2. The Functions of
Immittance Audiometry
Detection of middle ear pathology
Differentiating cochlear from retrocochlear pathology
Estimate sensitivity of hearing loss
Cross referencable with pure tone results
The Role of Immittance Audiometry in
Detecting Middle Ear Disease
John T. Jacobson
3. Acoustic immitance
◦ Impedance:
◦ Resistance to the flow of acoustic energy
◦ Useful diagnostic tool to detect presence of
fluid in the middle ear, evaluate EU tube
function, help evaluate the facial nerve and
help predict audiometry
Admittance
◦ Ease of which acoustic energy flows
Immitance is a term derived from the terms for two inversely related
processes for assessing middle ear function
◦ Impedance
◦ Admittance
6. Instrumentation
Major components
Probe tone oscillator and
loudspeaker
Monitor microphone
Pressure pump and
manometer
Ipsilateral reflex oscillator
and loudspeaker
Probe tip
7. Auditory Immittance
“ A way of assessing the manner in which energy flows through the
outer and middle ear into the cochlea”
10. Static compliance
Measure of ear canal volume under two specific physical condition
200mH20 of positive air pressure is applied to ear canal and a volume is
read
Second volume reading occurs at a pressure value of maximum eardrum
compliance
Under normal mddle ear conditions, maximum eardrum compliance occurs
when atmospheric pressure is equal on both sides of TM (0mmH2O)
Two volumes are subrtracted from one another and remaining volume
represents the static compliance of the middle ear
Because wide variety of middle ear pathologies produce overlapping
compliance values, static compliance is least applicable measure of
immitance test battery.
11. Tympanometry
“A way of measuring how acoustic immittance of the middle ear
system changes as air pressure is varied in the external ear
canal”
12. Tympanometry
Yields information about
◦ Air pressure status of the middle ear
◦ Static acoustic immitance (establishing parameters of stiffness or flaccidity at
the ear drum)
◦ The integrity and mobility of the eardrum and ossicular chain
◦ Resonance point of the middle ear system
15. Impedance as Equivalent
Volume
When the amount of reflected probe tone pressure is
high, it’s as if the volume has decreased. As volume
increases, sound pressure decreases
16. What is a Normal
Tympanogram?
Shape
Pressure: -100 mm H2O or DaPa
Compliance: 0.3-1.6 cc
20. Common Tympanograms
Type B
No peak compliance
Little change in
compliance with various
pressures
Middle ear effusion,
total perforation, or
impacted wax
22. Common Tympanograms
Type C
Peak compliance in
negative ranges
often beyond -100db
Eustachian tube
dysfunction,
inadequate
ventilation of ME
23. Tympanometry in very young
children
0 – 6 months
High frequency probe required
1000Hz for babies younger than
3months
3 – 9 months, initially use 1000hz, if
fails repeat tone with 226hz probe
Tympanometry with 226 and 1000 Hertz tone
probes in infants 2012
Luciana Macedo de ResendeI
; Juliana dos Santos
FerreiraII
; Sirley Alves da Silva CarvalhoIII
;
Isamara Simas OliveiraIV
; Iara Barreto BassiV
25. ASR
Defined as the lowest intensity required to elicit a stapedial muscle
contraction
Neural connection located in lower brainstem, with influences of higher
CNS structures on the reflex via the olivocochlear bundle
Afferent portion of the reflex is the ipsilateral eight nerve to cochlear
nuclei
Efferent limb is the facial nerve which innervates stapedial muscle
Contraction of the stapedial muscle tilts the anterior stapes away from
the oval window and stiffens the ossicular chain and results in
increased impedence, which is measured as small decrease in
compliance by the ear canal probe
26. ASR
3 primary acoustic reflexes characteristics commonly evaluated
◦ 1. presence or absence of the stapedial reflex
◦ 2.acoustic reflex threshold
◦ 3 acoustic reflex decay or adaptation
The time delay of acoustic reflex is thought to be 10ms
Acoustic reflex thresholds for tones in patients with normal hearing are usually
70 to 80 db above their tone thresholds and about 5db greater for the
contralateral threshold
27. The Middle Ear Muscles and
the Acoustic Reflex
Tensor tympani muscle
Stapedius muscle
32. Interpretation of an Absent
Acoustic Reflex Threshold
Possible pathologies that might lead to an absent
contralateral probe left reflex (right crossed)
33. CN VIII lesions
Demonstrate absent acoustic reflex when stimuli presented to affected
ear
Acoustic reflexes differ from cnVIII lesion versus cochlear lesion
◦ cnVIII refles will be absent or abnormal regardless of degree of hearing loss
◦ Cochlear lesion usually dependent on degree of hearing loss
Abnormal reflexes also recorded when stapedial muscle function is altered by
myopathic disease such as Myasthenia Gravis and Eaton – Lambert
syndrome or hyperthyroidism
Impedance properties of the middle ear are the result of complex interaction between the ossicular chain, the intra aural muscles and ligaments and atmospheric comdition within the middle ear space, all of which are reflected by the TM
Dynamic in nature, measuring compliance while introducing air pressure change in the external ear canal
Tympanometry reflects the mobility (compliance ) of tympanic membrane when air pressure is varied from 200 to -400dPa within the ear canal
Tympanometry may be considered analogous to pneumatic otoscopy, but with far greater precision
Tympanometry yields infor
Volume of ear canal ranges from 0.5 to 1ml for children
Type A. peak compliance between 0 and -100dpa, and within a normal range of compliance
Volume of calan ranges from 0.5 to 1mls for children and 0.6 to 2.0 for adults
Peak compliance between 0 and -100dpa, and within normal range of compliance
Peaks that are located within the normal pressure range may be overly compliant Ad with atrophic tympanic membrane or As with ossicular chain fixation or tympanosclerosis
As with ossicular chain fixation or tympanosclerosis
Ad with atrophic tympanic membrane
Volumes more than 1.0 for children and 2.0mls for adults may suggest tympanic membrane perforation or presence of patent ventilation tubes
Type C is often a precursor to type B as development of negative pressure precedes the presence of effusion
there may be a normal tympanometric curve when the 226 Hz probe is used, even in the presence of an air conduction component, which means that the tests carried out with this probe tone have a high rate of false-negative results.
Kiel et al, carvello et al,
In a normal ear void of middle ear pathology the reflex occurs at approximately 80 -90 db HTL
Even normal individuals may exhibit decay at higher frequencies, therefore lower frequency, 500 to 1000 Hz tones are used
If response decreases to less than half within 5 seconds retrocochlear pathology may be suspected
Acoustic reflex in ears with cochlear disorders is determined primarily by the degree of snhl. If auditory thresholds are below 50 – 55 db, reflex thresholds are normal
If auditory threshold are between 55 – 80 db, the reflex thresholds are elevated in proportion to auditory thresholds
If losses greater than 80 db acoustic reflexes absent
Acoustic reflex in ears with cochlear disorders is determined primarily by the degree of snhl. If auditory thresholds are below 50 – 55 db, reflex thresholds are normal
If auditory threshold are between 55 – 80 db, the reflex thresholds are elevated in proportion to auditory thresholds
If losses greater than 80 db acoustic reflexes absent
Normal acoustic reflex thresholds for broadband noise are approximately 20 – 25 db lower than reflex threshold for tones
Clinically important in evaluation of malingerers because it is not physiologically possible for the paritentto truly have behavioural thresholds that are higher or worse than acoustic reflex thresholds for tones
In patients with SNHL the difference between the broadband and tone thresholds is decreased inversely to that amount of hearing loss (degree of snhl in db increases, the diff in ac reflex thresholds for tones and noise decreases)
Efferent limb of reflex is absent in ossicular chain disorders, such as otosclerosis and discontinuity and facial nerve pathology
In vii paralysis, the acoustic reflex is absent or abn even when the probe is placed in ear ipsilateral to the lesion
Asr can also be helpful in locating cnvii lesion either proximal to or distal to stapedeal muscle
Acoustic reflex decay measures the ability of stapedial muscle to maintain sustained contraction, usually by presenting a signal 10db above the reflex threshold for 10s
Rapid decay found in cnVIII lesions