Distortion Product Otoacoustic Emission Data Research Articles

The effect of cumulative noise exposure on distortion product otoacoustic emissions

Objective This study aimed to identify the characteristics of distortion product otoacoustic emissions (DPOAEs) that can be used to differentiate noise-induced hearing loss (NIHL) from age-related hearing loss. A potential index to detect NIHL was defined in terms of its susceptibility to cumulative noise exposure but not to age. Design In this cross-sectional cohort study, a job-exposure matrix was used to calculate the cumulative noise exposure. Multivariate linear regression models were used to examine how age and cumulative noise exposure associated with DPOAEs at individual frequencies after adjusting for hypertension, dyslipidaemia, tobacco use and alcohol consumption. Study sample The pure-tone audiometry and DPOAEs data collected from 239 male workers in a steel factory. Results DPOAEs and DPOAE signal-to-noise ratios (SNRs) at all frequencies were found to be correlated with age, and those at 2, 3, 4 and 6 kHz were correlated with both age and noise exposure. The difference between DPOAE SNR at 1 and 3 kHz showed significant correlation with noise exposure but not with age. Conclusions The results showed that this DPOAE index, the DPOAE SNR at 1 kHz minus the DPOAE SNR at 3 kHz, could add values to audiometric evaluation of NIHL.

Weakened Cochlear Nonlinearity During Human Aging and Perceptual Correlates.

As humans age, compressive nonlinearity-a hallmark of healthy cochlear function-changes. The nonlinear distortion-component of the distortion product otoacoustic emission (DPOAE) provides a noninvasive gauge of cochlear nonlinearity. Earlier published work has suggested that weakened nonlinearity begins in middle age; the current work extends this investigation into the eight decade of life using advanced DPOAE data collection and analysis methods as well as multiple metrics of nonlinearity, including a test of loudness scaling. The 2f1-f2 DPOAE was recorded in 20 young adults, 25 middle-aged adults and 32 older adults from f2 = 0.78 to 9.4 kHz with primary tones (f2/f1 = 1.22) swept upward at a rate of 0.5 octave/sec. Only frequencies with audiometric thresholds ≤20 dB HL were included in the analysis and to the extent possible, ears were audiometrically matched to eliminate hearing threshold as a contributing factor to the observed age effects. Input/output functions were generated for the separated distortion-component of the DPOAE to probe compressive nonlinearity of the cochlea, and ipsilateral suppression of the DPOAE was conducted to probe two-tone suppression. To investigate the perceptual effects of weakening nonlinearity on loudness perception, the same subjects performed categorical loudness scaling. Age effects on both DPOAE and loudness scaling variables were assessed, and correlations were conducted between key OAE and perceptual metrics. Age × Frequency ANOVAs revealed that the compression knee of the DPOAE I/O function occurred at higher stimulus levels in both groups of older adults compared to young adults, suggesting an expanded linear range with aging; also, the compressive slope (growth beyond the knee point) was steeper in older-adults compared to young adults. These results were most notable at high frequencies. ANOVAs including age and auditory threshold as factors confirmed that the age effect observed was independent of threshold. Additionally, in smaller subsets of subjects with audiometrically matched data, these same trends persisted, further ruling out hearing threshold as an influential factor. The growth of DPOAE ipsilateral suppression was shallower near 4 kHz in middle-aged and older adults compared to young adults and elevated suppression thresholds were observed. Results of categorical loudness scaling showed steeper growth of loudness for older adults and, at fixed sensation levels (dB SL), the older-adult group rated tones as louder than did their young-adult counterparts, suggesting abnormal loudness growth and perception. Several correlations between the compression knee of the DPOAE I/O function and key metrics of loudness scaling were significant and accounted for up to one-third of the variance. Results indicate that the aging cochlea begins to show weakened nonlinearity in middle age and it progressively weakens further into senescence. The perceptual impact of weakened nonlinearity during aging is manifested as abnormal loudness judgments; that is, in older-adult ears, a tone considered comfortable or medium in young-adult ears can be considered loud. The biophysical origin of this weakened nonlinearity is not known. It is hypothesized to reflect aging-related damage to, or loss of, outer hair cells and their stereocilia. More work is warranted to better define the perceptual impact of a linearized cochlear response in older adults and to consider how this deficit might impact the fitting of hearing aids and other intervention strategies.

Objective parameters of auditory function in premature infants in the first year of life after taking ototoxic antibiotics

To compare the condition of auditory function during the first year of life according to the registration of distortion product otoacoustic emission (DPOAE) and short-latency evoked potentials (SLEP) in premature infants who received ototoxic antibiotics to those ones, who did not. Auditory function was examined in 145 premature infants. Auditory assessment was carried out by registration of DPOAEs, SLEPs and tympanometry. Statistical processing was performed using the program Statgraphics Centurion XV. In this study, according to DPOAE, the average response values of the cochlea in premature infants who had a history of ototoxic therapy, undergo final changes after children reach the age of 6 months. The study of latent periods and threshold values of the V peak of SLEP showed a delay in the maturation process of the perceiving and conducting auditory structures during the first year of life in children who received ototoxic antibiotics in the first month of life. We evaluated the timing of the completion of response changes in children of the control group using the DPOAE and SLEP registration data. In children of the study group, we evaluated the effect of the administered ototoxic antibiotics. Timing of audiological control of the hearing organ condition are demonstrated for premature children after ototoxicosis, required methods of its examination are established.

Detecting changes in distortion product otoacoustic emission maps using statistical parametric mapping and random field theory.

Distortion product otoacoustic emission (DPOAE) maps collect DPOAE emissions over a broad range of frequencies and ratios. One application of DPOAE mapping could be monitoring changes in intracranial pressure (ICP) in space, where non-invasive measures of ICP are an area of interest. Data were collected in two experiments to statistically assess changes in DPOAE maps. A repeatability study where four maps per subject were collected across four weeks to establish "normal" variability in DPOAE data, and a posture study where subjects were measured supine and prone with lower body negative pressure, lower body positive pressure (LBPP), and at atmospheric pressure. DPOAE amplitude maps were analyzed using statistical parametric mapping and random field theory. Postural changes produced regional changes in the maps, specifically in the range of 5-7.5 kHz and between primary tone ratios of 1.13-1.24. These regional changes were most pronounced in the prone LBPP condition, where amplitudes were lower from baseline for the Postural Cohort than the Repeatability Cohort. Statistical parametric mapping provided a sensitive measure of regional DPOAE map changes, which may be useful clinically to monitor ICP noninvasively in individuals or for research to identify differences within in cohorts of people.

Blast exposure in the military and its effects on sensory and cognitive auditory processing

Blast-induced traumatic brain injury (TBI) and hearing loss are the two most common types of injuries sustained by military personnel while serving in the U.S. Global War on Terrorism. Recently several VA audiology clinics have reported active duty service members complaining of having problems communicating in noisy listening environments despite having normal to near-normal pure tone thresholds. In addition to standard clinical measures, we used electroencephalography (EEG) to determine whether damage to suprathreshold responding auditory nerve fibers in the sensory periphery and/or trauma to cortical regions associated with attention and working memory were responsible for the reported listening complications. In separate auditory and visual selective attention tasks, behavioral and neural measures suggest no evidence of long term neurotrauma affecting normal cognitive function. We found while absolute measures of auditory brainstem encoding varied greatly in all study subjects, comparisons of how the envelope following response (EFR) changes with modulation depth hint at differences between blast and non-blast exposed service members. These findings are consistent with audiometric threshold and distortion product otoacoustic emission data that show subtle differences between groups within clinically defined normal limits. Taken together these results suggest subclinical differences in audiometric measures might explain differences in suprathreshold listening.

Optimizing Clinical Interpretation of Distortion Product Otoacoustic Emissions in Infants.

The purpose of this study was to analyze distortion product otoacoustic emission (DPOAE) level and signal to noise ratio in a group of infants from birth to 4 months of age to optimize prediction of hearing status. DPOAEs from infants with normal hearing (NH) and hearing loss (HL) were used to predict the presence of conductive HL (CHL), sensorineural HL (SNHL), and mixed HL (MHL). Wideband ambient absorbance was also measured and compared among the HL types. This is a prospective, longitudinal study of 279 infants with verified NH and HL, including conductive, sensorineural, and mixed types that were enrolled from a well-baby nursery and two neonatal intensive care units in Cincinnati, Ohio. At approximately 1 month of age, DPOAEs (1-8 kHz), wideband absorbance (0.25-8 kHz), and air and bone conduction diagnostic tone burst auditory brainstem response (0.5-4 kHz) thresholds were measured. Hearing status was verified at approximately 9 months of age with visual reinforcement audiometry (0.5-4 kHz). Auditory brainstem response air conduction thresholds were used to assign infants to an NH or HL group, and the efficacy of DPOAE data to classify ears as NH or HL was analyzed using receiver operating characteristic (ROC) curves. Two summary statistics of the ROC curve were calculated: the area under the ROC curve and the point of symmetry on the curve at which the sensitivity and specificity were equal. DPOAE level and signal to noise ratio cutoff values were defined at each frequency as the symmetry point on their respective ROC curve, and DPOAE results were combined across frequency in a multifrequency analysis to predict the presence of HL. Single-frequency test performance of DPOAEs was best at mid to high frequencies (3-8 kHz) with intermediate performance at 1.5 and 2 kHz and chance performance at 1 kHz. Infants with a conductive component to their HL (CHL and MHL combined) displayed significantly lower ambient absorbance values than the NH group. No differences in ambient absorbance were found between the NH and SNHL groups. Multifrequency analysis resulted in the best prediction of HL for the SNHL/MHL group with poorer sensitivity values when infants with CHL were included. Clinical interpretation of DPOAEs in infants can be improved by using age-appropriate normative ranges and optimized cutoff values. DPOAE interpretation is most predictive at higher F2 test frequencies in young infants (2-8 kHz) due to poor test performance at 1 to 1.5 kHz. Multifrequency rules can be used to improve sensitivity while balancing specificity. Last, a sensitive middle ear measure such as wideband absorbance should be included in the test battery to assess possibility of a conductive component to the HL.

Fractional-order modelling and simulation of human ear

ABSTRACTConventional integer-order lumped element models cannot fully describe the memory-dependent viscoelastic behaviour of bio-tissues. We propose a tunable and more predictive lumped element modelling of fractional-order sense for human ear, which is better adapted to the physical nature of the bio-materials. We develop a computational–mathematical framework for human ear to account for the power-law characteristics of viscoelastic bio-tissues. On the experiment side, we obtain impedance data and distortion product otoacoustic emissions data from several participants, to estimate the round-trip outer-middle ear gain, for parameter fitting and validation of the proposed model. This modelling approach provides a sound basis for data-driven modelling and simulation of the viscoelastic tissues of the human ear.Abbreviations: DPOAE: distortion product otoacoustic emission; FTF: forward transfer function; OMEG: round-trip outer-middle ear gain; RTF: reverse transfer function; TM: tympanic membrane

A DPOAE assessment of outer hair cell integrity in ears with age-related hearing loss

Distortion product otoacoustic emissions (DPOAEs) were used to assess outer hair cell (OHC) integrity in human ears with age-related hearing loss. Sound pressure measurements were made in the ear canal over the stimulus range 40–90 dB SPL (L2), with L1 = 0.45*L2 + 44 with F2 = 2 and 3 or 4 kHz. Model-generated DPOAE I/O functions were fit to DPOAE data to quantify the contribution of loss of nonlinearity (OHC loss) to the hearing loss. Results suggest OHC loss as a contributing cause of age-related hearing, regardless of audiogram configuration. It seems likely that OHC and strial pathology co-exist in ears with AHL.

TE and DP otoacoustic emission data from an Australian cross-sectional hearing study

Objective: This paper presents a summary of otoacoustic emission (OAE) data collected as part of an Australian hearing health survey (Carter, 2011; Williams et al, 2014) designed to: (1) examine the relationship between audiological indicators and participant characteristics, and (2) extract audiological data suitable for reference use. Design: Cross-sectional cohort study. Distortion product (DP) OAE and transient evoked (TE) OAE measures. Study sample: Age range 11–35 years; N = 1386 participants (2672 test ears). Results: Descriptive statistics for amplitude and signal-to-noise ratio (SNR) were calculated for 327 participants (589 test ears; age 13 to 32 years). DPOAE amplitudes down to the 25th percentile were > 0 dB SPL for test frequencies up to 6 kHz. TEOAE SNRs down to the 25th percentile were > 6 dB SPL up to 4 kHz. Summary: This dataset can be used as a clinical reference for similar populations, providing that the same test parameters are used. Conclusions: The clinical significance of OAE testing would be greater if agreed criteria were available. These data could be pooled with other datasets to build a substantial OAE database, similar to the existing international standards for pure-tone hearing threshold levels (HTLs) (ISO, 2000).

Distortion product otoacoustic emission data in perinatally HIV-infected and HIV-exposed but uninfected children and adolescents in the Pediatric HIV/AIDS Cohort Study.

The effect of perinatal HIV infection and exposure on sub-clinical auditory function can be measured with distortion product otoacoustic emissions (DPOAEs). DPOAEs were obtained at 4 frequency bins (1, 2, 3 and 4 kHz) and categorized by a signal-to-noise ratio. HIV infection was not associated with poorer DPOAEs. Among HIV-infected children, HIV viral load≥400 copies/mL had significantly lower odds of better DPOAEs.

Gender, Music, and Distortion Product Otoacoustic Emission Components

The prevalence of personal music (PM) system use with earphones is high among young adults. Although previous research has demonstrated that the majority of these adults may not be listening at levels or for durations considered dangerous, the long-term consequences of PM system use are not fully understood. In this report the relationship between self-reported PM use (i.e., non, light, moderate, or heavy) and peripheral auditory function as assayed through distortion product otoacoustic emission (DPOAE) components and fine structure was explored. The purpose was to evaluate the relationship between PM system use and peripheral auditory function. One hundred and one (N = 101) young adults, 18 to 30 years of age, with normal hearing. Survey data were first obtained to determine PM system user status along with type of earphones used, most common listening volume, and most common listening duration. Once normal-hearing sensitivity was confirmed with a hearing screening, the DPOAE research protocol was administered. DPOAEs (2f1 to f2) were measured between 1 and 6 kHz with stimulus levels fixed at L1, L2 = 55,40 dB SPL and f2/f1 = 1.22. DPOAE level as well as fine-structure depth and spacing in 1/3rd octave (oct) bands around 1, 1.5, 2, 3, 4, and 6 kHz were compared across various PM system user groups. The ear-canal DPOAE was separated into the so-called generator and characteristic frequency (CF) components. The characteristics of the components were also compared across user groups. Almost all participants reported listening to a PM system between < 1 hr/d to 3 hr/d, and 67% of the participants reported medium/comfortable as the most common volume used during a typical day. There was no significant effect of user status on 3rd oct DPOAE data, 1/3rd oct band component data, or fine-structure spacing data. Women exhibited significantly higher DPOAE as well as generator and CF component levels in the lower half of the frequency range evaluated. There were no significant gender differences for fine-structure spacing or depth. The slope of the CF component was significantly steeper in women. In this cross-sectional study, there were no significant effects of self-reported PM use on either the ear-canal DPOAE or its constituent parts. Fine-structure depth varied across user groups in a nonsystematic manner. Women exhibited higher DPOAE and component levels in the lower portion of the frequency range evaluated. It is interesting to note that a greater proportion of men reported listening to their PM system at loud or very loud levels. The size of the effect relative to the sample size of each user group may be masking the deleterious effects of PM system use on the peripheral auditory system.

Genome-wide linkage analyses identify Hfhl1 and Hfhl3 with frequency-specific effects on the hearing spectrum of NIH Swiss mice

BackgroundThe mammalian cochlea receives and analyzes sound at specific places along the cochlea coil, commonly referred to as the tonotopic map. Although much is known about the cell-level molecular defects responsible for severe hearing loss, the genetics responsible for less severe and frequency-specific hearing loss remains unclear. We recently identified quantitative trait loci (QTLs) Hfhl1 and Hfhl2 that affect high-frequency hearing loss in NIH Swiss mice. Here we used 2f1-f2 distortion product otoacoustic emissions (DPOAE) measurements to refine the hearing loss phenotype. We crossed the high frequency hearing loss (HFHL) line of NIH Swiss mice to three different inbred strains and performed linkage analysis on the DPOAE data obtained from the second-generation populations.ResultsWe identified a QTL of moderate effect on chromosome 7 that affected 2f1-f2 emissions intensities (Hfhl1), confirming the results of our previous study that used auditory brainstem response (ABR) thresholds to identify QTLs affecting HFHL. We also identified a novel significant QTL on chromosome 9 (Hfhl3) with moderate effects on 2f1-f2 emissions intensities. By partitioning the DPOAE data into frequency subsets, we determined that Hfhl1 and Hfhl3 affect hearing primarily at frequencies above 24 kHz and 35 kHz, respectively. Furthermore, we uncovered additional QTLs with small effects on isolated portions of the DPOAE spectrum.ConclusionsThis study identifies QTLs with effects that are isolated to limited portions of the frequency map. Our results support the hypothesis that frequency-specific hearing loss results from variation in gene activity along the cochlear partition and suggest a strategy for creating a map of cochlear genes that influence differences in hearing sensitivity and/or vulnerability in restricted portions of the cochlea.

Do “Optimal” Conditions Improve Distortion Product Otoacoustic Emission Test Performance?

To determine whether an "optimal" distortion product otoacoustic emission (DPOAE) protocol that (1) used optimal stimulus levels and primary-frequency ratios for each f2, (2) simultaneously measured 2f2 - f1 and 2f1 - f2 distortion products, (3) controlled source contribution, (4) implemented improved calibration techniques, (5) accounted for the influence of middle ear reflectance, and (6) applied multivariate analyses to DPOAE data results in improved accuracy in differentiating between normal-hearing and hearing-impaired ears, compared with a standard clinical protocol. Data were collected for f2 frequencies ranging from 0.75 to 8 kHz in 28 normal-hearing and 78 hearing-impaired subjects. The protocol included a control condition incorporating standard stimulus levels and primary-frequency ratios calibrated with a standard SPL method and three experimental conditions using optimized stimuli calibrated with an alternative forward pressure level method. The experimental conditions differed with respect to the level of the reflection-source suppressor tone and included conditions referred to as the null suppressor (i.e., no suppressor tone presented), low-level suppressor (i.e., suppressor tone presented at 58 dB SPL), and high-level suppressor (i.e., suppressor tone presented at 68 dB SPL) conditions. The area under receiver operating characteristic (A(ROC)) curves and sensitivities for fixed specificities (and vice versa) were estimated to evaluate test performance in each condition. A(ROC) analyses indicated (1) improved test performance in all conditions using multivariate analyses, (2) improved performance in the null suppressor and low suppressor experimental conditions compared with the control condition, and (3) poorer performance below 4 kHz with the high-level suppressor. As expected from A(ROC), sensitivities for fixed specificities and specificities for fixed sensitivities were highest for the null suppressor and low suppressor conditions and lowest for standard clinical procedures. The influence of 2f2 - f1 and reflectance on test performance were negligible. Predictions of auditory status based on DPOAE measurements in clinical protocols may be improved by the inclusion of (1) optimized stimuli, (2) alternative calibration techniques, (3) low-level suppressors, and (4) multivariate analyses.

Growth of suppression in humans based on distortion-product otoacoustic emission measurements.

Distortion-product otoacoustic emissions (DPOAEs) were used to describe suppression growth in normal-hearing humans. Data were collected at eight f(2) frequencies ranging from 0.5 to 8 kHz for L(2) levels ranging from 10 to 60 dB sensation level. For each f(2) and L(2) combination, suppression was measured for nine or eleven suppressor frequencies (f(3)) whose levels varied from -20 to 85 dB sound pressure level (SPL). Suppression grew nearly linearly when f(3) ≈ f(2), grew more rapidly for f(3) < f(2), and grew more slowly for f(3) > f(2). These results are consistent with physiological and mechanical data from lower animals, as well as previous DPOAE data from humans, although no previous DPOAE study has described suppression growth for as wide a range of frequencies and levels. These trends were evident for all f(2) and L(2) combinations; however, some exceptions were noted. Specifically, suppression growth rate was less steep as a function of f(3) for f(2) frequencies ≤ 1 kHz. Thus, despite the qualitative similarities across frequency, there were quantitative differences related to f(2), suggesting that there may be subtle differences in suppression for frequencies above 1 kHz compared to frequencies below 1 kHz.

Using Benefit-Cost Ratio to Select Universal Newborn Hearing Screening Test Criteria

Current protocols presumably use criteria that are chosen on the basis of the sensitivity and specificity rates they produce. Such an approach emphasizes test performance but does not include societal implications of the benefit of early identification. The purpose of the present analysis was to evaluate an approach to selecting criteria for use in Universal Newborn Hearing Screening (UNHS) programs that uses benefit-cost ratio (BCR) to demonstrate an alternative method to audiologists, administrators, and others involved in UNHS protocol decisions. Existing data from more than 1200 ears were used to analyze BCR as a function of Distortion Product Otoacoustic Emission (DPOAE) level. These data were selected because both audiometric and DPOAE data were available on every ear. Although these data were not obtained in newborns, this compromise was necessary because audiometric outcomes (especially in infants with congenital hearing loss) in neonates are either lacking or limited in number. As such, it is important to note that the characteristics of responses from the group of subjects that formed the bases of the present analyses are different from those for neonates. This limits the extent to which actual criterion levels can be selected but should not affect the general approach of using BCR as a framework for considering UNHS criteria. Estimates of the prevalence of congenital hearing loss identified through UNHS in 37 states and U.S. territories in 2004 were used to calculate BCR. A range of estimates for the lifetime monetary benefits and yearly costs for UNHS were used, based on data available in the literature. Still, exact benefits and costs are difficult to know. Both one-step (DPOAE alone) and two-step (DPOAE followed by automated auditory brainstem response, AABR) screening paradigms were considered in the calculation of BCR. The influence of middle ear effusion was simulated by incorporating a range of expected DPOAE level reductions into an additional BCR analyses Our calculations indicate that for a range of proposed benefit and cost estimates, the monetary benefits of both one-step (DPOAE alone) and two-step (DPOAE followed by AABR) NHS programs outweigh programmatic costs. Our calculations indicate that BCR is robust in that it can be applied regardless of the values that are assigned to benefit and cost. Maximum BCR was identified and remained stable regardless of these values; however, it was recognized that the use of maximum BCR could result in reduced test sensitivity and may not be optimal for use in UNHS programs. The inclusion of secondary AABR screening increases BCR but does not alter the DPOAE criterion level at which maximum BCR occurs. The model of middle ear effusion reduces overall DPOAE level, subsequently lowering the DPOAE criterion level at which maximum BCR was obtained BCR is one of several alternative methods for choosing UNHS criteria, in which the evaluation of costs and benefits allows clinical and societal considerations to be incorporated into the pass/refer decision in a meaningful way. Although some of the benefits of early identification of hearing impairment cannot be estimated through a monetary analysis, such as improved psychosocial development and quality of life, this article provides an alternative to audiologists and administrators for selecting UNHS protocols that includes consideration of societal implications of UNHS screening criteria. BCR suggests that UNHS is a worthwhile investment for society as benefits always outweigh costs, at least for the estimations included in this article. Although the use of screening criteria that maximize BCR results in lower test sensitivity compared with other criteria, BCR may be used to select criteria that result in increased test sensitivity and still provide a high, although not maximal, BCR. Using BCR analysis provides a framework in which the societal implications of NHS protocols are considered and emphasizes the value of UNHS.

Development of distortion product otoacoustic emissions in C57BL/6J mice

Distortion product otoacoustic emissions (DPOAEs) have been used to examine the development of hearing in the rat and gerbil. However, no reports of DPOAE measurement from the onset of hearing in mice are available. Commercially-available components were assembled and adapted to provide a suitable probe microphone and sound delivery system for measuring DPOAE in developing C57BL/6J mice. Furthermore, DPOAE data were compared with the findings of the auditory brainstem response (ABR). DPOAEs were obtained at 8 kHz from 11 days after birth, 20 kHz from 12 days, and 30 kHz from 13 days. Adult-like patterns of DPOAE were obtained 21 days at 8 and 20 kHz, and 28 days at 30 kHz. On the other hand, the ABR thresholds at 12 to 36 kHz appeared between 11 and 12 days and were saturated at 14 days. Based on these data, the onset of measureable DPOAEs in the mouse were earlier than in the rat and gerbil. The maturation of DPOAE in the mouse begins at a lower frequency in the high frequency range. In addition, the ABR threshold reached maturation earlier than DPOAE.

Factors Affecting Sensitivity of Distortion-Product Otoacoustic Emissions to Ototoxic Hearing Loss

(1) To determine the ototoxicity detection rate (sensitivity) for distortion-product otoacoustic emissions (DPOAEs) testing in adults who received ototoxic medications and experienced pure-tone threshold changes during the course of treatment; (2) to determine the extent to which DPOAE sensitivity to ototoxicity depends on the type of drug administered (platinum or antibiotic), magnitude of ototoxic threshold shifts, pre-exposure pure-tone threshold, and DPOAE data; and (3) to build a model to predict DPOAE sensitivity. DPOAE and audiometric data were obtained as part of a prospective Veterans Affairs study investigating methods of ototoxicity monitoring. Data were analyzed from 90 ears of 53 subjects receiving ototoxic medications and showing significant hearing changes in at least one ear. Pure-tone threshold data were obtained at frequencies from 0.5 to 20 kHz, using 1/6-octave precision near the upper frequency limit of hearing. DPOAE data are reported for f2's from 0.8 to 8.0 kHz in 1/6-octave increments using primary levels (L1/L2) of 65/59 dB SPL and a primary frequency ratio (f2/f1) of 1.2. Test results were evaluated at various times during drug treatment to determine whether DPOAE level changes were associated with behavioral hearing changes. Univariate and multivariate analysis techniques were used to determine factors that affected DPOAE sensitivity to ototoxic damage. Of the 90 ears examined, 82 (91%) had DPOAEs that could be monitored for changes. Sixty-four of these 82 ears (78%) had DPOAEs that were reduced or absent following drug treatment. DPOAE sensitivity to ototoxicity was unrelated to the type of ototoxic drug administered. Rather, DPOAE sensitivity depended on the magnitude of postexposure hearing changes and on variables related to pre-exposure audiogram and DPOAE measurements. Behavioral hearing changes not detected by DPOAEs were small on average (<7 dB). DPOAE sensitivity was reduced in ears with poorer pre-exposure hearing, and in ears with measurable DPOAE frequencies limited to f2's below 2.5 kHz or more than one octave from the frequency region where hearing change occurred. Results of logistic regression modeling showed that DPOAEs present at f2's greater than 2.5 kHz were associated with the eventual success of ototoxicity monitoring with DPOAEs. However, independent variables examined could not explain differences in the relative timing of behavioral and DPOAE changes. A roughly equivalent proportion of ears experienced DPOAE changes before, during, or after behavioral hearing changes. DPOAEs are a useful screening tool for ototoxicity in adults with pre-exposure hearing loss, but are less sensitive compared with a behavioral test method that targets thresholds near the upper limit of a subject's audible frequency range. Ears successfully monitored for ototoxicity with DPOAEs are those with better pre-exposure hearing, greater postexposure hearing changes, and baseline DPOAEs near the highest behavioral test frequencies and present at high f2's. Results suggest that successful monitoring of ototoxicity with DPOAEs may be predicted clinically by assessing the measurable DPOAE f2 frequency range and its relation to the highest behavioral test frequencies.

Measuring distortion product otoacoustic emissions using continuously sweeping primaries

Distortion product otoacoustic emission (DPOAE) level from normal hearing individuals can vary by as much as 30 dB with small frequency changes (a phenomenon known as DPOAE fine structure). This fine structure is hypothesized to stem from the interaction of components from two different regions of the cochlea (the nonlinear generator region and the reflection component from the DP region). An efficient procedure to separate these two components would improve the clinical and research utility of DPOAE by permitting separate evaluation of different cochlea regions. In this paper, two procedures for evaluating DPOAE fine structure are compared: DPOAE generated by fixed-frequency primaries versus continuously sweeping primaries. The sweep DPOAE data are analyzed with a least squares fit filter. Sweep rates of greater than 8 s per octave permit rapid evaluation of the cochlear fine structure. A higher sweep rate of 2 s per octave provided DPOAE without fine structure. Under these conditions, the longer latency reflection component falls outside the range of the filter. Consequently, DPOAE obtained with sweeping tones can be used either to get more rapid estimates of DPOAE fine structure or to obtain estimates of DPOAE from the generator region uncontaminated by energy from the reflection region.

Telemedicine for audiology screening of infants

Distortion product otoacoustic emissions (DPOAE) and automated auditory brainstem response (AABR) screening were conducted in infants at a distant hospital using remote computing. Eighteen males and twelve females ranging in age from 11-45 days were tested. Both DPOAE and AABR data were recorded using an integrated test system which was connected to the computer network at the Utah Valley Regional Medical Center. Using a broadband Internet connection, an examiner at Utah State University, 200 km away, could control the DPOAE and the ABR equipment. Identical hearing screening results were obtained for face-to-face and telemedicine trials with all infants. The DPOAE means for face-to-face and telemedicine trials were not significantly different at any frequency. In an analysis of variance, there was no significant difference for the test method (F = 0.8, P > 0.05). These results indicate that remote computing is a feasible telemedicine method for providing DPOAE and ABR hearing screening services to infants in rural communities.

Distortion product otoacoustic emission of symphony orchestra musicians before and after rehearsal

The 2f1-f2 distortion product otoacoustic emission (DPOAE) and hearing levels are obtained for 12 normal-hearing symphony orchestra musicians both before and after their rehearsal. The DPOAE fine structures are determined and analyzed according to the character and prevalence of ripples. Hearing levels, DPOAE levels, and DPOAE fine structures before and after rehearsal are similar, indicating that no or marginal temporary change of the state of hearing were caused by the exposure. The data were further compared to similar data for occupationally nonexposed subjects, one group which was age and gender matched, and other two groups of younger individuals (one group with better hearing levels than the other). The data for the age and gender matched group compared well with the musicians data (and the data for the group of better-hearing younger individuals). In general, the analyses of hearing thresholds and DPOAE data thus lead to the same conclusions concerning the state of hearing.