Audiometery: Anatomy and Physiology of Hearing for Audiologists - Term Paper Example

AUDIOMETRY HET242 INTRODUCTORY NEUROPHYSIOLOGY 22nd May, 2012 Abstract Sound waves can be detected at different frequencies and intensities depending on individual animal species. Loss of hearing leads to deafness. Human beings can be able to perceive sound wave frequencies of a up to 16000 hertz, but this range can be increased largely at the teenager ages up to frequencies of 24,000 Hz. At birth human beings can be able to detect sound waves of frequency ranges between 100 Hz to 2 kHz. H igh frequencies may lead to loss of hearing function by the ear. This can be tested using an audiometry experiment discussed below. Temporal and sudden loss of hearing may be corrected surgically but gradual loss of hearing can lead to permanent destruction of cochle and complete loss of hearing. Ageing results in the decreased of maximum frequency recognised by the human ear and by the age of 20 it usually ranges at below 16,000 hertz and at the age of 40 the range goes to 12,000 hertz. Whatever intensity of sound reaching the cochlea, on sensorineural ear soundness it can be detected regardless of the acoustic impedence of the middle ear. Introduction Hearing in human beings refers to the ability to recognise different sounds by the use of ears, and this usually depends on property of ears to detect various sound tones as produced by the source. Normally audible tones for human beings range from frequency of about 16 up to 16000 hertz (Hz), and 1 Hz is equivalent to one oscillation per second. This range varies within the animal kingdom and this is why some animals such as the domestic dog, can be able to detect sounds of low tones as compared to the human beings. Characteristically sound contains a different array of many harmonic frequencies which are multiples of fundamental or basic frequency. In general, the loudness of a sound usually correlates with sound wave amplitude as reflected in a sound wave; and generally louder sound is produced by sound waves of greater amplitude. However the sound pitch perceived by human ears usually correlates with the sound frequency, and high sound frequencies is reflected by high pitch. The frequency of a sound wave refers to the number of complete waves made per second (Martin and Clark, 2009). This ability to recognise a sound wave by the use of ears can be lost in human beings resulting to a form of disability commonly reffered to as a deaf. Hearing loss is avery significant handicap for human beings and this brings to difficulty in or complete loss of communication by speech with other people. It can be a gradual process where by at some point there would be partial hearing loss or a prompt process resulting to sudden loss of hearing function. Beginning impairment refers to an average hearing level loss of 16 decibels (dB) at the frequencies of 500, 1000 and 2000 Hz. One can be considered a deaf when the hearing loss for all the three frequencies occurs at or above 82 dB. Initially the hearing loss often appears at sound frequencies of 4000 Hz and this is followed by loss of hearing at sounds of lower sound frequencies. At each particular frequencies there is characteristic threshold sound intensity perceived by each individual human being. Materials and Methods: Part 1: The Conduction Test (Weber’s Test). The weber test was done using a 512 Hz tuning fork, which is considered to be the most accepted frequency for assessing hearing. The tuning fork was stroked on rubber mallet and held from the steam than placed on the center of the forehead while the fork is still vibrates, one ear was plugged at a time to detect simulate conduction deafness. Part 2: Determination of Pitch Range A function generator, an oscilloscope and headphone were used to determine the pitch range; the function generator was used to generate pure tones, different range of selected frequencies and intensities were practiced before the start of the experiment. A 1000 Hz was observed on the oscilloscope “sin wave” and heard on the headphone as a test to start the experiment. The experiment begun by wearing a headphone at low frequency while the intensity set in high to detect the lowest frequency possible. The frequency gradually increased while the intensity decreased to determine the highest frequency possible. Part 3: Audiometry Test The hearing tests using the audiometry sheet. To conduct the experiment, a quite room needed for better testing, however the room wasn’t completely quite which might affected our results. The test started while the subject was facing away from the equipment and wearing a headphone; “the device” was automatically set to test the right and the left ear at the same time. The device was set up at lowest frequency and the amplitude “dB” to zero. The results were recorded using the audiometry form by writing “O” for right ear and “X” for the left ear, the subject was informed about the start of the test, Whenever the subject heard a tone, indication was made by pressing a button quietly “yes” “no”, the amplitude increased with every press the subject made. The procedure was repeated until full frequency range had been tested. Bone conduction test A bone conduction oscillator was placed over each mastoid so that the diaphragm of the earphone is directly placed over the opening to the ear canal; the above procedure was repeated for each ear. And the results were recorded. Part 1: The Conduction Test (Weber’s Test) This is a test to distinguish between conduction and nerve deafness (sensorineural deafness). Conduction hearing is normal sound via the ear canal. Tuning forks are used with a frequency above 256 Hz, because at lower frequencies, sounds can be felt as well as heard. 1. Strike the tuning fork on the side of your hand (not on the table) and place the butt of the fork on the bridge of the nose. A subject with normal hearing will localise the sound at the midline between the ears. 2. Plug one ear with your finger to simulate conduction deafness.Strangely, the sound will be heard better in the plugged ear. The reason being that the unplugged ear will be subjected to competing surrounding noises whereas the plugged ear is spared. Part 2: Determination of Pitch Range This test requires a function generator, an oscilloscope and headphones. You will generate pure tones with the function generator using a wide range of selected frequencies and intensities. 1. Practise the use of the function generator by generating a 1000 Hz sound wave. Observe the waveform on the screen of the oscilloscope. Draw the waveform, taking note of the time scale and the voltage scale. Listen to the 1000 Hz tone through headphones. 2. The test subject should wear the headphones in a quiet room, starting at low frequency end. The intensity will be turned up to determine the lowest detectable frequency. 3. Increase the frequency and note that you must reduce the intensity as the pitch becomes higher in order to be able to tolerate the sound level. Determine the highest detectable frequency perceived by the subject. 4. The maximum range of pitch discrimination occurs in teenagers, and is about 20 to 24,000 Hz. By age 20 the upper range has decreased to 16,000 and a person at age 40 can seldom hear frequencies above 12,000 Hz. Record the following: Lowest: 18 Hz Highest: 14000 Hz Sustained loud sounds at specific frequencies can selectively damage hair cells in the cochlea associated with the perception of sound at the particular frequency. Part 3: Audiometry Test A. Working in pairs performs the hearing tests using the audiometry sheet. Test both the left and right ears. If time permits, perform the test again, but this time using the bone conduction head set. 1. Perform audiometry in a quiet isolated portion of a lab or room.Subject should be seated comfortably and facing away from the equipment.With the subject wearing headphones, the tester should select either the left or right ear to test (red or blue phones). 2. Wind the frequency dial to the lowest frequency and the amplitude dial (dB) to zero. 3. Record results using the audiometry form. 4. The audiogram key uses the circles for right ear and crosses for left ear; (both unmasked). Indicate to the subject that the test is about to begin. The subject should indicate when they can hear a tone. Depress the lever quietly which increases the amplitude with each subsequent press. 5. Continue until subject detects the tone, then reduce amplitude to zero, and switch to the next frequency. 6. Continue this procedure until the full frequency range has been tested. 7. Repeat with the other ear. Results: Part 1: The Conduction Test (Weber’s Test) The result for Weber test was recorded positively, and I was considered to have normal hearing tone, since the produced tone from the tuning fork heard equally on both ear while placed on the center of the forehead, the sounds were about the same volume in each ear. Part 2: Determination of Pitch Range When sound wave frequency is gradually increased with corresponding pitch decreased, there was a positive response in sound detection until it reached a point where there was negative sound detection abilities. This refers to the highest pitch at which each human individual can be able to recognise and usually it ranges from 16-16000 hertz. Part 3: Audiometry Test A. The hearing tests using the audiometry sheet. HET242 Worksheet. Simple auditory tests. Name: Sabri AL SAQLAB 1. What is your audible range of frequencies? 16 Hz to 16000 Hz. 2. Complete your audiogram below, using an ‘O’ for the right ear, and ‘X’ for the left ear. Frequency in Hz. 125 250 500 1k 2k 4k 8k -10 0 20 30 40 50 60 70 80 90 100 110 1. What is probably the most common cause of temporary conduction deafness? Loss of hearing is an impairment referred to as deafness and this can be either genetically transfered or environmentally acquired. It is basically loss of function of hearing and this impairment can be caused by a problem in the external or middle ear are called conductive hearing losses, because the difficulty lies in the conduction of sound to the cochlea. For example, excessive wax in the ear canal, fluid in the middle ear brought on by an infection, or a discontinuity between the ossicles would prevent sounds from reaching the inner ear efficiently. These types of hearing losses are often medically or surgically correctable for instance by administration of chemotherapies. This loss of hearing is dependent on the sound frequency range affected, which is determined by whether the conduction block increases the mass on higher frequencies or stiffness on lower frequencies or both. There are several causes for temporary conduction deafness, to be able to determine the best answer differential diagnosis must take a place to define which part/s of the ear is/are affected, one of the most important pieces of the diagnosis is the history of the patient, as well as questioning about when the problem started and whether the symptoms came on a sudden or gradually, and if any medication had been taken hence antibiotics, or any family history of hearing problems are found, if previous hearing test or surgeries were done. Most hearing problem can be related to genetic hearing loss also known as hereditary hearing loss or familial hearing loss which is due to the differences in the genes that are passed on by hereditary source, any hearing loss that is not associated with genetic of congenital origin is called an acquired hearing loss, which is a hearing loss that occurs after birth and caused by disease, trauma, drugs, or ageing. (Kramer, 2008). Hearing disorder can be described in terms of their time period, for example: an acute disorder which can last to a relatively short period of time; a chorionic disorder which can be present over a long period of time; an intermittent disorder which is a condition that comes and goes over time. On the other hand, other conditions can be associated with auditory disorders for example, Otorrbea; which related to the fluid in the middle ear “normally infection”. Nevertheless, the loss of hearing is idiopathic especially for the sudden hearing loss. (Kramer, 2008). Generally research studies have shown that some common cause of temporary conduction deafness and hearing loss can be related to the following: Middle ear loss of conduction Otitis Media is a clinical condition that is cased by poor function of Eustachian tube which leads to fluids build up in the middle ear causing difficulty hearing, this is commonly found in young children and can be treated by medical observation or antibiotics. Wax accumulation in the ear canal also may obstruct the flow of sound waves through the middle ear. Can be due to middle ear infection that produces inflammatory exudates or pus which fill the middle ear canal usually common in children. It is commonly associated with upper respiratory tract bacterial or viral infection because in children the eustachian tube is shorter and less slanted, facilitating entry of disease causing micro-organisms. Occassionally may result to rupture of the tympanic membrane or a temporal loss of hearing and affects a lot speech development. This usually affects low frequency sounds first such as speech identifications due to raised threshold frequencies. Mild Perforation This is usually caused by inserting sharp object into the ear, a slap to the ear or pressure equalization tube which can effect the tympanic membrane, there is no treatment for mild perforation, however it will usually heal itself as long as ear plugged is used to avoid water getting inside the ear and causing infection (Roeser et al., 2007). Inner ear This can also be referred to as sensorineural hearing loss, and usually it results due to neural pathologies in the hearing. This can be failure of effecient nerve impulse perception between the middle ear and the central nervous system such as the brain, which usually interpretes the sound wave. This can be due to a prolonged use of a certain ototoxic antibiotics such as aminoglycosides or basically by nose-induced hearing loss, and inability to transduce specific frequencies caused by the damage to the cochlea, auditory nerve or cochlear nucleus, hair cell damage or even stereocillia damage (Martin and Clark, 2009). Damage of the cochleal base which is the high frequency percption region, is one of the most sensitive to damage to internal ear and this can lead to permanent deafness. This can be as a result of different aetiologies. Nose-induced hearing loss Also known as acoustic trauma, it refers to an hearing loss that occurs due to a sudden exposure to a loud sound for example, explosion, gunshot, or listening to loud music for a long period of time which causes damage to cochlea (Roeser et al., 2007). There is no ultimate treatment of this kind hearing impairment, but there can be availability of ear protection devices to avoid such occurences. High frequency spectrum accompanied with intense sound wave also may facillitate potential for damage of bone conduction apparatus. Ototoxicity Ototoxicity is caused by aminoglycoside antibiotic such as gentamycin and amikacyn, which cause damage to the cochlear and/ or vestibular hair cells, it might be treated with drug therapy. These drugs are potential to cause toxic reactions to inner ear structures, and this includes the cochlea, vestibule, semicircular canals, and otoliths, and are referred to be ototoxic (Martin and Clark, 2009). These drug-induced damage to these structures of the inner ear responsible of the auditory and balance system can result in hearing loss, as well as tinnitus, and dysequilibrium or dizziness. Also prolonged use of loop diuretics for instance furosemide, which commonly block the Na+/K+/2Cl- transporter responsible for the generation of the endocochlear impulse potential. Discussion: Part 1: The Conduction Test (Weber’s Test) The weber test is used to help determine whether a unilateral hearing loss is due to sensorineural or conductive aetiologies. It is a lateralization test and it is based on patient identification of sound direction. They are required to indicate the direction from which a sound appears to be coming from which is also the sound source. This can be indicated by the difference in sound perception by each ear, that is the right and left ears (Gelfand, 1997). This test uses a vibrating tuning fork which is placed in the middle of the forehead or the vertex and the patient is asked in which ear the sound is heard. Normally in human beings, sound is detected and recognised equally in both ears. It is lateralised to the worse ear in conductive deafness and to the better ear in sensorineural deafness. In weber test, sound is channelled directly to the cochlea via bone ossicles placed in the middle ear. Generally lateralisation of sound detection in weber test with a tuning fork frequency of 512 Hz gives an implication of a conductive loss of 15-25 dB in the ipsilateral ear or a complete sensorineural loss in the contralateral ear (Martin and Clark, 2009). In the middle ear the mass of the ossicles offers a limitation to high frequency sound wave transmission, and therefore higher frequencies above 5 kHz have higher thresholds than lower frequencies. Similarly, on the other hand the stiffness of the air found in the middle ear cavity also offer a limitation to low frequency sound wave transmission, and thus frequencies lower than 1 kHz have higher thresholds (Clark and Ohlemiller, 2008). The high the intensity of a sound the greater the pain subjected on the hearing apparatus; and generally the pain threshold ranges between 110 and 140 dB SPL depending on the sound frequency. Conclusion Loss of hearing can be due to loss of structural transmission where sound waves fail to reach the cochlea through the middle ear, especially in otitis media and mild perforation. This can be corrected by surgical treatment which can successfully reverse this loss of hearing. However gradual loss of hearing as seen in prolonged use of antibiotics especially aminoglycosides, has no treatment nor correction as the cochlea is usually damaged completely. References Kramer, S, (2008). Audiology Science To Practice. 1st ed. San Diego: Plural Publishing. Roeser, J. Valente, M. Hosford, H (1st ed). (2007). Audiology Diagnosis. New York: Thieme Medical Publishers. Martin, F.Clark,J (10th ed). (2009). Introduction To Audiology. Boston: Pearson Education. Gelfand, S (1st ed). (1997). Essentials of Audiology. New York: Thieme Medical Publisher. Clark, W. Ohlemiller,K (1st ed). (2008). Anatomy and Physiology of Hearing for Audiologists. New York: Thomson Delmar Learning. Read More