Summary of various hearing testing
Test | Cochlear | Eighth nerve | Brainstem | Cortex | Corpus callosum |
Pure tones Audiometry | ● | ◐ | ○ | ○ | ○ |
Standard speech recognition in quiet | ◐ | ◐ | ○ | ○ | ○ |
Otoacoustic emissions | ◐ | ○ | ○ | ○ | ○ |
Acoustic reflexes | ◐ | ● | ◐ | ○ | ○ |
Dichotics | ㅤ | ◐ | ◐ | ● | ● |
Masking level difference | ㅤ | ◐ | ● | ○ | ○ |
Localization and lateralization | ㅤ | ㅤ | ● | ● | ㅤ |
Frequency and duration patterns | ㅤ | ㅤ | ○ | ● | ● |
Gap detection | ㅤ | ㅤ | ● | ● | ㅤ |
Low-redundancy speech | ㅤ | ㅤ | ◐ | ◐ | ○ |
- Relative contribution to differential diagnosis: ● = considerable; ◐ = moderate; ○ = minimal.
Property of test | Whispered tests | Tuning fork | PTA |
Distinguish L from R | Yes | Yes | Yes |
Distinguish SNHL from CHL | No | Yes | Yes |
Measure the degree of loss | No | No | Yes |
Masking used | Yes | No | Yes |
Bedside Tests
Whispered voice
- Requires no equipment or specialised understanding
- Examiner behind +arms length from pt
- Opposite ear tragal rub
- Whispered letters (numbers If fails-repeat then increase
- Failure —30dB hearing loss
- Do not need to repeat.
- Variation for children
- Same principle
- Child stands arms length in front
- Double digit number whispered
- If repeated correctly takes step forward
- No masking
- Both ears tested simultaneously
- But good engagement in lingual mobile children
- Advantages
- Simple
- Equipment free
- Attempt at masking
- Test each ear
- Disadvantages
- Lower sensitivity in children + cognitive impairment
- Large inter-test variability
- Cannot quantify degree of loss
- Cannot identify type of loss
Weber Test
Steps:
- Uses bone conduction and tests the lateralisation
- Use 512Hz tuning fork placed in midline
- Pt asked where sound heard - L R midline
Interpretation:
- Conduction deafness/unilate CHL: Patient lateralizes sound to the affected ear
- Sensorineural deafness/unilat SNHL: Patient lateralizes sound to the normal ear
- Normally/bilat equal loss: sound is heard equally on both the left and right side
Pros:
- Good to distinguish between SNHL and L vs R
- More substantial losses give clearer results
Cons:
- Unable to quantify degree of loss
- Less helpful in symmetrical losses
- Tests one frequency only
Rinne test
Steps:
- Place the stem of a 512Hz vibrating tuning fork on the mastoid bone of the subject and count the number of seconds the vibration is heard.
- When the subject no longer hears the tuning fork (bone conduction), place the tines of the fork near the ear (air conduction).
- Then count the number of seconds the sound is heard by air conduction.
Interpretation:
- Normally
- Air conduction > bone conduction, and thus the sound continues to be heard at the ear after it is no longer detectable at the mastoid bone, essentially twice as long, or a 2:1 ratio.
- SNHL or normal hearing.
- Sensorineural hearing loss,
- Equal decrement in both air and bone conduction, and thus air conduction remains greater than bone conduction, although in a less than 2:1 ratio.
- Conductive hearing loss,
- Bone conduction > air conduction,
- Tuning fork cannot be heard at the ear after it is no longer heard at the mastoid bone.
- Detects 20dB conductive loss in 50% pts.
- Detects 40dB conductive loss in 90% pts.
- Can be false -ve in profound unilat SNHL.
Audiometric Tests
Tympanometry
- Relative change in impedance with a change in ear canal air pressure at the plane of the tympanic membrane. The tympanogram provides indirect evidence of the mechanical integrity of middle ear structures
Acoustic reflex
- Measurement of the reflex stapedius muscle contraction bilaterally on presentation of an acoustic stimulus. In patients with a retrocochlear site of the lesion (cranial nerve VIII and low brainstem), the acoustic reflex may be elevated or absent
Pure-tone audiometry
- For adults and older children (> 5 years).
- Using headphones, each ear is tested individually for air conduction and, if necessary, bone conduction thresholds.
- A result of 0 dB (decibels) is the average normal threshold for hearing in young adults
- Establishes pure tone hearing threshold
- Sound proof booth
- Stimulator-creates pure tone
- Headphones /inserts
- Frequency dial
- Patient presses and holds button when sound appears and releases when gone
- Tests air conduction via headphones
- Bone conduction via vibrator on mastoid prominence
- Without masking not possible to tell which ear is picking up sound
- To ensure the test ear is the one picking up sound
- Required when sound maybe transmitted to other cochlear
- Start masking at >40 dB
- Depends on sound volume/type of headphones or inserts used and if bone or air conduction
- Masking by presenting continuous noise in non-test ear to obscure it from hearing test sound
- Test each frequency at different loudness (decibel)
- Decibel is on a log 10 scale:
- A difference in 10 dB is actually a difference in 100x in loudness
- Symbols for the graphical presentation of hearing threshold levels
Test type | Right Ear | Left Ear |
Air conduction — Unmasked | O | X |
Example of no-response symbols Air conduction — Unmasked | O (with arrow) | X (with arrow) |
Air conduction — Masked | △ | □ |
Bone conduction — Unmasked, mastoid | < | > |
Bone conduction — Masked, mastoid | [ | ] |
Bone conduction — Masked, forehead | ¬ | ¬ (reversed in 180C) |
Bone conduction — Unmasked, forehead | ∨ | ∨ |
Where symbols (O, X) are used for masked air conduction as well, the use of masking should be noted in the audiogram.
- Different diseases
- a. Normal right audiogram.
- b. Sensorineural hearing loss: the commonest cause is presbyacusis, with usually high-frequency loss.
- c. Sensorineural hearing loss predominantly of the lower frequencies may be seen in Meniere’s disease.
- d. Mixed conductive and sensorineural hearing loss: seen in patients with a combination of presbyacusis and middle ear pathology, or in a perilymph fistula.
- e. Conductive hearing loss: the difference between AC and BC demonstrates the conductive loss.
- f. Noise-induced hearing loss: commonly affects the frequencies around 4 kHz initially.
Masking
- When a patient has a substantial difference in hearing sensitivity between the two ears, it is necessary to rule out the potential participation of the better hearing ear when testing the poorer hearing ear. Masking is defined as the amount by which the threshold of audibility of a sound is raised by the presence of another (masking) sound
Speech recognition threshold
- Measurement of the hearing sensitivity/threshold (in dB) for speech
Speech recognition score
- Measurement of the speech recognition (discrimination) ability when presented above the SRT.
- Results
- Conductive hearing loss: normal/high discrimination
- Sensorineural hearing loss: decreased discrimination.
- Lesions at the cochlear or retrocochlear structures, consonant elements of speech is affected.
- Lesion at CNVIII or low-brainstem structures speech recognition can be severely affected.
- One of the early diagnostic signs of lesions of cranial nerve VIII or the low brainstem is severely reduced speech recognition scores in the presence of mild or moderate pure-tone hearing loss
Brainstem auditory evoked response
- Gives objective assessment of hearing thresholds (see earlier discussion)
Otoacoustic emission
- Universally used for neonatal screening of hearing.
- Presentation of an acoustic stimulus to the ear and monitoring of energy in the ear canal allows measurements of emissions from the outer hair cells of the cochlea.
- The outer hair cells f(x) is to help amplify the noise that the brain wants to hone down towards.
- It does this via the acoustic reflex arc
- Sound arrives at the basilar membrane which pushes the inner hair cells against the tectorial membrane → bending of the cillia → opening of K channels causing depolarization → etc
- When multiple sounds of similar fq arrives to the ear → multiple inner hair cells adjacent to each other are activated (each of these hair cells are detecting sound at different frequency.
- The acoustic arc work by getting acoustic information from the inner hair cells (Afferent limb) → out hair cells (Efferent limb) activates to pull the tectorial membrane down so that the contact point to the inner hair cells is greater. This pulling of the tectorial membrane by the outer hair cells is a dynamic process where it pulls the tectorial membrane in waves. This waves sets out an emission that is detectable by a microphone during otoacoustic emission testing
- In the case of a retrocochlear lesion, when there has been no retrograde degeneration of the outer hair cells, normal OAE can be evoked in the presence of significant sensorineural hearing loss.
- OAE represents the first available auditory function test with which it may be possible to differentiate neural from cochlear sites of a lesion when the potential exists for each site to be implicated in sensorineural loss.
- Any middle ear lesion typically precludes measurement of OAE
Electrically evoked auditory potentials
- Allow assessment of neural integrity, evaluation of cochlear implant function, and estimation of the psychophysical measures needed to program the cochlear implant speech processor, as well as an indication of performance after cochlear implantation
Further tests
Oto acoustic emissions
- Newborn screening
- Sounds originated in cochlear to check outer hair cells functioning
Electric response audiometry
- Records bioelectrical potentials from the auditory pathway
- Auditory brainstem response
- Measures electrical response in auditory nerve and brain stem
- Pre MRI was used to diagnose acoustic neuroma (latency in the produced waves indicative of AN)
- Electrode place on skull
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