3. Pure tone threshold audiometry, tympanometry. List of subjective and objective hearing tests. Tuning forl tests

What is pure tone audiometry

• subjective hearing test

• depends on cooperation of the patient

• tests air and bone conduction- AC, BC

Describe the procedure of PTA

• performed in soundproof room with audiometer that generates pure tone signals

• pure tone= sound containing only 1 frequency

• Air- headphones on ear

• Bone- vibrator on mastoid

How is the hearing loss in PTA expressed

• hearing loss expressed in dB

• -10 to 20 dB = normal hearing

• 20 to 40 dB = mild hearing loss

• 40 to 60 dB = moderate hearing loss

• 60 to 90 dB = severe hearing loss

• >90 dB = profound hearing loss

What are the results of a PTA

• normal AC= BC

• CHR AC> BC

  • BC in normal range

  • AC outside normal range

  • AB gap between >10dB

• SNHL AC=BC

  • hearing threshold is decreased

  • both below normal

  • gap is <10dM- no air-bone gap

• mixed hearing loss AC > BC

  • hearing threshold is decreased

  • both below normal

  • AB gap >10dB

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 subjective hearing tests

• Conversation, repeat words

• Tuning fork tests

• Audiometry- with measuring instrument

• Pure tone audiometry

• Speech test

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

• Stapedial reflex:

  • contraction of the stapedius muscle in response to loud sound

• 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

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 tuning fork tests

• performed to distinguish between CHL or SNHL

• tests

  • Weber

  • Rinne

  • Gelle

What is conductive hearing loss- CHL

• from failure of transmission of sound waves across the outer or middle ear

• prevents sound energy for reaching cochlear fluids

• involves outer ear, tympanic membrane or ossicles

• increased air conduction and bone conduction

What is sensorineural hearing loss- SNHL

• from defective function of cochlea or cochlear nerve

• involves inner ear, vestibulocochlear nerve and upper auditory pathways

• both air and bone conduction decreased

What is mixed hearing loss

Combination of conductive and sensorineural hearing loss

What is the Weber test

• comparison of bone conduction in both ears

• place vibrating tuning fork on middle of forehead and ask which ear is louder

What are the results of the Weber test

• Normal

  • Middle, equally

• Conductive hearing loss

  • In the "wrong" defective ear

  • Lateralisation to the worse hearing ear

• Sensorineural hearing loss

  • In the "good" normal ear

  • Lateralisation to the better hearing ear

What is the Rinne test

• comparison of air and bone conduction in one ear

• tuning fork on mastoid process of ear and in front of ear- ask where the sound is the loudest

What are the results of Rinne test

• Normal

  • Air conduction is better

  • Rinne positive R+

• Conductive hearing loss

  • Bone conduction is better

  • Rinne negative R-

• Sensorineural hearing loss

  • false negative- test appears negative because sound vibrates and its picked up by healthy ear!

What is the Gelle test

• fork against forehead and auditory canal is sealed using pneumatic speculum

  • creates positive pressure in external auditory canal

• positive pressure pushes tympanic membrane and ossicles inwards → increases immobility of basilar membrane of cochlea → decreases hearing

What are the results of Gelle test

• positive

  • sound of fork is perceived weaker with speculum than without

  • NORMAL!

• negative

  • no change in hearing in patient → otosclerosis or discontinuation