The Effect Of Variable Ambient Noise

Published Date: 02 Nov 2017

ABSTRACT

METHODOLOGY

RESULTS

DISCUSSION

ACKNOWLEDGEMENT

REFERENCES

APPENDIX

CHAPTER ONE

INTRODUCTION

1.1 OBJECTIVES

1.1.1 Main Objectives

1.1.2 Specific Objectives

1.1.3 Expectations

CHAPTER TWO

TUNING FORK

2.01 INTRODUCTION

2.02 PREREQUISITE FOR AN IDEAL TUNING FORK

2.03 METHODOLOGY USING TUNING FORK

2.04 ADVANTAGE OF USING TUNING FORK

2.05 CLINICAL USES OF TUNING FORK

2.1 RINNES TEST

2.2 WEBBER TEST

CHAPTER THREE

MASKING

3.01 MASKING FATIGUE

3.02 PRINCIPLE OF MASKING

3.03 RULES OF AUDITORY MASKING

3.04 MASKING DILEMA

CHAPTER FOUR

NOISE AND SOUND

4.01 TYPES OF NOISE

4.02 SOUND MASKING

4.03 AMBIENT SOUND

4.04 BACKGROUND NOISE

CHAPTER 5

5.01 CRITICAL BANDWIDTH

5.02 AUDITORY FILTERS

CHAPTER 6

6.01 EFFECT OF VARIABLE AMBIENT NOISE ON TUNING FORK

JUSTIFICATION FOR THIS STUDY

Tuning fork has been used since many years; however the effect of variable ambient noise on tuning fork examination has never been studied. To screen for hearing loss, Otologists traditionally use clinical tests such as finger rub, whispered speech, watch tick and tuning forks and self report (1) Evidence-based reviews have questioned the reliability of screening measures, citing lack of test standardization and validation (2,3) For this study, we sought to determine the effect of variable ambient sound on tuning fork examination among normal individual, using pure-tone audiometric as the standard reference.

ABSTRACT

The effect of ambient sound on tuning fork examination has been evaluated in 127 consecutive young adults with normal hearing, using pure-tone audiometry as the standard reference. Although variable ambient sound has no effect on air conduction; it does affect bone conduction when ambient sound is increased significantly. The diagnostic utility of tuning fork tests routinely administered by ENT in the presence of variable ambient sound to detect hearing loss requires further study.

METHODS.

This is a cross sectional study studying the effect of ambience noise at different levels on Rinne and Weber Tests. A universal sampling method was employed. We randomly selected 127 young nurses and medical students in Pusat Perubatan Universiti Malaya. The inclusion criteria are as below:

a) Nursing and medical students in Pusat Perubatan Universiti Malaya aged 21 to 25.

b) Normal hearing with no history of hearing loss, stroke, or clinically diagnosed dementia.

c) Consented to participate by written informed consent.

Subjects completed a four-item, self-assessment questionnaire about their hearing (table 2), Rinne and Webber tests in the simulation room with varying ambient noise and a confirmatory PTA. Questions were developed as a potential screening tool and not to elicit perceived social or emotional handicap secondary to hearing loss.

Tests included Rinne and Weber tuning fork tests using 512 tuning fork as standard. We chose 512hz as other frequencies are associated with high false positive (4). The same doctor performed the tests, with subjects seated in a simulation examination room (mean ambient noise 48 dB SPL) as well as otoscopic examination.

The room ambient noise was measured using SPL monitor which was calibrated to zero decimal points at 1khz as reference point prior to commencement of this study. Our simulation rooms ambient noise was recorded as 45 dB SPL. Then with the aid of a radio, a variable ambient noise was simulated at various decibel SPL in an increasing manner until 85 dB SPL. Every increase of 5dB was marked on the radio.

Students were vetted through the questionnaire, and only the ones which fulfilled our inclusive criteria were tested. At first we tested for both Rinne and Webber in the rooms ambient surrounding which were measured to be 45 dB SPL, the results documented.

For the Weber test, the vibrating tuning fork was placed midline on the forehead. Normal listeners detect no inter-aural loudness differences. Lateralizing responses indicate unilateral hearing loss.

For the Rinne test, the tuning fork was alternately placed on the mastoid and at the ear at about 4cm from pinna. Normal listeners and individuals with sensorineural hearing loss hear the sound louder at the ear (positive Rinne test result) because air conduction is more effective than bone conduction.

A negative Rinne test result occurs when sound is heard louder at the mastoid, consistent with conductive hearing loss.

Later we increased the ambient sound by 5db and re-performed Rinne and Webber test using the same tuning fork. At each interval the results were documented. The ambient noise was increased in a predetermined manner until we reached 85 dB SPL. The results tabulated.

After the test, Otoscopy were performed to exclude external or middle ear abnormalities. At this stage, if any abnormality detected, the patient would be excluded from the study. An audiologist, blinded to the bedside test results, performed pure-tone audiometry and tympanometry. Hearing thresholds were established for each ear at four octave frequencies (500 to 4,000 Hz) under headphones using a two-channel audiometer.

Hearing loss was defined as thresholds > 25 dB at one or more frequency in either ear and classified as mild (26 to 40 dB), moderate (41 to 55 dB), or severe (>55 dB) Three-frequency puretone averages (500 to 2,000 Hz) were computed.

Statistical analyses.

A cross sectional study involving student nurses and medical students in PPUM was performed. A sample size of 119 was needed to perform our study, this is based on a confidence interval of 9.0 and a confidence level of 95%. However we managed a total of 127 sample population. Thus with 127 sample population and maintaining a confidence level of 95%, our confidence interval has dropped to 8.7% assuming a modest 50% percentage to determine a general level of accuracy for our given sample. Of all the prospective study subjects, 127 subjects consented to be enrolled in this study. The descriptive analysis done on the sample revealed a uniformed findings in all the subjects in both the Weber and Rinnes Tests at different ambient noise levels. Because of this, further statistical analysis to validate any differences in findings is not needed. The findings are reported in the report section below.

The P value is significant when it is less than 0.05%.

RESULTS:

In all the study subjects, the bone conduction on Rinne tests is reduced starting from 70db ambient noise while Weber was not heard at 65 db ambient noise. For Renee Tests, there were some variations in reduction of bone conduction at different ambient noise level (between 70-75 db) among the study subjects. The difference however, is neither clinically nor statistically significant ( P>0.05). Non-parametric analysis was used to calculate P –value.

Ambient noise does have an effect on tuning fork examination. Using the concept of critical band width, we are able to explain our findings. When 2 tones of different frequencies are introduced simultaneously, the cochlea maps it out at different level. Thus the 2 two tone are distinguished and heard as 2 different entity. The ability of the human to focus on a particular sound in a noisy environment is explained by this phenomenon. When the ambient noise is increased, both the air and the bone conduction is muffled. Which is explained by the reduction in bone conduction when performing rinne. However due to critical band width and the ability of the ear to focus on particular sound in a noisy environment, explains the finding of why air conduction is still heard and only bone is perceived to be muffed.

Thus I conclude that ambient noise does effect the tuning fork examination in subjects with normal hearing. It needs to be studied further to determine its effect on those with hearing problems .

DISCUSSION:

1.0 INTRODUCTION

The ability of humans beings to perceive sound both by air and bone conduction was established from early years of 17th century. Then it was learnt that the threshold measurement between air and bone conduction could differentiate middle ear from inner ear pathology. It was in 1711, a trumpeter by the name of John Shore invented the tuning fork. Musicians relied on wooden pitch pipes to identify the frequencies prior to discovery of tuning fork. It was only in the 18th century did Weber and Adolf Rinne introduced the usage of tuning fork as how we know it today.

1.1 OBJECTIVES

1.11 Main objective

To determine whether ambient noise has an effect of tuning fork examination

1.12 Specific objective

To determine the effect of variable ambient sound on Rinne and Webber examination

1.13 Expectation

We hypothesize that ambient noise does have an effect on tuning fork examination, thus Rinne & Webber test done in clinic with ambient noise of 65dB would affect result.

2.0 Tuning Fork

2.01 Introduction

Tuning fork test are performed in order to assess a persons hearing acuity. For this test, tuning fork 512 is used. Frequencies below 245 Hz are better felt than heard and hence are not used. Whereas sensitivity for frequencies above 1024 Hz is rather poor and hence is not used.

2.02 Prerequisite for an ideal tuning fork

It should be made of a alloy

It should vibrate at the specified frequency

It should be capable of maintaining the vibration for at least one full minute

It should not produce any overtone

2.03 Methodology using tuning fork

The tuning fork must be struck against a firm surface (elbow of the examiner). The fork should be struck at the junction of upper 1/3rd and lower 2/3rd of the fork.

2.04 Advantage of using a tuning fork:

Easy clinical test to perform

Able to perform at bed side

gives a rough estimate of the patients hearing acuity

2.05 The following are some other uses of tuning fork:

Rinne test

Weber test

ABC test

Bing test

Stengers test

Gelle test

Chimani – Moos test

2.1 Rinne’s test:

Rinne’s test: clinically used to differentiate between conductive and sensor neural deafness. It is designed to compare air conduction with bone conduction thresholds. Under normal circumstances, air conduction is better than bone conduction. 512 tuning fork is prefered. It is struck in the elbow at the junction between upper 1/3 and lower 2/3 of the fork, the maximum vibratory area of the tuning fork. Care must be taken not to produce overtone. Then it is placed at the mastoid process of the patient. Once patient stops hearing, fork is transferred close to the external auditory canal making sure the vibratory prongs vibrate parallel to the acoustic axis. A Positive Rinne test (Air conduction is better than bone conduction). In case of conductive deafness (Bone conduction is better than air conduction). This is known as negative Rinne. If the patient is suffering from profound unilateral deafness then the sound will still be heard through the opposite ear this condition leads to a false positive Rinne.

2.2 Weber test:

It is used to detect a unilateral ear disorder either a conductive or sensorineural hearing loss. This test is best performed at a bone conduction level of 40 – 50 dB hearing threshold levels as any increase in this level would lead to distortion. The tuning fork 512 is again preferred. The vibrating fork is placed in the forehead. Patient would indicate which ear hears better. Midline response indicates a normal ear or a bilaterally equally deaf ears. This test is very sensitive and can pick out even a 5 dB difference between the ears. The principle behind the effect is that while the conduction problem masks the ambient noise of the room, the functioning inner ear picks the sound up via the skull bones. Thus its heard louder.

3.0 MASKING

Auditory masking occurs when the perception of one sound is affected by the presence of another sound (5) The amount of masking is the difference between the masked and unmasked thresholds.

3.01 Masking Fatigue

Care should be taken not to fatigue the subject as this can affect the reliability of the test results. If the test time exceeds 20 minutes, subjects may benefit from a short break.

3.02 The principles of masking

The problems of cross-hearing can usually be overcome by temporarily elevating the hearing threshold of the non-test ear by a known amount so as to enable an accurate assessment of the test ear threshold to be made. This may be achieved by presenting a masking noise into the non-test ear of the appropriate intensity to prevent it from detecting the test signals, and at the same time measuring the apparent threshold of the test ear with the test signals. There is approximately a 1:1 relationship between the increase in masking noise and the elevation of the masked threshold of the non-test ear.

3.03 The Rules of Audiometric Masking

The test ear is always the ear whose hearing threshold is being sought. It is the ear receiving the pure tone test signal directly. The non-test ear is the ear which may have to be masked to prevent detection of the test signal. There are several rules which needs to be observed with respect to audiometric masking

Difference between inter-aural air conduction is more then 40 dB .

Difference between ipsilateral air conduction and bone conduction is more then 15dB.

Difference between inter-aural air conduction and bone conduction is more then 40dB.

3.04 Masking Dilemma

When there is a moderate to severe conductive type hearing loss in both ears, a dilemma occurs whereby adequate intensity to mask the non-test ear crosses over to the testing ear and invalidates the thresholds. To overcome this one can use insert earphones.

 

4.0 NOISE & SOUND

Noise is unwanted sound, where as sound is what we hear. The difference between sound and noise is very much individual and circumstances specific.

Sound is produced by vibrating objects. As an object vibrates, it causes slight changes in air pressure. It is these air pressure changes which travel through the air and produce sound. Thus, as the fork surface vibrates, it creates alternating regions of higher and lower air pressure. These pressure variations travel through the air as sound waves and transmitted to bone when placed on bone.

4.01 Types of Noise

Noise can be variable, continuous, intermittent or impulsive. Noise is said to be continuous when it remains constant and stable over a period. Manufacturing noise is variable or intermittent. Noise is intermittent when there is a fluctuation between quite and noisy phase. Impulse noise is a very short burst of loud noise for example gun fire.

4.02 Sound masking 

This is the concept of masking by introducing a white noise into an environment to conceal undesired noise. This is called auditory masking.

4.03 Ambient sound or ambient audio 

This refers to the background sounds which are present in a scene or location. The higher the ambient sound, the more the test sound will be masked.

4.04 Background noise or ambient noise 

This is referred to unmonitored sound, which is other then the primary sound. It is this background noise which we hypothesize that it affects tuning fork examination. Examples of background noises in ENT clinic are those from airconds, computers etc.

5.0 CRITICAL BANDWIDTH

A simultaneous introduction of 2 tones of different frequencies, are heard as 2 different sound as opposed to a combination tone. The ability to separate these two tones are known as frequency resolution or frequency selectivity. Signals of a combination tone, are said to reside in the same critical bandwidth. Critical Bandwidth is an effect due to cochlea filtering. With the same concept, a complex sound is split into various different frequency components and placed in respective critical bandwidth. They are then coded separately onto auditory nerve. This individual coding only occurs if the frequency components are significantly different in frequency, otherwise they are in the same critical band and are coded at the same place and are perceived as one sound instead of two (6)

5.1 AUDITORY FILTERS

‘Auditory filters’ refers to the filters which distinguish one sound from another. A listener can choose to listen to certain sound while masking others. Frequency resolution occurs on the basilar membrane. A sharply tuned filter has good frequency resolution as it allows the centre frequencies through but not other frequencies (Pickles 1982). Damage to the cochlea and the outer hair cells in the cochlea can impair the ability to tell sounds a part (Moore 1986). This explains why someone with a hearing loss due to cochlea damage would have more difficulty than a normal hearing person in distinguishing between different consonants in speech (7)

6.0 EFFECT OF VARIABLE AMBIENT NOISE ON TUNING FORK,

The tuning fork once vibrated transmits sound through air conduction in Rinne and bone conduction in Webber. In a normal individual, air conduction is better then the bone conduction.

The ambient noise vibrates alters sound perception in air. Although an ambient noise is always present, one gets acclimatised to a surrounding sound. However when the ambient sound is increased drastically one cannot acclimatize fast enough.

By testing Rinne and Webber on a subject, and increasing the ambient sound by a fixed decibel point, one gets to compare the subjective change of perception of stimulus given, both by air conduction and bone conduction.

It is our hypothesis that an ambient sound vibrates the bone more readily then affecting the air conduction. Thus it competes with bone conduction in Rinne and Webber. This explains why patients Rinne is always positive despite an increase in ambient sound even up to the level of 85dB.

However, the subjective appreciation of bone conduction decreases as the ambient sound is increased, in our study bone conduction in Rinnes becomes appreciably fainter as the ambient noise is increases to about 75dB. However the effect on bone conduction in Webber tests is more sensitive to ambient noise as subjects claims unable to hear anything once ambient noise increases to 65 dB.

Thus from my study we conclude that ambient noise does have a effect on tuning fork examination, further studies are needed to compare the effect of ambient noise in various hearing defects.