Audiology - Middle Ear Flashcards
What do Tympanograms measure?
Performance of the ear drum (Tympanic Membrane) and middle ear (Ossicles)
What is the stapedius reflex?
The acoustic reflex which protects the cochlea from intense sounds
What type of energy is transferred in the middle ear?
Mechanical energy
What type of energy is transferred in the inner ear?
Hydraulic energy
What type of energy is transferred in the central pathway and temporal lobe?
Bio-electrical energy
When does the tympanic membrane vibrate most efficiently?
When the pressure in the ear canal equals that in the middle ear
If the middle ear wasn’t functioning, what would happen to the acoustic energy?
It would be reflected off the oval window (not transferred to the cochlea)
What are the acoustic repercussions of a non-functioning middle ear?
The loudness of sounds will be attenuated
What are some of the middle ear disorders which result in conductive hearing loss?
OME,
Down Syndrome,
Otosclerosis
Can deaf adults/children also suffer from conductive hearing loss?
Yes (usually temporary)
What type of testing are Tympanometry and Acoustic Reflex Threshold?
Objective
What is meant by impedance of the middle ear system?
Stiffness of the system which stops the system from working efficiently
Does the system become more / less compliant as impedance increases?
Less compliant
What is meant by compliance of the middle ear system?
Flexibility of the system, allowing it to work efficiently
What are the acoustic consequences of impedance of the middle ear?
Sound waves will not be conducted efficiently and loudness will be attenuated
What does the Acoustic Reflex Threshold test measure?
The functionality of the middle ear, inner ear, auditory nerve and lower brain stem
Who is Tympanometry usually used with?
Children
How do Tympanograms measure the function of the middle ear?
By providing graphical illustrations of the change in movement of the ear drum as a result of variations in pressure
Which is a quicker and more reliable test - bone conduction or Tympanometry?
Tympanometry
What steps are involved in a Tympanogram test?
- Pressure in the outer canal is changed relative to the pressure in the middle ear
- Changes in compliance / impedance are measured using a probe tone
- Reduce pressure in ear canal in successive steps
- Measurements taken at each step
What pressure do Tympanograms usually start at?
200 daPa
What frequency is the starting probe tone usually?
220 or 226 Hz
What is known by maximum compliance in a Tympanogram?
The level at which the ear drum is operating at maximal capacity
What are the axis labels on a Tympanogram?
X is pressure (decaPascals - daPa)
Y is compliance / impedance (ml of water)
What is it important to note regarding magnitude of greatest compliance on a Tympanogram?
The pressure at which this is achieved
What does a Jerger Type A Tympanogram represent?
Normal hearing
What is range of greatest compliance in normal hearing?
Minus 100 to Plus 50 daPa
What is the normal range of compliance?
0.3 to 1.5 ml of water
What does a Jerger Type As represent?
A stiffened middle ear system
What are the characteristics of a stiffened middle ear system (Jerger Type As)?
Normal middle ear pressure (middle ear pressure equal to ear canal) BUT low compliance
What are some of the causes of a stiffened middle ear system (Jerger Type As)?
Otosclerosis
Transitional OME
What does a Jerger Type As Tympanogram look like?
A flatter line - within normal range for pressure (daPa) but a lower level of compliance (ml)
What does a Jerger Type Ad represent?
A hypermobile Tympanic Membrane
What are the characteristics of a hypermobile Tympanic Membrane (Jerger Type Ad)?
Normal middle ear pressure (middle ear pressure equal to ear canal) BUT high compliance
What are some of the causes of a stiffened middle ear system (Jerger Type Ad)?
- Ossicular separation
- Scarred or thinned Tympanic Membrane (from several burst ear drums / recurring infections)
What does a Jerger Type Ad Tympanogram look like?
A pointier line - within normal range for pressure (daPa) but a high peak for level of compliance (ml)
What does a Jerger Type B represent?
Middle ear effusion
What are the characteristics of middle ear effusion (Jerger Type B)?
No point of greatest compliance!
What are some of the causes of middle ear effusion (Jerger Type B)?
Wax / liquid in middle ear
What does a Jerger Type B Tympanogram look like?
Low flat line - outside of normal pressure limits (daPa) and no point of greatest compliance (ml)
What type of Tympanogram is common in the elderly?
Tympanogram Type B
Why is the line relatively flat for middle ear effusion (Tympanogram Type B)?
Wax / liquid is stopping equalisation
What does a Jerger Type C Tympanogram represent?
Negative pressure in the middle ear / Eustachian Tube dysfunction
What are some of the causes of Eustachian Tube Dysfunction (Jerger Type C)?
Disease of the middle ear
What does a Jerger Type C Tympanogram look like?
Compliance (ml) peak within normal limits, but peak towards start of the X axis as pressure (daPa) is low
What is the most common middle ear pathology?
OME - Otitis Media with Effusion
What is meant by normal Eustachian Tube function?
The Eustachian Tube is closed 95% of the time
- Equalises pressure between the middle and outer ear
Why is pressure equalisation between the middle and outer ear important?
For the efficient transfer of sound vibrations
When does the Eustachian Tube open when functioning normally?
Yawning or swallowing
What are the stages of OME?
- Negative middle ear pressure
- Ear drum retraction
- Effusion of sterile fluid (as no refreshing of the middle ear)
- Fluid is watery at first, then becomes thickened
What is serous OME?
When the fluid in the middle ear is watery
What is secretary OME?
When the fluid in the middle ear is thickened
What is the Acoustic Reflex?
Reflex contraction of the stapedial muscle in response to loud sounds
What happens to the Acoustic Reflex over time if exposed to loud sounds?
It weakens and decays quickly
Where is the neural network for the reflex arc located?
The lower brainstem
What is meant by an ipsilateral pathway?
When a sound is made in one ear and measured in the same ear (no cross over)
Why can the Acoustic Reflex not protect the cochlea from loud impulse sounds?
It is too slow
How is the Acoustic Reflex measured?
Indirectly - measuring slight changes in stiffness of the ear drum caused by the contraction of the middle ear muscles
What is meant by Reflex Decay?
If the stapedius muscle does not maintain contraction during an above reflex threshold stimulus
What can Reflex Decay be indicative of?
Retro-cochlear disorder
What is meant by Reflex Latency?
The time difference between stimulus and response
When does Reflex Latency decrease?
With increased intensity of stimulus
What is the Acoustic Reflex Threshold?
The quietest sound level at which an acoustic reflex can be obtained (dBHL)
What is the normal range for the Acoustic Reflex Threshold?
80 - 85 dBHL
What is the procedure for measuring ART?
- Silence
- Use impedance measuring equipment
- Stimulus is a moderate to high intensity tone (must be audible to testee)
- Look for a decrease in Tympanic Membrane compliance in same/opposite ear
- Raise tone level until response seen
What will happen to the ART if there is a pathology at any point on the reflex pathway?
It will be raised or absent
What do ART results tell us?
The location of the pathology and an estimation of the patient’s dynamic range
What will the ART results be for sensori-neural hearing loss that is greater than 80 dBHL?
The ART results will be absent
What will the ART results be for sensori-neural hearing loss less than 50 dBHL?
Normal (80 -85 dBHL)
When is loudness recruitment likely to be present?
When the threshold of hearing and the ART differ by less than 60dB
What is a common feature of sensori-neural hearing loss?
A reduced dynamic range
Why can ART often not be measured in conductive hearing loss?
Because of middle ear impedance (e.g. glue ear)