Middle Ear Flashcards
What evokes the acoustic reflex?
Evoked by loud sound (>=80 dB pure tone; >=65 dB noise, SPL)
What is the role of the Acoustic Reflex?
To improve our perception of sounds by
1. protect cochlear from intense noise
2. Reduce masking from low-frequencies
3. Reduce hearing of own vocalization
4. prevent roll over of speech perception at high sound level
What causes a delay in the acoustic reflex?
Delay in neural circuit as well as Musclesc (20- 100ms)
Explain the relationship between binaural and unilaterality:
Binaural response to unilateral stimulation
What occurs to muscles in acoustic reflex at the time of vocalization?
When vocalizing, muscle contracts in advance (50-70 ms in chicken)
What else can evoke an acoustic reflex except for loud sounds?
Contraction of ME muscles can also be evoked by irritation of face, ear canal, etc. (Stronger for tensor tympani muscle)
What are the two types of Acoustic Reflex Measurements?
Direct and Indirect measurements
What is the Direct measurement of Acoustic reflex? (2)
Electromyogram
Direct observation through perforated TM
What is the indirect measurement of Acoustic reflex? (3)
- Measure deflection of eardrum
- Measure air pressure in sealed ear canal
- Measurement of ME impedance: AR changes ME impedance. This is an important diagnosis tool!!
In impedance, how do mass and stiffness influence frequency? (2)
XC = k/(2.pi.f) Stiffness decreases with frequency
XM = 2.pi.fm Mass increases with frequency
Explain what happens in the concept of admittance vs Impedance:
Y=1/XC =2f/k = 2fV/(c2) = kV
Z inverse XC=1/kV): Z for air in V with solid wall (R is ignored).
Admittance is proportional related to volume
It was shown that Impedance is inversely related to
Impedance is inversely related to Volume
Z inverse 1/V: smaller the V, larger the Z
What is the relationship between impedance and volume?
Acoustic impedance can be expressed as volume: smaller the volume, larger the impedance
If we say the impedance of a middle ear (ME) is 2cc:
It means the impedance of this ME equals to the impedance of 2cc of air at standard condition (a 2cc cell with solid wall)
What is Electroacoustic impedance test?
A microphone picks up sound pressure level in the ear canal which is influenced by ME impedance and volume of the cavity
What is Equivalent Volume?
The amount air volume in a solid cavity that will have the same impedance as the tested auditory system
What are the standard conditions of Equivalent Volume? (3)
Standard air pressure at sea level (1Pa)
Defined temperature (20 Celsius)
Cell with solid wall
What is the comparison between Ve and real ear volume?
Real V has soft end and therefore smaller impedance as compared with the cell of the same size but surrounded by solid wall. Therefore, a solid cell must have a larger volume to have equal impedance as that of the real ear. Therefore, Ve is larger than V in real ear.
How does the volume change in the external ear tell the impedance of middle ear (ME)?
Eardrum is acoustically transparent.
The middle ear impedance change will change the stiffness of the eardrum thus changing the Ve of the external ear
What is the principle of an impedance bridge?
To match the impedance until sound level detected by mic is minimal
If stiffness is increased when AR is activated, Ve will be ?
Decreased
What will happen to Ve if MD is full of water?
Decreased
What will happen to Ve if there is a large perforation on eardrum?
Increased equivalent volume (1 to 5.5 mL) suggests a perforation
What will happen to Ve if the bone chain is disconnected?
Increased
How does changing air pressure allows detecting of middle ear pressure?
The OE pressure that results in the smallest impedance is the pressure of ME.
What is Acoustic Reflex measurement in summary?
- We measure the AR by measuring the impedance change
- AR is due to ME contraction
- AR is evoked by loud sound
Why do we change the air pressure of the OE in AR measurement?
Changing air pressure allows detecting of middle ear pressure
What are the two sounds in AR measurement?
(1) continuous tone (low f) for impedance measuring,
(2) loud sound for impedance change (could be low and high in frequency)
What are the ME elements to admittance? (3)
Mass, Stiffness and Resistance
In the ME, the element of MASS to admittance comes from: (4)
Pars flaccida of TM
Ossicle chain
Perilymph in the cochlea
When ET open
In the ME, the element of STIFFNESS to admittance comes from: (4)
Ligaments
Muscle tendons
TM
Air enclosed in ear canal (during test) and middle ear
In the ME, the element of STIFFNESS to admittance comes from:
Bone joints and other; Cochlear mechanical structure
What Stimulation parameters that cause practice issue of AR? (6)
Signal Spectrum:
Signal Presentation laterality comparison:
Duration:
Intensity growth?
AR can be initiated by?
Other Factors:
.
What are the two effects of the Frequency on AR?
- Noise is better than puretone (lower threshold): suggests that bandwidth matters.
- Cross-band summation
When band is > CB, AR threshold decrease
Integration across different CBs.
How does the Cross-band summation work in AR? (2)
Separate two tones by frequency. Test AR threshold until it decreases significantly
When the separation is in CB, no change in AR threshold; when it is over CB, threshold drops down. Turning point tells CB.
What is the intensity effect on AR? (2)
- AR magnitude increases with intensity above threshold
- Appears as:
Increase in impedance
Decrease in latency
In AR examination, what are the effectiveness findings of laterality? (2)
- Bilateral > ipsilateral > contralateral
- However, contralateral AR is often requested due to the ability to exam the whole circuit for AR
How do we define AR threshold?
0.03 cm3 or intensity to elicit at 10% of the maximal AR response (85 dB HL)
What is the effect of sounds on latency in AR? (2)
Latency change with intensity from 150 ms to 25-30 ms
Higher the intensity shorter the latency
What are the two sources of AR latency?
Neural circuit delay
Delay of ME muscle
Which of the two sources, neural circuit delay and muscular delay is larger in AR?
Muscular delay
What are the effects of Stimulus Duration on the response of AR?
The longer duration of signals produce stronger response
What are the effects of signal duration on the AR?
AR threshold decrease with signal duration: larger time range for the temporal summation (up to 500 ms)
What conclusion can we make from Frequency to temporal summation in acoustic reflex?
The higher the frequency,higher the temporal summation in AR across frequency: more summation for high frequency
dB difference between 250 ms and 10 ms signals to produce the same AR
In AR adaptation, for 500 Hz long duration tone signals:
AR goes down after 10 seconds
What are the AR impact ME conduction?
Increases impedance by increasing stiffness
Attenuation at low frequency: A system with higher stiffness has high natural F because it does not respond well to low F signal
How can we explain the results from this finding related to oscillation in AR to low F signals? (2) PROOF 1
- Loud sound initiates AR
- AR reduces low-frequency sound into the cochlea
- AR is reduced
- Then more sound gets into cochlea—AR increases again
Repeated 1-4: oscillation
What is the effect of Bell Pasly in AR? PROOF 2
- Recording AR in the healthy ear, AR by stimulation ipsilateral (normal, solid line) versus contralateral ear (bell palsy, dashed line)
- Left Panel: low-frequency signal showing larger impact.
- Right panel: higher frequency signal showing less impact.
What is the third proof of AR bias to low-frequencies?
TTS induced by low-frequency noise
Solid line: a subject with no AR
Dashed line: normal control
What is the effect of increased stiffness in ME to AR?
- Increased stiffness attenuates sound transmission at low frequencies (< 1000 Hz).
- This is thought to provide some protection against noise exposure.
What are other factors that can cause ME muscle contractions?
Swallowing, yawning, tickling on face, etc
vocalization
What is the Intensity-control theory in AR?
- Reduces high level sound. Therefore provides protection
- Currently, this protection against noise is not considered as the main role of AR
What is the Perceptual theory of AR? (4)
Improve hearing by:
- Protection from intense noise
- Reducing low-f masking
- Distinguish between own vocalization and external signal
- Prevent roll-over
What is Roll-Over in AR?
Reduction of speech recognition scores that occurs at intensities above the level where PB max is obtained.
What are the potential sources of artifacts in AR measurements? (5)
What is Extra tympanic manometry?
One of the indirect methods involves monitoring air pressure changes in the external ear because of eardrum movement.
Explain the abnormal reflex decay:
When there is more than 50% decay in AR in the low frequencies in the Contralateral ear. Explains Retrocochlear pathology or Bell’s palsy
What is the impact the AR on ME Conduction? (2)
The AR Increases impedance by increasing stiffness
It attenuates low Frequencies (Higher stiffness affects low frequencies)
How can we explain the results from an AR cycle in these graphs?
There is a cycle of AR by from:
- AR evoked by loud sounds,
- then AR causes increased stiffness so reduces low-frequency sound into the cochlea
- AR reduces
- More sound gets into cochlea, so AR is increases again
Repeat
What can we see from this graph?
We can see high sound levels are more attenuated at low frequencies because of increased stiffness (<1000 Hz)
This is thought to provide some protection against noise exposure.
ME muscle contractions could be evoked by: (3)
- Swallowing, yawning, tickling on face, etc
- vocalization
- Loud Sounds
What can we see from this graph?
There is an attenuation in CM from AR attenuation which we can see from a decrease in CM magnitude
What is the effect of Bell’s palsy on speech dis?
Increased rollover in subjects with Bell’s palsy
What could affect your results of AR? (5)
Previous ME diseases
Sequential variability
Test operation (skill of tester)
Age
Medications
