Audiologic testing


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Audiologic testing

  1. 1. Ozarks Technical Community College HIS 125
  2. 2. You can’t fit a hearing aid until you can perform/interpret audiograms!  Being able to perform an accurate hearing test and interpret the obtained results are imperative to:  Making appropriate recommendations ○ Is a medical referral required? ○ Amplification options ○ Hearing aids versus cochlear implant?  Fitting hearing aids appropriately!
  3. 3. Basic Hearing Evaluation  Audiogram  Puretone audiometry ○ Air-conduction (AC) and bone-conduction (BC) testing  Speech audiometry ○ Speech reception threshold (SRT)  This may also be called speech recognition threshold ○ Word recognition score (WRS)  This may also be called speech discrimination score  The goal is to determine ○ How well you hear ○ How clearly you hear speech ○ If there is a medical reason for hearing loss ○ If there is a need for some sort of intervention
  4. 4. Hearing Loss is defined by…  Type of Loss  Conductive  Sensorineural  Mixed  Degree of Loss  Normal, mild, moderate, moderately- severe, severe, profound  Configuration of Loss  Flat, sloping, rising, etc.
  5. 5. Puretone Audiometry Recall that human ears have an audible bandwidth (frequency range) of 20 to 20,000 Hz  In audiometric testing, the stimuli are puretones from 250 to 8000 Hz.   Why? ○ because human speech falls within these frequencies  Most commonly octave bands at 250, 500, 1000, 2000, 4000, and 8000 Hz are tested  The interoctave frequencies of 3000 and 6000 Hz are also commonly tested in adults
  6. 6. Puretone Audiometry  Air-conduction testing  Performed with headphones or insert earphones  Takes into account the entire auditory pathway ○ Outer ear, middle ear, inner ear, nerve, brain  Bone-conduction testing  Performed with a bone-conduction oscillator placed on either mastoid bone (most common) or the forehead  Directly stimulates the inner ear and nerve ○ Bypasses the outer and middle ear
  7. 7. Puretone Audiometry   Threshold is the softest sound that a listener can hear 50% of the time A bracketing technique is used to establish threshold.  Remember…down 10, up 5.  If the patient responds, reduce the stimulus intensity by 10 dB. If no response, increase intensity using 5 dB steps. Repeat this procedure until you find threshold.   I prefer to start testing at 1000 Hz at 50 dB HL. I always use a pulsed puretone, as it is preferred for patient’s with tinnitus.
  8. 8. Normal Hearing    Normal AC and BC thresholds Many different scales exist regarding degree of HL For the purposes of this class, we will use the scale on the next slide.
  9. 9. Degree of Hearing Loss  This is the exact scale that I use in interpreting audiograms  Some clinics are more liberal and consider normal hearing to be any threshold up to 25 dBHL  In determining the degree of loss, the textbook approach would be to calculate the puretone average (PTA=average dB of AC thresholds at .5, 1, 2 kHz) and compare the PTA to the scale at right. From: Northern, J. Hearing Disorders (3rd ed)
  10. 10. Speech Audiometry  Speech reception threshold (SRT)  The softest level (dB HL) at which a patient can accurately repeat spondees (two-syllable words; i.e. baseball, hotdog, birthday) 50% of the time ○ Uses the same bracketing technique as puretone testing  SRT is primarily used as a reliability check ○ In comparing the SRT to the PTA, they should be within 10 dB of each other ○ If you have poor SRT-PTA agreement, then the reliability of your results should be considered to be questionable
  11. 11. Speech Audiometry  Word recognition score (WRS)  The percentage of phonetically- balanced, monosyllabic words that a patient can accurately repeat  Presented at either MCL (most comfortable level) or MIL (most intelligible level) ○ This is generally thought to be approximately 40 dB above the SRT  A pre-recorded list of 25 to 50 words should be presented to each ear  Each word should be preceded by a carrier phrase: ○ “Say the word pick” ○ “Say the word room”
  12. 12. WRS in determining site-oflesion     Patient’s with normal hearing or conductive hearing loss will perform normally on WR testing Patient’s with only high-frequency or a mild, flat SNHL will also generally perform near-normal The more severe the SNHL, the poorer a patient will perform on WR testing Neural losses result in poor performance  Asymmetrical WRS, especially in the presence of puretone asymmetries, should be considered a “red flag” for an acoustic neuroma  In patient’s with a retrocochlear lesion, roll-over may also be present on WR testing. This means that with increased presentation level, the patient’s performance will actually decrease (i.e. 56% at 85 dB decreasing to 12% at 95 dB).
  13. 13. Audiometric Interpretation If a patient has a disorder of the outer and/or middle ear ONLY, then AC thresholds will be abnormal in the presence of normal BC thresholds  Air-bone gap = greater than or equal to 15dB difference between AC and BC  This is called a conductive hearing loss, as sound cannot properly conduct through the outer and/or middle ear to reach the normal-hearing cochlea 
  14. 14. Some Causes of CHL          Anotia Microtia Atresia Outer ear infection Middle ear infection Otosclerosis Dislocation of the middle ear bones Cholesteatoma Ear wax!
  15. 15. Conductive Hearing Loss   Normal BC thresholds Abnormal AC thresholds  An air-bone gap is present at .5, 1, 2, and 4 kHz  WRS should be nearly normal, as there is no damage to the cochlea/nerve  *Note: recall that dB SL refers to sensation level, which is the intensity that is added to threshold. When performing WRS, the presentation level should be at the most comfortable/intelligible level for the patient. This level is generally thought to be the SRT + 35-40 dB SL. So in the example at right, the WR testing was performed at 65 dB HL. This patient has a mild CHL Image from:
  16. 16. Audiometric Interpretation If a patient has a disorder of the inner ear and/or auditory nerve, then AC thresholds will be equal to BC thresholds (no air-bone gap) and both will be abnormal  This is called a sensorineural hearing loss 
  17. 17. Some Causes of SNHL Aging (presbycusis)  Noise Exposure  Genetics  Acoustic Neuroma  Meniere’s Disease  Ototoxic Drugs 
  18. 18. Sensorineural Hearing Loss      Abnormal AC and BC thresholds No air-bone gap WRS will vary depending on degree of loss and cochlear vs. neural damage According to the PTA method of determining degree of HL, this patient has a slight SNHL. However, due to the sloping configuration, I prefer to define the loss as a slight-sloping-tosevere SNHL. It is more accurate. Image from:
  19. 19. Puretone Audiometry Interpretation If a patient has a disorder of the inner ear and/or auditory nerve AND an outer/middle ear disorder, then both AC thresholds and BC thresholds will be abnormal AND an air-bone gap will exist  This is called a mixed hearing loss  Example: 75 yo, male with age-related hearing loss and bilateral otitis media 
  20. 20. Mixed Hearing Loss     Abnormal AC and BC thresholds Air-bone gap present Expected WRS based on BC thresholds This patient has a mild to moderately-severe MHL. Image from:
  21. 21. Always keep these FDA Regulations in mind…  If any of the following conditions exist, a patient must be referred for a medical evaluation by a physician (preferably an ENT):  Visible congenital or traumatic deformity of the ear.  History of active drainage from the ear in the previous 90       days. History of sudden or rapidly progressive hearing loss within the previous 90 days. Acute or chronic dizziness. Unilateral hearing loss of sudden or recent onset within the previous 90 days. Audiometric air-bone gap equal to or greater than 15 decibels at 500 Hz, 1,000 Hz, and 2,000 Hz. Visible evidence of significant cerumen accumulation or a foreign body in the ear canal. Pain or discomfort in the ear.