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AUD fall 2019 electrophys I > Week 3 > Flashcards

Week 3 Flashcards

types of OAEs

1
Q

list the three physiological processes important for OAEs

A

1) the passive mechanics of the cochlea
2) the cochlear potentials
3) the active process of the cochlea= electromotility (main player of OAEs)

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2
Q

the passive mechanics of the cochlea explanation

A

there is a passive traveling wave which is frequency dependent
*does not travel along the basilar membrane but is caused by a pressure difference between cochlear partition, note that is there is a discontinuity of the BM, there is still a traveling wave beyond that point because of this

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3
Q

the cochlear potentials explained

A

basically the cochlea has a battery inside to create a current to send signals to the nerve
*endolymph and hair cells have a voltage difference of 150mv, this creates the voltage and current that goes through the hair cells

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4
Q

the active process of the cochlea explained

A
  • 2 mechanisms compliment each other
  • –1= stereocilia MET channels which are controlled by K+ and CA+2 current
  • –2= electromotility (prestin)
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5
Q

what are the two proposed hypotheses for how OAEs arrive to the ear canal

A

1) backward traveling wave= pressure change that propagates in reverse
2) acoustical compression wave=fluid compression wave

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6
Q

when do OAEs arrive to the ear canal

A

instantaneously after presentation of signal

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7
Q

what does research say is the correct hypothesis as to how OAEs get to the ear canal (as of now)

A

*compressional wave instead of backwards traveling wave

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8
Q

what are the 2 different ways to classify OAEs

A
  • stimulus based (more popular)

* mechanism based (newer)

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9
Q

break down of OAEs using the stimulus based classification

A
  • spontaneous
  • –no stimulus
  • –synchronizing stimulus (present signal, but then wait a bit before doing measurement)
  • Evoked
  • –TEOAE
  • –DPOAE
  • –SFOAE
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10
Q

spontaneous OAEs

A

(SOAEs)

  • no stimulus, just probe in ear and sit quiet and see what happens
  • prevalence increased from 40% -80% over time (equipment improvement)
  • infants have larger/stronger than adults
  • females have larger/stronger compared to males
  • –there is a hormonal component
  • amplitude is usually -15 to 0dB SPL, 800-4000Hz
  • presence is not related to hearing sensitivity, the number of SOAEs is a better indication and if people have them they normally have sharper tuning curves
  • ototoxicity and noise exposure could make them disappear
  • large SOAEs could result after cochlear damage
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11
Q

stimulus frequency OAEs (SFOAEs)

A
  • stimulus is pure tone and measure response associated with that pure tone
  • challenges are differentiating between the response and the stimulus itself
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12
Q

what are the two ways to measure SFOAEs

A

1) suppression
* you record at a moderate level (20dB SPL) and then at record with a suppressor at a high level neighboring frequency (60dB SPL), then subtract the two to get the OAE without the stimulus itself (vector subtraction)
2) compression
* you present at a low level (20dB SPL) and a high level (60 dB SPL). then scale down the 60 dB response by 100 times and subtract the 20 dB signal to remove the stimulus

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13
Q

Transient Evoked OAEs (TEOAEs)

A
  • stimulus is click at 80 microseconds

* looking at amplitude of response vs noise level at frequency bands

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14
Q

distortion product OAEs

A
  • use 2 frequency stimuli with specific relationship between frequencies
  • when you present 2 frequencies together, you get distortions
  • –the most common is the cubic difference tone which is 2F1-F2
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15
Q

what are the 3 mechanism based classifications of OAEs

A

1) reflection emissions
2) distortion emissions
3) mixed emissions
- –these are based on the reverse propagation theory

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16
Q

reflection emissions (place fixed)

A
  • are random reflections happening within the cochlea
  • there are irregular distributions of OHCs which don’t change place which is why they are place fixed
  • so traveling wave propagates and different OAEs are emitted at irregularities and reflected back to the ear canal
  • SOAEs are pure reflection (background and internal noise cause activation of BM which is random physiologic noise)
17
Q

distortion emissions (stimulus fixed)

A
  • distortions of the stimuli
  • also known as wave fixed
  • example is DPOAE, specifically basal product DPOAE
18
Q

mixed emissions

A
  • both reflection and distortion together
  • TEOAEs are mainly reflection but with distortion especially at lower levels
  • apical DPOAEs have a reflection component suppressed (using masking noise)
  • SFOAEs
19
Q

standards for OAE equipment

A
  • important to control for basic requirements
  • no ANSI standards
  • IEC (international electromechanic commission) 60645-6 (2009) guidelines for screening and diagnostic equipment
  • all equipment must be FDA approved
20
Q

hardware for OAEs

A
  • computer for generation, recording, analysis and display
  • 2 probes (many just one) for delivering stimulus
  • analog to digital converter allows computer to process signals
  • digital to analog converter allow computer to generate sound to ear (on per speaker/probe)
  • speaker drivers and mic preamplifier
21
Q

nyquist theorem

A

the sampling rate must be at least 2F the highest analog frequency component (all analog to digital converters should follow this)

22
Q

aliasing

A

when there are not enough samples of a signal to truly represent what is occurring

23
Q

system distortion of OAEs

A

happens at high levels

*use a 2cc coupler to measure OAE response at all levels

24
Q

cross talk with OAE equipment

A
  • can affect stimulus levels (and all stimulus levels)
  • manufacturer should report it on the spec sheet (20dB or lower)
  • ER-7 mic used in OAE probes: 40 dB below 5kHz and 20dB b/t 5-10 kHz
  • current clinical systems are safe up to 8 kHz
25
Q

checking the probe fit with OAEs

A
  • broadband signal is played and what happens in the ear is measured
  • can tell if there is a leak or probe block based off what happens in the ear canal
26
Q

sound level meter of OAEs

A
  • measures ambient noise

* records only when low ambient noise is present

27
Q

automatic leveling of sound intensity with OAEs

A

uses mic to measure stimulus levels and identify errors

28
Q

the stopping rule with OAEs

A
  • have ability to set to a particular OAE level
  • can set to stop at a particular noise level
  • can set to stop at a particular SNR (noise floor)
  • can set to stop at a particular recording time
29
Q

artifact rejection with OAEs

A
  • uses a high pass filter for frequency response
  • very loud signals are identified as artifact and rejected
  • averaging responses in 2 buffers and compares them
30
Q

output calibration of OAEs in a coupler or ear simulator

A
  • zwislocki or IEC 711 ear simulator
  • must be done every measurement
  • present sound and measure from mic at the end of the coupler
  • limitations:
  • –structure of the ear
  • –fit
  • –insertion
31
Q

output calibration in the ear

A
  • pros= based on the pt’s own ear
  • measurement: mic level (probe) as opposed to the TM level which can cause problems with standing waves
  • signal is presented and measurements made
  • -incident and reflected waves
  • -L=wavelength/4 and odd harmonics
  • -<3000Hz in okay, standing waves can occur above this frequency and are dependent on the depth of insertion
  • —-deeper makes smaller cavity so standing waves at higher frequnecies
  • system correction for intensity can cause a problem so need to insert probe as deep as possible
32
Q

the future of calibration for OAEs

A
  • power/intensity calibration
  • –not clinical yet except in reflectance measures
  • remember:
  • –pressure= force applied over an area (compressions and rarefactions) Pa
  • –power= work done over time over an area w/m(squared)

AUD fall 2019 electrophys I (11 decks)

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