4. Objective hearing tests. Tympanometry, Evoked Response Audiometry, otoacoustic emission.

What is tympanometry

• Pure tone signal of known intensity is directed into external auditory canal via ear probe

• Used to screen OME in children

Describe the procress of tympanometry

• microphone in probe measures the reflected sounds from tympanic membrane

• normally air pressure in ear canal and middleear are equal = atmospheric P

• in this condition tympanic membrane has lowest resistance and highest compliance- absorbds sound better

Describe how different pressures affect the tympanic membrane

1. decreased or increased air P in EAC

2. stiffening of tympanic membrane

3. increased acoustic impedance and decreased compliance

4. decreased sound absorption

5. more sound is reflected

What is a tympanogram

• graphic representation of compliance change sin middle ear against pressure gradient from -400 to +200mmH2O

• peak at maximum compliance → where pressure in external= middle

What are the results on tymapnogram

• normal -100 to +50mmH2O

  • type A curve

    • normal pressure peak at maximum compliance at 0 air pressure

• abnormal

  • type B

    • no pressure peak → fluid in tympanic cavity

    • eg tympanic perforation or OME

  • type C

    • negative pressure peak

    • eg eustachian tube dysfunction or early OM without effusion

What is the difference between subjective and objective hearing tests

• subjective- communication and active cooperationn with patient

• objective- without cooperation with patient

What are objective hearing tests

• Impedance audiometry

• Evoked responses

• Reflex- stapedius reflex

• Acoustic response- otoacoustic emission

• Electrical responses

  • Electrocochleaography, brainstem response, cortical response

What are some hearing tests based on reflexes

• Orientation reflex:

  • child turns towards a sound stimulus

• Classic Pavlovian conditional reflex:

  • child turns to the sound stimulus and a puppet lights up to reward (reinforce) the child’s listening behavior

• Auricle reflex:

  • movement of the ears (in animals) in response to a sound

• Auro-palpebral reflex:

  • contraction of the palpebral orbicularis muscle in response to loud sound

• Stapedial reflex:

  • contraction of the stapedius muscle in response to loud sound

What are hearing tests based on otoacoustic emission

• spontaneous and evoked OAE

  • OAE is a low level sound caused by the motion of the cochlea’s sensory hair cells in response to sound

  • The OAE is recorded by a probe after a series of click stimuli is given

  • Absence of emissions can be due to hearing loss or fluid in the middle ear

  • Often used in newborn screening

What are hearing tests bsed on electrical activity

• Electrical response audiometry (ERA):

  • Electrocochleography

  • Brainstem evoked response audiometry (BERA)

  • Cortical evoked response audiometry (CERA)

  • Auditory steady state response (ASSR)

What are electric response audiometry- ERA

• collective term for investigation of nerve activity

• APs within auditory pathway are recorded by electrodes attached to scalp and collected in a computer score

What are the indications of ERA

• detection of possible defects in vestibulocochlear nerves and brainstem auditory pathways

What are the types of ERA

• electrocochleography- ECOG

• Cortical evoked response audiometry- CERA

• Auditory brainstem response- ABR

• Brainstem evoked response audiometry- BERA

• Auditory steady state response- ASSR

Describe auditory brainstem response

• looks at amplitude/ number of neurons firing and latency

• indicated in

  • screening HL in newborns

  • diagnosis of HL in neonates and children

  • detection of audiotory nerve and brainstem lesions

  • detection of cochlear and retrocochlear lesions

• Waves

  • Wave I-III → generated by auditory branch of CN VIII

  • Wave IV-V → generated by upper brainstem

What is auditory state response

Looks at amplitude and frequency

Indicated in hearing aid fitting

What is the difference between ASSR and BERA

• ASSR- looks at amplitude and freq, rather than acmplitude/ latency

• ASSR is evoked using repeated sound stimuli at high repetition rate rather than abrupt sound at low repetition

• BERA- uses click or tone burst stimuli in one ear at a time

• ASSR- both ears while evaluating broach bands

• BERA depends on subjective analysis of amplitude/ latency

• ASSR uses statistical analysis