An Absorbance Peak Template for Clinical Assessment of Sound Conduction in Newborn Ears.

PURPOSE: Power absorbance measures recorded over a wide range of frequencies allow for clinical inferences about the outer/middle ears' acoustic mechanics. A frequency-dependent feature in the newborn wideband absorbance response, the prominent mid-frequency absorbance peak, has been linked to middle-ear resonance. However, current normative methods were not designed to assess subtle changes in such features. This work aims to develop and validate an absorbance peak template (APT) for assessment of absorbance peaks in newborns. Additional objectives are to compare test performance of absorbance peaks and APTs to existing normative methods, to demonstrate APT-based methods for categorization of abnormal absorbance peaks, and to describe absorbance peak test-retest variability. METHOD: Peak absorbance and peak frequency were analyzed in a training data set (490 measurements in 84 newborn ears who passed transient evoked otoacoustic emissions [TEOAEs] screenings), and an APT was developed by computing normal limits on these two absorbance peak variables. Split-set analysis evaluated the reproducibility of APT, and test-retest analysis was performed. Test performance analysis, conveyed by area under the receiver operating characteristic curve (AROC) and 95% confidence intervals (CIs), compared absorbance peak variables to absorbance area indices (AAIs) in a validation data set (359 ears that passed distortion-product OAE [DPOAE] screening and 64 ears that failed). APT-based assessment paradigms for normal and abnormal ears were compared to the common absorbance normative range paradigm. RESULTS: Split-set analysis demonstrated a good reproducibility of APT, and test-retest of absorbance peak variables showed that they were stable measures for clinical assessment. Test performance of peak absorbance (AROC = 0.83; 95% CI [0.77, 0.88]) was comparable to the top-performing AAI variables (AROC = 0.85; 95% CI [0.80, 0.90]). APT-based assessment categorized measurements based on their peak absorbance and peak frequency and enhanced the detection of subtle frequency changes that were missed by the normative range method. CONCLUSION: Analysis of absorbance peaks guided by APT has the potential to simplify and improve assessments of sound conduction pathways in newborn ears and can be used together with or in-place of current methods for analysis of wideband absorbance data.

Assessment of auditory functions in patients with hepatic glycogen storage diseases.

BACKGROUND: Hepatic glycogen storage diseases are a group of diseases manifesting mainly with hypoglycemia and hepatomegaly. The patients require frequent daytime and nocturnal feedings. Hypoglycemia may cause sensorineural hearing loss and nocturnal feeding is a risk factor for the development of gastroesophageal reflux that may cause chronic otitis media and hearing loss consequently. We aimed to determine the prevalence and characteristics of hearing loss in hepatic glycogen storage diseases. METHODS: A total of 24 patients with hepatic glycogen storage disease (15 glycogen storage disease type I and 9 non type I) and 24 age/sex matched healthy controls were enrolled in the study. Pure tone audiometer, immitansmetry, acoustic reflex measurement, otoacoustic emission test (OAE) and auditory brainstem response (ABR) tests were applied to all participants. RESULTS: Hearing loss was determined in 17/24 patients (12 glycogen storage disease type I and 5 non type I) with pure tone audiometer. Interpretation of all the findings revealed a total of 8 patients had conductive and 9 had mixed hearing loss. All parameters were significantly different than the control group. CONCLUSIONS: This is the first study to comprehensively assess the auditory functions of patients with hepatic glycogen storage disease. Audiological findings determined a significantly increased prevalence of conductive/ mixed type hearing loss in the patient group which is a new finding in the literature. Further studies with extended patient numbers are required to enlighten the underlying pathophysiology.

Assessment of hearing levels in children with nephrotic syndrome.

OBJECTIVE: Due to the similarities in the physiological mechanisms and antigenicity of the kidney and cochlea, they are simultaneously affected by certain diseases and drugs. Therefore, the purpose of this study was to investigate whether the hearing functions of patients with nephrotic syndrome (NS) were affected by the severity of the disease and the cyclosporine treatment. METHODS: The sample of this study consisted of 87 participants, including 65 patients (130 ears) with NS and 22 age- and sex-matched normal hearing children (44 ears). Based on the severity of the disease, the patients were divided into two groups: infrequently relapsing nephrotic syndrome (IRNS) and steroid-dependent or frequently relapsing nephrotic syndrome (SD/FRNS). Their audiologic tests, including Pure-tone Audiometry and Distortion-Product Otoacoustic Emission (DPOAE), were compared with the tests of the control group. In addition, the audiologic tests of the NS patients who received cyclosporine were compared with those who did not. RESULTS: In the pure-tone audiometry, there were statistically significant differences between the IRNS, SD/FRNS, and control groups at 2000, 4000 Hz, and pure-tone average (PTA). Hearing levels of the SD/FRNS group at 2000, 4000 Hz, and PTA were higher than those of the control group. At 6000 Hz in pure-tone audiometry, there was a very weak positive correlation between the hearing level and the number of relapses. At 250 Hz and PTA, hearing levels of the group that received cyclosporine were higher compared to the group that did not receive it. In DPOAE, there was no significant difference between the groups according to the severity of the disease and the use of cyclosporine. CONCLUSION: During the follow-up of the patients with NS, their hearing functions should be questioned, especially in patients with SD/FRNS and receiving cyclosporine treatment.

Distortion Product Otoacoustic Emission Test is Not the Test to Use in Nonclinical Safety Assessment.

Ototoxicity and ocular toxicity screening are but two examples of specialty product lines that are often employed as Tier II or III nonclinical safety/hazard screening assessments. Compared to the regulatory guidelines that govern over standard toxicology or neurotoxicology programs, there is a paucity of regulatory strategies to address these specialized product lines. With respect to ototoxicity testing, we argue for the inclusion of the "least burdensome principles" adopted by the US FDA in providing the most pragmatic, efficient, and directed identification of potential harm to auditory function in the nonclinical safety arena. We argue for the exclusive use of the auditory brainstem response and the exclusion of the distortion product otoacoustic emissions (DPOAEs) in these Tiered II safety assessment programs. The inclusion of both are a burden on operational staff and, due to the extended episodes of anesthesia required to conduct both assays, this strategy poses a health and welfare concern for the selected animal species to be used. The DPOAE does not provide any sufficiently valid or reliable data above and beyond the gold standard ABR data, followed by complete oto-histopathology and cytocochleogram combination designs.

Assessment of Hidden Hearing Loss in Normal Hearing Individuals with and Without Tinnitus.

OBJECTIVES: To evaluate the functions of cochlear structures and the distal part of auditory nerve as well as dead regions within the cochlea in individuals with normal hearing with or without tinnitus by using electrophysiological tests. MATERIALS AND METHODS: Nine individuals (ages: 21-59 years) with normal hearing with tinnitus were included in the study group. Thirteen individuals (ages: 25-60 years) with normal hearing without tinnitus were included in the control group. Immitancemetric examination, pure-tone audiometry (125Hz-16kHz), speech audiometry in quiet and noise environments, transient evoked otoacoustic emissions (TEOAEs), distortion product otoacoustic emissions (DPOAEs), threshold equalizing noise (TEN test (500Hz-4kHz), and ECochG tests, Beck Depression Questionnaire, Tinnitus Handicap Questionnaire, and Visual Analog Scale were performed. RESULTS: In the study group, three patients were found to have a minimal depression and six were found to have a mild depression. In pure-tone audiometry, the threshold (6-16 kHz) in the study group was significantly higher than that of the control group at all frequencies. In the study group, lower performance scores were obtained in speech discrimination in noise in both ears. In the control group, no dead region was detected in the TEN test whereas 75% of subjects in the study group had dead regions. DPOAE and TEOAE responses between study and control group subjects were not different. In the ECochG test, subjects in the study group showed an increase in the summating potential/action potential (SP/AP) ratio in both ears. CONCLUSION: Determination of the SP/AP ratio in patients with tinnitus may be useful in diagnosing hidden hearing loss. Detection of dead regions in 75% of patients in the TEN test may indicate that inner hair cells may be responsible for tinnitus.

Systematic Audiological Assessment of Auditory Functioning in Patients With Parkinson's Disease.

Purpose Alterations in primary auditory functioning have been reported in patients with Parkinson's disease (PD). Despite the current findings, the pathophysiological mechanisms underlying these alterations remain unclear, and the effect of dopaminergic medication on auditory functioning in PD has been explored insufficiently. Therefore, this study aimed to systematically investigate primary auditory functioning in patients with PD by using both subjective and objective audiological measurements. Method In this case-control study, 25 patients with PD and 25 age-, gender-, and education-matched healthy controls underwent an audiological test battery consisting of tonal audiometry, short increment sensitivity index, otoacoustic emissions (OAEs), and speech audiometry. Patients with PD were tested in the on- and off-medication states. Results Increased OAE amplitudes were found when patients with PD were tested without dopaminergic medication. In addition, speech audiometry in silence and multitalker babble noise demonstrated higher phoneme scores for patients with PD in the off-medication condition. The results showed no differences in auditory functioning between patients with PD in the on-medication condition and healthy controls. No effect of disease stage or motor score was evident. Conclusions This study provides evidence for a top-down involvement in auditory processing in PD at both central and peripheral levels. Most important, the increase in OAE amplitude in the off-medication condition in PD is hypothesized to be linked to a dysfunction of the olivocochlear efferent system, which is known to have an inhibitory effect on outer hair cell functioning. Future studies may clarify whether OAEs may facilitate an early diagnosis of PD.

Transient Otoacoustic Emissions and Auditory Brainstem Responses in Low-Risk Cohort of Newborn and One-Month-Old Infants: Assessment of Infant Auditory System Physiology in the Prenatal Alcohol in SIDS and Stillbirth Network Safe Passage Study.

BACKGROUND: The Prenatal Alcohol and Sudden Infant Death Syndrome and Stillbirth Network, known as the "Safe Passage Study," enrolled approximately 12,000 pregnant women from the United States and South Africa and followed the development of their babies through pregnancy and the infant's first year of life to investigate the role of prenatal alcohol exposure in the risk for sudden infant death syndrome (SIDS) and adverse pregnancy outcomes, such as stillbirth and fetal alcohol spectrum disorders. PURPOSE: Auditory system tests were included in the physiologic test battery used to study the effects of prenatal alcohol exposure on neurophysiology and neurodevelopment, as well as potential causal relationships between neurodevelopmental disorders and SIDS and/or stillbirth. The purpose of this manuscript is to describe normative results when using the auditory test battery applied. RESEARCH DESIGN: The test battery included the auditory brainstem response (ABR) and transient-evoked otoacoustic emissions (TEOAEs). Data were collected on individual ears of newborns and 1-month-old infants. STUDY SAMPLE: From a cohort of 6,070 with auditory system exams, a normative subsample of 325 infants were selected who were not exposed prenatally to alcohol, cigarette smoke, or drugs nor were they preterm or low birthweight. The subsample is small relative to the overall study because of strict criteria for no exposure to substances known to be associated with SIDS or stillbirth and the exclusion of preterm and low birthweight infants. Expectant mothers were recruited from general maternity at two comprehensive clinical sites, in the northern plains in the United States and in Cape Town, South Africa. These populations were selected for study because both were known to be at high-risk for SIDS and stillbirth. DATA COLLECTION AND ANALYSIS: ABR and TEOAE recordings were stored electronically. Peak latency and amplitude analysis of ABRs were determined by study personnel, and results were evaluated for differences by age, sex, test site, race, and ear (left versus right). RESULTS: TEOAE findings were consistent with existing literature including the increase in signal-to-noise (SNR) over the first month of life. The SNR increase is due to an increase in amplitude of the emission. TEOAE amplitude asymmetry favoring the right ear was found, whereas SNR asymmetry was not, perhaps because of the small sample size. A nonsignificant trend toward larger responses in female babies was found; a result that is generally statistically significant in studies with larger samples. Latencies were found to be shorter in ABRs elicited in the right ear with amplitudes that were slightly bigger on average. An expected decrease in wave V latency was observed from birth to 1-month of age, but the finding was of borderline significance (p = 0.058). CONCLUSIONS: One month is a short time to judge development of the auditory system; however, the ABR and TEOAE findings were consistent with current literature. We conclude that the auditory system data acquired for the Safe Passage Study, as reflected in the data obtained from this cohort of "unexposed" infants, is consistent with published reports of these auditory system measures in the general population.

Assessment Tools for Use in Patients with Ménière Disease: An Update.

A number of electrophysiological tests have been proposed for the initial diagnostic assessment or for the follow-up phase of patients affected by Ménière disease. The most common are: (i) vestibular evoked myogenic potentials (VEMPs); (ii) electrocochleography (ECochG); and (iii) otoacoustic emissions (OAEs). This paper presents the latest clinical developments with these 3 testing modalities. The PubMed, Embase, and Cinahl databases were searched from 2006 to December 2016. Full-text articles were obtained in cases where the title, abstract, or key words suggested that the study may be eligible for this review. The medical subject heading (MeSH) terms included the following: Ménière, hearing threshold, vestibule, otoacoustic emissions, inner ear, ECochG, VEMPs. There were 368 identified papers, out of which 87 were eligible for inclusion. Overall the data in the literature are still limited and the recommended procedures have not reached an international consensus. From the available data, one can conclude that none of the electrophysiological tests could be considered as pathognomonic, for the diagnosis of Ménière disease: presently, the tests could be mostly used in a supportive role to the clinical diagnosis. Hopefully, in the future, improved technology in electrophysiological testing could contribute to the development of better strategies for the diagnosis of Ménière disease.

Otoacoustic Emissions in Rural Nicaragua: Cost Analysis and Implications for Newborn Hearing Screening.

Objective (1) Determine the incidence and risk factors for congenital hearing loss. (2) Perform cost analysis of screening programs. Study Design Proportionally distributed cross-sectional survey. Setting Jinotega, Nicaragua. Subjects and Methods Otoacoustic emissions (OAEs) were used to screen 640 infants <6 months of age from neonatal intensive care unit, institutional, and home birth settings. Data on 15 risk factors were analyzed. Cost of 4 implementation strategies was studied: universal screening, screening at the regional health center (RHC), targeted screening, and screening at the RHC plus targeted screening. Cost-effectiveness analysis over 10 years was based on disability-adjusted life year estimates, with the World Health Organization standard of cost-effectiveness ratio (CER) / gross domestic product (GDP) <3, with GDP set at $4884.15. Results Thirty-eight infants failed the initial OAE (5.94%). In terms of births, 325 (50.8%) were in the RHC, 69 (10.8%) in the neonatal intensive care unit, and 29 (4.5%) at home. Family history and birth defect were significant in univariate analysis; birth defect was significant in multivariate analysis. Cost-effectiveness analysis demonstrated that OAE screening is cost-effective without treatment (CER/GDP = 0.06-2.00) and with treatment (CER/GDP = 0.58-2.52). Conclusions Our rate of OAE failures was comparable to those of developed countries and lower than hearing loss rates noted among Nicaraguan schoolchildren, suggesting acquired or progressive etiology in the latter. Birth defects and familial hearing loss correlated with OAE failure. OAE screening of infants is feasible and cost-effective in rural Nicaragua, although highly influenced by estimated hearing loss severity in identified infants and the high travel costs incurred in a targeted screening strategy.

An effective compromise between cost and referral rate: A sequential hearing screening protocol using TEOAEs and AABRs for healthy newborns.

OBJECTIVE: This study evaluated the efficacy of a sequential hearing screening protocol using transient evoked otoacoustic emission (TEOAE) and automated auditory brainstem response (AABR) tests in healthy newborns. DESIGN: A TEOAE screening was performed during the first 48-72 h of life. If the infants failed, an AABR test was performed at the same time, and they were referred for a TEOAE rescreening at six weeks old. The results of screening Protocol 1 (only TEOAE) were compared with those of screening Protocol 2 (sequential TEOAE + AABR screenings for the first screening and TEOAE for the rescreening). STUDY SAMPLE: A total of 1062 healthy newborns were enrolled in this research. RESULTS: For Protocol 1, the first screening and rescreening referral rates were 11.1% and 2.2%, respectively. In contrast, for Protocol 2, the referral rates were significant lower at 3.8% and 0.9%, respectively. Using the two protocols, six infants were diagnosed with hearing loss (0.57%). CONCLUSIONS: Adding simultaneous AABR tests for infants who fail TEOAE testing at the first screening stage can significantly reduce referral rates without increasing misdiagnosis rates. Although this sequential screening process involves slightly more time and has a higher cost than TEOAE alone, its greater accuracy compensates for this difference.

Objective assessment of subjective tinnitus through contralateral suppression of otoacoustic emissions by white noise; suggested cut-off points.

OBJECTIVE: Normative otoacoustic emission (OAE) suppression values are currently lacking and the role of cochlear efferent innervation in tinnitus is controversial. The aim of this study was to investigate the association between tinnitus and medial olivocochlear bundle (MOCB) malfunction. Potential suppression amplitude cut-off criteria that could differentiate participants with tinnitus from those without were sought. DESIGN: Mean suppression amplitudes of transient evoked OAEs and distortion product OAEs by contralateral white noise (50 dBSL) were recorded. Six mean suppression amplitudes criteria were validated as possible cut-off points. STUDY SAMPLE: The population consisted of normal hearing (n = 78) or presbycusic adults (n = 19) with tinnitus or without (n = 28 and 13, respectively) chronic tinnitus (in total, n = 138 78 females/60males, aged 49 ± 14 years). RESULTS: Participants with mean suppression values lower than 0.5-1 dBSPL seem to present a high probability to report tinnitus (specificity 88-97%). On the other hand, participants with mean suppression values larger than 2-2.5dBSPL seem to present a high probability of the absence of tinnitus (sensitivity 87-99%). Correlations were stronger among participants with bilateral presence or absence of tinnitus. CONCLUSIONS: This study seem to confirm an association between tinnitus and low suppression amplitudes (<1 dBSPL), which might evolve into an objective examination tool, supplementary to conventional audiological testing.

Assessment of otoacoustic emission suppression in women with migraine and phonophobia.

Given that the medial olivocochlear efferent system reduces the amplitude of otoacoustic emissions (OAE), the aim of this study was to establish whether such a pathway is affected in women with migraine and phonophobia by means of OAE suppression testing. In this prospective case-control study, 55 women (29 with migraine and phonophobia and 26 healthy women) were subjected to transient-evoked otoacoustic emission (TEOAE) testing at frequencies from 1 to 4 kHz. The amplitudes of the TEOAE response before and after exposure to contralateral noise and the magnitude of TEOAE suppression were assessed. The average TEOAE amplitudes in conditions with and without exposure to contralateral noise were not significantly different between the groups. However, the magnitude of TEOAE suppression was lower in the group with migraine; that difference was only statistically significant for frequencies 1 and 1.5 kHz (p = 0.042 and p = 0.004, respectively). In this study, women with migraine and phonophobia exhibited deficits in OAE suppression, which points to a disorder affecting the medial olivocochlear efferent system.

Assessment of hearing via otoacoustic emission in patients that underwent spinal anesthesia.

OBJECTIVE: In this study, our aim is to show the differences between the preoperative and postoperative otoacoustic emissions (OAE) value in patients, who underwent spinal anesthesia. PATIENTS AND METHODS: The presented study was carried out as a randomized, double-blinded, prospective study upon the approval of Ethics Committee of Medicine School, Erciyes University. The study was conducted in accordance with the Helsinki Declaration. The study involved 39 ASA I-II patients (aged 18-65 years), who underwent varicectomy operation in the Cardiovascular Surgery Department. For each of the patients, 3 OAE measurements were performed; the day before surgery, during surgery and the 1st day after surgery. RESULTS: Significant differences were detected between the 2000 F2 measurements performed before, during and after the surgery (p<0.05). The differences originated from measurements performed before and during surgery. Significant differences were detected among 3000 F1 measurements performed before, during and after surgery (p<0.05). Hearing loss is one of the late complications of spinal anesthesia. In this study, we observed the differences between the preoperative and postoperative OAE values. The incidence of hearing loss detectable with auditory measurements has been reported to vary between 10 and 50%. Of these, 25% is clinically relevant or recognizable. However, it is considered to be a subjective test, because it is influenced from mental, motor and psychological status of the patient. But the management in hearing loss following spinal anesthesia is still controversial. Hearing loss is generally spontaneously resolved within a few days. However, there are case reports of hearing loss lasting for months. CONCLUSIONS: In this study, we observed differences between some preoperative and postoperative OAE values.

Improving newborn hearing screening: Are automated auditory brainstem response ear inserts an effective option?

OBJECTIVE: Universal newborn hearing screening is an established practice among Hong Kong public hospitals using a 2-stage automated auditory brainstem response (AABR) screening protocol. To enhance overall efficiency without sacrificing program accuracy, cost reduction in terms of replacing the initial ear coupler-based screening with a more economical ear insert-based screening procedure was considered. This study examined the utility of an insert-based AABR initial screening approach and the projected cost-effectiveness of a combined probe-based plus follow-up ear coupler AABR screening procedure. METHODS: Following prenatal maternal consent, newborn hearing screening was conducted with 167 healthy neonates using a cross-sectional, repeated measures study design. The neonates were screened with AABR sequentially; using ear coupler and ear probe (insert) procedures, in both ears, with two different but comparable AABR instruments. Testing took place in the antenatal ward of a department of obstetrics and gynaecology, at a large public hospital. RESULTS: With the specific combination of instruments deployed for this study insert-based AABR screening generated a five-fold higher rescreen rate and took an additional 50% screening time compared to coupler-based AABR screening. Although the cost of consumables used in a 2-stage AABR screening protocol would reduce by 9.87% if the combined procedure was implemented, the findings indicated AABR screening when conducted with an ear probe has reduced utility compared with conventional ear coupler screening. CONCLUSIONS: Significant differences may occur in screening outcomes when changes are made to coupler method. Initiating a 2-stage AABR screening protocol with an ear insert technique may be impracticable in newborn nurseries given the greater number of false positive cases generated by this approach in the present study and the increased time required to carry out an insert-based procedure.

Inventory of current EU paediatric vision and hearing screening programmes.

OBJECTIVE: To examine the diversity in paediatric vision and hearing screening programmes in Europe. METHODS: Themes for comparison of screening programmes derived from literature were used to compile three questionnaires on vision, hearing, and public health screening. Tests used, professions involved, age, and frequency of testing seem to influence sensitivity, specificity, and costs most. Questionnaires were sent to ophthalmologists, orthoptists, otolaryngologists, and audiologists involved in paediatric screening in all EU full-member, candidate, and associate states. Answers were cross-checked. RESULTS: Thirty-nine countries participated; 35 have a vision screening programme, 33 a nation-wide neonatal hearing screening programme. Visual acuity (VA) is measured in 35 countries, in 71% of these more than once. First measurement of VA varies from three to seven years of age, but is usually before age five. At age three and four, picture charts, including Lea Hyvarinen, are used most; in children over four, Tumbling-E and Snellen. As first hearing screening test, otoacoustic emission is used most in healthy neonates, and auditory brainstem response in premature newborns. The majority of hearing testing programmes are staged; children are referred after 1-4 abnormal tests. Vision screening is performed mostly by paediatricians, ophthalmologists, or nurses. Funding is mostly by health insurance or state. Coverage was reported as >95% in half of countries, but reporting was often not first-hand. CONCLUSION: Largest differences were found in VA charts used (12), professions involved in vision screening (10), number of hearing screening tests before referral (1-4), and funding sources (8).

Hearing assessment data in HIV-infected and uninfected children of Cape Town, South Africa.

Researchers are showing that the rate of hearing loss in children with perinatal HIV infection (PHIV) is higher than in HIV-unexposed, uninfected children. These data, however, have been collected mostly in the USA; extensive hearing data from low- and middle-income countries are lacking. The purpose of this study was to collect audiometric data in PHIV and HIV-uninfected children living in Cape Town, South Africa. Questionnaire data along with distortion product otoacoustic emissions (DPOAEs) and pure-tone testing were completed. Hearing loss was determined using the pure-tone thresholds defined as a pure-tone average (PTA) of 500, 1000, 2000, and 4000 Hz of >15 dB HL in the poorer ear. All data were compared between PHIV and HIV-uninfected children. Sixty-one (37 PHIV and 24 HIV-uninfected) children had hearing data. HIV status was not significantly associated with DPOAEs. The rate of conductive hearing loss was 11.5%; five PHIV and two HIV-uninfected children. The rate of any hearing loss was higher in PHIV children, but this difference was not statistically significant. PHIV children had a significantly higher mean PTA in the poorer ear than HIV-uninfected children. Conductive type of hearing loss was more common than sensorineural hearing loss. The underlying cause of hearing loss in the present study therefore remains unclear. Future research should include an examination of auditory neural function in an effort to determine the possible reason for differences in hearing.

Low-cost blast wave generator for studies of hearing loss and brain injury: blast wave effects in closed spaces.

BACKGROUND: Military personnel and civilians living in areas of armed conflict have increased risk of exposure to blast overpressures that can cause significant hearing loss and/or brain injury. The equipment used to simulate comparable blast overpressures in animal models within laboratory settings is typically very large and prohibitively expensive. NEW METHOD: To overcome the fiscal and space limitations introduced by previously reported blast wave generators, we developed a compact, low-cost blast wave generator to investigate the effects of blast exposures on the auditory system and brain. RESULTS: The blast wave generator was constructed largely from off the shelf components, and reliably produced blasts with peak sound pressures of up to 198dB SPL (159.3kPa) that were qualitatively similar to those produced from muzzle blasts or explosions. Exposure of adult rats to 3 blasts of 188dB peak SPL (50.4kPa) resulted in significant loss of cochlear hair cells, reduced outer hair cell function and a decrease in neurogenesis in the hippocampus. COMPARISON TO EXISTING METHODS: Existing blast wave generators are typically large, expensive, and are not commercially available. The blast wave generator reported here provides a low-cost method of generating blast waves in a typical laboratory setting. CONCLUSIONS: This compact blast wave generator provides scientists with a low cost device for investigating the biological mechanisms involved in blast wave injury to the rodent cochlea and brain that may model many of the damaging effects sustained by military personnel and civilians exposed to intense blasts.

An objective assessment method for frequency selectivity of the human auditory system.

BACKGROUND: Frequency selectivity (FS) is an important aspect of auditory function, and is typically described by a tuning curve function. Sharply tuned curves represent a higher acuity in detecting frequency differences, and conversely, broadly tuned curves demonstrate a lower acuity. One way of obtaining tuning curves is from techniques based on subjective behavioral responses, which yields psychophysical tuning curves (PTCs). In contrast, other methods rely on objective auditory responses to sound, such as neuron responses and otoacoustic emissions, amongst others. The present study introduces an objective method that uses stimulus frequency otoacoustic emissions (SFOAEs) to assemble suppression tuning curves (STCs). Finding an objective method of accurately measuring human FS is very important, as it would permit the FS to be assayed in non-responsive patients (e.g., neonates or comatose patients). However, before the objective method can be applied, it must be demonstrated that its ability to estimate the FS, gives comparable results to those obtained by subjective procedures i.e. PTCs. METHODS: SFOAEs responses, generated in the peripheral auditory system, were used to produce STCs. PTCs were measured by behavioral responses. The validity of the objective measures of human FS were determined by comparing stimulus frequency otoacoustic emission suppression tuning curves (SFOAE STCs) to PTCs at common stimulus parameters in 10 individuals with normal hearing, at low probe-tone levels. RESULTS: The average Q10 ratios measured between PTCs and SFOAE STCs from subjects were close to 1 at various center frequencies (F2,24 = .15, p = .858). The estimates of FS provided by SFOAE STCs and PTCs were similar. CONCLUSIONS: This system could be used to estimate auditory FS by both objective and subjective methods. SFOAE STCs have the potential to provide an objective estimate of auditory FS.

Assessment of tinnitus with tinnitus severity index, tinnitus handicap inventory and distortion product otoacoustic emissions in patients with normal hearing and hearing loss.

OBJECTIVES: This study aims to assess ears with tinnitus and without distortion product otoacoustic emissions (DPOAE) in patients with and without hearing loss and to classify the tinnitus symptoms on the basis of tinnitus severity index (TSI) and tinnitus handicap inventory (THI) in both groups. PATIENTS AND METHODS: A total of 102 patients with tinnitus symptoms were included in the study. Of these patients, 48 had (32 males, 16 females; mean age 45±8.9 years) normal hearing and 54 patients (42 males, 12 females; mean age 52±12.1 years) had hearing loss. Pure tone audiogram, high-frequency audiometer and DPOAE were applied to patients. Tinnitus symptoms of patients were assessed with TSI and THI. RESULTS: Significantly higher tinnitus severity was monitored in group with hearing loss compared with group with normal hearing (p=0.024). There was a significant similarity in the frequencies affected from tinnitus between the groups (p<0.001). The TSI and THI showed significant similar results between two groups (p<0.001). A significant decrease was found in ears with tinnitus in frequencies of 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz and 6000 Hz with DPOAE compared to the ears without tinnitus in group with normal hearing (p<0.05). CONCLUSION: Our study results show that patients with TSI and THI are affected by tinnitus at the same rate in daily life whether they have hearing loss or not, but those with hearing loss have a higher tinnitus severity. Decreased DPOAE responses can be found in patients with normal hearing, which can be more profound in low-frequency tinnitus, particularly.

Why parents refuse newborn hearing screening and default on follow-up rescreening--a South African perspective.

OBJECTIVES: This study describes screen refusal and follow-up default characteristics together with caregiver reasons for screen refusal and follow-up default in two South African universal newborn hearing screening programs. METHODS: A retrospective record review of universal newborn hearing screening conducted at two hospitals (Hospital A n = 954 infants; Hospital B n = 2135) over a 31-33 month period. Otoacoustic emission screening was conducted with rescreen recommended within six weeks for a uni- or bilateral refer. Program efficacy was described according to coverage, referral and follow-up rates. A prospective telephonic interview with caregivers who declined the initial screen (n = 25) and who defaulted on follow-up (n = 25) constituted the next study component. Caregivers were randomly selected from the screening programs for a survey related to reasons for newborn hearing screening refusal and follow-up default. RESULTS: Screening coverage (89.3% Hospital A; 57.4% Hospital B), initial referral rates (11.6% Hospital A; 21.2% Hospital B) and follow-up return rates (56.1% Hospital A; 35.8% Hospital B) differed significantly between hospitals and were below benchmarks. The most frequent reasons for screen refusal were related to costs (72%), caregiver knowledge of newborn hearing screening (64%) and health care professional knowledge and team collaboration (16%). Almost all caregivers (96%) indicated that if costs had been included in the birthing package or covered by medical insurance they would have agreed to newborn hearing screening. Reasons for follow-up default were most commonly related to caregiver knowledge of newborn hearing screening (32%) and costs (28%). One in four caregivers (24%) defaulted on follow-up because they forgot to bring their infant for a rescreen. Only half of caregivers (48%) who defaulted on follow-up reported being aware of initial screen results while 60% reported being aware of the recommended follow-up rescreen. CONCLUSION: Caregivers most commonly refused screening due to associated costs and mostly defaulted on follow-up due to an apparent lack of knowledge regarding initial screen outcome and recommendations made for follow-up. Including NHS as a mandated birthing service is essential if coverage is to be increased, while reducing follow-up defaults requires proactive reminders and improved communication with caregivers.