Lecture 7

Question 1

What is immittance?

Answer 1

A generic term that encompasses impedance, admittance and their components
How easy or hard it is for air to flow into the system.

Question 2

What is impedance?

Answer 2

(Z) - in acoustic ohms; in the middle ear system is defined as the total opposition of this system to the flow of the acoustic energy.
How hard it is for energy to flow into the system.

Question 3

What is admittance?

Answer 3

(Y) - in acoustic mmhos; the reciprocal of impedance and is the amount of acoustic energy that flows into the middle ear system.
How easy it is for energy to flow into the system.

Question 4

In simple harmonic motion, what are the 3 forces that a mass, spring system has to overcome to set into motion?

Answer 4

Friction (resistance)
Mass (inertia)
Stiffness (elasticity)

Question 5

How do the 3 forces relate to impedance/admittance?

Answer 5

Periodic motion is controlled by resistance (friction), inertia (mass), and elasticity (spring). -> all vector quantities.
The mechanism of control of motion is through the impedance (Z).
The energy you put in is the energy you get back.

Question 6

The variables that determine admittance: what is compliance?

Answer 6

The inverse of stiffness - the admittance offered by stiffness elements in the middle ear system which is called compliant susceptance.

Reactance due to stiffness

Question 7

The variables that determine admittance: what is mass?

Answer 7

The admittance offered by mass elements in the middle ear system which is called mass susceptance. (Acoustic resistance - mechanical elements, like the ossicles, acoustical elements, like the ear canal = mass/spring, and eardrum). All share same position in relation to mass reactance and stiffness.

Question 8

The variables that determine admittance: what is friction or resistance?

Answer 8

Determines the absorption or dissipation of acoustic energy. In admittance terms, this element is called conductance.

Question 9

What are the three forces contributing to impedance?

Answer 9

Resistance, mass reactance and stiffness.

Question 10

In the variables that determine admittance, how to acoustic and mechanics play a part?

Answer 10

Acoustic: phase angle, magnitude, mass reactance, stiffness, resistance
Mechanics: magnitude and direction (mechanical motion - phase angle), sinusoidal motion, can happen at various phases. Which portion of circle will help determine where vibration starts.

Question 11

What are the components of admittance? (vector sum)

How can it be represented notation wise?

Answer 11

Is a two dimensional quality - and is a vector sum of conductance and the total susceptance.
Mathematically, admittance can be expressed in rectangular notation or polar notation:
Rectangular: admittance expressed as the sum of its conductance and susceptance elements.
Polar: admittance expressed by its magnitude and phase angle.

Question 12

What is the relationship between admittance components and frequency?
Mass/compliance susceptance
What is the relation to frequency?

Answer 12

Acoustic conductance is independent of frequency.
Compliance and mass susceptance are frequency dependent
- mass susceptance is directly proportional to frequency
- compliance susceptance is inversely proportional to frequency

As frequency increases, the total susceptance progresses from positive values (stiffness controlled), toward 0 (resistance) to negative values (mass controlled).

Question 13

What happens when there is middle ear pathology, high stiffness, high resistance - how does this affect the frequencies in admittance?

Answer 13

High frequency more impacted for middle ear pathology.
High stiffness - low frequencies more impacted
High resistance - will dampen all frequencies - not discriminating.

Question 14

What is tympanometry?

Answer 14

Admittance/impedance as a function of air pressure.

Question 15

What are the elements of standard low frequency tympanometry?
What frequencies used?
What is the normal middle ear system?

Answer 15

Performed using low probe tone frequency - 226Hz, measures the admittance magnitude in mmho as a function of ear canal pressure.
At low probe tone frequency - normal ME system is stiffness dominated and susceptance contributes more to overall admittance than conductance.

Question 16

What are the traditional parameters obtained from low frequency tympanometry?

Answer 16

Static admittance (SA)
Tympanometric shapes (to ID pathologies)
Tympanometric peak pressure (TPP)
Ear canal volume (ECV)
Tympanometric width (TW)

Question 17

How is the procedure done for tympanometry?

Answer 17

Probe in ear canal is placed at a distance from the eardrum. Ear canal and middle ear measure at the tip of the probe. Just want to measure eardrum at an ambient pressure.

Question 18

How do you measure the middle ear admittance?

Answer 18

Need to subtract the admittance due to the external ear canal from the overall admittance measure.
The estimate is subtracted from the peak value( TPP), which jointly reflects the admittance of external auditory canal and middle ear, to get just the admittance of the TM and the middle ear.

Question 19

What is static admittance (SA)?

Answer 19

Measuring admittance under changes in air pressure, provides a way to estimate the admittance due to ECV.
Accomplished by placing eardrum under sufficient tension by a high positive or negative pressure to drive the impedance of the middle ear toward infinity.

Question 20

What are variables that affect SA?

4

Answer 20

Choice of pressure value for compensation of ear canal admittance
Rate of ear canal pressure
Direction of ear can pressure change - SA greater for negative to positive than for positive to negative.
Ear canal correction: because admittance is a vector quantity, it cannot be added or subtracted unless the phase angle of the two admittance vectors is identical.

Question 21

In the guidelines for measuring SA, how should the pressure be, what should be recorded?

What are the two vectors?

Answer 21

Either direction of ear canal pressure change can be used for tympanograms. Decreasing pressure (+/-) used at 678Hz?

Both admittance components (B and G) should be recorded simultaneously. Admittance = B (total susceptance/pitch and ear canal volume = compensated admittance)

Question 22

What is the compensation method?

Answer 22

Calculate YTM first, divide in half, come down from peak at that numbers, find distance at x-axis.
TW will change accordingly if YTM does - obtained from +/- tail.
Peak = admittance of middle ear and ear canal.

Question 23

What it tympanometric peak pressure? (TPP)

Answer 23

TPP is the position of the tympanometric peak on the pressure axis (daPa). Provides estimate of the pressure within the middle ear space.

High negative middle ear pressure = abnormal.

Question 24

What is ear canal volume? (ECV)

Answer 24

Air volume in ear canal between tympanometer probe tip and TM.
Index to see if eardrum is perforated or not, categorize different pathologies.

Question 25

What do the different volumes of ECV mean:
Flat with high volume
Flat mid range volume
Flat low volume
Volcano looking

Answer 25

Flat high volume/volcano: eardrum perforation, or PE tube is open(working)
Flat mid range volume: otitis media with effusion, could be perforation
Flat low volume: canal blocked (by wax), probe tip blockage within canal wall.

Question 26

What is tympanometric width? (TW)

What is this the best predictor of?

Answer 26

The width of tympanogram (daPa) measured at one half the compensated static admittance
Measure provides an index of the shape of the tympanogram in the vicinity of the peak; quantifies the relative sharpness or roundness of the peak.

Best predictor for the presence or absence of fluid

Question 27

What are some various indicators from TW?
Wide
Narrow
Flat
Others (2)

Answer 27

Abnormally wide: effusion, peak will become rounder, and eventually go flat (moves more negative, more pressure = flat)
Narrow: flaccid eardrum, otosclerosis early stages
Flat: could be fluid, blockage, perforation
Also negative middle ear pressure
High amplitude - discontinuity

Question 28

What is multifrequency tympanometry?

What are some benefits?

Answer 28

Possible to record tympanogram at multiple probe tone frequencies and at multiple components (B + G).
Can record more variables in this method.
Much better ability to determine stiffness of ossicular chain.
At higher frequencies, better discrimination for pathologies undetectable for other tests.

Question 29

What are the two recording methods for multifrequency tympanometry?

Answer 29

Sweep frequency: pressure held constant while frequency is swept across multiple frequencies
Sweep pressure: frequency is held constant while the pressure is swept across a given range.

Question 30

What are the multifrequency tympanometry parameters?

Answer 30

Tympanometric configuration
Resonant frequency (good estimate to decipher pathologies)
Frequency corresponding to admittance phase angle of 45 degrees
SA at multiple frequencies

Question 31

What are the various tympanometric configurations?
1B1G
3B1G (3)
3B3G
5B3G

Answer 31

1B1G: 45-90 degrees, stiffness dominated
3B1G: 0-45 degrees
(1) notch above tail, stiffness dominated
(2) notch at tail = 0 (resonant frequency)
(3) notch below tail, mass dominated
3B3G: 0 to -45 degrees, mass dominated
5B3G: -45 to -90 degrees, mass dominated

Question 32

What is an indicator of otosclerosis and otitis media with tympanometric configurations?

Answer 32

Notch reaches tail at higher frequencies for otosclerosis

Notch reaches tail at lower frequencies for otitis media

Question 33

What does a receiver operating characteristic do?

Answer 33

The test that is capable of detecting pathology - tumour, fluid.