Unit 2 4801 Exam

where do you put the bone oscillator?

mastoid (most common)

Forehead is permissible (highlights that stimulating both cochleas)

Which cochlea responds during unmasked bone conduction

the better cochlea regardless were the bone oscillator is placed

Bilateral/identical hearing impairment

UM BC could represent both ears when…

1. AC thresholds are equal bilaterally

2. Both cochlea are impaired equally

If 2 cochlea are different

process more challenging because without doing anything the better cochlea will pick up sound

How to determine if you are testing the test cochlea?

determine if there could be cross hearing

if so, use a masker to isolate the test ear

Crossover of sound- Physical

phenomenon: soud energy presented to one mastoid physcially reaches both cochlea

both ears are embbeded in the skull, allowing viberations to transfer

this is why for BC testing, crossover occurs at all presentation levels

For AC testing, crossover occurs only at higher intensity levels when the sound is loud enough to set the skull into viberation

Cross-hearing can result from the crossover of sound

occurs if one cochlea can detect the amount of crossover

perceptual phenomenon the listener hears the signal in the NTE cochlea

sound presented to the TE crosses over (via BC) and is detected by the NTE

if the listener does not recognize this, responses could be incorrectly logged as a TE finding

if the L BC thresholds are worse than R what will happen

cross hearing will occur during UM BC

need to mask to isolate the L cochlea for testing

Cross over for BC sound

test any level by BC in one ear, the other cochlea recives it at the same level

20 dB HL presented to the L cochlea is also recived at 20 dB HL in the right cochlea

Cross over for AC supra-aural headphones

as AC signal becomes more intense, these cause the bones of the skull to viberate. Sound crosses the head to the other side

Cross over for AC insert phones

as AC signal becomes even more intense, these cause the bones of the skull to viberate, but you need to make sound even louder

this is bc different transducers have different interaural attenuations

interaural attenuations

amount of sound energy lost as it cross over from TE to the NTE

use this to calculate the expected amount of cross hearing

Descirbe the process of interaural attenuation

when sound is presented to the TE, some of it can cross over the head and reach the NTE

reduction in intensity during this transfer is the IA

Most problematic when the NTE has better hearing thresholds than the TE

Explain how IA works with supra-aural

tone presented to the TE 80 dB HL

with IA of 40 dB, the cochlea on the NTE receives a signal at 40 dB HL (80-40=40)

if the NTE’s threshold is < or equal to 40 dB HL, it will hear the tone

masking is needed in the NTE to ensure the response reflects the TE cochlea

How do you calculate IA?

difference between level of signal in TE (by AC or BC) and level of signal that reaches NTE cochlea (by BC)

IA= TE AC/BC - NTE BC

primarly reflection of how many dB HL it takes to get skull to viberate for each transducer

What is the IA for a supra-aural phones?

40 dB

What is the IA for insert earphones?

55 dB

What is the IA for bone oscillator?

0 dB

more physcial contact with head→ more BC crossover→ lower IA

lower IA means higher risk for cross hearing

how do you estimate the level reaching the NTE

presentation level at TE - IA

ex: present 70 dB HL to the RE through (IA about 55 dB)

sound reaching the LE about 25 dB

What might happen if you fail to mask when needed?

you risk testing the wrong ear- the better ear (NTE) responds even though it was presented to the poorer ear (TE)

can lead to…

false thresholds→ too good for the poorer ear, bc actually evaulting the better ear (NTE)

misdiagnosis of the type or degree of hearing loss→ can affect treatment

shadow curve audiogram

LE thresholds are parallel to the RE thresholds

could be the result of the right cochlea (NTE) picking up the sound presented to left (TE) = cross hearing

What is the real AC threshold in the left ear

we need to remove the RE from the equation in order to determine the true AC threshold of the LE

when should we mask?

we should be masking whenever there is a chance that the signal will crossover and be heard by the NTE (cross hearing)

BC thresholds- when ABG in TE > 10 dB, we need to mask the NTE

AC thresholds- when the difference between AC threshold of TE and Bc threshold of NTE > IA

the masker

always goes in the NTTE

presented through AC transducers

narrow band noise is effective masker for pure tones

What factors do you need to consider when masking

When the amount of crossover >= sensitivity in the NTE cochlea

level of the test signal→ presented to the test ear

IA→ value varies based on transducer

amount of crossover→ =(level presented to TE) - IA

sensitivity of the NTE→ BC threshold of the NTE (or UM BC threshold)

masking for bone conduction

the non test ear should be masked for BC thresholds whenver the test ear exhbits an air bone gap

masking is needed if ABG of TE >= 15 dB

What is contralateral masking?

eliminates stimulus detection in the better, non-test ear

When one sound interferes with the perception of another sound.

Narrowband noise is presented to the NTE as a masker for pure-tones

When should we mask?

cross hearing

whenever there is a chance that the signal will crossover and be heard by the NTE

should you mask when the amount of crossover exceeds sensitivity of NTE

yes when susupect cross hearing whne the amount of crossover meets or exceeds the sensitivity of the NTE

TE signal = 100 dB HL (in RE)

IA = 40 dB

crossover=100-40= 60 dB (to LE cochlea)

therefore cross hearing occurs if LE threhsold <= 60 dB

When should you mask during BC?

whenever the TE exhbits an ABG

ABG of TE >= 15 dB

initial masking level

the starting intensity of the masking noise you present to the NTE

to be an effective masker, the level needs to be above the thresold of the NTE (at that frequency)

then, we add a small cushion 10 dB above the threshold of the NTE and use that as the initial masking level

When do you know when masking is needed

when the patient’s AC responses shift compared to the unmasked condition

masking plateau

threshold in the TE stays constant over a range as masker level is increased

overmasking

after plateauing, if we increase masker in the NTE, the TE responses resume increasing

as the masker level is further increased, the thresold in the TE increases (the masker crosses over to TE)

undermasking

when you are evaluating the NTE (threhsold in the TE goes up as masking level increases)

when the masking noise presented to the non-test ear is too quiet to block that ear from detecting the test signal, leading to a falsely good hearing threshold for the test ear

What is immittance?

describes how easily energy flows through the ME system

How is immittance an objective measure

does not measure auditory perception (non-behavioral)

immittance is a physiological measure

what are the two related measures of immittance?

impedance + admittance

acoustic impedance (Z)

the resistance of the ME to sound energy flow

acoustic admittance (Y)

the ease with which sound energy passes through the system

Why is immittance important in audiology?

provides objective information about ME function- information we can’t get from pure-tone audiometry alone

what are two immittance tests:

tympanometry and acoustic reflexes

how does immittance work/flow through the ear

present an acoustic signal to the ear canal

measure sound energy remaining in the EAM to infer how much energy goes into the middle ear space

how is immittance an indirect measure?

we want to measure admittance at the tympanic membrane

make inferences about the middle ear based on what we measure at the probe-tip

why include immittance in audiologic test battery?

clinical importance

1. assesses ME integrity

   1. Helps identify problems like fluid, negative pressure, tympanic membrane perforation, or ossicular chain issues

2. Distinguishes conductive vs. sensorineural components of HL

3. Evaluates reflex pathways

4. Provides objective cross-check to behavioral results

Tympanometry

measures changes in admittance as a function of applied air pressure

sound is transduced best through ME when air pressure is equal on both sides of the TM (atmospheric pressure)

Where is balance normally kept

Eustachian tube

what is the typanometer probe assembly?

probe tone loudspeaker→ 85 dB SPL @ 226 Hz

microphone→measures residual sound in the ear canal

Pressure pump and manometer→ changes and measures air pressure

Tympanometry procedure

1. Perform an otoscopic examation

2. instruct patient

3. select a probe tip and insert in the ear facing TM

4. Begin pressure sweep

results of a Tympanometry are plotted on a

typanogram

graph that shows how the admittance into the ME changes as a fucntion of air pressure in the ear canal

Process of a tympanomy but all about the pressure of it

start with positive pressure

pressure pump changes pressure through ambient pressure to negative pressure

Where is admittance best?

when the pressure of the ME space and the OE are equal

What does admittance in the healthy ear look like

What is a normative range of admittance:

.25-1.7 mmho

what is the normative range for ear canal volume

children .3 - .9 ml

adults: .3 - 1.4 ml

but not pahsed until 2.9

can find it as a number next to the tympanogram

unit is the ml or cc

negative middle ear pressure (admittance)

fluid in the middle ear cavity (admittance)

eardrum perforation (admittance)

Type A tympanogram

peak near ambient pressure (100 daPa)

normal static admittance

normal ear canal volume

consistent with normal outer and middle ear function

Tympanogram- Type A d

peak near ambient pressure

high static admittance

normal ear canal volume

consistent with abnormally increased middle ear mobility

what could cause increase mobility? → ossicular disruption/discontinuity and flaccid TM

Tympanogram- Type A s

peak near ambient pressure

low static admittance

normal ear canal volume

consistent with reduced middle ear mobility

Cause? ossicular fixation, inflammation or infection of ME, ear drum scaring

Tympanogram- Type B

no clear peak- no point at which the TM is mobile

consistent with reduced compliance of tympanic membrane

look to ECV (ear canal volumne)

• high ECV (5.2)- perforation

• low to regular ECV (1.3)- otitis media

• really low ECV (.15) you’re hitting the wall or your probe tube is clogged

Tympanogram- Type C

peak at negative pressure (<150 daPa)

normal static admittance

normal ear canal volume

consistent with abnormally negative middle ear pressure

cause? emerging or resolving OME

tympanometry measures

measures how easily the ME moves in response to changes in air pressure

acoustic reflex measures

measures the involuntary ME muscle contraction in response to a loud sound

acoustic reflex how does the muscles contract

involuntary contraction of the stapedius muscle (primary) and tensor tympani muscle (minor role) in response to loud sounds

Bilateral reflex→ if you stimulate either ear, both R and L muscles will contract

when the muscle contracts, it pulls on the TM and causes stiffness in the ME system

• when this happens, admittance into the ME decreases

• SPL in the canal increases

how the reflex works

contraction of the muscle increases middle ear impedance for high intensity sounds

when a loud sound is presented…

• each muscle exerts force of the ossicles perpendicular to their normal manner of movement

• the force they exert stiffness the ME’s ability to transmit sounds

• The stiffness results in an increase in ME impedance

if normal hearing, at sound levels of 85 dB SL, the reflect will start to contract muscles

contraction results in TM movement that can be measured as a change in impedance of the system

function of acoustic reflex

protection→ potential injury to hearing is avoided by attenuating hgh intensity sounds

perception→ reduced interferences from unimportant sounds like when eating and talking. Redcues masking of high frequency sounds by lmiting low frequency admittance

acoustic reflex arc

the reflex is reflective of the sensory and motor pathways working properly.

sensory (afferent neurons)→ affects the brain and signal travels up to the brain

motor (efferent neurons)→ has an effect in the body and signal travels back down to whenever it’s going

acoustic reflex arc pathway

1. sound enters the ear→ ME→ cochlea

2. auditory nerve carries the neural signal to the brainstem (cochlear nucleus)

3. the signal travels bilaterally to the superior olivary complex

4. impulse sent to the facial nerve on both sides of the brainstem

5. the facial nerve carries the motor signal to the ME muscle

6. stapedius muscle contracts, pulling on the stapes and stiffening the ossicular chain, which reduces sound transmission to the cochlea

these structures must be intact for the AR to be present

if the reflex is absent, it could be a sign of toruble in one of the following places:

• middle ear

• cochlea

• AN

• Brainstem structures

• facial nerve

• stapedius muscle

AR testing- similarities and differences with typanometry

similar- same probe tone of 226Hz and measures changes in the SPL in the external aud canal

differences- air pressure is not varied, measure is made at peak pressure of the tympanogram, stimulus is ALSO played in addition to the probe tone

acoustic reflexes- acoustic signals

probe tone (y, 226 Hz)→ to measure change in impedance or admittance

stimulus/elicitor tone (1000 Hz)→ to elcit the reflex, “I”= ipsilateral condition

ART- the reflex threshold

lowest intensity at which a change is detectable in the immittance of the middle ear system

ART may be elicited in response to pure-tones and noise

For normal listners, the acoustic reflex is observed at about 85-100 dB HL for tones

Reflex is absent if not observed at 110 dB HL or max output

How to determine a threshold

1. >_ 0.02 mmhos

2. shows “growth” 5-10 dB above threshold

3. Repeatable

4. No artifact (test at low level)

Ipsilateral presentation

stim ear and probe ear are the SAME

ex: probe tone is measuring response in right ear and stimulus tone is being presented to the right ear

contralateral ARs

the response is measured in the contralateral (probe) ear using a continusous probe tone

• the probe is not another loud reflex-activating signal

low-level probe tone (usually 226 Hz) allows the instrument to continuously measure sound reflected back from the eardrum

when the stimulus/elicitor is presented…

middle ear system stiffens in both ears

in probe ear, this stiffening changes the amount of probe tone that is absorbed vs. reflected- i.e., a change in admittance

the tympanometer detects and records this small change as the reflex response