Lecture 22; Hearing diagnostics and rehabilitation Flashcards
What can cause hearing loss;
Outer ear;
- ear wax, obstruction (temporary)
Middle ear;
- Glue ear/ wax again/ conductive hearing loss (temporary usually)
Inner ear;
- Cochlea problems, IHC of OHC loss, neuropathy, brain lesions (usually permanent)
Describe how they basilar membrane is a mechanical analyser of sound.
The basilar membrane has differing mechanical properties.
Base: Thick, stiff, narrow, only high frequencies will resonate here
Apex; Thin, wide, compliant, low frequencies will resonate here.
What do audiologist intend to do?
Find which frequencies people hear at
What does range of hearing frequencies indicate?
Indicates which part of the basilar membrane may be damage based on hearing loss
How do outer hair cells enhance frequency resolution?
They enhance the intensity of low frequencies and seperate frequencies so greater frequencies resolution can be achieved.
What cells tend to damaged first with exposure to loud sounds?
OHC first (3 rows should be observed)
IHC can be damaged too.
How can OHC damage be rectified?
Hearing aids (increases sound intensity)
What do hearing tests also attempt to do?
Determine what sort of damage has occurred, as IHC damage cant be rectified with hearing aids.
Determine underlying pathology
What damage can occur from loud noise exposure?
- Damage to tip links
- Damage to stereocilia
- Change in stria vascularis structure
- Damage to auditory nerve fibres (excitotoxicity)
- Cerebral damage or changes
What can hearing loss also lead to?
Poorer cognition
To what extent is there tonotopic mapping in the auditory system?
throughout the auditory system from the basilar membrane to the auditory cortex
What happens to the auditory cortex tonotopic map if there is inner ear damage?
That region of Hz no longer receives input, the brain is plastic so the neighbouring regions take over with their Hz.
What is audiometry?
The mechanisms undertaken to access hearing.
What is pure tone audiometry?
- Hearing thresholds are obtained by air and bone conduction.
- In air conduction the signal travels through the ear canal, across the middle ear cavity and into the cochlear.
- Therefore, air conduction threshold reflects the integrity of the total peripheral auditory mechanism.
Bone conduction reflects inner ear function.
what are the audiometer variables?
- Intensity dial
- Frequency dial
- L/R switch
- Presentation button
- Headphones/inserts/Bone vibrator
Testing to find thresholds of sounds we are hearing.
What are the types of sound transducers?
- Circum aural
- Insert Headphones
- Supra aural
- Bone vibrator
What are the variables of an audiogram?
Frequency (typically for speech)
Intensity
How do they classify hearing loss on an audiogram?
Based on intensity loss
- moderate, profound (cant hear) etc
Can hearing loss just be countered by making sounds louder?
No, not all Hz are lost. Therefore only those Hz with loss must be addressed.
What are the types of hearing loss?
- Conductive hearing loss (outer or middle ear)
- Sensorneural hearing loss (inner ear, nerve or brain)
- Mixed hearing loss
Is hearing loss bilateral?
No it can be unilateral, for sensorneural and conductive hearing loss.
Must ask why it is one ear esp if sensorneural.
i.e infections at inner ear or tumors
On a pure tone audiogram for sensorneural hearing loss, what indicates OHC vs IHC damage
OHC damage will show a loss of Hz at low intensities while IHC damage will show loss of HZ at high db and in some cases, some Hz cant be heard at all regardless of db
High db loss usually OHC and IHC damage.
What is a dead region?
A region where there is nothing is heard regadless of db.
Usually loss of afferent innervation too
What is off frequency listening?
When the intensity of the Hz is so great that it stimulates adjacent Hz areas and gives the impression that something is being heard.
Describe sensorneural hearing loss and how it extends beyond loss of audibility;
Two components;
- Loss of audibility
- Loss of compressive signal processing due to loss of OHC. (strongly altered signalling capabilities) (compressive signalling allows frequency resolution and low intensity sound to be heard)
What does loss of OHC cause?
Loss of active signalling process;
- loss of compressive processing (discomfort to loud sounds)
- Loss of Hz selectivity (reduced pitch discrimination)
What does loss of IHC cause?
Loss of sensitivity to sound.
What does a hearing loss also lead to?
Inability to distinguish between Hz therefore they substitute the wrong sounds or hear the wrong thing.
So on an audiogram a patient cant tell the difference between a range of frequencies.. they range becomes broader as they become deafer..
What is loudness growth?
- Loud sounds are heard at the same threshold. quite sounds are not heard.
- Medium sounds are just right
What are the perceptual consequences of hearing loss?
Highly specialised mechanisms for signal analysis are strongly degraded
- Mechanisms for separating sound are missing
- Speech intelligibility especially in noise environments is degraded.
What is the purpose of speech testing?
- Obtain assessment of everyday communication difficulties the person is experiencing (how much of a word a person hears)
- cross check
- Diagnostic
- Hearing aid evaluation
What is acoustic immittance measures?
- Assess how sound travels through the middle ear
- If middle ear is blocked, most of the sound will get reflected back
- Reflected sound waves carries information about the status of the middle ear system
Stiff TM = increased sound reflection
Hole in TM = no reflection
What are the components of an acoustic immittance measures?
- Sound source that generates low HZ
- Microphone that measures the reflected sound wave
- air pump and manometer which varies the air pressure in the middle ear canal.
What is produced from acoustic immittance measures?
Tympanometry
What is tympanometry?
Air pressure is varied with positive and negative relative to ATP, and effects of air pressure changes how much sound is transmitted through the middle ear is measured
Tympanogram is a graphical representation of how sound travels through the ME as a function of ear canal pressure
How can loud sound be used to measure audiology?
Loud sounds can be used to test acoustic reflexes, indicates ME function and neural circuit functioning or if significant hearing loss.
How can hearing be objectively measured?
- Distorted Product Oto Acoustic Emmission
DPOAEs= sound own ear makes, healthy ear makes these in response to certain sounds , i.e play two tones and a third is present, made by the own ear, comes about because of OHC function
- Can use electrocochleargraphy.
- AEP
What is seen with AEP
Louder sounds produce larger waves.
What is auditory processing disorder?
Difficulties in processing auditory information in the CNS as demonstrated by poor performance on one or more of the following skills;
- Sound localisation and lateralization
- Auditory discrimination
- Auditory pattern recognition
- Temporal aspects of audition i.e temporal discrimination
- auditory performance in competing aucoustic signals
- Auditory performance with degraded aucoustic signals
