Key Points:
1- NB CE-Chirp ABR thresholds were found closer to PTA thresholds than
the TB ABR thresholds.
2- NB CE-Chirp ABR significantly shortens the test time.
3- Chirp stimulus is more available for hearing screening.
4- NB CE-Chirp ABR can be used in the prediction of behavioral hearing
thresholds in adults whose behavioral hearing thresholds are difficult
to determine.
5- Chirp stimulus provides larger and more detectable wave V amplitudes
according to Tone Burst.
1. Introduction
The auditory brainstem response (ABR) is an objective method to evaluate
the neurologic functioning of the auditory pathway, auditory brainstem
neurologic integrity, and an estimate of hearing thresholds in
individuals (1). ABR waveforms include a series of positives and
negatives waves occurring during the first 10 ms following an acoustical
stimulation. They reflect the synchronous activity of the auditory
system, and phrases with roman numerals (I–V) (2). (ABR) is used in
children and adults for universal newborn hearing screening, evaluation
of hearing functions, diagnosis of peripheral and central nervous system
diseases, and also intraoperative monitoring ( 3, 4). The ABR evaluation
represents a standardized and comprehensive method for determining the
potential risk of drug-induced hearing dysfunction (5). Also, ABR
studies have reported abnormal (prolonged) latencies for waves III
and/or V with autism spectrum disorders (6). Stimulus variants used in
ABR according to frequency bands (350-10,000 Hz) are click stimulus (all
frequency bands), Tone-Burst (TB) stimulus (narrow frequency band) and
chirp stimulus ( 1, 7). Chirp stimulus was developed to compensate for
the delay of the cochlear wave traveling in ABR by stimulated different
neural units along with the cochlear partition. (8). Different models of
chirp stimulus have been identified in the literature to obtain
efficiently ABR (9, 10).
Tone-Burst (TB) stimulus type is widely used to obtain
frequency-specific responses (11). However, the TB stimuli causes
cochlear wave travelling delay in a specific frequency range (12). It is
also difficult to identify the wave V at low stimulus levels
(<60 dB nHL) with Tone-Burst stimuli (13). Although the design
of CE-Chirp stimulation is an important development in the auditory
electrophysiological field, CE-Chirp stimulus is insufficient in the
estimation of frequency-specific thresholds (14). The Narrow Band (NB)
CE-Chirp stimulus has been developed for compensating for some
deficiencies of the Tone-Burst stimulus (9, 15). NB CE-Chirp stimulus
has designed for including four central frequencies as 0.5, 1, 2, 4 kHz.
The stimulated area of the NB CE-Chirp stimulus is slightly wider than
the TB stimulus and allows synchronized firing of different neural units
along the base to the apical end of the cochlea. (3). Ferm et al. (16)
compared NB Chirp and TB ABR and NB CE-Chirp ABR wave V amplitudes were
found to be larger than TB ABR wave V amplitudes. Rodrigues at al.(12)
detected that NB CE-Chirp ABR wave V amplitudes were greater than TB ABR
wave V amplitudes at all levels except 500 Hz 80 dB nHL.
Studies about the behavioral hearing thresholds (BHT) estimation by
electrophysiological methods are up to date in the literature(17). For
many years, TB ABR has been used to estimate behavioral hearing
thresholds (18). The elimination of the delay in the cochlear traveling
wave with the chirp stimulus and the synchronous stimulation of the
afferent nerves are superior to the traditional click stimulus. For this
reason, studies about the prediction of behavioral hearing thresholds
with chirp stimulus are increasing in the recent literature (19). BHT is
used clinically to detect hearing loss and to prescribe the
amplification of suitable hearing aids (20). In determining hearing
thresholds, PTA is used preferential, and Tone Burst ABR is commonly
used in children with hearing loss and neurological disease (21, 22).
Also, repeated measurements showed that hearing thresholds may be
detected false and not consistent with previous thresholds in 50% of
newborns with hearing loss, therefore the accurate estimation of
thresholds becomes essential (22).
In addition, there may be adults who cannot fully adapt to subjective
hearing tests (PTA). This can happen due to poor understanding of the
test procedure and low motivation. Even though there is no pathology in
the hearing system, people can act as if they have a hearing loss to get
personal or financial profit. This situation is called “nonorganic
hearing loss”, “pseudohypacusis” or “functional hearing loss” (23).
It is difficult to accurately determine behavioral hearing thresholds in
adults with nonorganic hearing loss or and intellectual deficit.
In this study, we aimed to determine which Tone Burst ABR and NB
CE-Chirp ABR thresholds are closer to frequency-specific behavioral
hearing thresholds in normal hearing adults. Thus, it can be determined
which ABR stimulus is more effective in estimating hearing thresholds in
adults whose behavioral hearing thresholds are difficult to determine
Accurate estimation of frequency-specific hearing thresholds can also
allow proper hearing aid adjustment in adults with hearing loss and
intellectual deficit.
2. Materials and methods
2.1Study Design: This study designed prospectively in the
audiology department of a tertiary university hospital between June 2018
and October 2018. The study included 24 adults (17 males, 7 females)
aged 20-48 years with normal hearing. Participants were tested in a
sound-treated room, pure-tone audiometer Interacoustics model AC40
(calibrated as per ANSI S3.6, 1996) (Interacoustics AS, Assens,
Denmark). Pure-tone audiometry for both air conduction (for the
frequency range 250–8000 Hz) and bone conduction (for the frequency
range: 500–4000 Hz) were tested using headphones TDH 39 (Telephonics
Co.Farmingdale, NY, USA) and bone vibrator RadioEar B-71 (RadioEar Co.
Middelfart, Denmark). Only those participants whose hearing sensitivity
was ≤ 20 dB HL at each frequency (250-8000) without any otological,
psychological or neurological dysfunction were selected for the study.
ABR recordings were taken using the Eclipse Ep 25 ABR system.
The assessment was done with two stimuli namely, NB CE-Chirp and Tone
Burst at four frequencies 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz. The
stimuli were calibrated to ISO 389-6 (2007) for the click and to
manufacturer’s data for the chirps. Positive (active) electrode was
placed on the top of the forehead (Fz), ground electrode was placed at
the bottom up the forehead (Fpz), reference electrodes were placed on
the right (M2) and left (Ml) mastoids, The measured potentials were
recorded with impedance below 5kΩ.
The four (0.5, 1, 2, 4 kHz) Tone Bursts and NB CE-Chirps® were presented
with rarefaction polarity through insert ER-3A (Etymotic Research)
earphones at a rate of 44.1/s. Measurements were carried out using High
Pass Filter (HPF): 75 Hz and Low Pass Filter (LPF): 1500 Hz. Tone Bursts
and Narrow Band CE-Chirps were presented monaurally.
ABRs records obtained for 0.5, 1, 2, 4 kHz and 60, 40, and 20 dB nHL
intensity levels for both Narrow Band (NB) CE-Chirp and Tone Burst (TB)
stimuli. Behavioral hearing thresholds (BHT) were identified at 0.5, 1,
2, 4 kHz. The ABR threshold was taken as the lowest of levels containing
a clear response. Tests were started from 60 dB nHL level, stimuli were
decreased until no response was obtained. Initially 10 dB nHL decreases
were used to estimate BHT, and then 5 dB nHL changes were made to
determine a clear wave V response. Each measurement was carried out
using an average of 2000 sweep to clarify the waveforms.
The absolute peak amplitude and absolute peak latencies were recorded
for wave V in all four frequencies (0.5, 1, 2, 4 kHz) for TB and NB
CE-Chirp stimulus. ABR wave V amplitudes and absolute latencies were
determined by visual inspection. Duration of TB and NB CE Chirp ABR
tests for each ear was recorded. The study was prepared with the
reporting guideline of the STROBE checklist.
2.2. Participants: Inclusion criteria were: adults with no
history neurological or otological dysfunction and audiometric
thresholds ≤ 20 dB HL for the 250-8000 Hz frequencies. Patients with
hearing loss, neurological, psychological were excluded from the study.
Also, patients with previous ear surgery, chronic otitis media,
Meniere’s disease, subjective tinnitus, tympanosclerosis were excluded,
Patients with chronic systemic disease (diabetes mellitus, autoimmune
diseases), chronic systemic drug use were not included in the study.
2.3. Statistical Analysis: Results were analyzed with the SPSS
22.0 package program. Threshold values were compared with the Paired
t-test and test times were compared with the Wilcoxon test and the
results with p significance value less than 0.05 were considered as
significant. Intraclass correlation coefficient (ICC) was used to
determine consistency of thresholds identify by PTA, TB, and NB CE-Chirp
stimulus. Sample calculation and power analysis were assessed with the G
Power 3.1 package program. By using the result of similar research of
Mourtzouchos and et al. (24), the effect size (d) 1.21 specified as
α=0.05 and β=0.80 and the sample size was calculated as 20.
2.4. Ethics Committee Approval: Verbal and written consent was
obtained after all participants were informed. This study was conducted
in accordance with the Declaration of Helsinki. Ethics committee
approval was obtained.