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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 4  |  Issue : 2  |  Page : 131-136

Auditory brainstem response to a chirp stimulus in infants with normal hearing


1 Audiology Unit, ENT Department, Al Azhar University, Cairo, Egypt
2 Audiology Unit, Hearing and Speech Institute, Live in Imbaba, Giza, Egypt

Date of Submission24-Jan-2020
Date of Decision26-Jan-2020
Date of Acceptance06-Feb-2020
Date of Web Publication29-Jun-2020

Correspondence Address:
Master Degree of Audiology Naglaa G Mohamed
Hearing and Speech Institute, Giza
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sjamf.sjamf_10_20

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  Abstract 


Background The CE-chirp stimulus shows promising results in auditory brainstem recording. The response to broad-band CE-chirp in normal infants and comparing it with the gold standard click stimulus is needed.
Objective The purposes of this study were to (a) standardize auditory brainstem responses (ABR) in infant using chirp stimuli in normal hearing infants, (b) compare them with those evoked by click stimuli, (c) determine whether chirp-evoked response is easier to detect at near threshold values, and (d) analyze the amplitude growth function of chirp-evoked ABR as a function of stimulus intensity in infants.
Patients and methods A total of 50 normal infants, with age ranging from 2 to 24 months, with normal hearing were included. The following procedures were done: a medical history, otologic examinations, behavioral observation audiometry, acoustic impedance, and ABR by click and CE-chirp.
Results The chirp stimulus shows higher amplitude at all intensities and shorter latencies in comparison with click at high intensity and longer at low and threshold levels. The early waves are less frequent in chirp at high intensities.
Conclusion The present study provides reference CE-chirp ABR values for infants. CE-chirp evokes lower threshold than click and easier peak identification at threshold, which is particularly helpful in infants.

Keywords: auditory brainstem response, CE-chirp, click


How to cite this article:
El-Mously MM, Omara A, Mohamed NG. Auditory brainstem response to a chirp stimulus in infants with normal hearing. Sci J Al-Azhar Med Fac Girls 2020;4:131-6

How to cite this URL:
El-Mously MM, Omara A, Mohamed NG. Auditory brainstem response to a chirp stimulus in infants with normal hearing. Sci J Al-Azhar Med Fac Girls [serial online] 2020 [cited 2020 Oct 23];4:131-6. Available from: http://www.sjamf.eg.net/text.asp?2020/4/2/131/288259




  Introduction Top


The auditory brainstem responses (ABR) are widely used to evaluate the hearing of infants. In click ABR, the cochlear traveling wave takes some time to reach from the base of the cochlea to its apical end. Therefore, the different neural units’ activity along the cochlear partition will not be stimulated at the same time and the neural activity across all nerve fibers will be smeared [1],[2].

In an attempt to compensate for the dispersion in the human cochlea, a chirp has been designed based on a cochlear delay model. In chirp, the arrival of each frequency component at its place of maximum excitation along the cochlear partition is delayed; subsequently, all components arrive at approximately the same time. Higher temporal synchronization of the elements that contribute to the evoked response is achieved and larger amplitude ABR is produced [3].

Most research studies evaluating chirp stimuli have focused on adults and older children, despite the use of ABR being most commonly indicated in infants. The general results of these studies have revealed larger waveform amplitudes that reduced the time required for wave detection and therefore produced more efficient ABR evaluations compared with using click stimuli [1],[2].

Infants’ normative ABR data for chirp stimulus have not been published for latency values, which are necessary for determining whether responses are normal or abnormal [4].

This study was designed to assess the use of the chirp stimulus to record ABRs in infants using broad-band CE-chirp. This study was designed to define normative ABR values using CE-chirp in infants.


  Aims Top


This study aims to (a) standardize ABR in infant using chirp stimuli in normal hearing infants, (b) compare them with those evoked by click stimuli, (c) determine whether chirp-evoked response are easier to detect at near threshold values, and (d) analyze the amplitude growth function of chirp-evoked ABR as a function of stimulus intensity in infants.


  Patients and methods Top


After approval by the local ethics committee, Faculty of Medicine for girls, Al-Azhar University, and parents gave verbal consents, this cross-sectional descriptive study was conducted at Hearing and Speech Institute, Audiology Unit, on a total number of 50 infants, and their age ranged from 2 to 24 months.

Inclusion criteria

Age ranges from 2 to 24 months; no prenatal, natal, and postnatal history suggestive of hearing loss; otologically and neurologically free; and normal peripheral hearing as evidenced by otological examination, tympanomertic evaluation, and ABR were the inclusion criteria.

Exclusion criteria

Children with history suggestive of hearing loss, children with neurological disorders, children with behavioral or mental abnormality, and children with any other ENT complaints were excluded.

Method

All infants were subjected to full medical history, general examination, ear examination, and basic audiological evaluation in form of tympanometry and behavioral observation audiometry. Click and CE-chirp-evoked ABR using Interacoustics eclipse 25 EP (Arlington Heights, Illinois,USA) (Interacoustics). Both stimuli are represented by 21.1/s repetition rate in rarefaction polarity, EEG band pass filter setting is 30–1500, recording window is 15 ms, presented by ER 3A insert earphones in decreasing stimulus level 70, 50, 30, and in 10 dB steps down to the threshold.

Electrode montage: active electrode was placed on the forehead (Fz). The reference electrode was placed on the ipsilateral mastoid (M1 or M2), and an electrode on the mid-frontal area (Fpz) serves as ground to minimize myogenic artifact. The electrode impendence was kept below 3 kohms. ABR responses were analyzed for latency of ABR waves (I, III, and V), amplitude (peak to following trough) for click and CE-chirp, and interpeak latencies interval (I–III, III–V, and I–V).

Statistical analysis

Statistical analysis was performed by statistical analysis program (IBM SPSS), version 23 (SPSS Inc., Chicago, Illinois USA). For quantitative variable mean, SD, and range was calculated. Qualitative data were presented as count and percentage. Analytical statistics were performed using χ2 test. The level of significance was 0.05.


  Results Top


In this study, the age ranged from 2 to 24 months (mean age, 14.66±5.9).

The interaural differences regarding latency and amplitude were recorded, with insignificant difference between the two ears, and results were collected from 100 ears.

In our study regarding identification of waves, chirp is better than click in identification of waves V at 20 and 10 dB. Early waves (I and III) chirp is better than click only at low intensity levels (30, 20, and 10 dB) ([Table 1]).
Table 1 Detection of waves (I, III, and V) by click-evoked and chirp at 70, 50, 30, 20 and 10 dB among the studied infants

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Regarding absolute latencies (I, III, and V), the normative values were obtained from our study regarding latency for chirp and its relation to click ([Table 2]). t test is done, and there is no significant difference between the click and chirp in relation to wave I latency. Wave III shows statistical significance, where chirp is shorter than click in 70 and 50 dB and longer than click at 30 and 20 dB ([Table 2]). There was significant difference in wave V latencies, where latency using chirp stimulus is statistically shorter at high intensity levels (70 and 50 dB) and statistically longer at lower intensity levels (30, 20 and 10 dB) ([Figure 1]).
Table 2 Mean absolute latencies of click and chirp-evoked auditory brainstem response waves (I, III, and V) at 70, 50, 30, 20, and 10 dB among the studied children (N=100)

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Figure 1 Latency intensity function of click and chirp-evoked wave (V) at 70, 50, 30, 20, and 10 dB.

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In our study, interpeak latencies done by obtaining waves I and III and V and subsequently calculating (I–III, III–V, and I–V) intervals. The CE-chirp-evoked short but insignificant interpeak latency (I–III). III–V and I–V were significantly shorter than their peers in click-evoked ABR. This is attributed to the fact of shorter absolute waves latencies evoked by chirp as explained earlier.

In our study regarding mean wave V amplitude, there was a statistical significant difference in wave V amplitude, where using chirp stimulus is statistically higher than click stimulus at all intensity levels ([Table 3]). In our study regarding threshold detection, great amplitude difference in favor of chirp when compared with click at threshold level (20 and 10 dB) which give chirp better wave V identification. The estimated mean chirp threshold was 12.60 dBnHL in comparison with 17.40 dBnHL to click. There is statistically significant difference.
Table 3 Amplitude of click and chirp-evoked auditory brainstem response wave (V) at 70, 50, 30, 20 and 10 dB (100 ears)

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The amplitude growth function was estimated by calculating the linear regression and its slope. For this study, wave V amplitude evoked slope was 7.15 nV/dB.


  Discussion Top


This study was designed to standardize ABR in infant using chirp stimuli in normal hearing infants, to compare them with those evoked by click stimuli, determine whether chirp-evoked response are easier to detect at near threshold values, and analyze the amplitude growth function of chirp-evoked ABR as a function of stimulus intensity in infants.

Normative values for chirp-evoked auditory brainstem responses

Regarding morphology of chirp-evoked ABR, waves I, III, and V are the most prominent waves in infants ABR waveform. Early waves I and III are more detected with CE-chirp stimulation, particularly at 30 dB down to threshold when compared with click response. The higher level of stimulation (70 and 50 dB) identification of early waves was reduced. This reduced morphology of early waveform components with the CE-chirp at high intensities can be explained by the upward spread of excitation, which causes excitation of many frequencies at different times. This, in turn, may cause desynchronization of the neural firing, which affects the morphology of the ABR.

Cobb and Stuart [5] confirmed similar performance for early waves (I and III).

Moreover, Parlak et al. [6] reported harder identification of waves I and III, to be 72 and 77%), respectively, at 90 dBnHL.

On the contrary, Cebulla et al. [7] found that wave I is detected by 97 and 82% at 60 and 40 dB, respectively, wave III was identifiable by 100 and 98% at 60 and 40 dBnHL, respectively. This difference among the two studies in both methodology and subject characteristics accounts for the reported variability.

Regarding absolute wave latency for CE-chirp-evoked ABR, the absolute waves (III and V) latencies in chirp-evoked ABR were significantly shorter, as expected in this age group based on data from literature [8],[9].

Parlak et al. [6] studied the normative data for absolute wave V latency in normal hearing adult. They reported latency of wave V at 70 dB 5.44 ms, 6.47 at 50 dB, 7.07 at 40 dB, and 8.24 dB at 20 dB, which agrees with the present study, taking in mind the effect of age and recording parameters.

On the contrary, in the study by Cobb and Stuart [5], wave V latencies at 60, 45, and 30 dB were 7.79, 8.47, and 9.03 ms, respectively, which disagree with the present study after compensating for age. This difference can be attributed to change in the recording parameters (repetition rate).

Regarding amplitude, wave V amplitude values of the current study are in agreement with the study by El Danasoury et al. [10]. The wave V amplitude was 0.44, 0.55, and 0.69 µV at 30, 50, and 70 dB, respectively, in contrast to 0.4, 0.54, and 0.57 reported in the current study after compensating for wave V amplitude maturation.

On the contrary, Parlak et al. [6] results disagreed with most of the reported amplitude in age-matched data in literature as well as the current study. They reported small mean wave V amplitude; the mean wave V amplitude was found to be 0.21, 0.25, 0.38, and 0.42 µV at 20, 40, 50, and 70 dBnHL, respectively.

Comparison between click and CE-chirp-evoked auditory brainstem responses

Regarding absolute wave latencies, significantly short latency for waves IIII and V by chirp stimulation in comparison with click at intensity level 70 and 50 dBnHL. At lower intensity levels (30, 20 and 10 dBnHL), the opposite occurred. Click latencies were shorter than those obtained with CE-chirp stimulus. Similar findings were confirmed by Rodrigues and Lewis [11] where chirp latency is shorter at 80 and 60 dBnHL and longer than click at 40 and 20 dBnHL.

The study by El Danasoury et al. [10] is in agreement with the present study; the wave latencies to chirp waves III and V were earlier in chirp in 90, 70, and 50 dB, and then became longer at 30 dB.

Similar finding are reported by El Kousht et al. [12] regarding prolonged CE-chirp latency at threshold level.

On the contrary, Cobb and Stuart [13] reported significant longer CE-chirp latencies than corresponding click for wave V at 60 and 45 dB, with repetition rate 57.7/s, which disagrees with the current work, which can be attributed to the effect of repetition rate on chirp-evoked ABR.

Regarding interpeak latencies, this study agrees with Cebulla et al. [7]. They measured interpeak latencies at 60 dB for click and chirp. The estimated interpeak latency when a chirp stimulus is used is slightly shorter for waves I–III and significantly shorter for waves I–V. Moreover shorter interpeak latencies for chirp-evoked ABR in comparison with those by click were obtained by Cobb and Stuart [13].

Regarding the amplitude differences between click and chirp in the current study, the chirp mean waves amplitude differences were significantly higher than click, with widening of the gap between them as the intensity decreased. This is explained by the effect of reducing the intensity on the ABR is that the spectrum will also shift to the lower frequencies which explains the improved chirp amplitude at lower intensities. These results are similar to those reported by Rodrigues and Lewis [11] where larger amplitude to chirp was found at 60, 40, and 20 dBnHL.

Threshold detection by chirp and click

The current study detects a significant difference between the stimuli. The mean chirp threshold was 12.6 in comparison with 17.4 for click, with a difference of 4.8 dB in advantage to chirp. The results of El Danasoury et al. [10] are in agreement with the current study. The mean wave V amplitude at threshold for ears had same hearing threshold values for both stimuli. Wave V amplitude was larger for chirp stimulus by 109%. Larger amplitude facilitates visual inspection of the response especially at threshold. The latency was significantly longer in chirp response.

Amplitude growth function

Although the intensity–amplitude–function of the ABR is not strictly linear, this method provides a simple and robust estimate of the intensity–amplitude–function for a limited intensity range. For the current study, it was 7.15 nv/dB.

Muller et al. [14] tested the hypophysis of maturation on chirp evoked ABR by studying the amplitude growth function. The mean slope for infants below 18 months was 6.2 nV/dB and 8.7 nV/dB for infants between 18 and 48 month which agreed with the current study.


  Conclusion Top


  1. For the clinical application, it is advisable to use chirp-evoked ABR for the estimation of hearing thresholds rather than click-evoked ABR. Chirp-evoked ABR is much more reliable and can also be measured at higher levels of residual EEG noise, especially when wave identifiability is not clear as in infants.
  2. The present study provides reference CE-chirp ABR values for infants.
  3. CE-chirp stimulus could elicit lower thresholds than click stimulus with higher amplitude and longer latency.
  4. Click has better detection of early waves (I and III) than CE-chirp at high intensity level; thus, click-evoked ABR is still considered a better indicator of brainstem transmission time.


Recommendations

  1. CE-chirp can evoke consistent, fast, and accurate threshold estimation in infants in hand with click, if no response in high intensity level to chirp, or if auditory neuropathy was suspected.
  2. Chirp stimulus can be implemented in screening for its high amplitude and fast response.
  3. The normative CE-chirp values obtained from the study can be used for application in clinic and for further research.
  4. Future studies are recommended to study CE-chirp-evoked ABR in premature infants and elderly.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
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2.
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Cebulla M, Lurz H, Dieler W. Evaluation of waveform, latency and amplitude values of chirp ABR in newborns. Inter J Ped Otolaryng 2014; 78:631–636.  Back to cited text no. 7
    
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Gorga M, Kaminski J, Beauchaine K, Jesteadt W, Neely S. Auditory brainstem responses from children three months to three years of age: normal patterns of response II. J Speech Hear Res 1989; 132:281–288.  Back to cited text no. 8
    
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El Danasoury I, El Kholy W, El-Kabarity R, Abdel-Moteleb R. Prediction of pure tone threshold in sensorineural hearing loss patients using chirp stimuli [MD thesis]. Cairo, Egypt: Faculty of Medicine, Ain Shams University (2016).  Back to cited text no. 10
    
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Mühler R, Rahne T, Verhey JL. Auditory brainstem responses to broadband chirps: amplitude growth functions in sedated and anaesthetized infants. Int J Pediatr Otorhinolaryngol 2013; 77:49–53.  Back to cited text no. 14
    


    Figures

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    Tables

  [Table 1], [Table 2], [Table 3]



 

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