in test and retest, respectively) in the right ear.

Conclusion

The activation of the auditory efferent pathways through contralateral acoustic stimulation produces alterations in response patterns of acoustic reflectance, increasing sound reflection and modifying middle ear acoustical energy transfer.

Characterization of spontaneous otoacoustic emissions in full-term newborns

OBJECTIVE

To analyze the characteristics of spontaneous otoacoustic emissions (SOAEs) in full-term newborns.

METHODS

A total of 236 ears from 147 randomly selected full-term Chinese neonates (82 females and 65 males), who had passed the initial newborn hearing screening, were assessed for SOAEs using the Capella OAE equipment (Madsen, Denmark). The test was performed in a sound booth.

RESULTS

(1) The overall prevalence of SOAE was 56.77% of the ears. The prevalence of SOAEs was significantly higher in females (69.23%) than in males (41.51%, p<0.01), as well as in the right ears (64.17%) than in the left ears (49.14%, p<0.05). (2) The overall mean level of SOAE was 11.78±8.36dB SPL, with no significant differences between males (11.73±8.25dB SPL) and females (11.81±8.43dB SPL) or between the left (11.97±8.56dB SPL) and the right ears (11.65±8.22dB SPL). (3) The 25th and 75th percentiles of SOAE frequencies were 2.31 and 4.36kHz in females and 1.93 and 3.94kHz in males, which were statistically significantly different (p<0.01). In contrast, the SOAE frequency was not significantly different between ears (2.22-4.18kHz in the left ears and 2.17-4.14kHz in right ears). (4) The overall mean number of SOAEs was 3.70±2.75, with no significant differences in females (3.62±2.70) and males (3.86±2.87) or in right (3.70±2.55) and left ears (3.70±3.02).

CONCLUSIONS

The prevalence rate of SOAE is significantly higher in females than in males and in the right ears than in the left ears in Chinese newborns. The frequencies of the SOAEs in newborns appeared to be higher than those reported in normal-hearing adults in the literature.

Factors that introduce intrasubject variability into ear-canal absorbance measurements

Wideband immittance measures can be useful in analyzing acoustic sound flow through the ear and also have diagnostic potential for the identification of conductive hearing loss as well as causes of conductive hearing loss. To interpret individual measurements, the variability in test–retest data must be described and quantified. Contributors to variability in ear-canal absorbance–based measurements are described in this article. These include assumptions related to methodologies and issues related to the probe fit within the ear and potential acoustic leaks. Evidence suggests that variations in ear-canal cross-sectional area or measurement location are small relative to variability within a population. Data are shown to suggest that the determination of the Thévenin equivalent of the ER-10C probe introduces minimal variability and is independent of the foam ear tip itself. It is suggested that acoustic leaks in the coupling of the ear tip to the ear canal lead to substantial variations and that this issue needs further work in terms of potential criteria to identify an acoustic leak. In addition, test–retest data from the literature are reviewed.

Wideband reflectance in newborns with present transient-evoked otoacoustic emissions

PURPOSE

To characterize the normal values of acoustic energy reflectance obtained with pure-tone stimulation in neonates prior to hospital discharge.

METHODS

Seventy-seven infants (37 girls and 40 boys) were evaluated by measuring acoustic reflectance using pure-tone stimuli, transient-evoked otoacoustic emissions, and tympanometric probe frequencies of 226 Hz and 1 kHz.

RESULTS

At low frequencies (258-750 Hz), greater energy reflectance was observed, while at medium frequencies (1-3 kHz), greater energy absorption was observed. There was no difference between ears or between genders.

CONCLUSION

Normal energy reflectance values were obtained for the studied population. The data indicate a reflectance curve with a distinct configuration for the studied age.

Maturation of the human medial efferent reflex revisited

Past work applying otoacoustic emissions to gauge maturational status of the medial olivocochlear (MOC) reflex in human newborns has produced mixed results. The present study revisits the question while considering the dual nature of the 2f(1) - f(2) distortion product otoacoustic emission (DPOAE) and expanding measures of medial efferent function. Subjects included premature and term-born neonates, 6-month-old infants and young adults. The MOC reflex was elicited with contralateral acoustic stimulation (CAS) while shifts in amplitude and phase of the DPOAE, and its distortion and reflection components, were monitored. Overall, CAS-elicited reductions in DPOAE level did not differ among age groups. For all ages, the MOC reflex was strongest at frequencies below 1.5 kHz, and the reflection component of the DPOAE was most affected, showing maximally reduced amplitude and shallower phase slope when contralateral noise was presented. Results suggest that the MOC reflex likely reaches maturation prior to full-term birth. However, prematurely born neonates show markedly more episodes of CAS-induced DPOAE level enhancement. This may be due to more intrusive component mixing in this age group or disruptions in the formation of the MOC pathway or synapse in the most premature neonates.

Normative wideband reflectance measures in healthy neonates

OBJECTIVE

Presently, normative wideband reflectance data are available for neonates who have passed a distortion product otoacoustic emission test. However, passing the distortion product otoacoustic emission test alone does not ensure normal middle ear function. The objective of this study was to establish normative wideband reflectance data in healthy neonates with normal middle ear function, as justified by passing a battery of tests.

METHOD

Wideband reflectance was measured in 66 infants (mean age=46.0 h, SD=21.0, range=13.3-116.5h) who passed a test battery that included high frequency (1000 Hz) tympanometry, acoustic stapedial reflex, transient evoked otoacoustic emissions and distortion product otoacoustic emissions.

RESULTS

The analysis of variance (ANOVA) results showed significant variations of reflectance across the frequencies. There was no significant difference between ears and genders. The median reflectance reached a minimum of 0.21-0.24 at 1-2 kHz, but increased to 0.45-0.59 below 1 kHz and 0.24-0.52 above 2 kHz.

CONCLUSIONS

The normative reflectance data established in the present study were in agreement with, but marginally smaller than, those of previous normative studies, except for the Keefe et al. (2000) study. While the use of a test battery approach to ensure normal middle ear function in neonates has resulted in slightly reduced reflectance across most frequencies when compared to studies that have used only otoacoustic emissions, further research is needed to accurately determine the middle ear status of neonates using test performance measures.

Wideband aural acoustic absorbance predicts conductive hearing loss in children

OBJECTIVE

This study tested the hypothesis that wideband aural absorbance predicts conductive hearing loss (CHL) in children medically classified as having otitis media with effusion.

DESIGN

Absorbance was measured in the ear canal over frequencies from 0.25 to 8 kHz at ambient pressure or as a swept tympanogram. CHL was defined using criterion air-bone gaps of 20, 25, and 30 dB at octaves from 0.25 to 4 kHz. A likelihood-ratio predictor of CHL was constructed across frequency for ambient absorbance, and across frequency and pressure for absorbance tympanometry. Performance was evaluated at individual frequencies and for any frequency at which a CHL was present.

STUDY SAMPLE

Absorbance and conventional 0.226-kHz tympanograms were measured in children of age three to eight years with CHL and with normal hearing.

RESULTS

Absorbance was smaller at frequencies above 0.7 kHz in the CHL group than the control group. Based on the area under the receiver operating characteristic curve, wideband absorbance in ambient and tympanometric tests were significantly better predictors of CHL than tympanometric width, the best 0.226-kHz predictor. Accuracies of ambient and tympanometric wideband absorbance did not differ.

CONCLUSIONS

Absorbance accurately predicted CHL in children and was more accurate than conventional 0.226-kHz tympanometry.