Chapter 6: Physiological Tests of the Auditory System Flashcards
Immittance
term to describe the measurements made of the tympanic membrane impedance, compliance, or admittance
Acoustic Immittance
Can indirectly determine middle ear function based on tympanic membrane measurements
Measurements of Acoustic Immittance Meters
Static acoustic compliance, tympanometry, acoustic reflex
Contributors to Impedance
The impedance of any object is determined by its frictional resistance, mass, and stiffness
Resistance in the ear
determined primarily by the ligaments that support the three bones in the middle-ear cavity
Mass in the ear
determined primarily by the weight of these three bones and the weight of the tympanic membrane
Stiffness in the ear
determined primarily by the load of fluid pressure from the inner ear on the base of the stapes, the most medial bone of the middle ear
Equipment
-Three rubber tubes attached to a metal ear probe
-Miniature loud-speaker: emits a pure tone (typically at 220 or 226 Hertz)
-Tiny microphone: picks up the sound in the external ear canal
-Air pump: creates either positive or negative air pressure within the canal
-A plastic or rubber cuff of an appropriate size is placed around the probe to attain an hermetic (air tight) seal
Static Acoustic Compliance
Compliance is comprised of two automatic measures that can tell the equivalent volume of the external ear canal and the mobility (compliance) of the tympanic membrane (T M).
Measure 1 of SAC
The immittance meter takes a first reading c1 with the TM mobility decreased due to the positive pressure (+200 daPa) introduced into the ear canal
Measure 2 of SAC
The second measure (determination of c2) is attained when the pressure in the external ear canal is decreased until the T M achieves maximum compliance (equal pressure on both sides)
High c1 readings in SAC
Indicative of a TM perforation or presence of a patent (open) ventilation tube.
What does c1 represent
compliance of the middle ear and reflects the equivalent volume of the external ear canal in cubic centimeters
What does C2 represent in SAC
The compliance of the outer ear and middle ear combined
What does cx represent in SAC
Middle ear compliance
Very low middle ear compliance
suggests a change in the stiffness, mass, or resistance of the middle ear system as may be seen with fluid accumulation in the middle-ear space
Very high middle ear compliance
suggests abnormal elasticity of the TM or a disruption in the normal connections of the middle-ear bones
Tympanometry
Measurement of middle-ear pressure, determined by the mobility (compliance) of the T M as a function of various amounts of positive and negative air pressure in the external ear canal
Type A Tympanogram
normal middle-ear function
Peak pressure near 0 daPa
Type As Tympanogram
Shallow peak compliance, but normal middle ear pressure
Characteristic of stiffness of the middle-ear system
Type Ad Tympanogram
High amplitude of curve
Normal peak pressure
Potential separation of middle-ear bones or tympanic membrane flaccidity
Type B Tympanogram
No peak pressure or compliance reading
Tympanogram looks flat
Potential fluid in middle ear space, ear wax occlusion, or hole in the TM
Type C Tympanogram
Peak pressure below negative 200 daPa
Reflection of negative pressure in the middle-ear cavity
Acoustic Reflex
-Stapedius muscle contracts reflexively and bilaterally in response to an intense sound presented to either ear
-Causes tympanic membrane to stiffen and decrease in compliance
Acoustic Reflex Threshold
the lowest level at which an acoustic reflex can be obtained
Acoustic reflex threshold for normal hearing
bilateral reflexes 85-100dB
Acoustic Reflex Decay
-A test to see how well the muscles hold on to the contraction produced by the loud stimulus
-Positive decay is bad
Ipsilateral
Same side
Contralateral
opposite side
Otoacoustic Emissions (OAEs)
The normal cochlea’s production of a sound response immediately following stimulation. Reflect activity of the outer hair cells
Spontaneous Otoacoustic Emissions (SOAEs)
Occur when a cochlea produces sounds in the absence of external stimulation
Occur in over half of the population of normal hearing individuals
Transient Evoked Otoacoustic Emissions (TEAOEs)
-More of a screening approach.
-Broadband clicks
-Present in individuals with hearing thresholds less than 40 dB
Distortion-Product Otoacoustic Emissions (DPOAEs)
-Favored approach because it is more frequency specific.
-More diagnostic in it’s approach.
-Tone
-Present in individuals with hearing thresholds less than 40 dB to 50dB
What does the presence of an EOAE suggest
-very little or no conductive hearing loss caused by middle ear abnormality
-the responding frequency regions of the cochlea are normal or exhibit no more than mild hearing loss
EOAE present in sensory/neural hearing loss suggests
outer hair cell function is intact and the locus of the disorder is known to be retrocochlear
Absent EOAEs in sensory/neural hearing loss suggests
Confirm cochlear pathology but do not rule out the possibility of concomitant retrocochlear involvement.
Auditory Evoked Potentials (AEPs)
analyze the electric activity of the brain when stimulated by acoustic stimuli
AEP Tests
ECoG: Electrocochleography
ABR: Auditory brain-stem response
AMLR: Auditory middle latency response
ALR: Auditory late response
Electrocochleography (ECoG)
The procedure of measuring electrical responses from the cochlea of the inner ear
Auditory Brain Stem Response (ABR)
-The procedure of analyzing the integrity of the auditory brain-stem pathway using broadband clicks, tone pips, or bursts
-Analyze wave V (5). Sound is heard if wave five is present.
Auditory Steady State Response (ASSR)
-AEP used for threshold determination for children.
-Evokes a steady state neural response
Auditory Middle Latency Response (AMLR)
-Assesses middle latency responses, which occur between 15 and 60 milliseconds after signal presentation
Auditory Late Responses (ALRs)
-Assesses the late cortical auditory-evoked potential, which includes responses that appear at least 60 milliseconds after signal presentation
