Hearing Test

If you suspect that you (or a loved one) has a hearing problem, it can often be a difficult time trying to decide what to do next. FC Milnes and Nationwide Hearing Services are here to help, we will diagnose the problem and after completion of the hearing tests we can then advise as to your next course of action.

About Hearing Tests

With regard to the type of hearing loss, the audiologist is looking for information that suggests the point in the auditory system where the loss is occurring. The loss may be conductive, which means that the sounds are not being sent to the cochlea, this is not common and affects only ten percent of people that have a hearing loss. This condition can be temporary or permanent due to abnormal conditions of the middle or outer ear.
Sensorineural damage is often permanent and it affects the inner ear and the cochlea, or the eighth cranial nerve. It can come about as a result of disease, or be caused by some medicines, or it may be genetic or as a result of trauma. Hearing loss may be due to mixed causes where both sensorineural and conductive hearing defects are involved or sometimes the brain cannot process the sounds that have been heard, in other words the brain can’t decipher what they are.

Hearing difficulties may be in one or both ears, it may be only over a certain frequency, it can be progressive or sudden, precipitous or gradual, it may occur under all conditions or as a result of one condition.
Once a hearing loss has been established that is only part of the story, then comes the task of rehabilitation. This may involve surgical intervention, personal hearing aids, skills development through aural rehabilitation, assistive listening devices or sometimes monitoring the condition. Assuming that a hearing aid is the only device necessary then it may have to be fine tuned for your individual purposes.

The term hearing test does not really apply although part of the battery of tests will be an evaluation of your hearing capabilities. Each part of the tests is independent but they are also complimentary and together the results build a complete picture of the state of your hearing.

The case history of your hearing is the first vital step to establish the record of your hearing.

Typical questions for your hearing case history are:
    
•    Have you noticed difficulty with your hearing?
•    If so for how long
•    What have you noticed?
•    When did the hearing loss begin?
•    How many ears are affected?
•    Has your difficulty with hearing been gradual or sudden?
•    Can you hear a ringing noise in your head or ears?
•    Do you have a history of chronic ear infection?
•    Have you a discharge from your ears?
•    Are you in pain?
•    Do you feel dizzy?
•    Is it easier to hear children’s voices or adults?
•    Can you hear men or women’s voices more clearly?
•    Have any close family members got a hearing problem?
•    Do you feel the need to ask people to repeat themselves?
•    Have others told you your TV is too loud?
•    Do people say you speak very loud?
•    Can you hear voices but are not able to understand what is being said?
•    Have you worked in a very noisy place?
•    Is background noise a problem?
•    How long have you had the problem with hearing?

Audiological Assessment

The purpose of an audiological assessment is to establish whether or not there is a hearing loss, to establish whether it is temporary or permanent, what type of hearing loss, and the degree of loss. If the hearing loss is temporary, then it may be that the ear needs further medical treatment. After a hearing test the audiologist can advise you whether you need to go and see your doctor. The audiologist can also inform you of any abnormality of the ear or even if you have excessive wax. Just because you cannot hear does not mean that you need a hearing aid. Government statistics in 2002 reported that a higher percentage of people who had purchased a hearing aid were satisfied with it than those that were supplied by the NHS.
 

 

In this initial examination the audiologist will examine your ears with an otoscope, this is neither painful nor uncomfortable it is merely a light shining in your ear. If the audiologist thinks that you will benefit from a hearing aid then he will suggest you have an audiogram. Many years ago the method of establishing whether or not someone could hear relied very much on the patient’s cooperation. These days the methodology is a science called audiometry and it means the accurate assessment of the level of hearing. Without knowing what type of hearing loss you are suffering from and how much, the audiologist cannot make an assessment to plan the rehabilitation of the hearing loss.

The majority of us when we have normal hearing are capable of hearing within the 20 to 20,000 Hz range, especially when young. It is the hair cells along the organ of Corti that detects frequency, the highest frequencies are detected near the base of the cochlea at the oval window, and the remainder of the sound spectrum detected in a progressive fashion which means the hair cells near the tip detects the lowest frequencies.
On average we all hear the middle range best, whilst having a more sensitive ear to the higher or lower frequencies. It is normal that we lose the sensitivity to higher frequencies as we age. The ageing process does not necessarily affect the tones of frequencies that are usually heard in average daily life, but there are not many over the age of 65 that can hear tones with a frequency of 10,000 cycles per second. What this means in real terms is that it is difficult to understand speech in a group context, and it is harder to be certain that you can identify a voice by hearing alone. However there is often a difference in pure tone thresholds, the ability to perceive speech also depend on intellect as well as individual listening habits.

Audiogram

To accurately test what you can actually hear an audiometer is used. This delivers sound to you at an accurate and a precisely controlled intensity, within a sound proof environment.
The standard tests are for
•    Pure Tone Audiometry,
•    Speech Audiometry, 
•    Immittance Audiometry.

Pure Tone Audiogram
In acoustics, sound can be recognized by its regularity of vibration, a simple tone has only one frequency, although its intensity may vary. It is now possible to measure an individual’s hearing threshold for a series of pure tones ranging from a lower frequency of 125 hertz to an upper frequency of 8,000 or 10,000 hertz. This span includes the three octaves that are most important for speech which are between 500 and 4,000 hertz.

To test pure tone audiometry it has to be done in a soundproofed room where there is no background noise to interfere with the test results. Earphones are worn and the sound travels by air conduction to stimulate the eardrum and then the auditory nerve. The intensity range is usually 100 decibels in steps of 5 decibels. The “zero dB” level is the international standard used representing normal hearing for teenagers’ under ideal laboratory conditions. The audiologist uses a calibrated machine called an audiometer to present tones at different frequencies or pitches and louder and softer. For instance a sound of a particular frequency is presented to one ear, and its loudness is adjusted until the patient no longer hears it consistently; an example of this sound may be a piano note. This is repeated for at least half a dozen times, and then the other ear is tested in the same way, the other ear is shielded so that it cannot hear and you respond to the test with hand signals.

The audiologist must determine the lowest intensity for each frequency that the person being tested can hear fifty percent of the time. Someone who hears the tone of 4,000 hertz only half of the time at the 40-decibel setting has a 40-decibel hearing level for that frequency, which is 40 decibels above the normal threshold.

The frequency or pitch of the sound is referred to in Hertz (Hz). The loudness of the sound is measured in decibels (dB). The responses are recorded on a graph, the audiogram that provides a graph of intensity levels for each frequency tested. It plots the hearing levels for each ear by octaves and half octaves across the frequency range of 125 to 8,000 hertz. The shape of the audiogram provides the otologist or audiologist with important information they require to determine the nature and cause of the hearing defect. The audiologist measures the degree of hearing impediment but otologist diagnoses and treats defects and diseases of the ear, either medically or surgically.

A calibrated bone-conduction vibrator is used so that hearing by bone conduction also can be measured. In this test, the sound as a tone is introduced to the ear by a small vibrator placed on the forehead or the mastoid bone. The purpose of this is to bypass the outer ear and send the vibrations through the skull to the auditory nerve. This bypasses wax, and fluid that may be present as blockages and just tests the inner ear. In simple terms it tells us whether the inner ear is functioning correctly without the outer and middle ear being involved in the process of hearing.

The air conduction tests of the outer and middle ear indicate hearing losses that are either conductive or sensorineural, but bone conduction test show only the sensorineural component. If the air and bone conduction thresholds are the same, the loss is sensorineural. If there is a difference between air and bone thresholds, it is referred to as an air-bone gap, and the hearing loss is conductive or mixed. The air-bone gap is the difference in the measure of the loss in transmission of sound across the middle ear and indicates the maximum improvement that may be obtained through successful corrective surgery. When the inner ear is damaged there is a sensorineural impediment and a hearing aid can be helpful and improve speech intelligibility.

Sensorineural impairment normally means that you cannot hear a faint noise at all, but if a sound is louder you may hear it as well as someone who has normal hearing. This rapid increase in loudness above the threshold level is called recruitment. Sometimes you may have a normal ear and recruitment can be measured by a binaural loudness balance test.

A binaural loudness balance test means that you set the controls so that the loudness of the tone heard in the defective ear is equal to that of the tone heard by the normal ear. This comparison is used at several levels of higher intensity until the absence or presence of recruitment can be detected. Unfortunately when recruitment is excessive, the range of hearing between the threshold and the level at which loudness becomes intolerable may be very narrow, and this means that a special type of hearing aid is necessary.

Recruitment causes your perception of sound to be amplified; there is only a small increase, but it is sufficient to cause real discomfort, and it may mean that all sound are affected or just some. As the hair cells in the cochlea start to malfunction they "recruit" the neighbouring cells to hear, as they are still functioning. So the sound is heard and perceived to be louder by the brain. Hearing ranges then narrow between the quietest sound you can hear as a result of a hearing loss and the sound that you can tolerate as a result of the recruitment. However because this is a condition of the cochlea, and specifically the hair cells, if your hearing loss is conductive then you do not have recruitment.

Below is an example of the patient’s thresholds of auditory sensitivity for pure tone. Threshold hearing levels are indicated for each frequency tested. By convention, the normal hearing levels are depicted at top of the graph, whilst a decrease in hearing sensitivity is indicated by larger values of hearing level. Hearing level is plotted on a logarithmic decibel scale. Sounds are tested by air conduction with earphones and bone conduction by a skull vibrator. An air bone gap indicates a conductive component of hearing loss. A decrease in threshold sensitivity by bone conduction reflects a sensory or neural loss.
 

 Hearing levels are expressed in decibels based on the pure tone average for the frequencies 500 to 4000 Hz and then the range is

•    Normal hearing (0 to 20 dB HL),
•    Mild hearing loss (20-40 dB HL),
•    Moderate hearing loss (40-60 dB HL),
•    Severe (60 to 80 dB HL)
•    Profound hearing loss (80 dB HL or greater).

Speech Audiometry

Speech audiometry includes determining speech reception threshold (SRT) and testing of word recognition and understanding Speech reception threshold determines the softest level a person can hear and correctly repeat spondaic words. Spondaic words are two syllable words which are easily distinguishable because they do not sound like other words and should not be confused, as they have equal stress on each of the syllables. Examples are "ice cream", "hot dog", "outside", and "airplane." The individual repeats words as the level of the voice gets fainter. The faintest level, in decibels, at which 50% of the two-syllable words are correctly identified, is recorded for each of the ears as the Speech Reception Threshold (SRT).

Word recognition tests means recognizing monosyllabic words when speech is comfortably loud. Examples of words used in this test are "come", "high", "knees", "chew." There is no change in the loudness of the voice as it merely tests word recognition and the patient again repeats what they think they have heard.

These tests are designed to measure the patients’ ability to comprehend spoken words and sentences rather than pure tones and assess sensitivity. The threshold is the level that the patient can repeat fifty percent of the spoken words, correctly, and intelligibility is the level a patient can correctly repeat when presented at supra-threshold levels. This is a useful test to determine whether a hearing aid may be useful.

Immittance Audiometry

Sound is vibration and to send it to the inner ear, the vibrations must be changed from air vibrations to vibrations in the cochlear fluids. Sounds are absorbed and reflected in the eardrum membrane, and it vibrates as a result of absorbed sound only. However there is a difference in the resistance to the passage of sound between air and fluid, and this called impedance and it reduces the amount of the sound that can be transmitted. When sound conducted by air hits water all its energy is reflected and less 0.1 percent passes through the water. In hearing terms this physical fact would represent a transmission loss of 30 decibels, fortunately the middle ear acts as a transformer and it prevents this enormous loss of sound.

The degree of the impedance depends on the mass and the stiffness of the membrane. When the eardrum absorbs sound it vibrates like a stiff cone, bending inwards and outward and the greater force of the sound wave means the greater deflection of the membrane and the louder the level of sound that is heard. The higher frequencies of sound cause it to vibrate faster. At higher frequencies the motion of the membrane becomes more complex and less effective.

The malleus and the incus in the middle ear are finely balanced, but they are tightly bound together and move in unison with the eardrum. When the sound pressures are low, the vibrations are passed to the third bone of the inner ear the stapes, and the whole ossicular chain of the three bones move as one mass. The Incus and the stapes are not bound together tightly and a lot of energy can be lost. The stapes rocks on its footplate, which then touches the membrane covering the oval window in the inner ear. The rocking of the stapes transmits the sound to the inner ear.

The equalisation of the impedance between air and water is accomplished in two ways, firstly the area between the tympanic membrane and the stapes footplate contracts and secondarily by the mechanical advantage of the lever that has been formed by the malleus and incus. The contraction increases the pressure by about thirteen times. As the handle of the malleus is longer than the incus the pressure goes up 1.3, which means the pressure increases by about seventeen times.

The ossicular chain not only concentrates sound in a small area but it can also generate sound to a specific window of the cochlea, the oval window. Thanks to these mechanical adaptations of the middle ear, the hair cells of the cochlea are able to respond, at the threshold of hearing for frequencies to which the ear is most sensitive.

The electroacoustic immittance bridge is a device designed to quantify the impedance of the conductive mechanism of the ear by bouncing a probe tone off the tympanic membrane and measuring the proportion of reflected sound. Impedance audiometry tests whether the ear is functioning at the cochlea and the brain stem. Two tiny tubes are sealed inside the external canal and one tube receives sound from a small loudspeaker, the other tube notes how much of this sound is reflected from the tympanic membrane, and it goes to a microphone, amplifier and it is then recorded. When a sudden but intense sound is applied to the other ear, it causes the stapedius muscle to contract, and the impedance or resistance is increased, and the recorder shows the sound being reflected.

An acoustic bridge quantifies the resistance to movement of the conductive mechanism of the ear because it bounces a probe tone off the tympanic membrane and measures what proportion of sound is reflected. The listener can then hear the sound reflected from the tympanic membrane of the patient and a sound of equal intensity reflected in an artificial cavity. They can also adjust the volume to that of the external canal of the ear being tested.
Once the two sounds have been equalized the impedance can be read. This reveals any conductive defects of the middle ear, including separation of the ossicular chain and immobility of the malleus or the stapes. This test ascertains whether the facial nerve that activates the stapedius muscle is functioning and also the auditory path of the medulla, as well as the cochlea

Tympanometry introduces air pressure into the ear canal making the eardrum move back and forth. The test measures the mobility of the eardrum. Tympanograms are produced which show stiffness, flaccidity, or normal eardrum movement. A tiny muscle in the ear contracts when a loud sound occurs. The loudness level in decibels at which the acoustic reflex occurs, and the absence of the acoustic reflex, gives information that aids in the diagnosis of problems in the auditory pathway.

Through static acoustic measures, the physical volume of air in the ear canal is measured. This test is useful in identifying a perforated eardrum or the openness of ventilation tubes. Tympanometry introduces air pressure into the ear canal forcing the eardrum to move. The test measures the mobility of the eardrum; the tympanograms show the stiffness, flaccidity, of the eardrum movement.

We all have an acoustic reflex to sounds. A tiny muscle in the ear contracts when a loud sound occurs. The loudness level in decibels at which the acoustic reflex occurs, and/or the absence of the acoustic reflex, gives diagnostic information that aids in identifying location of the problem along the auditory pathway. Through static acoustic measures, the physical volume of air in the ear canal is measured. This test is useful in identifying a perforated eardrum or the openness of ventilation tubes.

How to interpret an audiogram in simple terms.

Each line from left to right represents a pitch or frequency in Hertz (Hz) with the lowest pitches on the left side, and graduating to the highest frequencies tested on the right. The range of frequencies tested by the audiologist are 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 1500Hz, 2000 Hz, 3000Hz, 4000 Hz, 6000Hz and 8000 Hz.. It is using a similar process to the piano keyboard with the low notes at the left and the high notes at the right; "middle C" key on the piano corresponds to 250 Hz on the audiogram.

Low Frequency sounds or low pitched sounds
•    Bass drum,
•    Tuba,
•    Vowel sounds such as "oo" in "who".
•    Consonant sounds such as the “m” in “moon”.
High Frequency sounds or high pitched sounds
•    Chirping of the birds,
•    A triangle playing
•    Consonant sounds such as “f” in fly or  "s" in "sun."

Loudness or intensity of sounds on an audiogram

Each row from top to bottom represents loudness or intensity of sound in units of decibels (dB). The minus number at the top represents the soft sounds whilst the bottom reflects the loudest sounds. Soft sounds mean the background noise of electrical machinery at work such as the refrigerator, or the ticking of a clock or the consonant sound "t" in the word "too”. Loud noises are a car horn, or a lawnmower, loud music, or the vowel sound "o" as in the word "poke". However all sounds are relative if you compared the sound of heavy hydraulic machinery with a vacuum cleaner than you would have to conclude that the vacuum cleaner was a soft sound. Other sounds are subjective for instance you may be able to stand a dog barking, but the low pitched whine of a dog may drive you to distraction. Normal conversation levels typically record around 60 dB, whilst whispering is around 30 dB, and a comparison of the two would reflect that.

If the shape of the audiogram is dipping then you hear best the lower frequencies, if it is peaking to the top of the graph then you hear better at high frequencies. It may be asymmetrical, reflecting that the hearing loss is different in each ear, or it may be symmetrical indicating the loss to be the same. Once the audiogram is completed, the audiologist calculates the pure tone average for each ear, which is the average of the results of the hearing thresholds at 500, 1000, and 2000 Hz, because these are the major frequencies that speech falls into. The degree of hearing loss is always represented in decibels.

Other types of test for hearing

Auditory brainstem response (ABR)

During an auditory brainstem response (ABR) test electrodes are placed on babies’ heads to check if they have any brain wave activity in response to sound. It is a check for babies and infants to test whether their auditory nerve is functioning. Its purpose is to diagnose deafness earlier than the usual eighteen months, so that a child cannot lose that crucial time of development as a result of a hearing impediment.

Oto-acoustic Emissions (OAE)

The purpose of this test is to establish whether the hairs within the cochlea are functioning.

It is used as a screening test usually in infants or individuals who have developmental disabilities. However it can also partially estimate hearing sensitivity within a limited range.
The normal cochlea does not just receive sound; it emits low-intensity sounds called OAEs. These sounds are produced by the cochlea and, by the cochlear outer hair cells as they expand and contract, this causes an inaudible sound that is echoed back to the middle ear, and these can be recorded by a small probe; carrying a sensitive low noise microphone.  Everyone who has normal hearing produces these soundless emissions, yet those with a hearing loss greater than 25-30 dB do not produce any at all.

Balance Assessment

Three different things, our visual system, the inner ear, and our sense of movement determine our sense of balance, when all three fail to work together we become dizzy. Any disturbance in the inner ear, with or without a hearing loss or ringing in the ears has the potential to cause dizziness. A balance assessment becomes necessary when there is rapid involuntary eye movement, or an apparent balance dysfunction in terms of gait abnormalities, or when they complain of feeling dizzy, and when another disease is suspected.

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