The Audiogram Understood

Transcription

1 People are often confused and afraid of medical tests. They are afraid the results will be bad or that they will fail. No one can fail a hearing test! The information can only be good since the information provides knowledge about yourself and helps make decisions about what to do next about your hearing. Take a hearing test when there is change in how you are hearing since the last time tested. The Audiogram Understood Hearing test is a misnomer. It is really a hearing evaluation to see how well a person hears sounds and understands speech. The process consists of a whole series of evaluations of different things that add up to the full report. Hearing loss is a misnomer. The audiogram indicates the levels of hearing acuity that a person has. Just like eye examinations give visual acuity; hearing evaluations provide information on the levels of hearing acuity. An audiological report compiles the audiologist s impressions, interview data, physical ear inspection notes, summary of scores and implications of results in a narrative form. In addition, there are usually recommendations for follow up for therapy, additional evaluations, or hearing devices. The full report consists of 8 or less separate tests, depending on the situation. Typically, these steps are: 1. A hearing history interview 2. A physical inspection of the ear and canal to identify problems including wax build up 3. A tympanogram to assess ear drum health [see Appendix for examples of healthy and not healthy tympanic membrane results] 4. The results of pure tone testing 5. The results of speech recognition testing (SRT) 6. Identification of the most comfortable listening level for speech (MCL) 7. Identification of the uncomfortable listening level for speech (UCL) 8. The results of assessment of speech discrimination (comprehension) Items #3-#8 above are typically found on an audiogram. An audiogram is a paper with various graphs and charts that indicates all or most of the following: the raw scores of the person s air conduction testing and bone conduction testing; person s speech levels (SRT, MCL, and UCL); and, usually, the tympanography results. There is other information on an audiogram and in an audiological report; ask an audiologist or assistant to discuss for a thorough understanding of the audiological results. The remainder of this document will define and explain some of the results that are shown in the audiological report. To fully comprehend this document, viewing a completed audiogram while reading will provide examples of the definitions explained. P a g e 1 C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s

2 Physical Inspection of the Ear The Outer Ear and Ear Canal are evaluated by sight and touch with an Otoscope that has a black tip and a light to looks inside the ear. The examination is looking for the amount of ear wax, any obstructions or deformity, scarring on the ear drum, or any other information on the physical condition of the ear. Parts of the Ear and Testing The Three Chambers of the Ear are tested differently. The hearing mechanism is evaluated using Air Conduction testing. Air Conduction measures the ability to perceive sounds that are introduced into the Outer Ear and onto the ear drum, conveyed on the bones of the Middle Ear, across the oval window, through the Inner Ear and onto the Auditory nerve. (see additional information below) A comparison of the effective functioning of the Middle to Inner Ear is done using Bone Conduction testing. Bone Conduction measures the ability to perceive sounds that are introduced into the Inner Ear through the mastoid bone or the forehead. The sounds travel through the bones of the skull to the Inner Ear and onto the Auditory nerve. (see additional information below) Another way to measure the physical responses that show the existence of hearing acuity is the Auditory Brainstem Response (ABR) test. ABR is a neurological test that measures the responsiveness of the brainstem to click stimulus sounds introduced into the Outer Ear. 2 P a g e C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s

3 Pure Tone Testing The primary purpose of pure-tone testing is to determine the type (conductive, sensorineural, mixed), degree (mild, moderate, severe, etc.), and configuration (shape of loss, etc.) of your hearing loss. [see definitions for some of these words below] Pure-tone audiometry is done in a soundproof booth to ensure that background noise does not affect the test results. As a result, a person hears sounds in a perfect hearing environment. The sounds are introduced either though earphones (air conduction response), bone conduction oscillator (bone conduction response) or though speakers located in the room (sound field response). These tests are not meant to reflect real-world listening situations. This means that the results of these tests only reflect how well a person hears under ideal listening situations. In real-world situations, a person will hear less speech than is indicated on the form. Air Conduction Testing The purpose of the pure-tone air-conduction hearing test is to document the softest tones heard at least 50% of the time at selected test frequencies. During this test, the person wears headphones and listens for these tones first in one ear, then in the other ear. Each time a sound is heard, the person presses a button or raises a hand to indicate hearing the sound. The machine making the sounds is called an audiometer (ah-dee-ahm-it-ter). The audiometer produces a series of tones ranging from very low to very high pitches (frequency). At each pitch (frequency) of sound, there are a series of tones (beeps) of varying intensities (loudness). The volume of each tone is lowered until there is no consistent response. The testing is done between 250 Hz and 8,000 Hz. because these are the speech frequencies. The frequency or pitch of the sound is referred to in Hertz (Hz). The intensity or loudness of the sound is measured in decibels (db). Results are recorded on a chart called an audiogram. By convention, the air conduction results are displayed on audiograms using blue Xs for your left ear and red Os for your right ear. Results may also be shown as masked a process to attempt to only assess one ear at a time using triangles for right and squares for left. After the test, the audiologist calculates Pure Tone Average (PTA) - the average of hearing loss at 500, 1000 and 2000 Hz - and uses this calculation to describe your hearing loss. Normal 0-25 db Borderline db Mild Moderate Moderately-Severe Severe Profound P a g e C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s

4 For example: If hearing loss was 35 db at 500 Hz, 45 db at 1000 Hz and 55 db at 2000 Hz respectively = 135 divided by 3 means that the PTA is 45 db. Matching 45 db on the chart shows a moderate hearing acuity. Note about how to describe hearing loss: Never say 45% hearing loss. This is totally meaningless. You cannot express decibels (db) as percentages since they do not stop at 100. Stick to decibels, or use the mild, moderate, severe, or profound as words not a percentage hearing loss. Bone Conduction Testing Bone conduction testing is the same procedure for air conduction testing, but this time, instead of wearing earphones, a special bone conduction oscillator (vibrator) is placed on the mastoid process - the bony bump behind the ear. Bone conduction testing assesses how well sound is heard through the bones of the skull and into the cochlea. Bone conduction testing determines how well the inner ears work bypassing any problems that might be in the outer and middle ears. Bone conduction results are always better than, or equal to, the air conduction results. Bone conduction results are displayed on the audiogram using angle brackets (<>) - blue greater than (>) for the left and red less than (<) for the right. If masking is needed, blue square bracket ([) is used for the left and red square bracket (]) is used for the right. If bone conduction results are normal and air conduction results show a hearing loss, then there is a conductive hearing loss. This means the middle ear are not working properly. Many forms of conductive hearing loss are medically treatable. However, if both bone conduction and air conduction results show a similar degree of loss (within 10 db), then there is a sensorineural hearing loss. This means middle ear is working properly. Therefore, hearing loss is in the inner ear or auditory nerve. If both air and bone conduction results show a hearing loss, and there is more than a 10 db difference between the air conduction and bone conduction results (what they call the air-bone gap), then the person has both a conductive loss (in middle ear) and a sensorineural loss (in inner ear). Appropriately, they call this a mixed loss. It is interesting to note that when a person wears headphones, it takes 40 db or 60 db of sound to vibrate a skull depending on the type of headphone. This means that if a person has normal hearing, when wearing headphones, the ear opposite to the test ear will typically hear any sounds though the skull (bone conduction) that are presented at a level greater than 40 db. 4 P a g e C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s

5 This graph represents the sounds heard in the various levels. The gray area shows where sounds for speech are found. It is sometimes called the Speech Banana. ACTIVITY: This graph can be matched next to a student s personal audiogram to help indicate sounds that they can probably hear. Note: A full scale version of this is in the appendix. Speech Recognition Threshold (SRT) So far, all the testing has been to determine the degree and type of hearing loss. The following tests now look at how well a person responds to speech. It is important to recognise that level of hearing acuity (PTA) does not tell the whole story. Speech comprehension may differ significantly among people with the same hearing loss. The first speech test is typically the Speech Recognition Threshold (SRT) test. It is sometimes called by its older name, Speech Reception Threshold. The purpose of the Speech Recognition Threshold (SRT) test is to determine the softest level at which a person begins to recognize speech in the environment only 50% of the time. Audiologists determine SRT by asking to repeat a list of easy-todistinguish, familiar spondee words. (Spondee words are two-syllable words with equal stress on both syllables). When a spondee word is repeated, each syllable is said at the same volume. Examples of Spondee Words: Baseball Hot dog Airplane Railroad Birthday Air chair Ice cream Ear drum Spondee words were chosen because they are easy to understand at faint hearing levels. Some people are concerned that because they have had their hearing tested so often they have memorized the SRT word list. This is not a problem. Remember, the purpose of this test is not to test hearing acuity, but to determine at which level a person begins to recognize that there are speech sounds in the environment. The words are not said in the same order and the point is accurately repeating the word that is heard. 5 P a g e C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s

6 When taking the Speech Recognition Threshold (SRT) test, the audiologist will say, Say the word baseball. The audiologist will record what word is said. The volume will be adjusted to find the softest sound level words are heard and correctly repeated for 50% of these words. This level is SRT score expressed in decibels (db) for each ear. The Speech Recognition Threshold test serves several purposes. First, it is a measure of the reliability of the pure-tone air-conduction test. In fact, the SRT should be within 5 db of the Pure Tone Average (PTA). Second, the SRT suggests the level of loudness at which words should be presented for the Word Discrimination (WD) testing that will follow. Third, SRT determines how much power (gain) needed in a hearing aid that is right for the degree of hearing loss. Here s some interesting facts about SRT values and what they mean in the real world. An SRT of 5 db (normal hearing) means a person can understand speech well at 21 feet in a quiet space and can still catch some words at over 100 feet. A mild hearing loss and an SRT of 30 db means a person can hear well at 1 foot but could still hear some words at 18 feet. A moderate severe hearing loss and an SRT of 60 db (a moderately severe hearing loss) means a person would need the speaker to be only 1 inch from the ear in order to hear well and within 1 foot to still hear some of the words correctly. It is readily apparent that an SRT of 70 or more indicates that speech is not readily heard. Closely related to the SRT is the Speech Awareness Threshold (SAT), sometimes called the Speech Detection Threshold (SDT). An SAT score is the lowest level at which sound can be identified, but not understood. Most Comfortable Listening Level (MCL) After determining SRT, the audiologist will typically determine the Most Comfortable (listening) Level by talking and making the volume louder and louder until the person indicates that it is just right. This is the volume at which speech is heard best and where hearing aids will be set. Typically, MCL is about 40 db louder than SRT level with normal hearing. Uncomfortable Loudness Level (UCL) or Threshold of Discomfort (TD) Testing Typically after finishing the MCL testing, the audiologist will test how loud a sound a person can stand. This is the Uncomfortable Loudness Level (UCL) or Threshold of Discomfort (TD. It is the loudest level of sound that the person would ever want to hear. Anything louder would be painful. To do this test, the audiologist keeps talking and slowly raises the volume while the person indicates when the voice is almost, but not quite, painful. The UCL is very important for properly adjusting hearing aids. Hearing aids should be set so that no sounds ever exceed UCL, and in fact, should stay 5 db or so below this level. 6 P a g e C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s

7 Speech Discrimination (SD) Testing The final speech test is Word Recognition (WR) testing, formerly called Speech Discrimination (SD) testing. The purpose of Word Recognition testing is to determine how well a person understands speech in a perfectly-quiet environment when the volume is set at Most Comfortable Level (MCL). To do this, the audiologist says a series of 25 or 50 single-syllable phonetically-balanced (PB) words. The words in this test cover the whole spectrum of sounds made in English. They are single syllable words. For this test, the audiologist will say, Say the word come and will document what word is repeated throughout the list. Each ear is tested separately. During this test, the audiologist keeps the voice (or a recording) at the same loudness throughout. With normal hearing, the volume is typically set to 40 db above SRT; with significant hearing loss, it is set to MCL. Examples of single syllable words: box dish five need pants crash end job pick smile This is the only test where the results are recorded in percentages. The rest of the hearing tests are all expressed in decibels. Word Recognition score is an important indicator of how much difficulty a person will have communicating, and how well the person may do wearing a hearing aid. If word recognition is poor, speech will sound garbled. For example, a Word Recognition score of 100% indicates that every word was heard and repeated correctly. If scoring 0%, it means that no speech was understood speech no matter how loud it is - speech is either not heard or gibberish. Scores over 90% are good and are considered to be normal. Scores below 90% indicate a problem with word recognition. Scores under 50% indicate poor word recognition. This indicates significant trouble following a conversation, even when it is loud enough to hear. Incidentally, people with conductive hearing losses frequently show excellent speech discrimination scores when the volume is set at their Most Comfortable Level. On the other hand, people with sensorineural hearing losses typically have poorer discrimination scores. People with problems in the auditory parts of their brains tend to have even poorer Word Recognition scores although they may have normal auditory pure-tone thresholds. 7 P a g e C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s

8 References and Resources: The Audiogram Understood ASHA Bauman, Neil Ph.D., June Demystifying Hearing Tests. Guide for families of infants and children with hearing loss: Birth to Vermont Center for the Deaf and Hard of Hearing Parent Infant Program; Burlington, VT. Ingrao, Brad Tympanometry. Electronic Deaf Education Network. Jamaica Association for the Deaf, Audiological Clinic Sample audiograms. Onusko, Edward Tympanometry. American Family Physician. 8 P a g e C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s

9 Appendix A: Measuring Tympanic Membrane Health Normal pressure on the tympanic membrane No pressure indicated usually indicating fluid in the ears and some hearing difficulty expected in the evaluations. 9 P a g e C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s

10 Appendix B: The Speech Banana [Taken from a presentation of Hearing Loss done through Jamaica Association for the Deaf] 10 P a g e C o m p i l e d f o r J a m a i c a n D e a f S t u d i e s