L6: Immittance

Question 1

What do “stim” and “contra” represent on an audiogram?

Answer 1

they are reflex thresholds

Question 2

what population is tympanometry most common to do in and why?

Answer 2

pediatric because they commonly have middle ear problems

Question 3

Who is Otto Metz?

Answer 3

He was a Jewish German doctor who was interested audiological analysis

Question 4

What was Otto Metz initially trying to study?

Answer 4

He wanted to distinguish sensorineural from conductive hearing loss (in a time when tuning forks were still the main tool for diagnosis).
He ultimately studied immitance and acoustic reflexes.

Question 5

What did Otto Metz compare the ear drum to that helped him further his research?

Answer 5

Construction materials. He looked at the ear drum as if it was a wall, and investigated how sound moved through walls/connstruction materials.

Question 6

What is the general timeline of Otto Metz discoveries/work?

Answer 6

1938: In Germany, beginning his work, he escaped to Denmark
1943: Nazis were going to lock up all Jews in Denmark. He escaped to Sweden.
1945: continued his work during this time, returned safely to Copenhagen in 1945
1946: Published the “basic principles of immittance audiometry”
1951: Published first workr on acoustic reflexes

Question 7

What is acoustic immittance?

Answer 7

it is a measaurement of of how easily sound energy can flow through the middle ear.

Question 8

what information does tympanometry provide us?

Answer 8

rich information about the middle ear– it measures acoustic immittance by collecting information about the movement of the eardrum and the pressure in the ear

Question 9

Tympanometry is ___ to obtain

Answer 9

easy

Question 10

what information do acoustic reflexes provide us?

Answer 10

• mainly info about auditory and facial nerves and the lower brainstem
• some information about hearing

Question 11

acoustic reflexes are ____ to obtain

Answer 11

easy

Question 12

What three things that Otto Metz left us as his legacy?

Answer 12

1. that we can learn about something based on its impedance to sound
2. the ossicular chain and tympanic membrane can be thought of as one unit and as the “wall” of the middle ear
3. these findings are powerfull for studying the middle ear

Question 13

what is acoustic impedance?

Answer 13

the degree to which a sounnd is absorbed or not absorbed by something

Question 14

Which would have lower impedance? A good paper towel, or a paper towel covered in butter?

Answer 14

the good paper towel would have higher impedance than the paper towel with butter

Question 15

High impedance = (____) absorption

Answer 15

low absorption

the material is impeding the absorption

Question 16

Low impedance = ____ absorption

Answer 16

high absorption

low impedance means very little stopping the absorption

Question 17

What absorbs more sound (low impedance)?: carpet or hardwood floors?

Answer 17

Carpet – the material absorbs more sound, so lower impedance
Hardwood – higher impedance (sound reflects/bounces off of it)

Question 18

Would a small room or large room have lower impedance?

Answer 18

a large room would have lower impedance (because the sound pressure decreases as it dissipates across the larger space before hitting a wall)

Question 19

How could we make a room very quiet?

Answer 19

Having a larger room that is carpeted will have the lowest impedance allowing the sound to be highly absorbed

Question 20

How does impedance work in the ear (where is sound absorbed)?

Answer 20

sound is absorbed from the ear canal into the ossicular chain when acoustic energy sets the ossicular chain in motion

Question 21

Under what impedance condition would the ossicular chain move well?

Answer 21

low impedance

Question 22

If your at a bar and your favourite song comes on and it makes you want to dance your life away, what level of impedance are you experiencing?

Answer 22

Low impedance (things are moving more freely)

Question 23

does low impedance equate to better hearing?

Answer 23

NO
there might be low impedance, and the ossicular chain freely moving BUT it is due to ossicular disconnection (bad hearing outcome)

Question 24

What are the three componnents of impedance?

Answer 24

Stiffness, Mass, Resistance

Question 25

In the middle ear, friction is basically _\_\_\_

Answer 25

negligible

Question 26

How would increasing the resistance (friction) in the system impact impedance?

Answer 26

there would be a loss of energy that is NOT dependent on frequency | resistance is minnimal in ear system

Question 27

Which two components do play a role in the ear system?

Answer 27

stiffness and mass

Question 28

What is mass reactance?

Answer 28

- the opposition to the movement of a mass in a system due to its inertia - it is a component of impedance - it increases as frequency goes up

Question 29

why is it more difficult to move larger masses back and forth quickly?

Answer 29

due to acceleration -- takes longer to aaccelerate and decelerate the mass

Question 30

a larger mass will have _\_\_\_ mass reactance and _\_\_\_ impedance for high frequencies

Answer 30

higher, higher/more

Question 31

a larger mass will move better at a _\_\_\_frequeny

Answer 31

low

Question 32

for a larger mass at low frequencies, there is _\_\_\_ mass reactance and thus _\_\_\_ impedance

Answer 32

less, lower

Question 33

Examples of lower frequency things that make sounds ## Footnote hint: bigger things make lower frequency sounds

Answer 33

tuba, kick drum,

Question 34

What is stiffness reactance?

Answer 34

- component of impedance that involves elastic properties

Question 35

stiffness reactance _\_\_\_ as frequency _\_\_\_

Answer 35

stiffness reactance decreases as frequency goes up

Question 36

If something is very stiff it wants to return to the resting position _\_\_\_, than if it was looser

Answer 36

faster

Question 37

what does high stiffness interfere with?

Answer 37

low frequencies

Question 38

at low frequencies there is _\_\_\_ stiffness reactance and thus _\_\_\_ impedance

Answer 38

low frequencies: more stiffness reactance and more impedance

Question 39

what frequency level would a highly stiff system move best at?

Answer 39

high frequency level

Question 40

at high frequencies, a highly stiff system would have _\_\_\_stiffness reactance anda thus _\_\_\_ impedance

Answer 40

at high frequencies: a highly stiff system would have less stiffness reactance anda thus less impedance

Question 41

Which frequencies will be heard better when our tympanic membrane and ossicles are stiff?

Answer 41

high frequencies

Question 42

which frequencies will be heard better if our middle ear unit is more relaxed/looser?

Answer 42

lower frequencies

Question 43

why is resistance on a different plane than stiffness and mass?

Answer 43

because resistance is independent to frequency, whereasa stiffness and mass are influenced by frequency

Question 44

mass reactance and stiffness reactance are _\_\_\_ related to frequency

Answer 44

inversely

Question 45

How does increasing the frequency influence mass reactance and stiffness reactance?

Answer 45

increasing frequency will increase mass reactance but decrease stiffness reactance

Question 46

how will decreasing frequency influence mass reactance and stiffness reactance?

Answer 46

decreasing frequency will decrease mass reactance and increase stiffness reactance

Question 47

what mass and stiffness are in balance (cancel out), the frequency would be \_\_\_

Answer 47

resonant

Question 48

what is the resonant frequenccy of the middle ear?

Answer 48

800 to 1200Hz

Question 49

changes in middle ear impedance are primarily due to changes in what?

Answer 49

stiffness (mass and resistance are negligible in middles ear)

Question 50

What are clinical impedance measure comparable to?

Answer 50

stiffness measures

Question 51

Which frequencies are not transmitted as well due to high stiffness and low mass in the middle ear?

Answer 51

low frequencies

Question 52

how could you improve low frequencies?

Answer 52

making the system less stiff

Question 53

which frequencies are not transmitted ass well due to the presence of some mass?

Answer 53

high frequencies

Question 54

how could we improve high frequency response?

Answer 54

reduce the mass and make it stiffer

Question 55

clinically what do we typically say instead of impedance?

Answer 55

admittance

Question 56

what is admittance?

Answer 56

opposite of impedance, it is how much energy is absorbed

Question 57

what is admittance measure?

Answer 57

mhos | usually milli-mhos

Question 58

what is immittance

Answer 58

general term that referes to both impedance and admittance

Question 59

\_\_\_ admittance = low impedance

Answer 59

high admittance=low impedance

Question 60

\_\_\_\_ admittance = high impedance

Answer 60

low admittance = high impedance

Question 61

what is acoustic admittance equal to?

Answer 61

sound flow (volume velocity)/sound pressure

Question 62

how can acoustic admittance be estimated?

Answer 62

by measuring the reflected sound, anything not reflected would be admitted

Question 63

when admittance is high, reflection is \_\_\_?

Answer 63

low

Question 64

when admittance is low, reflection is \_\_\_?

Answer 64

high ## Footnote not alot beeing absorbed, so high reflection

Question 65

when admittance is low, the middle ear unit has high impedance, what level of stiffness does it have?

Answer 65

high stiffness because it has low admittance

Question 66

what pathological conditions are associated with decreased admittance (more stiff)?

Answer 66

1. Otitis media (fluid cause ossicles to be stiffer) 2. ossicular fixation 3. no middle ear space (very stiff, admittance very low)

Question 67

what pathological conditions are associated with increased admittance (less stiff)?

Answer 67

ossiccular discontinuity (dislocataed ossicles)

Question 68

how does admittance relate to volume?

Answer 68

a larger volume space would absorb more energy (less reflection)

Question 69

Why is 226Hz used to test admittance? | related to volume and sea level

Answer 69

for a 226Hz tone at sea level, air in a 1cm^3 (or 1 ml) cavity hass about 1millimho of admittance so, 1mmho of admittance = 1cm^3 of space (one to one relationship)

Question 70

How do we measure ONLY middle ear admittance?

Answer 70

need to subtract the outer ear admittance from the total ear admittance

Question 71

how do we isolate the outer ear admittance?

Answer 71

- we need admittance to be of middle ear to be very low, so we can make the tympanic membrane very stiff by usinng air pressure, so that it does not move and acts as a wall - then the tympanic membrane will reflect energy, rather than admitting it to the middle ear space

Question 72

how much should we tighten the ear drum?

Answer 72

as much as possible without pain

Question 73

what are the 2 ways we can achieve zero middle ear admittance?

Answer 73

1. add pressure to the ear, creating negative pressure in the middle eaer space (retracted TM) 2. remove pressuree from the ear, creating positive pressure in the middle ear space (TM pushed out)

Question 74

In order to vary the pressure in the eaar, we ned a good \_\_\_\_?

Answer 74

seal

Question 75

review these points

Answer 75

- when pressure (on x-axis) is low or high, we are looking at ONLY outer ear admittance - the peak in between is both middle and outer ear admittance

Question 76

What did Paul Madson create?

Answer 76

the tympanometer

Question 77

what is a tympanometer?

Answer 77

it is a device that has a pump, speaker, and microphone

Question 78

what frequency tone does the tympanometer play?

Answer 78

226 Hz

Question 79

where on a tympannogram is the eardrum moving its best?

Answer 79

at the peak

Question 80

how do we release negative aair pressure in the ear?

Answer 80

we need to match the pressure - if there is negative pressure behind eara drum, then we need negative pressure in front of ear drum to equalize it

Question 81

what does the peak tell us about pressure levels

Answer 81

tells you what the pressure is behind the eardrum - if the person has -50 pressure behind ear drum then the peak of the tymp will be at -50 - if the person yawned and the pressure behind eardrum become 0, then the peak shifts to 0 - peak is at 0 when at atmospheric pressure

Question 82

what does the peeak of a tymp tell us about admittance?

Answer 82

it is peak admittance -- the TM and ossicles are maximally set in motion,

Question 83

what does thee line on a tympanogram represent?

Answer 83

the admittance at different pressure levels

Question 84

what is static compliance of middle ear

Answer 84

the admittance of the middle ear

Question 85

what is a compensated tympanogram?

Answer 85

it is when the OE admittance is subtracted from the OE+ME admittance automatically (the line gets shifted down to sit on x-axis) - the volume of ear canal will be given to you