Otoacoustic Emissions Flashcards
Who first demonstrated OAEs in an experimental context?
British physicist David Kemp, in 1978
What are OAEs?
the sounds measured in the ear canal that represent the movement of the OHCs in the cochlea
The energy produced by the movement of the OHCs serves as a what?
a cochlear amplifier, which contributes to better hearing (sharper fx resolution)
What do OAEs allow AuDs to do clinically?
- early detection of inner ear abnormalities of various etiologies, including non-pathologic ones like noise exposure and aging
- can sometimes prevent serious consequences of hearing loss
OAEs can be described as … because?
pre-neural; their activity occurs before the very first synapse in the afferent auditory system
How do OAEs present in individuals with no auditory nerves, severed nerves, or improper neurotransmitters?
- they can be normal
What are the 4 types of OAEs?
- spontaneous
- transient
- distortion product
- sustained frequency
Spontaneous OAEs
sounds emitting from the OHCs without an acoustic stimulus
Transient (evoked) OAEs
- sounds emitted from the OHCs in response to a stimulus of very short/brief duration (usually clicks, sometimes tone bursts)
- presented at 80 dB SPL
- generally recorded at 500-4000 Hz
Distortion product OAEs
- sounds emitted from the OHCs in response to 2 simultaneous pure tones (f1, f2) of different frequencies
- stimuli presented at 55 and 65 dB SPL
- typically recorded from 500-8000 Hz, sometimes even higher
Sustained frequency OAEs
sounds emitted from the OHCs in response to a continuous tone
Which types of OAEs are mostly used in clinical settings?
- distortion product
- transient evoked
In what settings are sustained frequency OAEs typically used?
for research
What types of OAEs can be measured clinically with FDA-approved equipment?
- distortion product
- transient evoked
What type of HL can transient OAEs detect?
- mild HL
- faster to administer, so it’s popular for screening babies
What type of HL can distortion product OAEs detect?
moderate or higher HL
What are 2 other conditions that can be indicated by absent OAEs in the lower frequencies?
- middle ear infections
- Ménière’s disease
What are some advantages of OAEs?
- don’t require behavioral responses, so it’s good for babies, infants, and younglings
- good for nontraditional testing due to factors like language, cognitive function, motivation, and attention
What is the advantage of OAEs involving specificity?
- OAEs are ear specific, unlike free-field behavioral responses
Do OAEs require a sound-treated room?
NO, and they’re portable too! An averaging process reduces background noise, and the ear is tightly sealed with a probe.
OAEs are also advantageous for using with kids because?
they are super quick; about 30-45 seconds per ear is common. Also pretty inexpensive as a screening tool!
What are some disadvantages of OAEs?
- susceptible to noise; more sound = more difficult to record
- ME status is important!! any dysfunction in the ME can stifle the OAE response
- we only get info about the hair cells, nothing else
Smaller ear canals result in a what?
higher effective SPL
Recording Parameters for Spontaneous OAEs
- measured in narrow frequency bands (< 30 Hz bandwidth)
- no stimulus needed
- multiple recordings should be made for replicability and to distinguish responses from the noise floor
- usually span the 500-7000 Hz range
Recording Parameters for Transient OAEs
- clicks are the most common stimuli, but can be tone bursts too
- typically presented at 80-85 dB SPL
- stimulation rate is <60 stimuli/second
- generally recorded over approximately 20 msec
Recording Parameters for Distortion Product OAEs
- stimuli = 2 pure tones at 2 frequencies (f1, f2; f2>f1) and 2 intensities (L1, L2)
- relationship between L1L2 and f1f2 dictates the frequency response
- for optimal response, set intensities so that L1 equals or exceeds L2
- intensity typically set at 65/55 dB SPL L1/L2
What are the prereqs for obtaining OAEs?
- unobstructed ear canal
- proper seal with the probe
- optimal positioning of the probe
- no ME pathology
- quiet, still patient
- relatively quiet recording environment
What is the general OAE procedure?
- non-invasive and simple to record, only requiring a few minutes to record
- sedation not indicated, even for children
- no behavioral response required
- soft probe tip is inserted into the external ear canal
- mini speaking within the probe generates the stimulus at a moderate intensity level
How can OAE test protocol be modified?
there are specific protocols for different clinical settings (diagnostics vs screening vs ototoxicity monitoring)
What are some important things to remember about the probe fit for OAEs?
- deep probe insertion essential
- there’s an inverse relationship between canal volume and OAE stim/response
- a good fit helps reduce external noise
What should be remembered about selecting an eartip for recording OAEs?
- maximum OAE amplitudes are achieved with a deeply sealed eartip
- shallow placement of the eartip in the ear canal reduces both the stimuli level and the measured level of the emission
What can verify a deep insertion of the ear tip?
2-3 mm of the tip should be visible
What are some non pathological problems that can cause OAEs to be absent?
- poor probe tip placement/poor
- cerumen occlusion of canal, or it’s blocking the probe
- debris and foreign objects in the ear canal
- vernix in neonates (common after birth)
- uncooperative patient(s)
What are some pathologic problems that can cause the absence of OAEs?
- outer ear stenosis
- external otitis
- abnormal ME pressure
- TM = perforation; PE tubes don’t necessarily prevent good recordings
- ME otosclerosis
- ME disarticulation
- cholesteatoma
- cyst
- ototoxic medication or noise exposure (including music) = OAE changes may precede threshold changes in the conventional fx range
- any other cochlear pathology
What are some conditions that do NOT affect OAEs?
- CN VIII pathology (only affects OAEs if the cochlea is affected as well)
- central auditory disorder
What is an example of a CN VIII pathology that could affect OAEs?
- a vestibular schwannoma that impinges on the cochlear vascular supply
What are some conditions that elicit abnormal OAEs and normal behavioral thresholds?
- tinnitus: could have abnormal OAEs in the fx region of the tinnitus
- excessive noise exposure (may cause increase or decrease in amplitude)
- ototoxicity (can cause vestibular pathology)
What are some conditions that elicit normal OAEs and abnormal behavioral thresholds?
- functional HL
- attention deficits
- autism
- IHC damage, but normal OHCs (no human reports yet)
- auditory neuropathy (includes CANS dysfunction and CN VIII dysfunction)
What are the 3 general steps for OAE analysis?
- verify adequate measurement conditions
- determine whether repeatable OAEs are recorded
- the difference between OAE amplitude and noise floor should be > 6 dB SPL
How can you verify adequate measurement conditions?
- noise levels should be sufficiently low (typically less than 10 dB SPL)
- stimulus intensity levels should be close to the desired levels
How can we ensure we are obtaining repeatable, reliable OAE measurements?
the OAE amplitudes should exceed the noise level by 6 dB or more at the test frequencies
In approximately how many normal hearing individuals do spontaneous OAEs occur?
40-50% (about 30-60% are adults, and about 25-80% are babies)
In which individuals are spontaneous OAEs not typically observed?
those with hearing thresholds above 30 dB HL (thus, the absence of SOEAs is not necessarily abnormal)
Characteristics of spontaneous OAEs
- typically bilateral (typically more present in the right than left if unilateral)
- occur more often in females, across all ages
- usually not associated with tinnitus
- seldom used for clinical hearing screenings
What is the main purpose of transient OAEs?
- to screen infant hearing
- to validate behavioral/electrophysiologic auditory thresholds
- to assess cochlear function relative to the site of the lesion
Stimulus parameters for transient OAEs
- very short (transient) stimulus
- has limited fx specificity
The transient OAEs emanate from what?
very broad cochlear regions
What does the presence of a transient OAE in a fx band generally indicate?
that the cochlear sensitivity of that region is approximately 20-40 dB HL or better
Most clinicians use the presence of transient OAEs in particular octave bands as a suggestion of what?
that hearing sensitivity should be 30 dB HL or better, unless a functional or neural component is present
Recording Parameters for Transient OAEs
- usually uses a click stimulus that contains a broad fx range (also possible to use a tone burst, but they’re limited fx)
- can usually be measured between 1000 - 4000 Hz
When will transient OAEs most often be absent?
when a hearing loss is greater than 35 dB HL
When do Robinette, Cevette, & Probst indicate that transient OAEs are present 99% of the time?
when all pure-tone thresholds are better than 20 dB HL
When are transient OAEs ALWAYS absent?
when pure-tone thresholds are greater than 40 dB HL
In what scenario would transient OAEs be or not be present?
when pure-tone thresholds are 25-35 dB HL
What stimulus activates distortion product OAEs?
- 2 pure tones (f1, f2)
- f2>f1
What actually is a distortion product OAE?
it is a 3rd tone created in response to f1 and f2
What does the expression 2f1-f2 signify?
the largest distortion product that can be evoked by tonal stimulation in the human ear
What range do distortion product OAEs usually test?
1000-6000 Hz/500-8000Hz, sometimes even higher (varies with manufacturer)
Distortion product OAEs allow greater what?
frequency specificity; they can record at higher frequencies that transient OAEs
Distortion product OAEs can be useful for detection of what conditions?
- ototoxicity
- noise induced HL
When is the reliability of distortion product OAEs greatest?
above 1000 Hz
Which OAE protocols are using for infant hearing screenings?
distortion product and transient
Which OAE protocol is more established for assessing/predicting behavioral thresholds?
transient OAEs
Which OAE protocol usually represents the audiometric configuration of a cochlear hearing loss?
distortion product OAEs
Describe the clinical applications of OAEs.
- question/validate other threshold measures
- provide information about a lesion site
- screen hearing
- partially estimate hearing sensitivity within a limited range
- monitor for ototoxicity
- diagnostic assessment of tinnitus and auditory dysfunctions
- differentiate between the sensory and neural components of SNHL
- test for functional HL
Describe the clinical limitation of OAEs.
They can’t fully describe an individual’s auditory thresholds.
How are OAE screening outcomes described?
- as pass or fail
- pass = when OAEs are present (>6dB above the noise floor) for the majority of test frequencies
What should AuDs do for patients who have a refer outcome for their OAE screening?
they should be referred for a diagnostic assessment, and possible audiological/medical management
