Ear-canal reflectance, umbo velocity, and tympanometry in normal-hearing adults

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 as a screening tool for the diagnosis of superior semicircular canal dehiscence

HYPOTHESIS

Power reflectance (PR) measurements in ears with superior canal dehiscence (SCD) have a characteristic pattern, the detection of which can assist in diagnosis.

BACKGROUND

The aim of this study was to determine whether PR coupled with a novel detection algorithm can perform well as a fast, noninvasive, and easy screening test for SCD. The screening test aimed to determine whether patients with various vestibular and/or auditory symptom(s) should be further considered for more expensive and invasive tests that better define the diagnosis of SCD (and other third-window lesions).

METHODS

Power reflectance was measured in patients diagnosed with SCD by high-resolution computed tomography. The study included 40 ears from 32 patients with varying symptoms (e.g., with and without conductive hearing loss, vestibular symptoms, and abnormal auditory sensations).

RESULTS

Power reflectance results were compared to previously published norms and showed that SCD is commonly associated with a PR notch near 1 kHz. An analysis algorithm was designed to detect such notches and to quantify their incidence in affected and normal ears. Various notch detection thresholds yielded sensitivities of 80% to 93%, specificities of 69% to 72%, negative predictive values of 84% to 93%, and a positive predictive value of 67%.

CONCLUSION

This study shows evidence that PR measurements together with the proposed notch-detecting algorithm can be used to quickly and effectively screen patients for third-window lesions such as SCD in the early stages of a diagnostic workup.

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.

Non-invasive estimation of middle-ear input impedance and efficiency

A method to transform the impedance measured in the ear canal, ZEC, to the plane of the eardrum, ZED, is described. The portion of the canal between the probe and eardrum was modeled as a concatenated series of conical segments, allowing for spatial variations in its cross-sectional area. A model of the middle ear (ME) and cochlea terminated the ear-canal model, which permitted estimation of ME efficiency. Acoustic measurements of ZEC were made at two probe locations in 15 normal-hearing subjects. ZEC was sensitive to measurement location, especially near frequencies of canal resonances and anti-resonances. Transforming ZEC to ZED reduced the influence of the canal, decreasing insertion-depth sensitivity of ZED between 1 and 12 kHz compared to ZEC. Absorbance, A, was less sensitive to probe placement than ZEC, but more sensitive than ZED above 5 kHz. ZED and A were similarly insensitive to probe placement between 1 and 5 kHz. The probe-placement sensitivity of ZED below 1 kHz was not reduced from that of either A or ZEC. ME efficiency had a bandpass shape with greatest efficiency between 1 and 4 kHz. Estimates of ZED and ME efficiency could extend the diagnostic capability of wideband-acoustic immittance measurements.

Age and Gender Effects on Wideband Absorbance in Adults With Normal Outer and Middle Ear Function

PURPOSE

This study examined the effects of age and gender on wideband energy absorbance in adults with normal middle ear function.

METHOD

Forty young adults (14 men, 26 women, aged 20-38 years), 31 middle-aged adults (16 men, 15 women, aged 42-64 years), and 30 older adults (20 men, 10 women, aged 65-82 years) were assessed. Energy absorbance (EA) data were collected at 30 frequencies using a prototype commercial instrument developed by Interacoustics.

RESULTS

Results showed that the young adult group had significantly lower EA (between 400 and 560 Hz) than the middle-aged group. However, the middle-aged group showed significantly lower EA (between 2240 and 5040 Hz) than the young adult group. In addition, the older adult group had significantly lower EA than the young adult group (between 2520 and 5040 Hz). No significant difference in EA was found at any frequency between middle-aged and older adults. Across age groups, gender differences were found with men having significantly higher EA values than women at lower frequencies, whereas women had significantly higher EA at higher frequencies.

CONCLUSIONS

This study provides evidence of the influence of gender and age on EA in adults with normal outer and middle ear function. These findings support the importance of establishing age- and gender-specific EA norms for the adult population.

Restoration of middle-ear input in fluid-filled middle ears by controlled introduction of air or a novel air-filled implant

The effect of small amounts of air on sound-induced umbo velocity in an otherwise saline-filled middle ear (ME) was investigated to examine the efficacy of a novel balloon-like air-filled ME implant suitable for patients with chronically non-aerated MEs. In this study, air bubbles or air-filled implants were introduced into saline-filled human cadaveric MEs. Umbo velocity, a convenient measure of ME response, served as an indicator of hearing sensitivity. Filling the ME with saline reduced umbo velocity by 25-30 dB at low frequencies and more at high frequencies, consistent with earlier work (Ravicz et al., Hear. Res. 195: 103-130 (2004)). Small amounts of air (∼30 μl) in the otherwise saline-filled ME increased umbo velocity substantially, to levels only 10-15 dB lower than in the dry ME, in a frequency- and location-dependent manner: air in contact with the tympanic membrane (TM) increased umbo velocity at all frequencies, while air located away from the TM increased umbo velocity only below about 500 Hz. The air-filled implant also affected umbo velocity in a manner similar to an air bubble of equivalent compliance. Inserting additional implants into the ME had the same effect as increasing air volume. These results suggest these middle-ear implants would significantly reduce conductive hearing loss in patients with chronically fluid-filled MEs.

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.

Assessment of ear disorders using power reflectance

This article describes the effect of various pathologies on power reflectance (PR) and absorbance measured in human adults. The pathologies studied include those affecting the tympanic membrane, the middle-ear ossicles, the middle-ear cavity, the inner ear, and intracranial pressure. Interesting pathology-induced changes in PR that are statistically significant have been reported. Nevertheless, because measurements of PR obtained from normal-hearing subjects have large variations and some pathology-induced changes are small, it can be difficult to use PR alone for differential diagnosis. There are, however, common clinical situations without reliable diagnostic methods that can benefit from PR measurements. These conditions include ears with a normal-appearing tympanic membrane, aerated middle-ear cavity, and unknown etiology of conductive hearing loss. PR measurements in conjunction with audiometric measurements of air–bone gap have promise in differentiating among stapes fixation, ossicular discontinuity, and superior semicircular canal dehiscence. Another possible application is to monitor an individual for possible changes in intracranial pressure. Descriptions of mechanisms affecting PR change and utilization of PR measurements in clinical scenarios are presented.

Reliability of Broadband Middle-Ear Power Reflectance in Younger and Older Adults: Application of Generalizability Theory

Purpose

To assess the reliability of broadband middle-ear power reflectance (BMEPR) and transmittance profiles for chirp and tonal stimuli using generalizability theory (GT).

Method

In adults without a history of middle-ear disease, the authors assessed the reliability of BMEPR to chirp and tonal stimuli using a multivariate approach based on an analysis of variance model (GT). For comparisons with other published studies, Pearson's product–moment correlation coefficients (Pearson's r ) also were used.

Results

Based on GT with chirp stimuli, overall BMEPR measures had good reliability; however, the reliability of individual profiles across frequencies and ears was less than optimal. Lower generalizability coefficients were found when transmittance was evaluated. Test–retest reliability using Pearson's r was better for right versus left ears, and mid-frequencies were generally more reliable than those at either extreme of the frequency range. In contrast, tonal stimuli had higher generalizability coefficients and Pearson's r values than chirps for all frequencies tested; Pearson's r values were also higher for right versus left ears.

Conclusion

The authors extended the use of GT as a preferred way to evaluate reliability of BMEPR and transmittance profiles for chirps and tones because it allows for a more comprehensive evaluation compared with unidimensional pairwise correlations.

Wideband energy reflectance measurements: effects of negative middle ear pressure and application of a pressure compensation procedure

The wideband energy reflectance (ER) technique has become popular as a tool for evaluating middle ear function. Negative middle ear pressure (MEP) is a prevalent form of middle ear dysfunction, which may impact application of ER measurements in differential diagnosis. A negative MEP may be countervailed by application of an equivalent negative ear canal pressure. The present study examined ER in the same ears under normal and experimentally induced negative MEP conditions. Thirty-five subjects produced at least one negative MEP each (-40 to -225 daPa). Negative MEP significantly altered ER in a frequency-specific manner that varied with MEP magnitude. ER increased for low- to mid-frequencies with the largest change (~0.20 to 0.40) occurring between 1 and 1.5 kHz. ER decreased for frequencies above 3 kHz with the largest change (~-0.10 to -0.25) observed between 4.5 and 5.5 kHz. Magnitude of changes increased as MEP became more negative, as did the frequencies at which maximum changes occurred, and the frequency at which enhancement transitioned to reduction. Ear canal pressure compensation restored ER to near baseline values. This suggests that the compensation procedure adequately mitigates the effects of negative MEP on ER. Theoretical issues and clinical implications are discussed.

Investigation of bacterial biofilm in the human middle ear using optical coherence tomography and acoustic measurements

Children with chronic otitis media (OM) often have conductive hearing loss which results in communication difficulties and requires surgical treatment. Recent studies have provided clinical evidence that there is a one-to-one correspondence between chronic OM and the presence of a bacterial biofilm behind the tympanic membrane (TM). Here we investigate the acoustic effects of bacterial biofilms, confirmed using optical coherence tomography (OCT), in adult ears. Non-invasive OCT images are collected to visualize the cross-sectional structure of the middle ear, verifying the presence of a biofilm behind the TM. Wideband measurements of acoustic reflectance and impedance (0.2-6 [kHz]) are used to study the acoustic properties of ears with confirmed bacterial biofilms. Compared to known acoustic properties of normal middle ears, each of the ears with a bacterial biofilm has an elevated power reflectance in the 1 to 3 [kHz] range, corresponding to an abnormally small resistance (real part of the impedance). These results provide assistance for the clinical diagnosis of a bacterial biofilm, which could lead to improved treatment of chronic middle ear infection and further understanding of the impact of chronic OM on conductive hearing loss. This article is part of a special issue entitled "MEMRO 2012".

Characterizing the ear canal acoustic impedance and reflectance by pole-zero fitting

This study characterizes middle ear complex acoustic reflectance (CAR) and impedance by fitting poles and zeros to real-ear measurements. The goal of this work is to establish a quantitative connection between pole-zero locations and the underlying physical properties of CAR data. Most previous studies have analyzed CAR magnitude; while the magnitude accounts for reflected power, it does not encode latency information. Thus, an analysis that studies the real and imaginary parts of the data together, being more general, should be more powerful. Pole-zero fitting of CAR data is examined using data compiled from various studies, dating back to Voss and Allen (1994). Recent CAR measurements were taken using the Mimosa Acoustics HearID system, which makes complex acoustic impedance and reflectance measurements in the ear canal over a 0.2-6.0 [kHz] frequency range. Pole-zero fits to measurements over this range are achieved with an average RMS relative error of less than 3% with 12 poles. Factoring the reflectance fit into its all-pass and minimum-phase components estimates the effect of the residual ear canal, allowing for comparison of the eardrum impedance and admittance across measurements. It was found that individual CAR magnitude variations for normal middle ears in the 1-4 [kHz] range often give rise to closely-placed pole-zero pairs, and that the locations of the poles and zeros in the s-plane may systematically differ between normal and pathological middle ears. This study establishes a methodology for examining the physical and mathematical properties of CAR using a concise parametric model. Pole-zero modeling accurately parameterizes CAR data, providing a foundation for detection and identification of middle ear pathologies. This article is part of a special issue entitled "MEMRO 2012".

Wave motion on the surface of the human tympanic membrane: holographic measurement and modeling analysis

Sound-induced motions of the surface of the tympanic membrane (TM) were measured using stroboscopic holography in cadaveric human temporal bones at frequencies between 0.2 and 18 kHz. The results are consistent with the combination of standing-wave-like modal motions and traveling-wave-like motions on the TM surface. The holographic techniques also quantified sound-induced displacements of the umbo of the malleus, as well as volume velocity of the TM. These measurements were combined with sound-pressure measurements near the TM to compute middle-ear input impedance and power reflectance at the TM. The results are generally consistent with other published data. A phenomenological model that behaved qualitatively like the data was used to quantify the relative magnitude and spatial frequencies of the modal and traveling-wave-like displacement components on the TM surface. This model suggests the modal magnitudes are generally larger than those of the putative traveling waves, and the computed wave speeds are much slower than wave speeds predicted by estimates of middle-ear delay. While the data are inconsistent with simple modal displacements of the TM, an alternate model based on the combination of modal motions in a lossy membrane can also explain these measurements without invoking traveling waves.

Measurements of wide-band cochlear reflectance in humans

The total sound pressure measured in the ear canal may be decomposed into a forward- and a reverse-propagating component. Most of the reverse-propagating component is due to reflection at the eardrum. However, a measurable contribution to the reverse-propagating component comes from the cochlea. Otoacoustic emissions (OAEs) are associated with this component and have been shown to be important noninvasive probes of cochlear function. Total ear-canal reflectance (ECR) is the transfer function between forward and reverse propagating components measured in the ear canal. Cochlear reflectance (CR) is the inner-ear contribution to the total ECR, which is the measured OAE normalized by the stimulus. Methods are described for measuring CR with a wide-band noise stimulus. These measurements offer wider bandwidth and minimize the influence of the measurement system while still maintaining features of other OAEs (i.e., frequency- and level-dependent latency). CR magnitude decreases as stimulus level increases. Envelopes of individual band-limited components of the time-domain CR have multiple peaks with latencies that persist across stimulus level, despite a shift in group delay. CR has the potential to infer cochlear function and status, similar to other OAE measurements.

Comparison of umbo velocity in air- and bone-conduction

This study investigates the ossicular motion produced by bone-conducted (BC) sound in live human ears. Laser Doppler vibrometry was used to measure air conduction (AC)- and BC-induced umbo velocity (V(U)) in both ears of 10 subjects, 20 ears total. Sound pressure in the ear canal (P(EC)) was measured simultaneously. For air conduction, V(U) at standard hearing threshold level was calculated. For BC, ΔV was defined as the difference between V(U) and the tympanic ring velocity (an estimate of the skull velocity measured in the ear canal). ΔV and P(EC) at BC standard hearing threshold were calculated. ΔV at standard BC threshold was significantly smaller than V(U) at standard AC threshold between 500 Hz and 2000 Hz. Ear canal pressure at BC threshold tended to be smaller than for AC below 3000 Hz (with significant differences at 1000 Hz and 2000 Hz). Our results are most consistent with inertia of the ossicles and cochlear fluid driving BC hearing below 500 Hz, but with other mechanisms playing a significant role at higher frequencies. Sound radiated into the external ear canal might contribute to BC hearing at 3000 Hz and above.

Comparison of ear-canal reflectance and umbo velocity in patients with conductive hearing loss: a preliminary study

OBJECTIVE

The goal of the present study was to investigate the clinical utility of measurements of ear-canal reflectance (ECR) in a population of patients with conductive hearing loss in the presence of an intact, healthy tympanic membrane and an aerated middle ear. We also sought to compare the diagnostic accuracy of umbo velocity (VU) measurements and measurements of ECR in the same group of patients.

DESIGN

This prospective study comprised 31 adult patients with conductive hearing loss, of which 14 had surgically confirmed stapes fixation due to otosclerosis, 6 had surgically confirmed ossicular discontinuity, and 11 had computed tomography and vestibular evoked myogenic potential confirmed superior semicircular canal dehiscence (SCD). Measurements on all 31 ears included pure-tone audiometry for 0.25 to 8 kHz, ECR for 0.2 to 6 kHz using the Mimosa Acoustics HearID system, and VU for 0.3 to 6 kHz using the HLV-1000 laser Doppler vibrometer (Polytec Inc, Waldbronn, Germany). We analyzed power reflectance |ECR| as well as the absorbance level = 10 × log10(1 - |ECR|). All measurements were made before any surgical intervention. The VU and ECR data were plotted against normative data obtained in a companion study of 58 strictly defined normal ears ().

RESULTS

Small increases in |ECR| at low-to-mid frequencies (400-1000 Hz) were observed in cases with stapes fixation, while narrowband decreases were seen for both SCD and ossicular discontinuity. The SCD and ossicular discontinuity differed in that the SCD had smaller decreases at mid-frequency (∼1000 Hz), whereas ossicular discontinuity had larger decreases at lower frequencies (500-800 Hz). SCD tended to have less air-bone gap at high frequencies (1-4 kHz) compared with stapes fixation and ossicular discontinuity. The |ECR| measurements, in conjunction with audiometry, could successfully separate 28 of the 31 cases into the three pathologies. By comparison, VU measurements, in conjunction with audiometry, could successfully separate various pathologies in 29 of 31 cases.

CONCLUSIONS

The combination of |ECR| with audiometry showed clinical utility in the differential diagnosis of conductive hearing loss in the presence of an intact tympanic membrane and an aerated middle ear and seems to be of similar sensitivity and specificity to measurements of VU plus audiometry. Additional research is needed to expand upon these promising preliminary results.