The Effect of Noise Exposure on Signal to Noise Ratio Changes of

Distortion Product Otoacoustic Emissions (DPOAE) Examination in

Rattus Norvegicus

Tengku Siti Hajar Haryuna

* and Susi Mulyana

Department of Otorhinolaryngology-Head and Neck Surgery, Faculty of Medicine, Universitas

Sumatera Utara, Jl. dr. Mansur Kampus USU Indonesia Medan 20155

Keyword: Noise-exposure, Outer hair cell, Otoacoustic emissions, Signal to noise ratio.

Abstract: Distortion Product Otoacoustic Emission (DPOAE) was used to assess outer hair cells. The aim of this study

is to assess the damage to outer hair cells of the noise model Rattus norvegicus by assessing the Signal to

noise ratio (SNR). Twenty-seven Rattus norvegicus were grouped into 3: controls; 2-hours 100 dB noise-

exposure; and 2-hours 110 dB noise-exposure. DPOAE was assessed 3 times in the beginning before

treatment, 2 hours after the second day of exposure (day 2), and after 3 days of no exposure (day 5). The

results showed that the SNR of DPOAE after the noise exposure decreases at all frequencies compared to

before the treatment. A significant decrease in SNR especially at 2000Hz - 4000Hz frequencies. These results

suggest that DPOAE may be used as a sensitive procedure at various frequencies for early diagnosis and

screening of NIHL

1 INTRODUCTION

Noise is an important issue in occupational health;

excessive exposure to noise has the social and

psychological impacts caused by noise-induced

hearing loss (NIHL) (Nassiri et al., 2016). The

bilateral sensorineural hearing loss may cause

irreversible and progressive cochlear damage (Souza

Alcaraz et al., 2012;Jahani et al., 2016) In NIHL, a

notch at 3000, 4000, or 6000 Hz is a common finding

in audiometric examination (Derekoy et al., 2004;

Lee Preel &Miller, 2016).

Physiological changes from noise exposure can be

assessed on cochlear cells, where the outer hair cells

are more susceptible to damage than inner hair cells.

Degenerative outer hair cell is the most sensitive

initial process against sound (Balatsouras, 2004).

Otoacoustic emission measures the microscopic

biochemical activity of healthy outer hair cell. OAE

provides bicochlear mechanical stimulation that flow

from the tympanum to the external ear through the

external acoustic meatus (Nassiri et al.,

2016;Moussavi-Najarkola et al., 2012).

The DPOAE measures the bicochlear intensified

emissions recording of a different frequency (f1 and

f2) (Moussavi-Najarkola et al., 2012). The DPOAE

examination uses two simultaneous pure sound

stimuli, of different frequencies and intensities, called

f1 and f2 (f1 < f2) (Janssen et al., 2006;Prieve &

Fitzgeral, 2015).

Studies on animal noise-model have used high-

frequency DPOAE of 1-8 kHz and assess the Ldp

(level distortion product). In this study, the group and

intensity of noise exposure were different from prior

studies which use a low-frequency DPOAE of 1-5

kHz, which is expected to be able to assess the

damage to cochlear outer hair cell of noise model

Rattus norvegicus by Signal to Noise Ratio (SNR)

from DPOAE.

2 METHOD

Twenty-seven Rattus norvegicus aged 2-3 months

with 200-300 gr of weight. All Rattus norvegicus

were examined by the veterinarian and declared

542

Haryuna, T. and Mulyana, S.

The Effect of Noise Exposure on Signal to Noise Ratio Changes of Distor tion Product Otoacoustic Emissions (DPOAE) Examination in Rattus Norvegicus.

DOI: 10.5220/0010077505420546

In Proceedings of the International Conference of Science, Technology, Engineering, Environmental and Ramiﬁcation Researches (ICOSTEERR 2018) - Research in Industry 4.0, pages

542-546

ISBN: 978-989-758-449-7

healthy. The animals are placed in polycarbonate

cage at 25°C with humidity ranging from 40%-60%.

In its care, they get sufficient light source and free

access to water and food until the end of the study.

All procedures are carried out in accordance to

Animal Research Ethicss Committees/AREC Faculty

of Science University of North Sumatera

(No.560/KEPH-FMIPA/2017).

The study group was divided into 3 groups (n =

9), Group I (control); Group 2 (2-hours 100 dB noise-

exposure); and Group 3 (2-hours 110 dB noise-

exposure). The noise was exposed to Rattus

norvegicus in a noise-box of 64.5 x 45 x 40 cm made

by the Faculty of Electro University of North

Sumatra. The source of sound provided by Compact

Disc (CD) containing sound recordings, CD player,

and amplifier which generate the noise with a

frequency of 1-10 kHz and an intensity of 100 dB and

110 dB as measured by a sound level meter.

The Distribution Product Otoacoustic Emission

(DPOAE) examination (Elios Elito Otodia, Echodia

Ltd., London, UK) were performed on all animal

under anesthetic drugs with ketamine 50 mg/kg body

weight and Xylazine 10 mg/kg body weight

intraperitoneal in a soundproof room. The probe was

modified from a plastic pipe adjusted to the size and

placed in the ear canal. DPOAE was assessed 3 times:

early before treatment; 2 hours after the second day

of noise exposure and after 72 hours of the noise-free

period. Acoustic emission results that can be

evaluated at frequencies of 1.5, 2, 3, 4, 5 kHz. All

study samples must have normal SNR (equal to or

more than 6) before noise exposure.

To assess the SNR differences between groups

and between frequency, the data were averaged

between right and left SNR then analyzed with

independent K Kruskal Wallis followed by Mann

Whitney Test, significancy demonstrated as P < 0.05.

3 RESULTS AND DISCUSSIONS

Table 1 shows the mean and standard deviation of

SNR on DPOAE at the frequency of 1500-5000 Hz in

the control group. Table 2 and Table 3 show the mean

and standard deviation of SNR DPOAE at 100 dB and

110 dB, respectively; there was a decrease of SNR

value on the second and fifth day in both groups of

100 dB and 110 dB.

Table 1. The mean and standard deviation of SNR in control

group.

Frequency

(Hz)

Signal to noise ratio (dB)

Day 0 Day 2 Day 5

1500 18,3±9,71 16,7±7,95 9,2 ±8,53

2000 4,1 ± 1,28 8,1 ± 4,81 6,1 ±2,02

3000 9,7 ± 1,88 8,6 ± 3,2 9,7 ±4,11

4000 10,4±3,97 15,8 ±3,25 11,1±2,80

5000 12,1±5,72 11,7 ±7,91 10,7 ±5,12

Table 2. The mean and standard deviation of SNR in 100

dB group.

Frequency

(Hz)

Signal to noise ratio (dB)

Day 0

Day

1500 16,6±10.91 6,8 ±4,54 7,9 ±8,69

2000 10,5 ± 4,27 4,8 ±2,74 5,8 ±4,07

3000 11,00 ±4,32 3,0 ±4,34 6,4 ±2,87

4000 12,7 ± 4,92 2,0 ±2,68 5,4 ±2,17

5000 6,7 ± 9,29 5,3 ±1,81 6,2± 4,00

Table 3. The mean and standard deviation of SNR in 110

dB group.

Frequency

(Hz)

nal to noise ratio

(

)

0 Da

2 Da

1500 18,2 ±9,42 6,8 ± 8,29 7,1 ±8,69

2000 9,1 ± 2,01 5,9 ± 6,23 6,3 ± 4,81

3000 8,9 ± 3,78 2,3 ± 2,42 4,3 ±5,66

4000 11,8±3,25 1,2 ± 3,39 5,2 ± 3,17

5000 7,1 ± 6,1 5,2 ± 6,47 6,0 ±4,73

Figure 1 and 2 show the SNR value after the noise

exposure (day 2) in the 100 dB and 110 dB group was

decreased at frequencies of 1500-4000 Hz compared

to the SNR value before the exposure (day 0), this

occurs particularly on 3000 Hz and 4000 Hz

frequencies where the SNR value is 3.0 dB and 2.0

dB, respectively. At the 3000 Hz and 4000 Hz

frequencies, the SNR value was 2, 3 dB and 1.2 dB in

the 100 dB and 110 dB group, respectively. At the

5000 Hz frequency, there is a decrease of SNR but not

significant either in 100 dB or 110 dB group.

Meanwhile, after 3 days of noise-free period (day

5), the SNR value was slightly improved compared to

after exposure (day 2); the SNR value was decreased

and did not return to baseline value before the noise

exposure (day 0) on all frequencies in both group of

100 dB and 110 dB. This study showed that the noise-

break was able to improve the SNR value after the

noise exposure.

The Effect of Noise Exposure on Signal to Noise Ratio Changes of Distortion Product Otoacoustic Emissions (DPOAE) Examination in

Rattus Norvegicus

543

Figure 1. Average SNR changes in 100 dB group on

day 0, day 2, day 5.



Figure 2. Average SNR changes in 110 dB group on

day 0, day 2, day 5.

There is a difference of SNR value at the

frequency of 1500 Hz after noise exposure (day 2) (p

< 0.005) both in the 100 dB and 110 dB group. A

similar finding was found at the frequency of 2000,

3000 and 4000 Hz. At the frequency of 5000 Hz, there

were not any significant differences in SNR value (p>

0.005) both in the 100 dB and 110 dB group.

At all 1500-5000 Hz frequencies, no significant

differences in SNR value were found in days 0, day 2

and day 5 compared between groups of 100 dB with

110 dB (p> 0.005). This shows the difference in

intensity of 100 dB and 110 dB does not demonstrate

the difference of SNR value.

In this study, DPOAE examination showed a

decrease of the SNR after noise exposure at every

frequency, especially at 2000-4000 Hz. NIHL occurs

at high frequencies, especially at the frequency of

3000 Hz-6000 Hz; on audiometric examination, there

was a notch at 4000 Hz frequency (Dobie, 2014).

Several theories have been proposed to understand

why the 4000 Hz frequency is the more susceptible

region to noise exposure. The most popular theory is

that the anatomical structure in the area is weaker

(Dhingra, 2015). Damage to the cochlear structure

due to the noise was observed, especially in the initial

8-10 mm diameter at the cochlear base which is a

sensitive area caused by metabolic, vascular, and

anatomical factors, with corresponding topography to

the frequency of 4000 Hz (Yilmaz et al., 2015).

Salehi et al. (2012) assessed the performance of

outer hair cells in the noise-exposed rabbits, the result

showed that the noise exposure reduces the DPOAE

threshold at a frequency of 4-10 KHz (Salehi et al.,

2011). Nassiri et al. (2016) assessed the effect of

noise exposure on mice by assessing SNR changes at

the intensity of 65 dB, 95 dB and 105 dB concluded

that higher noise intensity will decrease DPOAE level

and sensitive DPOAE examination at various

frequencies (Nassiri et al., 2016).

Distortion product otoacoustic emission

(DPOAE) is an initial and rapid test to detect the

cochlear damage due to noise exposure. DPOAE

sensitively measures the activity of cochlear outer

hair cells recorded in the ear canal (Doosti et al.,

2014). Simultaneous stimulus response to the cochlea

with 2 pure tone frequencies f1 and f2, where

frequency f2 is slightly higher than f1 (2f1-f2)

(Moussavi-Najarkola et al., 2012; Janssen et al.,

2006;. The DPOAE examination measures the Signal

to noise ratio (SNR) which defines the emission

levels generated by noise levels as the background or

ratio of signal strength to noise expressed in decibels

(Nassiri et al., 2016).

The noise impact depends on some sound

characteristics i.e. intensity, spectrum/frequency,

duration and pattern of exposure (Demirel et al.,

2009;Agrawal et al., 2008). The damage to the outer

hair cells depends on the intensity of noise. High-

frequency noise exposure also causes damage to

stereocilia and hair cells that eventually cause

permanent damage. Primary exposure to noise will

damage cochlear hair cells. Initially, the damage

occurs to the outer hair cells, but if the exposure is

continuing, it could evolve to destruct the hair cell

(Nandi&Dhatrak, 2008). Noice-induced cochlear

injury not only affects outer and inner hair cells, but

also damage the fibroblasts of lateral cochlear wall

(Haryuna et al., 2015; Haryuna et al., 2016; Haryuna

et al., 2016; Haryuna et al., 2016). In this study, the

SNR value after the exposure and the noise-free

period was decreased compared to before exposure.

1500 2000 3000 4000 5000

SNR (dB)

Frequency (Hz)

Mean of 100 dB-intensity SNR

Day0 Day2

1500 2000 3000 4000 5000

SNR (dB)

Frequency ( Hz)

Mean of 110 dB-intensity SNR

Day0 Day2

Day5

ICOSTEERR 2018 - International Conference of Science, Technology, Engineering, Environmental and Ramiﬁcation Researches

544

This confirms that there was a cochlear outer hair cell

injury measured by DPAOE at both groups.

This experimental study used mice as an animal

model. The mice also have similar inner ear structures

to humans and have been used as animal models for

genetic deafness studies (Vazquez et al., 2001; Salvi

& Boettcher, 2008). The most common gender in the

animal model is males. A study by Najarkola et. al.

using only male animal model showed that gender

affects the measurement of level distortion product

(Ldp). The Ldp is greater in females than in male.

Several studies have reported these differences due to

hormonal influences, and some reported due to the

difference in electromotility of outer hair cells, and

the mechanisms responsible for stereocilia motility,

due to gender difference of lipid membrane that alter

lipid-protein interactions (Moussavi-Najarkola et al.,

2012).

4 CONCLUSIONS

In this study, the SNR of DPOAE examination

decreased at each frequency after the noise exposure,

the decrease was especially seen at the frequency of

3000 and 4000 Hz. There was an improvement in

SNR values after the break period, and between the

100 dB and 110 dB group, there were not any SNR

differences in each frequency.

ACKNOWLEDGMENTS

The authors express their greatest gratitude to the

Research Institute of the Universitas Sumatera Utara

for their full support in this research. The support is

under the TALENTA of the Universitas Sumatera

Utara Year 2017 Number: 5338/UN5.1.R/PPM/2017.

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