Navid Shahnaz

Purpose: Studies in rodents, and more recently humans, suggest that noise exposure can cause permanent damage to synaptic ribbons between cochlear inner hair cells and auditory nerve synapses. Because this damage occurs before it is apparent in outer hair cells, it remains undetectable on traditional clinical assessments. Individuals may present with difficulty listening to speech in noise, tinnitus, hyperacusis, or a combination. This neuropathy, known as cochlear synaptopathy, or “hidden hearing loss”, is relatively uninvestigated, and there is currently no known test protocol to detect it. This study aims to identify the diagnostic potential of thresholds in quiet and noise on noise-induced cochlear synaptopathy. Methods: 42 young adults (mean age = 20 years) were recruited. Twenty music students with normal hearing (≤ 25 dB, HL 250-8000 Hz) and 22 normal-hearing controls with limited noise exposure were tested. Lifetime noise exposure, hearing thresholds 250-16 000 Hz in quiet, and TEN test thresholds at 1000 Hz and 4000 Hz were recorded. Bayesian inference was used to analyze differences between thresholds by group, and interactions between noise exposure and thresholds in quiet and in noise. Results: Threshold differences between groups were found at 1000 Hz TEN. There was a trend for a negative association between thresholds in quiet and thresholds in noise in most multiple regression models; however, unexpected results were found with two outcomes involving lifetime noise exposure as an additional predictor. Though trends were observed, none of them were overtly conclusive. Conclusion: The present study found inconclusive evidence for differences between thresholds in quiet or in noise between early-career musicians and non-musicians. It is possible that the cohort tested did not yield conclusive results due to the nature of noise exposure, or other inherent characteristics of the group such as age and clinical symptoms. Further research is required to develop a reliable behavioural test battery sensitive to cochlear synaptopathy in humans.

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Purpose: Hidden hearing loss, also known as cochlear synaptopathy, describes auditory deficits in individuals with clinically normal hearing sensitivity in the conventional frequency range (250–8000 Hz) which include difficulty understanding speech in background noise. Individuals with central auditory processing disorder report similar complaints. We aimed to investigate the utility of a central auditory processing test battery, the Multiple Auditory Processing Assessment (MAPA), as a potential diagnostic tool for hidden hearing loss. An additional objective was exploration of the link between noise exposure and hidden hearing loss. Previous studies on mice have found a reduction in hair cell synaptic connections subsequent to noise exposure. Design: Three groups of participants completed the MAPA: a control group (n = 24), a musician group (n = 20), and a symptomatic group (n = 11). The control group had young individuals with normal hearing (≤ 25 dB HL thresholds at 250–8000 Hz) and no significant history of noise exposure, the musician group had young students with normal hearing who were considered to be at high risk for noise exposure due to their studies, and the symptomatic group had individuals with normal hearing who reported difficulties in challenging listening environments. Lifetime noise exposure was estimated using the Noise Exposure Structured Interview (NESI), and Bayesian logistic regression was used to model the relationship between the outcomes of MAPA subtests and noise exposure history.Results: The symptomatic group exhibited poorer performance on the MAPA compared to the control and musician groups. A right-ear advantage for all groups was apparent on several measures. The musician group had higher estimated lifetime noise exposure compared to the other groups. With the exception of the dichotic advantage score, NESI scores did not predict performance on the MAPA.Conclusion: Consistent with their reported difficulties, the symptomatic group performed more poorly on the MAPA. Despite their higher estimated lifetime noise exposure, no noise-induced central auditory processing deficits emerged in the musician group. Future studies should include older musicians with more lifetime noise exposure, and adjust for age effects by using a longitudinal study design or by age-matching across participant groups.

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PURPOSE: Recent studies suggest synaptic connections between hair cells and the auditory nerve may be more vulnerable to noise-induced damage than the cochlear hair cells. The resulting neuropathy may be associated with an increased difficulty with speech perception in noise than expected from a normal audiogram. This type of hearing loss has been named “hidden hearing loss”. Studies with animal models indicate that suprathreshold wave I auditory brainstem responses are sensitive to the loss of synaptic ribbons in mice, but humans studies remain inconclusive. This work aims to identify the diagnostic potential of tympanic membrane electrocochleography on noise-induced cochlear synaptopathy.DESIGN: We recruited 18 music students (n = 32; mean age = 21.7) with normal hearing (≤ 25 dB, HL 250-8000 Hz) and 19 normal hearing controls (n = 35; mean age = 22.5). Lifetime noise exposure was obtained using the Noise Exposure Structured Interview. Electrocochleography was measured in response to 95 dB nHL broadband click with tympanic membrane electrodes. A factorial ANOVA was used to investigate the effect of music background and sex on the lifetime noise exposure. Mixed model ANOVA was used to analyze effect of noise exposure, sex, and ear on absolute SP and AP amplitudes, SP/AP amplitude ratio, and SP/AP area ratio.RESULTS: There was a trend for higher lifetime noise exposure scores for the music students but the difference did not reach significance. There were no significant group differences on any of the electrocochleography measures.CONCLUSION: In the present study, there is no evidence that AP amplitude, SP/AP amplitude ratio, or SP/AP area ratio are associated with noise exposure. It is possible that the effects of noise exposure may be observed in individuals with greater lifetime noise exposure than the cohort tested within this study. The use of tympanic membrane electrocochleography to assess cochlear synaptopathy in humans remains inconclusive. Additional research would be needed to develop a diagnostic protocol for early cochlear damage that precedes sensory hair cell loss in humans.

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Purpose: Wideband acoustic immittance (WAI) is a field of noninvasive diagnostic measures that are used to evaluate the status of the middle ear. Wideband absorbance (WBA) is a WAI tool that distinguishes normally-hearing from pathological middle ears with a high level of diagnostic accuracy. This work aims to further improve the diagnostic efficiency of WBA, by providing a set of normative data which represents the typical inter-aural difference of WBA in adults of Caucasian, Asian and Mixed ethnicities.Design: This retrospective analysis examined records of WBA obtained from normally-hearing adults (N=122; mean age= 24.16 yrs) using the Titan by Interacoustics immittance equipment. Norms were established for individual ear measures, and the inter-aural difference of WBA measured within-subjects. A mixed model ANOVA was used to analyze how normative WBA measures are affected by factors of ethnicity, gender, and test pressurization method. A comparison of the diagnostic efficacy of the two WBA measurements was conducted with an ROC analysis, using WBA records from 28 subjects with surgically confirmed otosclerosis as a clinical group.Results: The ROC analysis confirmed that diagnostic accuracy of WBA individual ear and inter- aural difference measures was equal for the detection of otosclerosis; however, these measurements may provide complementary information regarding middle ear status. WBA norms based on individual ear data varied significantly depending on ethnicity, gender, and test pressurization method across frequencies. WBA norms based on inter-aural difference values only varied significantly with test pressurization method across frequencies, though the difference was small and likely does not have any clinical relevance, at least for the detection of otosclerosis.iiiConclusion: WBA norms based on inter-aural difference values did not depend on population- based factors of ethnicity or gender; the same set of normative data may be used reliably across these populations. Parameterization of norms for individual ear WBA data is recommended based on ethnicity, gender and test pressurization method. Inter-aural difference norms for WBA may be instrumental in interpreting immittance results for individuals with unilateral conductive pathology, or for populations for which other forms of normative data are not available.

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Purpose: There are few data on the prevalence of Otitis Media (OM) in neonates of all ethnicities, especially First Nations and Metis (FNAM) neonates, at birth. There is a need to diagnose type of hearing loss at the time of Newborn Hearing Screening (NHS) to determine prevalence and to refer neonates for timely assessment and intervention. Wideband Acoustic Immittance (WAI) is a viable tool that can aid in the diagnosis of conductive hearing loss (CHL) at time of hearing screening. Design: This cross-sectional study examined the application of WAI measures (Wideband Absorbance (WBA) at Ambient and Tympanometric Peak Pressure (TPP), and Admittance Phase (Yφ) as part of a regular NHS protocol. NHS pass/fail rates, likely diagnoses and WAI measurements in FNAM newborns were compared to newborns of other ethnicities. 213 neonates (426 ears) were recruited from the Royal University Hospital in Saskatoon, Saskatchewan. 382 ears met the inclusion criteria: 42 FNAM, 212 Caucasian, 48 Other Ethnicities, and 80 Undeclared Ethnicity. Results: FNAM neonates had a significantly higher NHS fail rate than Caucasian neonates. The WBA of FNAM neonates was significantly lower than that of neonates of other ethnicities in both NHS pass and fail conditions. WBA was significantly lower for neonates who failed the test battery and who failed Transient Evoked Otoacoustic Emission (TEOAE) testing. The difference in WBA at peak pressure was larger than the difference at ambient pressure for neonates who passed or failed a NHS test battery. Yφ was significantly lower in neonates who passed the test battery and who had a likely diagnosis of normal hearing. Conclusions: WBA and Yφ are effective in distinguishing ears with likely CHL from normal hearing ears. Pressurized WBA may be more effective than ambient WBA and Yφ is a promising measure in the diagnosis of CHL. FNAM neonates have a higher NHS fail rate and a greater prevalence of likely CHL. WBA of FNAM neonates is lower than that of other ethnicities. Further research is needed to determine if lower WBA in FNAM neonates indicates a greater prevalence of OM or a difference in middle ear anatomy.

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This study investigated the impact of positive and negative middle ear pressure (MEP) on evoked otoacoustic emissions (EOAEs) both distortion-product OAEs (1.5 to 8 kHz) and transient evoked OAEs (1 to 5 kHz), as well as wideband acoustic immittance measures of power absorbance (PA) in a normal-hearing young adult population between the ages of 18 and 35. The effectiveness was evaluated, of testing at ambient compared to a compensated pressure level corresponding to participants’ tympanic peak pressure. Outcome measures were analyzed considering factors of gender, ethnicity, frequency, and MEP magnitude. For each participant, testing was conducted at a natural state MEP and at a MEP level induced by either the Toynbee or Valsalva maneuver. Titan Suite by Interacoustics was used to collect all measures and is the only commercially available system for assessing EOAEs at a compensated pressure level. One-hundred and four participants (67 female and 37 male, providing 208 ears) were recruited for testing. EOAE absolute amplitude and PA varied significantly as a function of test frequency and across test pressure conditions. Significant differences in PA and EOAE measures were observed between gender and ethnic groups. Mean PA magnitude at frequencies ≤4 kHz was significantly greater testing at peak compared to the ambient pressure in the presence of MEP deviating from 0 daPa. EOAE amplitude was similar between the post-maneuver (induced MEP) condition and baseline measures when assessed at peak pressure. Frequency-dependent changes in PA magnitude with alterations in MEP and ear canal pressure were linked to frequency-dependent changes in EOAE amplitude. Results of this study suggest clinical benefit for a more accurate assessment of middle ear status and cochlear integrity for patients with abnormal MEP when EOAE are assessed at a compensated pressure level. This study provided a database of PA measures over a range of MEPs measured at both ambient and tympanic peak pressure.

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This study investigated whether wideband acoustic immittance (WAI) values differed significantly in a normal hearing young adult population based on gender, ethnicity, and instrument. Normative data collected from this study can be utilized to create a repository of norms for clinical use as suggested by consensus among researchers in the Eriksholm Workshop. Eighty normal hearing young adults (age 18-34) were recruited from the University of British Columbia to undergo WAI testing with two hand-held devices (Otostat Mimosa Acoustics and Titan Interacoustics) and two non-portable devices (Reflwin Interacoustics and Mimosa Acoustics HearID). Approximately twenty participants were recruited from each of the male, female, Caucasian and Chinese groups. It was found that Caucasians had significantly higher mean power absorbance (PA) in the low frequencies between 630 – 1250 Hz and the Chinese had significantly higher mean PA in the high frequencies from 5000 - 6300 Hz overall collapsed across all devices. When the effect of equivalent ear canal volume (ECV) was adjusted for, mean PA for females were significantly higher than males at high frequencies between 4000 – 6300 Hz depending on the device used and at 5000 Hz across all devices. Mean PA at peak pressure were significantly higher than ambient pressure between 250 – 2000 Hz and significantly lower between 3150 – 5000 Hz collapsed across all devices tested (ReflWin and Titan), genders, trials, ears, and ethnicities. Mean PA did vary slightly across some frequencies for the Interacoustics devices but not the Mimosa Acoustics devices between trials; however, the test-retest differences were no more than those observed across various studies of a normal hearing population and much smaller than the difference between normal and pathological ears indicating good reliability. Mean PA varied across frequencies between devices, but using HearID instrument specific data didn’t greatly improve the ability to distinguish the normal group from a sample with surgically confirmed otosclerosis obtained using the HearID system at 800 and 2000 Hz. It is advised that future investigations utilize gender, ethnicity, and instrument-specific data to determine whether these factors improve the sensitivity and specificity of identifying middle ear pathologies using a larger frequency bin for analysis.

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Objectives: The present study used tympanometric parameters to evaluate application of the current norms in Caucasian and Chinese school-aged children. The goals of this study were 1) to establish normative tympanometric data for school-aged children; 2) to determine whether the results vary significantly between Caucasian and Chinese children, male and female children, and children and adults; and 3) to compare normal paediatric tympanometric data with tympanometric data obtained from children with middle-ear pathology.Design: Tympanometry was measured in 98 subjects with normal middle-ear function with an average age of 5.8 years. There were a total of 66 participants who had abnormal middle-ear condition with a mean age of six years. Control group subjects were recruited from elementary schools in the Greater Vancouver area. Subjects with middle-ear effusion (MEE) were consisted of two groups. Those with confirmed middle-ear effusion (21 subjects) classified as “OTL confirmed” and those who recruited at elementary schools (eight subjects) were classified as “not OTL confirmed”. Statistical analysis (mixed-model ANOVA) was performed for effects of gender, ethnicity (Caucasian versus Chinese), age (child versus adult), and middle-ear condition. Conventional 226-Hz and multi-frequency tympanometry performed using GSI- Tympstar tympanometer (v. 2). . Results: Vanhuyse patterns were single peak (1B1G) at 226-Hz probe-tone frequency, but more complex patterns (e.g. 1B3G) were observed at higher probe-tone frequencies. Chinese school-aged children had lower Vea and Ytm, wider TW, and higher RF values than did Caucasian school-aged children. Diseased group tympanometric data was significantly different from normal group data. Statistical comparison of the area under receiver operating characteristic curve (AUROC) plots revealed that Ytm at 678-Hz had better test performance in distinguishing normal middle-ear status from MEE than did Ytm at other probe-tone frequencies (226-, and 1000-Hz). The results showed that Ytm from a 678-Hz probe-tone frequency, TW, and RF had the highest sensitivity, highest specificity, and statistically higher test performance in identification of MEE.Conclusions: A preliminary set of normative tympanometric data revealed significant differences between Caucasian and Chinese school-aged children and also between children and adults. Therefore, application of ethnic-specific criteria changes sensitivity or specificity of tympanometry in clinics.

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Objective: The current screening protocol of the British Columbia Early Hearing Program for neonatal intensive care unit infants is unable to differentiate between conductive and sensorineural hearing losses at the time of detection. A critical need exists for developing standardized screening procedures for differentiating conductive, sensory, and neural loss in early infancy to provide an appropriate course of intervention and to avoid later consequences on health and the development of speech and language.Design: The current study examined a novel protocol for the hearing screening of neonatal intensive care unit (NICU) infants that involved the measures of 1000 Hz tympanometry, transient evoked otoacoustic emissions (TEOAE), and ipsilateral broadband middle-ear muscle reflex (MEMR) at a 1 kHz probe tone frequency. The GN Otometrics Accuscreen device was used for automated auditory brainstem response (AABR) and TEOAE screening and the GN Otometrics Otoflex diagnostic immittance meter recorded 1000 Hz tympanometry and the MEMR. A total of 90 infants (180 ears) from the NICU of the Royal University Hospital in Saskatoon, Saskatchewan was recruited, of which 78 infants (143 ears) met the inclusion criteria. The participants mean chronological age was 31.38 days. The novel protocol was examined for three components: 1) if it generated equivalent results with the current two-stage AABR hearing screening protocol for NICU infants; 2) for testing length; and 3) for challenges encountered during testing.Results: Results revealed that 70.6% of infants passed both the current AABR and novel protocols. TEOAE accounted for most of the referrals for infants who passed the current AABR screening protocol and referred on the novel protocol (70%) and for infants who referred on both protocols (83.3%). Conclusion: The novel protocol might provide more information regarding the reason for a screening referral, including the identification of middle-ear dysfunction and the detection of mild hearing impairment.

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Objective: Eustachian tube function remains an area of middle ear analysis in which suitable clinical tests are lacking. Eustachian tube malfunction has been linked to pathology of the middle ear such as otitis media with effusion. Wideband reflectance (WBR) is a new clinical technique which determines the ratio of sound energy that enters the middle ear to that which reflects back into the ear canal. This technique could provide information regarding Eustachian tube function that other tympanometric measures do not. Design: Measures of WBR were taken in 50 Chinese and Caucasian young adult subjects before and after performing Valsalva and Toynbee manoeuvres. Subjects were students or affiliates of the University of British Columbia. Data were analysed based on static and dynamic power absorbance measures, power absorbance tympanograms, 226 Hz tympanograms and 1000 Hz tympanograms provided by the Interacoustics REFLWIN wideband reflectance system. Baseline measurements were compared between gender and ethnicity. Similarities to measurements using other clinical WBR devices were also analysed. Finally, comparisons were made on each variable between baseline and post-manoeuvre state.Results: Baseline results were comparable with previous wideband reflectance research in this subject population. Notable differences were observed between the current study and a previous version of the same device. Differences between the current system and the Mimosa Acoustics system were minimal. For both the Valsalva and Toynbee manoeuvres significant shifts in middle ear pressure were indicated by changes in tympanometric peak pressure and power absorbance tympanogram peak pressure. However, dynamic power absorbance did not differ between baseline and either manoeuvre state. Conclusion: The current version of the Interacoustics REFLWIN system provides comparable estimates of WBR to the other major clinical system available on the market. The measures of wideband reflectance did not offer information regarding Eustachian tube function in addition to that already provided by measures of tympanometry following physical manoeuvres. However, the equivalent performance of wideband reflectance to tympanometry shows that it can be used to evaluate Eustachian tube function in the same manner as tympanometry. There is still a need to devise a clinical test to accurately distinguish between healthy and pathological Eustachian tubes.

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Objectives: The specific goals of this study were: 1) To understand the mechano-acoustical properties of the normal ear canal and middle ear and its maturation as a function of age using conventional and high frequency tympanometry 2) to establish tympanometric guidelines and normative data of the normal ear canal and middle ear in infants birth to 6 months of age. Design: Thirty-one normal hearing newborns were tested longitudinally in 1-month intervals up to 6 months of age for a total of 6 visits. Tympanograms were recorded and the distributions of patterns were analyzed using the Vanhuyse model at 226 Hz, 678 Hz, and 1000 Hz. Additionally, tympanometric recordings of admittance (Ya), susceptance (Ba), and conductance (Ga) were analyzed at 226 Hz and 1000 Hz probe tones. Lastly, the variation of compensated susceptance and conductance were recorded at extended frequencies from 250-2000 Hz in 50 Hz intervals for 16 infants. Results: Results showed that 1000 Hz tympanograms were the simplest to quantify as most recordings were single-peaked. 226 Hz and 678 Hz recordings were often multi-peaked. Both positive and negative admittance and susceptance tail values increased with age for 226 Hz and 1000 Hz. However, tail values at 1000 Hz increased faster than for 226 Hz. Negative tail values were smaller compared to positive tail values which resulted in smaller compensated admittance values for the positive tails compared to negative tails across all 6 visits. Admittance magnitude decreased with age at 226 Hz as susceptance increased and conductance decreased. However, at 1000 Hz, admittance magnitude increased as susceptance remained relatively constant and conductance increase. Conclusion: Results suggest that the infant middle ear and ear canal develop towards compliance with age although is not yet a purely acoustically compliant system by 6 months of age, particularly at high frequencies. An increase in volume in the middle ear cavity, reduction of middle ear debris, and overall decrease in resistive elements may be contributing to these changes. Significant differences were observed between each visit and warrant the use of age-specific norms when applying tympanometric data to infants below 6 months of age.

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