Audiology

COnductive hearing loss (1)
Normal hearing
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Which tuning fork would you use for Rinne’s and Weber’s?

  • 512 kHz. This frequency is preferred as the tone does not fade too quickly and produces limited overtimes. Similarly the vibrations are not tactile. 

https://www.thebsa.org.uk/wp-content/uploads/1987/04/Recommended-Procedure-Tuning-Forks-2016.pdf

What result would you get for Rinne’s and Weber’s in the audiogram above?

  • Weber lateralises to left ear
  • Rhines negative on left BC>AC
  • Rhines positive/ normal on right AC>BC

Based on the British Audiology Society guidelines, describe the symbols used in a Pure tone Audiogram.

  • X – left ear air conduction
  • O – right ear air conduction
  • Δ – bone conduction not masked
  • [ – right bone conduction masked
  • ] – left bone conduction masked

What are the rules of masking based on?

Based on theory of interaural attenuation. Can overcome cross-hearing by temporarily elevating hearing thresholds of the non-test ear by a known amount. Enables accurate assessment of the test ear thresholds.

Describe the 3 rules of masking.

Masking needs to be applied at any frequency if any of the three rules apply:

 

  1. The difference between the left and right not-masked air conduction thresholds is 40 dB or more

  2. Where the not-masked bone conduction threshold is more acute than the air-conduction threshold of either ear by 10 dB or more 

  3. When rule 1 has not been applied, but where the bone conduction threshold of one ear is more acute by 40 dB or more than the not-masked air conduction threshold attributed to the other ear. 

What are the audiometric descriptors for hearing loss and their thresholds in dBHL?

  • Mild – 21-40dBHL
  • Moderate 41-70dBHL
  • Severe – 71-95dBHL
  • Profound – >95dbHL

https://www.thebsa.org.uk/wp-content/uploads/2017/02/Recommended-Procedure-Pure-Tone-Audiometry-Jan-2017-V2-1.pdf 

Supporting Information

Definitions:

  • Conductive loss– hearing loss due to anything from the outer ear to stapes.
  • Sensorineural loss– hearing loss due to cochlear and cranial nerve VIII  (vestibulocochlear nerve)
  • Bone conduction– testing sensorineural loss as it bypasses the EAC, TM and ossicles
  • Air conduction– testing both conduction and sensorineural
  • In normal conditions AC>BC

Tuning fork tests– 512hz, with a foot-plate- Strike on own knee or elbow.

  1. Rinnes– air with bone conduction.
    1. Air- prongs 2cm and in line with EAC
    2. Bone- base of fork against mastoid process with other hand on contralateral skull.
    3. Ask them which is louder.
    4. Normal hearing = Rinne’s positive = air louder
    5. Conductive loss of 20db or more = Rinne’s negative = bone louder
    6. In severe sensorineural loss– BC>AC- heard in contralateral ear.
  2. Weber’s test– place fork on forehead and contralateral skull supported. Ask patient where it is louder. 
    1. Localises to the side with conductive loss as no competing stimuli from AC
    2. Localises away from the side with sensorineural loss
    3. If normal both ears are equal
 

Weber lateralises left

Weber lateralises right

Rinne positive both ears AC>BC

Sensorineural loss in right

Sensorineural loss in left

Rinne negative left BC>AC

Conductive loss left

Sensorineural loss left 

Rinne negative right BC>AC

Sensorineural loss right

Conductive loss right

  1. Stengers test– test for true or fake hearing loss- use 2 same frequency forks:
    1. Close eyes
    2. First tuning fork 15cm from good ear- they will hear it
    3. Take it away
    4. Place second 5cm from bad ear- they will deny hearing it
    5. Now keep the second there and replace the first tuning fork 15 cm from good ear:
      1. If genuine hearing loss they will hear the first tuning fork
      2. If not genuine then they will just hear the 2nd one and say they don’t hear anything

Voice testing– difficult to standardise:

  • Test each ear separately at 60cm.
  • First whisper (12dB), normal voice (36dB) then shout (48dB)
  • Then repeat at 15cm – whisper (34dB), normal voice (56dB) then shout
  • Repeat 2 numbers of 2 syllable words until 50% correct.
  • Mask by rubbing contralateral tragus with finger

Pure tone audiometry

  • Measurement of the minimum amplitude heard at a specific frequency in dB
  • 0-20dB is normal
  • Air conduction tested by headphones with masking in other ear
  • Bone conduction is by a metal probe on the head with a masking ear insert
  • 250-8000Hz tested. Amplitudes reduced by 10db until none heard and then increased by 5dB until 50% heard.
  • Symbols-
    • O- right unmasked air conduction
    • X- left unmasked air conduction
    • Masked is filled in Os and Xs or ∆ right and □ left
    • ∆ or </>- unmasked bone conduction
    • [right ear bone conduction masked
    • ]left ear bone conduction masked

Rules of masking: Based on theory of interaural attenuation:

  1. Air conduction audiometry – mask if the difference between the right and left air conduction thresholds is 40dB or more.
  2. Bone conduction audiometry – mask where bone conduction threshold is better than air conduction by 10dB or more.
  3. Air conduction audiometry – mask where bone conduction of the better ear is 40dB or more better than air conduction threshold of the worse ear.
  4. Masking is required for BC testing whenever there is any difference in the AC and BC thresholds, since there is essentially no interaural attenuation by bone conduction.

Stapedial reflex– contraction of stapedius and tensor tympani in response to noise >85dB

Tympanogram

Used to measure TM compliance and to detect middle ear pathology .

  • X-axis- pressure- daPa
    • Adult= -50 –> +50 daPa
    • Child-= –150–> 50 daPa
  • Y- axis compliance – ml – 0.3-1.6cm3
  • Sound intensities
    • 3 month- 1000Hz
    • 3 years and above- 226 Hz @ 85db = sound pressure level
  • Canal volume-
    • adult- 0.6-1.5ml
    • Child- 0.4-0.9ml

Types include:

  1. Normal
  2. Reduced compliance- fixed ossicles- otosclerosis or tympanosclerosis
  3. Increased compliance- dislocated ossicles, or healed perforation
  4. Retracted TM
  5. Resolving OME
  6. Depends on canal volume
    1. OME if normal
    2. Perforation if large
    3. False if small- tip pushed against canal wall
  7. Bifid tympanogram above- healed perforation with large monomeric segment.
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