Pure-Tone Audiometry With Forward Pressure Level Calibration Leads to Clinically-Relevant Improvements in Test–Retest Reliability

Validity and reliability of integrated pressure level real-ear-to-coupler difference measurements

OBJECTIVES

(1) To validate the measurement of foam-tip real-ear-to-coupler differences (wRECD) using an integrated pressure level (IPL) method and (2) to compare the reliability of this method to SPL-based measurement of the wRECD.

DESIGN

SPL-based wRECD and the proposed IPL wRECD measurement were completed bilaterally. Test-retest reliability of IPL wRECD was determined with full re-insertion into the ear canal and compared to published SPL wRECD test-retest data.

STUDY SAMPLE

22 adults with normal hearing and middle ear status were recruited.

RESULTS

Differences between SPL-based wRECD and IPL wRECD measurements were within 1.51 dB on average below 5000 Hz. At and above 5000 Hz, IPL wRECD exceeded SPL wRECDs by 6.11 dB on average. The average test-retest difference for IPL wRECD across all assessed frequencies was 0.75 dB with the greatest improvements in reliability found below 750 Hz and above 3000 Hz.

CONCLUSIONS

IPL wRECD yielded improved estimates compared to SPL wRECD in high frequencies, where standing-wave interference is present. Independence from standing wave interference resulted in increased wRECD values above 4000 Hz using the IPL measurement paradigm. IPL wRECD is more reliable than SPL wRECD, does not require precise probe-microphone placement, and provides a wider valid wRECD bandwidth than SPL-based measurement.

A Clinically Viable Medial Olivocochlear Reflex Assay Using Transient-Evoked Otoacoustic Emissions

OBJECTIVES

The contralateral medial olivocochlear reflex (MOCR) strength may indicate various auditory conditions in humans, but a clinically viable assay and equipment are needed for quick, accurate, and reliable measurements. The first experiment compared an earlier version of the assay, which used a nonlinear-mode chirp stimulus, with a new assay using a linear-mode click stimulus, designed to give reliable MOCR measurements in most normal-hearing ears. The second experiment extended the improved assay on a purpose-built binaural hardware platform that used forward-pressure level (FPL) calibration for both the stimulus and the contralateral MOCR elicitor.

DESIGN

Transient-evoked otoacoustic emission (TEOAE) tests were measured with and without a 60-dB SPL MOCR-evoking contralateral broadband noise. The normalized MOCR strength (MOCR%) was derived from the TEOAE responses for each trial pair using the complex pressure difference weighted by the TEOAE magnitude. Experiment 1 compared MOCR% within-subject and across-day using two TEOAE stimuli: nonlinear-mode chirps (50 dB SPL, bandpass 1-5 kHz, 14 ms window delayed by 2 ms) and linear-mode clicks (50 dB SPL, bandpass 0.5-2.5 kHz, 13 ms window delayed by 5 ms). TEOAE responses were analyzed in the 0.5 to 2.5 kHz band. Thirty adult participants with normal hearing (30 ears) completed the study. The TEOAE stimulus was calibrated in situ using spectral flattening, and the contralateral noise was calibrated in a coupler. Twelve TEOAE trial pairs were collected for each participant and condition. Experiment 2 used a purpose-built binaural system. The TEOAE stimuli were linear-mode clicks (50 dB SPL, bandpass 1-3 kHz, 13 ms window delayed by 5 ms), analyzed in the 1 to 3 kHz band over ~12 trial pairs. After a probe refit, an additional trial pair was collected for the two early-stopping signal-to-noise ratio criteria (15 and 20 dB). They were evaluated for single-trial reliability and test time. Nineteen adult participants with normal hearing (38 ears) completed the study. The TEOAE clicks and contralateral elicitor noise were calibrated in situ using FPL and delivered with automated timing.

RESULTS

MOCR% for linear-mode clicks was distinguishable from measurement variability in 98% to 100% of participants' ears (both experiments), compared with only 73% for the nonlinear-mode chirp (experiment 1). MOCR detectability was assessed using the MOCR% across-subject/within-subject variance ratio. The ratio in experiment 1 for linear-mode clicks was higher (8.0) than for nonlinear-mode chirps (6.4). The ratio for linear-mode clicks (8.9) in experiment 2 was slightly higher than for the comparable linear-mode stimulus (8.0) in experiment 1. TEOAEs showed excellent reliability with high signal-to-noise ratios in both experiments, but reliability was higher for linear-mode clicks than nonlinear-mode chirps. MOCR reliability for the two stimuli was comparable. The FPL pressure response retest reliability derived from the SPL at the microphone was higher than the SPL retest reliability across 0.4 to 8 kHz. Stable results required 2 to 3 trial pairs for the linear-mode click (experiments 1 and 2) and three for the nonlinear-mode chirp (experiment 1), taking around 2 min on average.

CONCLUSIONS

The linear-mode click assay produced measurable, reliable, and stable TEOAE and MOCR results on both hardware platforms in around 2 min per ear. The stimulus design and response window ensured that any stimulus artifact in linear mode was unlikely to confound the results. The refined assay is ready to produce high-quality data quickly for clinical and field studies to develop population norms, recognize diagnostic patterns, and determine risk profiles.

Validation of an integrated pressure level measured earmold wideband real-ear-to-coupler difference measurement

OBJECTIVE

To validate measurement of predicted earmold wideband real-ear-to-coupler difference (wRECD) using an integrated pressure level (IPL) calibrated transducer and the incorporation of an acoustically measured tubing length correction.

DESIGN

Unilateral earmold SPL wRECD using varied hearing aid tubing length and the proposed predicted earmold IPL wRECD measurement procedure were completed on all participants and compared.

STUDY SAMPLE

22 normal hearing adults with normal middle ear status were recruited.

RESULTS

There were no clinically significant differences between probe-microphone and predicted earmold IPL wRECD measurements between 500 and 2500 Hz. Above 5000 Hz, the predicted earmold IPL wRECD exceeded earmold SPL wRECDs due to lack of standing wave interference. Test-retest reliability of IPL wRECD measurement exceeded the reliability of earmold SPL wRECD measurement across all assessed frequencies, with the greatest improvements in the high frequencies. The acoustically measured tubing length correction largely accounted for acoustic effects of the participant's earmold.

CONCLUSIONS

IPL-based measurements provide a promising alternative to probe-microphone earmold wRECD procedures. Predicted earmold IPL wRECD is measured without probe-microphone placement, agrees well with earmold SPL wRECDs and is expected to extend the valid bandwidth of wRECD measurement.

Predicting wideband real-ear-to-coupler differences in children using wideband acoustic immittance

Individual differences in ear-canal acoustics introduce variability into hearing aid output that can affect speech audibility. Measuring ear-canal acoustics in young children can be challenging, and relying on normative real-ear-to-coupler difference (RECD) transforms can lead to large fitting errors. Acoustic immittance measures characterize the impedance of the ear and are more easily measured than RECD. Using 226 Hz tympanometry to predict the RECD is more accurate than using age-based average RECD values. The current study sought to determine whether wideband acoustic immittance measurements could improve predictions of wideband real-ear-to-coupler difference (wRECD). 150 children ages 2-10 years with intact tympanic membranes underwent wRECD and wideband acoustic immittance measures in each ear. Three models were constructed to predict each child's measured wRECD: the age-based average wRECD, 226 Hz admittance wRECD, and wideband absorbance wRECD. The average age-based wRECD model predicted the child's measured wRECD within 3 dB in 62% of cases, but both the 226 Hz admittance and wideband absorbance wRECD were within 3 dB in 90% of cases. Using individual 226 Hz or wideband absorbance to predict wRECD improved the accuracy and precision of transforms used for pediatric hearing aid fitting.

Comments on forward pressure and other reflectance-based quantities for delivering stimuli to the ear

The forward pressure has been proposed as an "optimal" reflectance-based quantity for delivering stimuli to the ear during evoked otoacoustic-emission measurements and audiometry. It is motivated by and avoids detrimental stimulus-level errors near standing-wave antiresonance frequencies when levels are adjusted in situ. While enjoying widespread popularity within research, the forward pressure possesses certain undesirable properties, some of which complicate its implementation into commercial otoacoustic-emission instruments conforming to existing international standards. These properties include its inability to approximate the total sound pressure anywhere in the ear canal and its discrepancy from the sound pressure at the tympanic membrane, which depends directly on the reflectance. This paper summarizes and comments on such properties of the forward pressure. Further, based on previous published data, alternative reflectance-based quantities that do not share these properties are investigated. A complex integrated pressure, with magnitude identical to the previously proposed scalar integrated pressure, is suggested as a suitable quantity for avoiding standing-wave errors when delivering stimuli to the ear. This complex integrated pressure approximates the magnitude and phase of the sound pressure at the tympanic membrane and can immediately be implemented into standardized commercial instruments to take advantage of improved stimulus-level accuracy and reproducibility in the clinic.

Effect of hearing loss on cognitive function in patients with mild cognitive impairment: A prospective, randomized, and controlled study

Background

Hearing loss (HL) may increase the risk of cognitive decline in the elderly. However, the randomized controlled study on the effect of HL on cognitive function in mild cognitive impairment (MCI) is very limited.

Methods

From 1 November 2020 to 30 March 2022, 1,987 individuals aged 55–65 years were randomly divided into the MCI with hearing impairment (MCI-HI), MCI without HI (MCI-nHI), and no MCI (nMCI) groups by stratified sampling, with 30 participants in each group. The Mini-Mental State Examination (MMSE), the Montreal Cognitive Assessment (MoCA), the pure tone audiometry (PTA), and the auditory brainstem response (ABR) were measured at baseline and a follow-up 12 months later. The trial protocol was registered with ClinicalTrials.gov with the registration number NCT05336942.

Results

Among the 90 participants, the average age was 60.41 ± 6.48 years. In the MCI-HI group at baseline, the PTA score of both the ears was negatively correlated with the naming and memory score (p < 0.05), and the PTA score of both the ears was negatively correlated with the MoCA and abstraction score at the 12-month follow-up (p < 0.05). However, there were no significant differences among the PTA, the ABR, the MMSE, and the MoCA scores in the MCI-nHI and nMCI groups (p > 0.05). Regression analysis showed that the PTA score of the right ear at baseline was an important factor associated with the MoCA, visuospatial/executive, naming, and abstraction scores at the 12-month follow-up (β = −0.776 to −0.422, p < 0.05).

Conclusion

HL was significantly negatively associated with cognitive function only in patients with MCI with hearing impairment (HI), and the PTA of the right ear may be a predictor of cognitive decline after 1 year in patients with MCI with HI. This information may help primary healthcare clinicians to prevent MCI by screening and intervening in care for elderly patients with HL.

Extended high-frequency audiometry in research and clinical practice

Audiometric testing in research and in clinical settings rarely considers frequencies above 8 kHz. However, the sensitivity of young healthy ears extends to 20 kHz, and there is increasing evidence that testing in the extended high-frequency (EHF) region, above 8 kHz, might provide valuable additional information. Basal (EHF) cochlear regions are especially sensitive to the effects of aging, disease, ototoxic drugs, and possibly noise exposure. Hence, EHF loss may be an early warning of damage, useful for diagnosis and for monitoring hearing health. In certain environments, speech perception may rely on EHF information, and there is evidence for an association between EHF loss and speech perception difficulties, although this may not be causal: EHF loss may instead be a marker for sub-clinical damage at lower frequencies. If there is a causal relation, then amplification in the EHF range may be beneficial if the technical difficulties can be overcome. EHF audiometry in the clinic presents with no particular difficulty, the biggest obstacle being lack of specialist equipment. Currently, EHF audiometry has limited but increasing clinical application. With the development of international guidelines and standards, it is likely that EHF testing will become widespread in future.

One-eartip solution for pure-tone audiometry and acoustic immittance measurements: using insert earphone with an immittance probe ear tip

OBJECTIVE

Two consecutive studies sought to determine the (1) Equivalent Threshold Sound Pressure Levels (ETSPLs) and, (2) real ear attenuation thresholds (REAT) for the KUDUwave earcup configured with an insert earphone using a typical immittance probe tip (TPT).

DESIGN

(1) Hearing thresholds were measured for frequencies 125 to 8000 Hz using the TPT. ETSPLs were calculated in an IEC 60318-4 occluded ear simulator. (2) REAT were obtained by measuring sound field thresholds with ears uncovered and covered with the investigational transducer. The attenuation values were used to determine the maximum permissible ambient noise levels (MPANLs).

STUDY SAMPLE

(1) Study 1 included twenty-five adult participants with no otologic diseases (8 females; 18 - 33 years). (2) Study 2 included fifteen normal hearing participants aged 21-31 years.

RESULTS

Established ETSPLs, REAT, and MPANLs for the TPT are presented in this paper. The determined TPT ETSPLs differed from the ER-3A foam tip insert earphone's RETSPLs reported in ISO 389-2.

CONCLUSIONS

The investigational transducer can be used for pure-tone audiometry provided the reported MPANLs are adhered to, and ETSPL values are employed for calibration purposes. The advantage is to achieve a cost-effective one-probe tip solution for pure tone audiometry and immittance measurement.

Test-retest reliability of distortion-product thresholds compared to behavioral auditory thresholds

When referred to baseline measures, serial monitoring of pure-tone behavioral thresholds and distortion-product otoacoustic emissions (DPOAEs) can be used to detect the progression of cochlear damage. Semi-logarithmic DPOAE input-output (I/O) functions enable the computation of estimated distortion-product thresholds (EDPTs) by means of linear regression, a metric that provides a quantitative estimate of hearing loss due to cochlear-amplifier degradation. DPOAE wave interference and a suboptimal choice of stimulus levels limit the accuracy of EDPTs. This work identifies the test-retest reliability of EDPTs derived from short-pulse DPOAE level maps (EDPT_LM), a method that circumvents limitations associated with both wave interference and suboptimal choice of stimulus levels. The test-retest reliability was compared to that of EDPTs derived from semi-logarithmic I/O functions (EDPT_I/O) and that of behavioral thresholds acquired with pure-tone audiometry (PTA) and modified Békésy tracking audiometry (TA) to provide a foundation for identifying and interpreting significant threshold shifts. The DPOAE-based auditory thresholds (EDPT_LM and EDPT_I/O) and behavioral thresholds (PTA and TA) were recorded seven times within three months at 14 frequencies with f₂ = 1-14 kHz in 20 ears from ten subjects with normal hearing (4PTA_0.5-4kHz < 20 dB HL). To obtain EDPT_LM, short-pulse DPOAEs were recorded using 21 L₁,L₂ pairs. Reconstruction of DPOAE growth behavior as a function of L₁ and L₂ using nonlinear curve fitting enabled the derivation of EDPT_LM for each frequency. Test-retest reliability was determined using three different approaches: 1) centered thresholds, 2) average threshold differences, and 3) average absolute threshold differences, between each possible test session (N = 21). Test-retest reliability based on centered thresholds and average threshold differences showed no statistically significant difference between EDPT_LM, EDPT_I/O, PTA, and TA for the pooled analysis incorporating all stimulus frequencies. Average absolute threshold differences presented small but significant differences in test-retest reliability with median values of 3.00 dB for PTA, 3.20 dB for TA, 3.34 dB for EDPT_LM, and 3.51 dB for EDPT_I/O. A considerable frequency dependence of test-retest reliability was found; namely, the highest test-retest reliability was for EDPT_LM at f₂ = 11 - 14 kHz. Otherwise, at lower frequencies, the highest test-retest reliability was for TA at f₂ =1 - 2 kHz. Overall, the test-retest reliability of EDPT_LM was better than that of EDPT_I/O and was similar to that for behavioral thresholds. Hence, deriving EDPT_LM from individual level maps is a promising and sensitive method for objectively monitoring the state of the cochlea. Furthermore, the detection of an equidirectional threshold change at a single frequency in both EDPT_LM and TA might allow reducing the threshold shift as indication of a follow-up examination from the clinical standard of 10 dB down to 5 dB. This stricter indicator might be beneficial when monitoring cochlear damage, for example ototoxicity, in the presence of (remnant) cochlear amplification at baseline.

Hearing threshold levels of Australian coal mine workers: a retrospective cross-sectional study of 64196 audiograms

OBJECTIVE

This study examined the hearing threshold levels (HTL) of workers commencing employment in Australian coal mines in the State of New South Wales (NSW). The aim was to establish if some degree of hearing loss was identifiable in the mandatory pre-employment audiograms of workers.

DESIGN

This was an observational, retrospective, repeated cross-sectional study.

STUDY SAMPLE

De-identified audiometric records of 64196 employees entering NSW coal mining in three representative five-year periods between 1991-2015 were utilised.

RESULTS

Although HTLs were lower (better) in more recent years, the results showed clinically significant hearing loss (≥25dBHL) for older workers, 45-60 years. Pure tone average (PTA) hearing losses were greater at the higher frequencies associated with excessive noise exposure (3-6 kHz), than at the speech frequencies (0.5-4 kHz). Hearing loss in the left ears were higher compared to the right ears, with higher prevalence of audiometric notches in males.

CONCLUSION

Almost a fifth (14.8-20.1%) of male workers commencing work in NSW coal mines presented with an audiometric notch at 4 kHz. Further research is required to determine if these notches represent true NIHL, and how the residual hearing of workers may be conserved.

Effects of Forward- and Emitted-Pressure Calibrations on the Variability of Otoacoustic Emission Measurements Across Repeated Probe Fits

OBJECTIVE

The stimuli used to evoke otoacoustic emissions (OAEs) are typically calibrated based on the total SPL measured at the probe microphone. However, due to the acoustics of the ear-canal space (i.e., standing-wave interference), this method can underestimate the stimulus pressure reaching the tympanic membrane at certain frequencies. To mitigate this effect, stimulus calibrations based on forward pressure level (FPL) can be applied. Furthermore, the influence of ear-canal acoustics on measured OAE levels can be compensated by expressing them in emitted pressure level (EPL). To date, studies have used artificial shallow versus deep probe fits to assess the effects of calibration method on changes in probe insertion. In an attempt to better simulate a clinical setting, the combined effects of FPL calibration of stimulus level and EPL compensation of OAE level on response variability during routine (noncontrived) probe fittings were examined.

DESIGN

The distortion component of the distortion-product OAE (DPOAE) and the stimulus-frequency OAE (SFOAE) were recorded at low and moderate stimulus levels in 20 normal-hearing young-adult subjects across a five-octave range. In each subject, three different calibration approaches were compared: (1) the conventional SPL-based stimulus calibration with OAE levels expressed in SPL; (2) FPL stimulus calibration with OAEs expressed in SPL; and (3) FPL stimulus calibration with OAEs expressed in EPL. Test and retest measurements were obtained during the same session and, in a subset of subjects, several months after the initial test. The effects of these different procedures on the inter- and intra-subject variability of OAE levels were assessed across frequency and level.

RESULTS

There were no significant differences in the inter-subject variability of OAE levels across the three calibration approaches. However, there was a significant effect on OAE intra-subject variability. The FPL/EPL approach resulted in the overall lowest test-rest differences in DPOAE level for frequencies above 4 kHz, where standing-wave interference is strongest. The benefit was modest, ranging on average from 0.5 to 2 dB and was strongest at the lower stimulus level. SFOAE level variability did not show significant differences among the three procedures, perhaps due to insufficient signal-to-noise ratio and nonoptimized stimulus levels. Correlations were found between the short-term replicability of DPOAEs and the benefit derived from the FPL/EPL procedure: the more variable the DPOAE, the stronger the benefit conferred by the advanced calibration methods.

CONCLUSIONS

Stimulus and response calibration procedures designed to mitigate the effects of standing-wave interference on both the stimulus and the OAE enhance the repeatability of OAE measurements and reduce their dependence on probe position, even when probe shifts are small. Modest but significant improvements in short-term test-retest repeatability were observed in the mid- to high-frequency region when using combined FPL/EPL procedures. The authors posit that the benefit will be greater in a more heterogeneous group of subjects and when different testers participate in the fitting and refitting of subjects, which is a common practice in the audiology clinic. The impact of calibration approach on OAE inter-subject variability was not significant, possibly due to a homogeneous subject population and because factors other than probe position are at play.