Audiometry + tympanometry Flashcards
What is the purpose of audiometry?
identify and differentiate conductive and sensorineural hearing loss
What is the normal hearing range (dB)?
all readings between 0 and 20 dB (at the top of the chart)
Audiometry - Hearing is tested in both ears separately. Bothairandbone conductionare tested independently.
The following symbols are used to mark each of these separate measurements:
- X
- ]
- O
- [
- X- Left-sided air conduction
- ] - left-sided bone conduction
- O - right-sided air conduction
- [ - right-sided bone conduction
Example audiogram
Normal hearing - all readings between 0 and 20 dB (at the top of the chart)
Bilateral sensorineural hearing loss
- both air and bone conduction readings will be more than 20 dB, plotted below the 20 dB line on the chart
Bilateral conductive hearing loss
- bone conductionreadings will be normal (between 0 and 20 dB)
- air conductionreadings will be greater than 20 dB, plotted below the 20 dB line on the chart
(In conductive hearing loss, sound can travel through bone but is not conducted through air due to pathology along the route into the ear)
Mixed hearing loss:
- Bothairandboneconduction readings will be more than 20 dB
- However, there will be a difference ofmore than15 dB between the two (bone conduction >air conduction)
Audiometry - What is masking?
introducing noiseto thenon-test earduring a pure-tone audiogram - aims to ensure that test ear hears the presented tone and is not ‘cross-heard‘ by the non-test ear
Normal audiogram (above 20dB in all frequencies)
Audiometry - What is the air-borne gap?
- the difference betweenair-conductionandbone-conductionaudiometric thresholds
- found in patients with conductive or mixed hearing loss generally due to outer and/or middle ear diseases (eg. otitis external, tymp membrane perf, chronic suppurative otitis media)
. - Typically an air-bone gap is considered if there is a difference ofgreater than 10dBat a given frequency
Sensorineural hearing loss (right ear): no air-bone gap present
Conductive hearing loss (right ear): air-bone gap present:
Common causes of sensorineural hearing loss (SNHL)
- Noise-induced hearing loss
- Presbyacusis
- Vestibular schwannoma
- SSNHL (sudden sensorineural hearing loss)
Common causes ofconductive hearing loss (CHL)
- Acute otitis media
- Otitis media with effusion
- Tympanic membrane perforation
- Otosclerosis
- Foreign body
- Cerumen impaction (earwax)
- Trauma to ossicles
Presbycusis (age-related hearing loss)
- characterised by bilateral hearing loss above 2000Hz
Noise-induced hearing loss
- sensorineural hearing loss with a notch at 4000Hz
Meniere’s disease (right ear)
- typically characterised bylow-frequency sensorineural hearing loss
What is the triad of symptoms seen in Meniere’s disease?
- vertigo
- tinnitus
- hearing loss
Otosclerosis (right ear)
- characterised byconductive hearing losswith loss in bone conduction at2000 Hz(referred to as Carhart’s notch)
Conductive hearing loss
Sensorineural hearing loss (right ear): no air-bone gap present
What is tympanometry used for?
shows how well your middle ear is working. It does this by measuring how youreardrummoves
- provides information regarding ear canal volume and middle ear pressure
- Type A - Normal middle ear system (teepee shape)
- Type B - Flat line (middle ear pathology –> infection behind eardrum OR perforation in eardrum
(note: a larger ear canal volume indicates a perforation in the eardrum) - Type C - Indicates negative pressure in ear (teepee shape but negatively shifted on graph), consistent with sinus or allergy congestion, ear infection, or commonly Eustachian tube dysfunction
Tympanometry example
Normal
- looks like a teepee and indicates normal middle ear system
Flat line
- Indicates middle ear pathology like fluid, infection behind the eardrum OR a perforation in the eardrum
- NOTE: a larger ear canal volume indicates a perforation in the ear drum
Still shaped like a teepee, but shifted negatively on the graph
- indicates negative pressure in ear, consistent with sinus or allergy congestion, end stages of cold, or ear infection
- Often suggest a Eustachian tube dysfunction
