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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 25  |  Issue : 2  |  Page : 59-65

Comparison of frequency-Specific hearing thresholds between pure-tone audiometry and auditory steady-state response


1 Department of ENT-HNS, Command Hospital Airforce, Bangalore, India
2 Department of ENT, Military Hospital, Roorkee, Uttarakhand, India

Date of Web Publication16-Aug-2019

Correspondence Address:
Dr. Himanshu Swami
Department of ENT, Command Hospital Airforce, Bengaluru - 560 007, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/indianjotol.INDIANJOTOL_97_18

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  Abstract 


Introduction: Hearing assessment in difficult to assess persons gives inconsistent response in free field hearing and pure-tone audiometry (PTA). We have been performing brainstem evoked response audiometry (BERA) as an objective assessment in such cases. BERA has limitations that it is not frequency specific, measures thresholds in higher frequencies only, signal intensity levels cannot be higher than 90 dB and presents the data in waveform which needs to be interpreted by experienced audiologist to deduce correct information. All these limitations can be negated with use of auditory steady-state response (ASSR) which can present intensity levels till 120 dB, is frequency specific, even for lower frequencies and has automated response and deduction analysis. The aim of our study was to compare pure-tone thresholds with ASSR thresholds in normal hearing and hearing loss subjects with an objective to validate the ASSR as a tool for objective hearing assessment. Materials and Methods: In this prospective cross-sectional study of 70 adults (n = 140 ears) of both genders, with and without hearing complaints, Group 1 consisted of 24 individuals of normal hearing, Group 2 consisted of 25 individuals of sensorineural hearing loss, and 21 individuals with conductive hearing loss in Group 3. The patients were evaluated with PTA and ASSR test. The mean pure tone and ASSR thresholds for each frequency were calculated and analyzed using the SPSS IBM software. Results: The mean difference of ASSR with PTA was noted at 9.92 dB in the right ear and 10 dB in the left ear. A high significant correlation was noted between ASSR and PTA with P(0.0005) across all the three groups. The relationship between the PTA and ASSR measurement for measuring average hearing threshold levels is described by the equation: PTA = ASSR mean × 0.99–9.92. Conclusion: ASSR is an excellent tool to predict accurate level of frequency-specific hearing threshold. It has constant relationship with pure tone thresholds. ASSR can predict true hearing thresholds in “difficult to assess” patients such as children and malingerers. This can also be used in the prediction of disability assessment objectively.

Keywords: Auditory steady-state response, hearing threshold, pure-tone audiometry


How to cite this article:
Swami H, Kumar S. Comparison of frequency-Specific hearing thresholds between pure-tone audiometry and auditory steady-state response. Indian J Otol 2019;25:59-65

How to cite this URL:
Swami H, Kumar S. Comparison of frequency-Specific hearing thresholds between pure-tone audiometry and auditory steady-state response. Indian J Otol [serial online] 2019 [cited 2019 Nov 17];25:59-65. Available from: http://www.indianjotol.org/text.asp?2019/25/2/59/264678




  Introduction Top


Since the introduction of universal neonatal screening, hearing loss has been diagnosed earlier. Obtaining early, precise, and objective hearing information for a patient would guide cochlear implant and other treatment decisions. Therefore, there is a need to define the characteristics of hearing loss to choose the most appropriate treatment.[1],[2],[3]

Pure tone audiometry (PTA) is the Gold Standard for hearing evaluation, but it is a subjective evaluation of the auditory acuity. At times, it may be inconclusive, in children younger than 6 years of age, especially when some psychomotor impairment is present. It is also inaccurate in uncooperative adults and malingerers. Due to these limitations of the responses obtained in behavioral tests in children and adults, electrophysiological methods such as auditory brainstem response (ABR) and auditory steady-state response (ASSR) are the most used resources.

Due to the objective nature of the test auditory evoked potentials like ABR were introduced in screening children for hearing loss worldwide.[4],[5],[6] This technique has difficulties in the determination of the participating frequency ranges because the test collects responses from the whole basement membrane with a stimulus tone of short duration. As a result, the ABR method has little frequency specificity. In addition, ABR tests conducted with click stimuli are of limited use in identifying threshold levels at low-frequency ranges.[7] The ABR test is also has limitations in identifying characteristics of severe hearing loss over 90 dB HL because this range is beyond its detection limit.[8]

In this aspect, the ASSR method is a more promising approach, as it provides frequency-specific information facilitated by the use of a modified pure tone for gathering the response. This can be particularly useful for assessing low medical category and disability in serving and retired armed forces personnel.

The ASSR is a type of auditory evoked potential, elicited with modulated tones that can be used for determining hearing sensitivity for patients of all ages. It is a far-field auditory evoked potential recording.[9],[10] The ASSR reflects activity from different portions of the brain, depending on the modulation rate used. Brain's central structures respond to slower rates, while the brainstem and peripheral auditory nerves responds to a faster modulation rates. The results are shown as an electrophysiological audiogram, which allows the physician to see the configuration of an individual's hearing.[9],[10],[11]

According to John and Picton[12] and Valdes et al.,[13] the method has advantages, such as the objective threshold detection as well as the simultaneous evaluation of multiple frequencies and the presentation of high-intense stimuli.[14]

Higher strength stimulus tones are used in the measurement of ASSR than that used in ABR test, and due to the continuous and regular characteristics of the tones used, the technique can detect more frequency-specific responses.[15] Hence, the ASSR measurement provides frequency-specific hearing threshold and a better information for individuals with profound sensorineural hearing loss (SNHL) of 90 dB HL and above in whom ABR cannot be applied.[16]

The advantages of ASSR are that multiple frequencies and/or two ears can be tested simultaneously[14] and hence saving time when compared to ABR. ASSR can be used to predict behavioral auditory threshold because of its ability to measure frequency-specific responses in the background electroencephalogram to auditory stimuli presented across a broad range of frequencies and sound pressure levels.[15] The test stimuli are reasonably frequency specific regardless of the mode of modulation because they are not pure tones. These stimuli are continuous too, making the calibration straightforward.[16] ASSR can even differentiate patients of severe SNHL from that of the profound degree of SNHL, because of steady tonal stimuli used permitting higher outputs for analysis.[17] Moreover finally, the most important advantage is that the spectrum of the response is predicted precisely by that of the stimulus spectrum without the need for subjective interpretation of the recorded response.[18] Hence, ASSR overcomes the common limitation of most clinical tests of auditory evoked potentials.

However, the limitations of ASSR are that the standard test is highly affected by test individual behavioral status (e.g., sleeping or awake),[19] and it is, therefore, difficult to gain reliable results from infants.[20],[21] A second disadvantage is that ASSR has reduced response amplitude when several stimuli are introduced simultaneously.[14] ASSR may be less suitable to test individuals with normal hearing.


  Materials and Methods Top


The study was conducted at tertiary care hospital of armed forces, and informed consent was obtained from each patient. The study was conducted on patients who visited the Department of Otolaryngology suspected of abnormal hearing and on young adults with normal hearing. Patients were excluded if they had an ear disease such as chronic otitis media or otitis media with effusion.

There were 70 test individuals consisting of 38 males (54.3%) and 32 females, that is, 45.7% participated in the study. A total of 140 ears were tested. The average age of test individuals was 41.71 years, the youngest being 20 years, and the oldest person in the study was 76 years. PTA test was performed for all and depending on their hearing acuity they were divided into three groups. Group 1 consisted of 24 individuals of normal hearing; Group 2 consisted of 25 individuals of SNHL, and 21 individuals with conductive hearing loss were placed in Group 3. ASSR was performed on all these individuals.

PTA was performed with using clinical audiometer model 2001 digital (Arphi) calibrated according to the American National Standards Institute S3.6–1996 standards. Tone thresholds by air conduction were obtained with PT at frequencies of 500, 1000, 2000, and 4000 Hz, respectively.

The ASSR was performed using Neurosoft version 1.14 (Neurosoft, Ivanovo, Russia). The electrodes were placed on the scalp at locations similar to that of ABR, as it's a far-field auditory evoked potential recording.[10] A noninverting electrode was placed over the vertex of the head or forehead, and the inverting electrodes were placed over the mastoid prominence on one side. The ground or earthing electrode was placed over the opposite mastoid. Each ear was tested for frequencies of 500, 1000, 2000, and 4000 Hz, respectively. The testing intensity at 60 dB at modulation frequency of 80–100 Hz was presented initially and gradually increased till response was obtained. Click stimulus was presented through TDH-49 insert ear phones with modulation frequency between 80 and 100 Hz. When intensity of the modulated tone reached above the individual's threshold, it evoked an electrical activity in the brain. These electrical activities were processed through an analyzing software to check the amplitude and the variability of these responses to see if it is following the modulation envelope, and the results are shown as an electrophysiological audiogram, which allows the physician to see the configuration of an individual's hearing.[9],[10],[11]

The collected data were analyzed with IBM SPSS statistics software 23.0 Version (IBM, USA). To describe about the data descriptive statistics frequency analysis, the percentage analyses were used for categorical variables, and the mean and standard deviation were used for continuous variables. To find the significant difference between the bivariate samples in paired groups and the paired sample t-test was used. For the multivariate analysis, the one-way analysis of variance (ANOVA) with Tukey's post hoc test was used. To assess the relationship between the variables Pearson's correlation was used. To find the significance in categorical data, the Chi-square test was used. In all the above statistical tools, the P = 0.05 is considered as statistically significant level.


  Results Top


Age distribution

The study patients were homogenously distributed throughout the three groups, with significance value of 0.0005 as per ANOVA and post hoc tests.

[Table 1], shows the mean age throughout the three groups is 41.71 with ages ranging from 20 years to 76 years, and with 95% confidence interval (CI) ranging from 38.01 to 45.42.
Table 1: Age distribution

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[Table 2], denotes the high significance of 0.0005 for the homogenous distribution of cases with respect to their age in ANOVA test.
Table 2: Analysis of variance test

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Assessing the difference between pure-tone audiometry and auditory steady-state response

PTA test for Group 1 consisting of 24 individuals with normal hearing showed mean threshold levels for 500, 1000, 2000, and 4000 Hz at 4.6, 5.2, 6.04, and 5.3 dB, respectively, in the right ear, and the ASSR in the same ear for 500, 1000, 2000, and 4000 Hz were at 14.4, 15.2, 16.04, and 15.3 dB, respectively. Similarly, in the left ear PTA for 500, 1000, 2000, and 4000 Hz at 5.7, 5.0, 5.9, and 6.4 dB, respectively. Moreover, ASSR for 500, 1000, 2000, and 4000 Hz at 15.7, 15.0, 15.9, and 16.4 dB, respectively. In this group, ASSR was specifically able to detect thresholds at about 10 dB higher than that of PTA.

On PTA evaluation of the second group of 25 cases of SNHL, hearing thresholds in the right ear for 500, 1000, 2000, and 4000 Hz were recorded at 38.9, 38.7, 42.9 and 41.2 dB, respectively. ASSR in the same ear for 500, 1000, 2000, and 4000 Hz were recorded at 48.6, 48.7, 52.5, and 51.4 dB, respectively. Similarly, the mean for hearing thresholds in the left ear for PTA at 500, 1000, 2000, and 4000 Hz were 41.5, 42.9, 43.7, and 46.1 dB, respectively. ASSR in the left ear for same frequencies was 51.7, 52.6, 53.7, and 56.1 dB, respectively.

Again ASSR was consistently able to detect thresholds specifically at 10 dB higher than that of PTA.

Finally, the third group of 21 individuals with conductive hearing loss showed PTA values at 19.7, 20.5, 19.8, and 20.3 dB for 500, 1000, 2000 and 4000 Hz, respectively in the right ear. ASSR in the same ear and for same frequency was 29.1, 30.5, 29.8, and 30.3 dB, respectively. Similarly in the left ear, hearing thresholds measured at 500, 1000, 2000, and 4000 Hz with PTA and ASSR were 21.3, 20.0, 21.9, 19.1, and 31.4, 30.3, 31.5, 29.1 dB, respectively. This group had similar findings of ASSR being 10 dB higher than that of PTA.

[Table 3] depicts mean PTA and ASSR values for all the groups (n = 70) in frequency-specific manner. The ASSR values were consistent with PTA, about 10 dB higher, in all the groups.
Table 3: Mean values for pure tone audiometry and auditory steady-state response

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Considering the mean PTA and ASSR thresholds, no statistically significant difference existed between the right and left ears with respect to PTA and ASSR thresholds at different frequencies.

As shown in [Table 4], PTA and ASSR tests were compared using paired t-test for the group of SNHL individual and there is statistically high significant correlation between the two tests with P = 0.0005.
Table 4: Paired samples test in sensorineural hearing loss (Group 2)

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As seen in [Table 5], the paired t-test done among the conductive hearing loss individuals also shows that the ASSR is correlated to PTA with highly significant P = 0.0005 at different frequencies and both in the right and left ears.
Table 5: Paired samples test in conductive hearing loss (Group 3)

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Correlation between pure-tone audiometry and auditory steady-state response

As seen in [Table 6] ANOVA test and Tukey honestly significant difference (HSD) multiple comparison tests were done to compare the PTA with ASSR within the group as well as between the three groups and found to have a strong correlation between the two with P = 0.0005 in both the tests.
Table 6: ANOVAa

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As seen in [Table 7] Multiple comparison Tukey HSD test shows mean thresholds detected by ASSR at 500 Hz in right ear having 95% CI values similar to that of PTA with 0.0005 significance value. Similarity between the 95% CI levels has been noted between PTA and ASSR for 1000, 2000, and 4000 Hz in both right and left ears which are depicted in [Table 8], [Table 9], [Table 10].
Table 7: Coefficients (Dependent variable PTA at 500 Hz)

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Table 8: Coefficients (for Dependent Variable: PTA at 1000Hz)

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Table 9: Coefficients (for Dependent Variable: PTA at 2000Hz)

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Table 10: Coefficients (for Dependent Variable: PTA at 4000Hz)

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[Figure 1] and [Figure 2] depicts mean PTA and ASSR of right ear, whereas, [Figure 3] and [Figure 4] represents mean PTA and ASSR of right ear of all the groups. It shows the clinical correlation between the PTA and ASSR with ASSR values being 10 dB higher than that of PTA.
Figure 1: Pure tone audiometry right

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Figure 2: Auditory steady-state response right

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Figure 3: Pure tone audiometry left

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Figure 4: Auditory steady-state response left

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Deducing the relationship between pure-tone audiometry and auditory steady-state response

The ASSR and PTA were conducted for all the study patients in a single setting. Hence, no cases were lost throughout the study. The averages of ASSR and PTA were compared for all the frequencies and hence, there were no rejection or removal of variables during the study period.

At 500 Hz, the coefficient constant was calculated to be 9.773. Hence, the ASSR could be represented as PTA 500 = ASSR (500 Hz) × 0.995 − 9.773.

Similarly at 1000 Hz, the constant is 9.986 so the equation for PTA is PTA (1000 Hz) = ASSR (1000 Hz) ×1 − 9.986.

At 2000 Hz, the ASSR could be represented as PTA (2000 Hz) = ASSR (2000 Hz) ×1.004−10.

At 4000 Hz, the equation deduced to calculate PTA using ASSR is PTA (4000 Hz) = ASSR (4000 Hz) ×0.998–9.957.

Finally, the relationship between the PTA and ASSR measurement for measuring average hearing threshold levels throughout all four frequencies as described by the equation derived by regression analysis is:

PTA = ASSR mean × 0.99–9.92.


  Discussion Top


The ASSR provides a window for viewing the function of the brain's response to sound, which has proven to be useful in the diagnostic assessment of neurologic function. Auditory evoked potentials provide an objective means of assessing the integrity of the peripheral and central auditory systems. For this reason, evoked potential audiometry has become a powerful tool in measuring the hearing acuity.

Canale et al. noted 32 dB difference between the mean values of PTA and ASSR.[18] Recently, Beck et al. reported the mean difference of 8.175 dB HL between audiometric and electrophysiological thresholds. Similar studies agree that there is a significant correlation between hearing thresholds determined by the ASSR and the PTA, but the difference was found to be between 4 and 34 dB HL.[22],[23],[24],[25],[26] They have also reported a better correlation of PTA thresholds with that of ASSR in patients with SNHL as compared to those with normal hearing. It has been suggested that this difference may reflect an increase in the amplitude of response due to the presence of recruitment.[21]

In our study of 70 individuals males contributed to 54.3% and 45.7% were females. The average age of test patients was 41.71 years with 95% CI ranging from 38.01 to 45.42. ANOVA test indicated high significance of 0.0005 for the homogenous distribution of cases with respect to their age.

We assessed ASSR predictability of hearing thresholds among individuals of normal hearing and conductive hearing loss, and those with SNHL and we noticed there is no difference between ASSR and PTA thresholds across all the three groups by using single stimulating frequency and with multiple simultaneous frequencies. In our assessment, the mean difference between ASSR and PTA among normal hearing individuals was found to be at 9.95 dB in the right ear and 10 dB in the left ear. The mean difference of 9.87 dB was seen between ASSR and PTA in right ear and 9.97 dB in left ear among the SNHL individuals. There is a difference value of 9.85 dB and 10 dB for right and left ear, respectively for individuals with conductive hearing loss. Across the three groups, ASSR was specifically able to detect thresholds at about 10 dB higher than that of PTA.

No statistically significant difference existed between the right and left ears, with respect to PTA and ASSR thresholds at different frequencies. Similarly, no difference was noted with the PTA and ASSR thresholds between the gender and age of the test individuals.

Over all mean difference of ASSR with PTA was noted at 9.92 dB in right ear and 10 dB in left ear. A high significant correlation was noted between ASSR and PTA with P = 0.0005 across all the three groups.

Paired samples test of PTA and ASSR for air and bone conduction were conducted for all the three groups showed the ASSR is correlated to PTA with highly significant P = 0.0005 at different frequencies in both the right and left ears.

ANOVA test and Tukey HSD multiple comparison tests done to compare the PTA with ASSR within the group as well as between the three groups were found to have strong correlation between the two with P = 0.0005 in both the tests. Moreover with a significantly high CI level of 95% across all frequencies in both the ear.

PTA can be represented in terms of ASSR for each frequency by the equation derived by regression: PTA (500 Hz) = ASSR (mean 500 Hz) × 0.995−9.773, PTA (1000 Hz) = ASSR (mean 1000 Hz) ×1−9.986, PTA (2000 Hz) = ASSR (mean 2000 Hz) ×1.004–10, and for PTA (4000 Hz) = ASSR (mean 4000 Hz) ×0.998−9.957. When calculated for across the study, the following equation was derived:

PTA = ASSR mean × 0.99–9.92

The results obtained have shown that the ASSR is a valid procedure to predict the hearing threshold. However, there is a need to have a comparative study between ASSR and ABR to assess the benefits of ASSR over the ABR.


  Conclusion Top


ASSR is an excellent tool, to predict accurate level of frequency-specific hearing threshold. It has a constant relationship with PTA thresholds. ASSR can predict true hearing thresholds in “difficult to assess” patients such as children and malingerers. This can also be used in the prediction of disability assessment objectively.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]



 

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