Conduction and Middle Ear ll Flashcards
1 pascals gives you _______ dB SPL needed to produce 1mm/sec
94 dB
Increased TM mass _______________BC sensitivity, increased stiffness_________________ BC
Increased TM mass enhances BC sensitivity, increased stiffness decreases BC
What occurs in this picture?
Ac is more efficient because less dB is needed to produce a 1mm/s of vibrations. Lower the curve higher the sensitive. BC stimulation with an occluded ear canal is more sensitive than BC stimulation with open ear canal to get 1mm/s and the difference is called the occlusion effect.
Explain the 1mm/s per pascal theory:
It is relative to 1 pascal (94 dB SPL), how much dB in sound level is needed to produce 1 mm/s velocity
In the 1mm/s per pascal, the higher the curve…
higher the sound pressure is needed: lower the efficiency
Following this graph, BC efficiency is ________ than AC
LESS efficient
*But critical info is the difference between open and closed ear canal in BC.
What occurs in this graph related to the occlusion effect? (5)
- OE increases SPL in ear canal: low-fre.
- The reference is 1 pascal (94 dB SPL) per Newton.
- Exact SPL produced by 1 N varies with Fre. and occlusion
- Larger negative values mean lower SPL
- When the ear is occluded, at low frequencies more dB is needed to get the same perception of intensity than an unoccluded ear.
Newton is the unit of
force
0 dB or the reference is that one :
one N produces 1 pascal of sound in ear canal
A lower curve value means a
less SPL (than 94 dB SPL) is produced by 1 N force
What is the Bing Test Proposed by a German otologist Albert Bing? (3)
Detect occlusion effect by vibrating low-f tuning fork on mastoid.
Normal or SNHL subjects heard sound louder when ear canal close (Bing test positive)
Bing test negative: no difference, conductive HL
To avoid the occlusion effect in the Bing test we must:
Must leaves the ear canal open because of OE impact on Standard of BC test
Describe the ME bone-chain inertial effect:
Ossicles-ligaments: a spring-mass system
Initial effect: the mass of the ossicle chain
Evidence: increased TM mass enhances BC sensitivity, increased stiffness decreases BC
Frequency region: low frequency (<2kHz, or around resonant Fre: 1-3 kHz)
Confusion in discussion of frequency:
At low fre., springs move ossicles in phase with skull
At high fre., inertial force overcomes spring’s stiffness, resulting a relative motion of stapes
In Inertial Bone Conduction the BC is
enhanced by ME structure difference of 10 dB
How does the removal of the ossicles impact the BC?
Removal of ossicles impacts BC threshold slightly, but not significant in normal subjects
The compression of bone conduction depends on what factors?
- Volume difference between SV and ST
- Flexibility difference between OW and RW
- Vestibule space and endolymphatic sac through cochlear aqueduct
Fre: <=4kHz
Distortion Bone Conduction
.
Explain the intertial cochlear fluids from BC:
- Inertial force of cochlea fluids can cause fluid movement when allowed
- The allowance is established by two windows, driving force is pressure gradient between them
- It is the most important contributor
Explain the intertial cochlear fluids from BC:
- Inertial force of cochlea fluids can cause fluid movement when allowed
- The allowance is established by two windows, driving force is pressure gradient between them
- It is the most important contributor
Through what fluid does the BC sounds goes through?
Through CSF by the cochlear aqueduct and we can see that when blocking the aqueduct affects BC.
What does this table summarize?
This table shows a summary of contributors to BC and AC
What can we conclude by the results of Stenfelt 2015 modeling on the IE contribution to BC hearing? (4)
What are some practical issues of the BC? (2)
Occlusion Effect
Impact of conductive loss on BC (Middle ear problems)
Describe the Occlusion Effect briefly:
Definition
How will thresholds change?
What frequency?
What can we do about it?
Definition: sound through BC becomes louder when external ear is blocked. Threshold also decreases
When does it occurs? When using earphone
How will thresholds change? (Better than it should be)
What frequency? (low frequency)
What can we do about it? Leave the canal open when doing BC test.
What is SNHL?
sensorineural hearing loss
What is SNHL?
sensorineural hearing loss
What is CHL?
conductive hearing loss
What is the finding on CHL in the Bing Test?
Bing test (on mastoid)—comparison between outer ear closed and open: no diff in CHL
What is the finding on CHL and SNHL on Weber’s test?
Weber’s test (256 Hz, on forehead)—defective ear hear better: CHL, normal ear hear better: SNHL
What is the finding on the AC and BC from the Rinne Test for normal?
Rinne test (512 Hz)—first on mastoid (for BC), and then outside the ear (for AC). Normal: AC>BC
Explain the impact of conductive loss on BC (Middle ear problems)?
Bone chain Fixation issues: Loss of mechanisms______ and_____
Bone chain disconnection:
ME filled with fluid:
Typical behavior on audiogram:
.
What is Carhart notch?
Typical behavior seen in the audiogram which shows an increased BC threshold at 2k, in AC pathology, A case of Otosclerosis
What does the Cahart notch tells us? (3)
- Smallest Air-bone gap at 2kHz
- AC pathology impacts BC threshold
- Why at 2 kHz (not entirely clear)?
due to the loss of the middle ear component close to the resonance point of the ossicular chain
In a case of malleus fixation, what occurs at the high frequency related to the Cahart notch?
The Carhart notch is “masked” by the mixture of SNHL at high frequency. The “preop BC (frontal)” shows less impact by the fixation.
What can we say about the placement of vibrator and age?
ME Inertia effect change with place
Soft tissue varies around skull
Force change with location
Age and skull development impacts BC
What is the effect of age on BC? (3)
What is the purpose of masking in BC?
To mask untested ear
Which intensity level is safe in masking in BC?
50 HL
In Masking in BC the masker must be delivered through:
Air Conduction
How can we deal with the Conductive HL and Masking dilemma?
Insert earphone for masking.
What is AR?
It is the Acoustic middle ear reflex which is the efferent control to IE and Startle reflex.
What is AR?
It is the Acoustic middle ear reflex which is the efferent control to IE and Startle reflex.
Fill in the blanks related to AR of the ME:
Briefly describe the steps in AR and ME muscles and the effect:
- Loud sound evokes acoustic reflex (AR)
- The output is the contraction of ME muscles
- The effect is increased stiffness (Low frequency)
What evidence supports the role of the stapedius muscle in AR through observation in NORMAL ear? (3)
Eardrum movement during AR
Recording of muscular potential during AR
Measure air pressure change during AR
What evidence supports the role of the stapedius muscle in AR through observation in the PATHOLOGICAL ear? (2)
- Bell’s palsy
- Selective fixation or damage to certain muscle (or paralysing)
What are the Neural circuits for AR in the left and right sides?
What is the short and long binaural innervation of AR pathway? Is there a pathway from SOC to contralateral FNN?
Short way: CN-FNN
Long way: CN-SOC-FNN
Is there a pathway from SOC to contralateral FNN? Yes
What are the basic features of the AR? (3)
Evoked by:
Neural circuit and muscle __________
___________response to_____________
Evoked by loud sound (>=80 dB pure tone; >=65 dB noise, SPL)
Delay in neural circuit as well as Muscles
Binaural response to unilateral stimulation
What are the basic features of the AR? (3)
Evoked by loud sound (>=80 dB pure tone; >=65 dB noise, SPL)
Delay in neural circuit as well as Muscles
Binaural response to unilateral stimulation
In ME inertia: increased TM mass _____________BC sensitivity, increased stiffness____________ BC sensitivy
Increased TM mass enhances BC sensitivity, increased stiffness decreases BC
What is Osseotympanic Bone Conduction?
Vibration to the skull cause the bone and cartilage of the external ear to receive energy, most of which escapes the unoccluded ear. Some of this energy hits the tympanic membrane and combines with inertial bone-conduction, stimulating the inner ear
What is Middle Ear inertia?
The inertial-ossicular mechanism refers to the case where the BC excitation is transmitted to the cochlea through vibrations of the middle-ear ossicles
What is Compressional Bone Conduction?
The compressional BC mechanism refers to the case where the skull vibration is transmitted directly to the cochlea via vibrational distortions of the bone enclosing the cochlea fluid.
