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Intro to Audiology > Otoscopy & Immitance > Flashcards

Flashcards in Otoscopy & Immitance Deck (31):
1

Acoustic Immitance




Routine in audiological test battery

Also called:
Impedance audiometry
Middle ear measurements
Tympanometry

2

Immittance

all-encompassing term for measurements of:

Impedance
Compliance
Admittance

Checks movement of TM in response to air pressure

3

Acoustic Reflex

involuntary contraction of middle-ear muscles -Tensor tympani & stapedius- in response to intense sounds

Normal hearing = bilateral intra-aural muscle reflex around 85 to 100 dB SPL

4

Impedance

volume of air pressure in the ear canal

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Compliance

measurement of stiffness of eardrum

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Admittance

mobility of the TM in response to air pressure in the external ear canal

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Factors Governing Acoustic Immitance

R M S

Resistance- ligaments that support the ossicles; bone movement

Mass- weight of the ossicles; most important for high frequencies

Stiffness- load of fluid pressure from the inner ear on the base of the stapes; most important for low frequencies

Stiffness-dominated system
Responses through low frequency are most effective

8

Tympanometry

TM vibrates most efficiently when the pressure on both sides of the eardrum is equal

Generally conducted with LF probe tone of 220 or 226 Hz.

Use of higher frequencies can change results- only used with kiddos under the age of 6 mos

Under six months, use 1000Hz probe tone to test flex of TM until eardrum gets bigger and the ear canal widens; Ear canals fully developed after 6 mo

9

Steps in Tympanometry

1. Clear canal from all wax and debris

2. Press tip of probe into ear, creating a complete seal between the ear canal and the outside ear

3. Positive pressure is increased to about +200 daPa then brought back to 0

4. Probe tone sent increases to around 85 to 90 dB

5. Detecting compliance- pressure of external ear is gradually decreased until TM achieves max compliance

6.Overall compliance of ME is difference between positive and negative pressure

*many factors can change the type of the tymps!
Cerumen, stenosis, ET trouble

10

Normal Tympanometry Values

Adults
Compliance: .3 to .7
Pressure: 50 to 114 daPa
*Volume: .9 to 2.0 cm2

Peds
Compliance: .25 to 1.05
Pressure: 80 to 159 daPa
*Volume: .3 to .9 cm2

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Compliance Types

Type A
As-
Ad-

Type B

Type C

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Type A:

Normal


13

Type Ad:

deep system; may be caused by Flaccidity of the TM or separation of the chain of ossicles

deep TM moves a lot; goes way back and then returns; drums can be thin or ossicles weak; can also be hitting a healing perforation and that skin moves a lot

Often seen in older men

14

Type B:

Flat line w/ no peak: often caused by Fluid

is fluid (normal volume) or a perforation/tubes (large volume); TM doesn’t move; associated with conductive HL

15

Type C:

negative pressure; may be caused by a Sinus infection or cold

is max compliance obtained at a negative pressure; TM sucked way back in; associated with conductive HL

16

Type As:

stiff/shallow system: may be caused by Stapes immobilization

stiff TM moves just a little; TM may be thick; not completely stopped

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Reflex-Activating Stimulus (RAS)

stimulus presenting the acoustic signal to the ear

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Ipsilateral Acoustic Reflex

one probe; reflex measured in same ear tone is introduced

19

Contralateral Acoustic Reflex

two probes; reflex is measured in the ear not receiving the tone

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Outcomes of Acoustic Reflex Testing

1. Reflex is present and normal at 85 dBSL

2. Reflex is absent at the limit of the activating system a 125 dB HL (Severe hearing loss most often shows no response)

3. Reflex is present, but at a low SL (less than 60 dB above the audiometric threshold

4. reflex is present but at high sensation level (greater than 100 dB above the audiometric threshold)

21

Acoustic Reflex Testing

Facial nerve supplies innervation to the stapedius muscle; any disruption in any part of the pathway can interfere with the reflex

You can have normal ipsi with abnormal contra

Most important for cross-check findings!

22

Acoustic Reflex Test Process

Reflex Activating Stimulus (RAS) presented @ 500, 1000, 2000, & 4000 Hz

Start at 70 dBHL and increase until response is seen

Response observed? Down 10, up 5 for threshold (raised in 5dB intervals until response is pinpointed)

Lowest level observed: acoustic reflex threshold (ART)

23

Acoustic Reflex Decay

Decay: as stapedius muscle is stimulated, it will eventually relax

24

Acoustic Reflex Decay Test Process

Typically occurs at higher frequencies

Tone presented @10 dB above the reflex threshold

Test is complete when
reflex is at half the original amplitude
OR at the end of 10 seconds

Normal = >5 second hold; (most people hold for 8 seconds)

Not done often in the clinic; most often performed during research

25

Otoacoustic Emissions (OAE)

Reflects the activity of an intact and active cochlea; Unknown reason for occurrence; “phenomenon”; tests the outer hair cells

When two tones enter the ear, the cochlea produces additional frequencies which bounce back, or echo into the EAM

Spontaneous: Natural sound out of ear

Evoked: Occurs immediately during or after stimulus

Transient-Evoked OAE (mostly research)
Clicks or tone tips

*Distortion-Product OAE (newborn HT and often in clinic)

26

OAE Testing

Kiddos typically checked at 2, 3, 4, 5 kHz (most important speech frequencies); adults whole spectrum

*Two tones, 55dB and 65dB played into ear; ear will “make up” the third tone, usually 45dB or less

(tone's frequencies combine and bounce back, but diminished by the time the machine can read the return echo; Has to go thru the TM, thru the ME space; bounces at the cochlea and reverses through all the space)

30 seconds long; typically run twice for accuracy

Typically cannot have more than a 40 dB hearing loss; Responses typically absent at 30dB HL

Cross check for everything; can’t fake the OAE

Cannot come back if there is fluid in ME (conductive HL)

Should mimic the hearing test

27

Interpreting the OAE

Measured by the difference between the OAE level and the noise floor

Present >5 dBSPL difference and above 0 (robust >15)

Reduced >5 difference but below 0 dBSPL on the graph

Absent

28

Noise Floor

Ambient room noise

29

Auditory Evoked Potentials (AEPs)

electrical responses in the brain; occur within the first 10-15 milliseconds after a signal is presented

Originate in the 8th CN and the brainstem

Electrodes placed on mastoids, forehead, & back of neck

Insert tips placed in ears

7 wavelengths
Typically only look at I-V
I, III, V are the main waves

When only the V wave remains visible, the threshold is called

30

Recruitment


small range for soft to loud; quick increase.
Common in children with underdeveloped brains and aren’t used to the normal curve

Using SL threshold of 40 dBHL, play sound at 60 dBHL- quick increase growth (perceive the sound with 60 dBSL)

Problem?? Hearing Aids! If the range is small, there isn’t much room to try to give all the ranges back

31

Decruitment

Using SL threshold at 40 dBHL, play sound at 60 dBHL, perceive it at 90 dBHL (50 dBSL)
*not common!