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OJHAS Vol. 10, Issue 2:
(Apr-Jun 2011) |
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| Effect of Intensity
on Prevalence of N3 Potential in Ears with Severe to Profound Hearing
Loss |
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Kaushlendra Kumar,
Jayashree S. Bhat,
Ashwini S. Guttedar,
Department of Audiology & Speech
Language Pathology, Kasturba Medical College (Manipal University), Mangalore, India |
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Address for Correspondence |
Assistant Professor,
Department of Audiology & Speech
Language Pathology,
Kasturba Medical College (Manipal University),
Attavar, Mangalore - 575001,
India.
E-mail:
kaushlendra84@rediffmail.com |
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Kumar K, Bhat JS, Guttedar AS.
Effect of Intensity
on Prevalence of N3 Potential in Ears with Severe to Profound Hearing
Loss. Online J Health Allied Scs.
2011;10(2):17 |
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Submitted: Apr 27,
2011; Accepted: Jul 15, 2011; Published: Jul 30, 2011 |
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| Abstract: |
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Objective of the
study: To look for the presence of N3 potential at two different
intensities in children and in adults.
Method: A total of
260 ears with severe to profound hearing loss
were studied from the participants
in the age range of 1 to 50 years, with 170 subjects in the age group
below 10 years and remaining 90 subjects
of more than 10 years. Auditory brainstem response (ABR) was recorded at two
intensities, 90 and 99dBnHL, to look for the presence of N3 potential.
Result: N3 potential was observed in 30% of the
total ears taken in the study at 90dBnHL and 38.8% at 99dBnHL. Presence
of N3 potential in children was 45%,
which was higher than the age group of above
10 years. When the intensity was increased there was an increase in
amplitude and a reduction in latency with better wave morphology.
Conclusion: It is
better to use higher intensity for the identification
of the N3 potential while doing ABR and thus with the
single recording, auditory assessment as well as saccular assessment can be done.
Key Words:
N3
potential; Auditory brainstem response; Saccular origin
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The
auditory brainstem response (ABR) allows one to objectively gauge peripheral
hearing acuity as well as neurological abnormalities in the auditory
brainstem pathway. It serves an important role in the testing of physiological
function. Neural responses to acoustic stimuli could
be recorded after destruction of cochlear hair cells in guinea pigs, the
response probably originating from the saccule of
the vestibular system. The results of these animal experiments suggested
that a vestibular evoked response to acoustic stimulation can be recorded
in humans.(1-3) A
large negative deflection with a latency of 3ms in the ABR wave forms
of some patients with profound deafness of peripheral origin. This negative deflection
has been termed as the N3 potential, and it has been assumed that the N3
potential might be a vestibular-evoked potential to acoustic stimulation, saccule
being the most likely site
of origin.(4)
It has been
reported that as the stimulus intensity increased, the amplitude of the
potential increased and the latency decreased.(4) It has also been stated that
N3 potential could be recorded from all electrode placements, and the amplitudes
and latencies were almost consistent, and no polarity inversion was observed
over the scalp.(4) N3 potential is reported to be widely distributed over the
scalp, rather than being limited to the stimulated side. This means that an N3
potential has a far-field nature similar to an ABR. Manabe et al (5) also
recorded a potential similar to the N3 potential, and indicated that this
potential is not an artifact which might be due to any particular recording
condition or equipment, but that it arises as a physiological neural
response to a loud stimulus sound and this is well supported by the important
fact that the latency decreases when the stimulus becomes louder and prolonged
when a higher repetition rate is used.(5)
Acoustically
evoked short latency negative response (ASNR) was found only in profound
hearing loss ears under intense stimuli (80 to 120dBnHL). Click-evoked ASNRs
were present in 12.3% patients (11.9% ears), having neural response characteristics, that
is the latency and amplitude shortened and increased respectively in
response to the change in the stimulus intensity.(6) N3 potentials
were recorded by Ochi K et al in 41.7% ears and VEMP was detected in 66.7% ears in subjects
having hearing threshold ranging from 65 to above 110dB.(7) They suggested
that although VEMP and N3 potential appear to originate from saccule, the characteristics of these two responses
being not identical, the mechanisms
responsible for the generation of these two responses are somewhat different,
so that an additional factor might exist for the generation of the N3
potential.(7)
It
is clear from the literature that N3 potential has not been studied
extensively. Moreover the effect of different intensities on the occurrence
of N3 potential has not been focused in any of these studies. The present
study was taken up with an aim to look for the presence of N3 potential
and the latency and amplitude effect at two different intensities, 90
and 99dBnHL, in ears having severe to profound hearing loss. The second
aim of the present study is to see the presence of N3 potential in two
age groups, children and adults at 99dBnHL.
This is a retrospective study involving 260 subjects
with severe to profound hearing loss ears (160 subjects), with age
ranging from 1 year to 50 years. Auditory brainstem response (ABR) data
were collected during June 2005 to May 2009 and was analyzed for N3 in
all the subjects. A total of 170 ears were having
age range below 10 (mean age 4.2 years) and remaining 90 ears were more than 10 years old (Mean age 21.3 years).
The following subject selection criteria were adopted for the study:
- Hearing loss of severe to
profound degree and of sensory neural type.
- The absence of ABR responses
at 99dBnHL.
- Absent distortion product
otoacoustic emission (DPOAE).
- None of the subjects had recent
history or presence of any otological problem (like ear discharge, ear
ache etc) or any neurological symptoms.
- ‘A’ type tympanogram with
absent ipsi and contra reflexes.
Procedure
All the procedures
were executed in a soundproof room. Initially each subject underwent
a pure tone audiometry across octave frequencies from 250 to 8000 Hz
for air conduction and from 250 to 4000 Hz for bone conduction using
GSI-61 audiometry and same instrument was used for Behavioral Observation
Audiometer (BOA). BOA was performed using ascending method for 0.5,
1, 2, and 4 KHz frequencies. Subjects below 2 years underwent BOA
and above 2 years either went for conditioning audiometry
or pure tone audiometry. Subsequently tympanogram and acoustic reflexes
were established using 226 Hz probe tone using GSI Tympstar. Acoustic
reflex threshold were obtained for ipsilateral and contralateral for
0.5, 1, 2, and 4 KHz frequencies. GSI-Audera DPOAE was performed for
all the subjects for 1, 1.5, 2, 3, and 4KHz. GSI-Audera instrument was
used for recording of auditory brainstem response.
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Table 1: Acquisition
and stimulus parameters used to record the ABR. |
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Analysis time |
15 msec |
| Filter setting |
High pass: 30Hz or 100Hz
Low pass: 1500Hz or 3000Hz |
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Gain |
100000 |
| Type of stimulus |
100 µsec click as well as 0.5 KHz tone
burst with 2-cycle rise/fall time. |
| Rate |
30.1 |
| Polarity |
Rarefaction |
| Intensity |
90 and 99dBnHL |
| Total number of stimulus |
1500 |
| Electrode montage |
Non-inverting electrode (+): vertex(Cz)
Inverting electrode (-):
Test ear mastoid(M1 /M2)
Ground electrode: forehead(Fz) |
ABR
was done at two intensity levels, 90 and 99dBnHL. The N3 potential was
visually detected by two experienced clinical audiologists at both the
levels. Obtained data was analyzed in terms of percentage of occurrence
of N3 potential and to see the differences between two intensity levels
the chi-squared test was administered.
In
the present study, a total of 260 ears were studied at two different
intensities, 90 and 99dBnHL. Almost 65% of the subjects were children,
younger than 10 years.
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Table 2: Presence of N3
potential at different intensities
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Intensity (dBnHL) |
Total number of ears |
Total number of ears with presence of
N3 potential |
Presence of N3 potential in
percentages |
Absence of N3 potential in
percentages |
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90 |
260 |
78 |
30% |
70% |
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99 |
260 |
101 |
38.8% |
61.2% |
As
it can be seen, N3 potential was observed in 30% of ears at 90dBnHL
and 39% at 99dBnHL. So the trend observed was, as the intensity increased
from 90 to 99dBnHL, there was an increase in the presence of N3 potential.
It was also observed that all the subjects who had N3 potential at 90dBnHL
also showed the presence of N3 potential at 99dBnHL.
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Table 3: Prevalence of
N3 potential at 99dBnHL in two different age groups. |
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Age group |
Total number of ears |
Presence of N3 potential in percentages |
Absence of N3 potential in percentages |
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Below 10 years |
170 |
76(44.7%) |
94(55.2%) |
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Above10 years |
90 |
25(27.7%) |
65(72.2%) |
Table 3 shows that in children the presence of N3 potential
is 45% which is higher than the age group of above 10 years, among whom only
28% had N3, suggesting that children have higher incidence of N3 potential
than adults at the same intensity.
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Table 4: Mean and standard
deviation of latency and amplitude at two different intensity 90 and
99dBnHL. |
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Intensity |
VEMP parameters |
Mean |
Standard deviation |
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90 |
Latency |
3.12msec |
0.17 |
| Amplitude |
172.89nV |
64.37 |
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99 |
Latency |
3.04mesc |
0.15 |
| Amplitude |
265.08nV |
75.75 |
As
depicted in Table 4, as the intensity increased from 90 to 99dBnHL,
the latency was reduced from 3.12 to 3.04 msec and there was an increase
in amplitude from 172 to 265 nanovolt. The standard deviation of the
N3 potential latency was less, but the standard deviation of amplitude
was high. The Chi-squared test was administered to see the significance of
difference between two different intensities at 90 and 99dBnHL. The
chi-squared test for latency is 671.58 with an associated
p<0.005, suggesting a significant difference in latency
between 90 and 99dBnHL. The chi-squared test for amplitude
is 1263.87 with an associated p<0.005, suggesting a statistically significant difference between the two intensity levels. Raw scores indicated a slight difference in amplitude between the two
intensities.
In
the present study, N3 potential was present in 30% of the ears taken
at 90dBnHL and in 39% ears at 99dBnHL. Ochi K et al (7) reported the detection of
N3 potential in 41.7% of the total ears whereas in the present
study N3 potential was observed in 39% of ears. This may be due to the difference in stimulus intensity used, which was
105dBnHL in Ochi et al compared to 99dBnHL in the present study. This indicates that the
stimulus intensity plays a role in the occurrence of N3 potential. The
absence of N3 potential in many subjects could be attributed to the
individual variation of vestibular function, particularly under unphysiologic
stimulation. Nong DX (6) reported that the N3 potential were present
in 11.9%. The lesser percentage of the presence of N3 potential in
their study is due to the intensity used which was between 80 and 120dBnHL.(6)
It
was also observed in the present study that as the intensity increased,
there was an increase in amplitude and reduction in latency. Kato T et al (4)
had reported two case reports in which as the intensity was increased, there was
an increase in amplitude and a decrease in the latency. Nong DX (6) also
reported that the N3 potential had neural response characteristics as the
latency and amplitude being shortened and increased respectively in response to
the change in the stimulus intensity.
In
the present study, 45 % of the children below 10 years had the presence of N3
potential and 28% of the participants above 10 years of age showed the presence
of N3 potential. In contrast Nong DX (6) reported significantly higher
appearance rates in young subjects especially in the 20 to 30 years group. In
the present study, the higher rate of occurrence of N3 potential in children
might be due to the higher sound pressure level generated at tympanic membrane
as the ear canal volume is less for children than adults. The sound pressure
level changes might cause the presence of more N3 potential in children than in
adults.
In
conclusion it can be put forth that as the intensity increases, there
is higher rate of the presence of N3 potential with a shorter latency
and higher amplitude. The presence of N3 potential is higher in children
than in adults. It is better to use a higher
intensity in identifying N3 potential while doing ABR so
that auditory assessment as well as saccular assessment can be done at the same
recording in subjects with severe to profound hearing loss.
- Cazals Y, Aran J, Erre J, Guilhaume A. ‘Neural’ responses to acoustic stimulation after destruction
of cochlear hair cells. Eur Arch OtoRhinolaryngol. 1979;224:61-70.
- Cazals Y, Aran J, Erre J,
Guilhaume A. Acoustic responses after total destruction
of the cochlear receptor: Brainstem and auditory cortex. Sci. 1980;210:83-86.
- Cazals Y, Aran J, Erre J,
Guilhaume A, Aurousseau C. Vestibular acoustic reception in the guinea
pig: A saccular function? Acta Otolaryngol (stockh). 1983;95:211-217.
- Kato T, Shiraishi K, Eura
Y, Shibata K, Sakata T, Morizono T, Soda T. A ‘Neural’ response
with 3-ms latency evoked by loud sound in profoundly deaf patients.
Audiol Neurootl.1998; 3:253-264.
- Manabe T, Nishizawa N, Koba
K. A reliability of auditory brainstem response test in profoundly deaf
children. Audiol Jpn. 1982;25:433-434
- Nong DX, Ura M, Owa
T, Noda Y. An acoustically evoked short latency negative response in
profound hearing loss patients. Acta Otolaryngol. 2000;120:960-966.
- Ochi K, Ohashi T, Nishino
H. Variance of vestibular-evoked myogenic potentials. Laryngoscope.
2001;111:322-327.
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