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. Although this knowledge was available since those days, little progress was made in this direction as it had very little therapeutic value. It was in 1711, a trumpeter by the name of John Shore, who changed the whole scenario by inventing the tuning fork. Musicians relied on wooden pitch pipes to identify the frequencies prior to discovery of tuning fork. The problem of wooden pitch pipes were it was sensitive to temperature and humidity changes, thus affecting the wooden pipes. Thus Tuning fork not only was a breakthrough for musicians, it was also an eye opener for clinical otologists, as they started believing that they had a diagnostic tool which could differentiate middle ear deafness from inner ones.
18th Century:
In 1800 German Physicist E.F.F Chladini studied the exact physics of tuning fork and reported the mode of vibration of tuning fork around its nodal points. In 1802 Italian Physicist Venturi proved that the perception of sound was due to the fact that one ear is hit by more intense sound than the other. In 1827 Wheatstone a London based physicist investigated the mode of vibration of ear drum using a tuning fork. He concluded that direction of sound is perceived by maximally vibrating ear drum. Weber a German anatomist confirmed the earlier finding by Wheatstone. 1845: E. Schmalz an otologist from Dreaden Germany introduced the tuning fork test in otology and later named it in honor of Weber. Although he was the first to claim the diagnostic possibility of using a tuning fork, this achievement did not attract that much attention during his times. It was Tondroff who stressed the importance of tuning fork as a diagnostic tool in the field of otology. Tondroff offered the most detailed and complete explanation of the working mechanism of the bone conduction hearing. He later identified four major bone conduction components. Middle ear inertia/ Middle ear compliance/ Inner ear compression/ Round window release.
1.2 OBJECTIVES
1.21 Main objective
To determine whether ambient noise has an effect of tuning fork examination
1.22 Specific objective
To determine the effect of variable ambient sound on Rinne and Webber examination
1.23 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 subjectively assess a persons hearing acuity. This test can in fact be performed by using tuning forks of the following frequencies ( 245 Hz, 512Hz, and 1024 Hz) 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 good alloy
It should vibrate at the specified frequency
It should be capable of maintaining the vibration for 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 (rubber pad/ elbow of the examiner). The fork should be struck at the junction of upper 1/3rd and lower 2/3rd of the fork. It is this area of the fork which is capable of maximum vibration.
2.04 Advantage of using a tuning fork
Easy to perform
Can even be performed at bed side
Will give a rough estimate of the patients hearing acuity
2.05 The following are some tests which can be performed using a 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: is a tuning fork test used to clinically test hearing deficiencies in patients. It is designed to compare air conduction with bone conduction thresholds. Under normal circumstances, air conduction is better than bone conduction.
Ideally 512 tuning fork is used. It should be struck against the elbow or knee of the patient to vibrate. While striking care must be taken that the strike is made at the junction of the upper 1/3 and lower 2/3 of the fork. This is the maximum vibratory area of the tuning fork. It should not be struck against metallic object because it can cause overtones. As soon as the fork starts to vibrate it is placed at the mastoid process of the patient. The patient is advised to signal when he stops hearing the sound. As soon as the patient signals that he is unable to hear the fork anymore the vibrating fork is transferred immediately just close to the external auditory canal and is held in such a way that the vibratory prongs vibrate parallel to the acoustic axis. In patients with normal hearing he should be able to hear the fork as soon as it is transferred to the front of the ear. This result is known as Positive Rinne test. (Air conduction is better than bone conduction). In case of conductive deafness the patient will not be able to hear the fork as soon as it is transferred to the front of the ear (Bone conduction is better than air conduction). This is known as negative Rinne. It occurs in conductive deafness. This test is performed in both the ears.
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.
Use of Rinne test in quantifying conductive deafness:
Conductive deafness of more than 25 dB is indicated by negative Rinne with 512 Hz fork, while it is positive for 1024 Hz. If Rinne is negative for 256, 512 and 1024 Hz then conductive deafness should be greater than 40dB.
2.2 Weber test:
Is a tuning fork test (quick) used to assess hearing levels in an individual. This can easily detect unilateral conductive and unilateral sensorineural hearing loss. This test is name after Ernst Heinrich Weber (1795 - 1878). This test is ideally performed at a bone conduction level of 40 - 50 dB hearing threshold levels. Any increase in this level would lead to distortion.
Procedure:
Tuning forks used - 256 Hz / 512 Hz
Commonly used frequency is 512 Hz.
A vibrating fork is placed over the forehead / vertex / chin of the patient. The patient should be instructed to indicate which ear hears the sound better. In normal ear and in bilateral equally deaf ears the sound will be heard in the mid line. This test is very sensitive in identifying unilateral deafness. It can pick out even a 5 dB difference between the ears.
Theory:
A patient with a unilateral (one-sided) conductive hearing loss would hear the tuning fork loudest in the affected ear. This is because the conduction problem masks the ambient noise of the room, whilst the well-functioning inner ear picks the sound up via the bones of the skull causing it to be perceived as a louder sound than in the unaffected ear.
Inadequacies:
This test is most useful in individuals with hearing that is different between the two ears. It cannot confirm normal hearing because it does not measure sound sensitivity in a quantitative manner. Hearing defects affecting both ears equally, as in Presbycusis will produce an apparently normal test result.
3.0 MASKING
Auditory masking occurs when the perception of one sound is affected by the presence of another sound (5)
The unmasked threshold is the quietest level of the signal which can be perceived without a masking signal present.
The masked threshold is the quietest level of the signal perceived when combined with a specific masking noise. 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
This situation occurs when there is a conductive type hearing loss in both ears, which is moderate to severe. The dilemma is that an adequate intensity to mask the non-test ear crosses over to the testing ear and invalidates the thresholds.
Enough masking is too much masking. There are several ways to overcome this. When one is masking air conduction, use insert earphones.
Other methods include using bone-ABR testing, ABR is unaffected by the central effect of masking but the sound still stimulates both ears and also one is limited by one's bone stimulator.
Another method is the sensorineural acuity level (SAL) technique. In the SAL method, both ears are masked equally through an oscillator placed over the forehead. This is done by performing air conduction thresholds while using bone masking, and then doing some adjustments for the "air conduction shift". This method involves a large number of subtractions of noisy values, and for this reason it is an intrinsically unreliable method.
Thus when one encounters the "masking dilemma", this is noted on the audiogram and one accepts that it is impossible to determine the details of the hearing loss.
4.0 NOISE & SOUND
Sound is what we hear. Noise is unwanted sound. The difference between sound and noise depends upon the listener and the circumstances.
Sound is produced by vibrating objects and reaches the listener's ears as waves in the air or other media. When an object vibrates, it causes slight changes in air pressure. These air pressure changes travel as waves through the air and produce sound. To illustrate, A tuning fork after striking it. It vibrates back and forth. As it moves forward, it pushes the air in contact with the surface. This creates a positive (higher) pressure by compressing the air. When the surface moves in the opposite direction, it creates a negative (lower) pressure by decompressing the air. 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 continuous, variable, intermittent or impulsive depending on how it changes over time. Continuous noise is noise which remains constant and stable over a given time period. The noise of boilers in a power house is relatively constant and can therefore be classified as continuous. Most manufacturing noise is variable or intermittent. Different operations or different noise sources cause the sound changes over time. Noise is intermittent if there is a mix of relatively quiet and noisy period. Impulse or impact noise is a very short burst of loud noise which lasts for less than one second. Gun fire are examples of such noise.
4.02 Sound masking is the addition of natural or artificial sound (such as white noise) into an environment to cover up unwanted sound by using auditory masking. This is in contrast to the technique of active noise control. Sound masking reduces or eliminates awareness of pre-existing sounds in a given area and can make a work environment more comfortable, while creating speech privacy so workers can better concentrate and be more productive. Sound masking can also be used in the outdoors to restore a more natural ambient environment.
Sound masking can be explained by analogy with light. Imagine a dark room where someone is turning a flashlight on and off. The light is very obvious and distracting. Now imagine that the room lights are turned on. The flashlight is still being turned on and off, but is no longer noticeable because it has been "masked". Sound masking is a similar process of covering a distracting sound with a more soothing or less intrusive sound
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 any sound other than the sound being monitored (primary sound). Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise regulations.
Examples of background noises are environmental noises such as waves, traffic noise, alarms, people talking, bioacoustic noise from animals or birds and mechanical noise from devices such as refrigerators or air conditioning, power supplies or motors.
The prevention or reduction of background noise is important in the field of active noise control. It is an important consideration in many fields particularly medicine ( medical diagnosis or imaging).
5.0 CRITICAL BANDWIDTH
If two sounds of two different frequencies are played at the same time, two separate sounds can often be heard rather than a combination tone. The ability to hear frequencies separately is known as frequency resolution or frequency selectivity. When signals are as a combination tone, they are said to reside in the same critical bandwidth. This effect is thought to occur due to filtering within the cochlea, the hearing organ in the inner ear. A complex sound is split into different frequency components and these components cause a peak in the pattern of vibration at a specific place on the cilia inside the basilar membrane within the cochlea. These components are then coded independently on the auditory nerve which transmits sound information to the brain. 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
The filters that distinguish one sound from another are called 'Auditory filters'. Frequency resolution occurs on the basilar membrane due to the listener choosing a filter which is centered over the frequency they expect to hear, the signal frequency. 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.
