Otoscopy & Immitance Flashcards
Acoustic Immitance
Routine in audiological test battery
Also called:
Impedance audiometry
Middle ear measurements
Tympanometry
Immittance
all-encompassing term for measurements of:
Impedance
Compliance
Admittance
Checks movement of TM in response to air pressure
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
Impedance
volume of air pressure in the ear canal
Compliance
measurement of stiffness of eardrum
Admittance
mobility of the TM in response to air pressure in the external ear canal
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
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
Steps in Tympanometry
- Clear canal from all wax and debris
- Press tip of probe into ear, creating a complete seal between the ear canal and the outside ear
- Positive pressure is increased to about +200 daPa then brought back to 0
- Probe tone sent increases to around 85 to 90 dB
- Detecting compliance- pressure of external ear is gradually decreased until TM achieves max compliance
- Overall compliance of ME is difference between positive and negative pressure
*many factors can change the type of the tymps!
Cerumen, stenosis, ET trouble
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
Compliance Types
Type A
As-
Ad-
Type B
Type C
Type A:
Normal
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
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
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
Type As:
stiff/shallow system: may be caused by Stapes immobilization
stiff TM moves just a little; TM may be thick; not completely stopped
Reflex-Activating Stimulus (RAS)
stimulus presenting the acoustic signal to the ear
Ipsilateral Acoustic Reflex
one probe; reflex measured in same ear tone is introduced
Contralateral Acoustic Reflex
two probes; reflex is measured in the ear not receiving the tone
Outcomes of Acoustic Reflex Testing
- Reflex is present and normal at 85 dBSL
- Reflex is absent at the limit of the activating system a 125 dB HL (Severe hearing loss most often shows no response)
- Reflex is present, but at a low SL (less than 60 dB above the audiometric threshold
- reflex is present but at high sensation level (greater than 100 dB above the audiometric threshold)
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!
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)
Acoustic Reflex Decay
Decay: as stapedius muscle is stimulated, it will eventually relax
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
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)
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
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
Noise Floor
Ambient room noise
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
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
Decruitment
Using SL threshold at 40 dBHL, play sound at 60 dBHL, perceive it at 90 dBHL (50 dBSL)
*not common!
