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Hearing disorders (Exam 1)

Terms in this set (148)

How often a vibration repeats itself is known as
frequency and expressed in hertz
psychoacoustic correlate is
pitch
higher frequencies have blank wavelengths
shorter
lower frequencies have blank wavelengths
longer
an increase of an octave is a doubling of
frequency
speech sounds are perceived as louder than pure tones at the
same intensity level
low frequency sounds are
bass
when stiffness is introduced to a system, low frequencies are
dampened (reduced)
hearing disorders that stiffen the system cause a hearing loss for
low frequencies
problems that stiffen the ear system cause more hearing loss in the
lower frequencies
problems that introduce more mass in the system are called "mass weighting" and
affect all frequencies
Much of the loudness in speech is carried in the
bass components
clarity is mainly in the
treble components (consonants)
Talking louder doesn't make it
clearer
Amplitude describes the
intensity of sound
psychoacoustic correlate is
loudness
Decibel is the
measurement scale for intensity/amplitude
Intensity on audiograms is expressed in dB HL to "flatten" the
dB SPL curve
dB A scale to measure
sound exposure risks
dB A is used with
sound level meters in sound field
dB scales reflects human
sound sensitivity
Inverse square law has huge impact on
speech intelligibility
the farther you are from the speech source the
softer the speech
The important high frequency speech sounds are less intense at the
source
Speech audibility is synonymous with
speech to noise ratio
Signal to noise ratio is the ratio of the intensity of the desired signal to the
background noise
How to find signal to noise ratio
subtract the dB level of the noise from the dB level of the signal
Children require as much as +20 dB S/N to
sustain intelligibility and maintain attention
Ways to improve signal to noise ratio
-preferential seating
-sound field systems
Outer ear collects and funnels sound through the
auditory system
Resonant frequency of the combination of pinna and external auditory canal is approximately
2.7 kHz
Meatus:
opening
Distal:
away from the center
Proximal:
toward the center
Peripheral:
a part that is not central
end organ:
the outer organ as opposed to neural pathways or the central nervous system (eye, cochlea, vestibular system)
Middle ear concepts:
1. Transduces acoustic energy into mechanical energy
2. Overcomes the impedance mismatch between air and liquid
3. Amplifies sound due to
a) the area differences between the TM and the oval window
b) The curved shape of the TM
c) The lever advantage function of the ossicles and their joints
4. Equalizes middle ear pressure
Inner ear concepts:
- AKA bony labyrinth, a membraneous labyrinth is suspended inside the bony labyrinth
- Tranduces mechanical energy into hydromechanical (hydraulic) and then neural/electrical energy
- Tonotopic arrangement- high frequencies processed at the base, low frequencies at the apex
The bony labyrinth contains both the
cochlea and the vestibular (balance) organs
Outer hair cells (OHCs)
mainly efferent
Inner hair cells
mainly afferent
Tonotopic arrangement continues all the way to the
cerebral cortex
Audiogram key symbols
- AC (unmasked) circle (right) X (left)
- AC (masked) triangle (right) square (left)
- BC (unmasked) < (right) > (left)
- BC (masked) [ (right) ] (left)
- No response (on any symbol) arrow to the left down (right) arrow to the right down (left)
- Sound-field (non ear specific) S
Threshold is the
lowest intensity level a person reliably responds 50% of the time
3 frequency pure tone average of 500, 1,000, and 2,000 Hz should correlate with
speech recognition/reception threshold (SRT)
Pure tone average is very important in order to consider
an audiogram to be valid
Interaural attenuation of bone conduction is
0 dB
Bone conduction (unmasked) testing yields the thresholds from the
best hearing cochlea not the ear closest to the bone oscillator
Bone conduction transducers have a more limited output than
air conduction transducers
Bone conduction tests only go up to 4,000 Hz and to about 80 dBHL; Air conduction tests have
wider ranges for both frequency and intensity
Vibro-tactile responses
occur mostly at lower frequencies (250-500 Hz)
Conductive hearing loss (CHL)
hearing is reduced due to a problem in the outer of the middle ear but the inner ear functions normally
Sensorineural hearing loss (SNHL)
hearing is reduced due to a problem in the inner ear but the outer and the middle ear function normally
Mixed hearing loss
hearing is reduced due to a problem in both the outer and or the middle ear AND the inner ear
Sensorineural
- air and bone are the same or are very close
- no air/bone gap
Conductive
- bone is completely normal, air conduction is not normal
- air/bone gap
Mixed
- bone conduction is not normal and air conduction is worse than bone
- air/bone gap
The term "rule out" means
that the disorder is not present
audiologists scope of practice:
-remember we determine site of lesion but not medical diagnoses
- must refer any potentially treatable conditions to physicians/ENT
- newly diagnoses kids with hearing loss must be referred to ENT
Things that aren't in the audiology scope of practice
- diagnosing disease
- medical or surgical treatment
- ordering imaging such as MRI
- recommending or providing medication
- recommending surgery
Hearing aids:
DO NOT fit hearing aids on patients with potentially treatable diseases like Meniere's disease or with conductive or mixed losses without ENT clearance (don't offer a wavier)
Case history:
- "admits" means that the patient was asked a specific question and he/she answered in the affirmative
- "denies" means that the patient was asked a specific question and he/she answered in the negative
- "reports" means that the patient offered the information freely
SOAP
- subjective (statement of problem)
- objective (observations)
- assessment (summary of results)
- plan (recommendations)
Screening is
pass/fail
Screening is NOT
diagnostic and it does not yield threshold values
Reliable
if the person was tested numerous times and by different people a similar result would be obtained
Valid
The test is appropriate for what you are trying to measure
Four possible outcomes of a screening
1. True positive (hit)
2. True negative
3. False postive
4. False negative
Sensitivity
How well the screening identifies those with the disorder
Specificity
How well a screening will filter out those that don't have the disorder
Newborn screening is done via
ABR and/or OAE prior to baby leaving the hospital
JCIH "1-3-6" rule
- Screening by 1 month of age
- Diagnosis of hearing loss by 3 months of age
- Entry into early intervention services by 6 months of age
Houghson-Westlake procedure
- Present tone for approximately 2 seconds
- May use pulsed tones, especially for patients with tinnitus
- Vary timing to avoid rhythm
- No visual cues
- No coaching
- When you get a response, drop 10 dB
- No response, raise 5 dB
- Threshold is 2 out of 3 responses at the same level in ascending trials
False positives
patient responds when no sound is present (tinnitus, highly anxious kids
False negative
Patient does not respond even when a sound is audible (malingerer, someone who doesn't understand task like dementia its or kids)
Masking is when we put the noise into the
non test ear
Pure tones use
narrowband noise
Speech uses
speech noise
Why mask?
because there are times when we deliver a sound to the test ear, but the non-test ear hears it. This is called crossover, or cross hearing. We want to know that we are testing the ear we intend to test, therefore we mask
How much the non-test ear hears depends on
inter-aural attenuation (IA)
Every transducer has its own IA
- bone = 0dB
- headphones = 40dB
- Inserts = 55dB
Cross hearing or crossover occurs whenever a stimulus exceeds the
IA
We mask for bone conduction and air conduction for
pure tones and for air conduction for speech
Interaural attenuation of bone conduction =
0dB
Regardless of where you place the bone oscillator on the head,
the better hearing cochlea will always respond
We mask less often for air conduction testing than for bone conduction testing because
it takes more energy for cross hearing to occur
With sufficient intensity of an air conduction stimulus the resulting vibration of the earphone will be
transferred to the skull and will travel to the non-test ear
Headphones sit against bone whereas inserts sit against
cartilage
The inter-aural attenuation for air conduction depends on the type of ear phone (or transducer)
- supra-aural headphones = 40dB
- Inserts = 55dB
With a bilateral conductive loss, sometimes you need so much masking that you
cannot get a valid threshold
The masking is so intense that it crosses over and
artificially raises the level of the test ear threshold (over-masking)
Absence of a shadow curve is a red flag for
functional hearing loss
Benefits of speech testing
- results correspond with patient complaints
- helps predict/validate pure tones
- helps predict hearing aid success
- hard to test populations (sometimes the only measure you can get)
Two basic categories of speech testing
1. Threshold measures
2. Supra-threshold measures
Speech recognition threshold or speech reception threshold (SRT)
The level at which a patient can understand words and respond with 50% accuracy
Spondees
2 syllable compound words
Uses easy words in a
closed set
SRT should be consistent with the
PTA; if not, suspect functional/nonorganic loss
MCL
Most comfortable loudness level
UCL
Uncomfortable loudness level
Dynamic range
The amount of useable hearing
How to determine dynamic range
Subtract the threshold from the UCL
People with hearing loss sometimes have reduced dynamic ranges compared to people with
normal hearing
PB max is the highest word recognition score a patient obtains with notation of the intensity level at which
it is reached
normal/conductive hearing loss word recognition scores generally very good
>90%
With conductive hearing loss WRS is usually
very good
The higher the SNR the
easier it is to understand speech
MRL
minimum response level
When deciding which test method to use, consider the developmental age, not the
chronological age of the child
Infants < 6 months
Physiological measures (ABR/OAE) are the only measures that can be trusted at this age because behavioral responses are NOT reliable
Babies 6 months- 2 years
Visually reinforcement audiometry (VRA): usually performed in soundfield does NOT provide ear specificity
2.5-4 years
Speech testing is often done first (before pure tones) more cooperative kids can use SRT like adults
Physiological tests are NOT
test of hearing
The best practice for both threshold determination and for showing that hearing has occurred is normally
behavioral audiometry
Otoacoustic emissions (OAEs)
Emissions originate in the outer hair cell of the cochlea (in a normal functioning ear) and the emissions travel outward through the middle ear bones and into the ear canal
The presence of OAEs rules out anything worse than a
mild hearing loss
OAE's are great for
nonorganic loss
OAE's are NOT neural signals that are
Acoustic signals (sound) that emanate from the hair cells
Challenges of OAEs
- patient must be still, quiet and the test room must be relatively quit
- if emissions are absent, it does not tell you the degree of hearing loss
- will be absent with middle ear disorders
A "neurologic" ABR is used to rule out
tumors
A "threshold" ABR is used to make an estimate of the degree of
hearing loss
ABR test
must be still and quiet, after 3 months generally have to test under sedation
Automated ABR is a screening but sedated ABR is
NOT a screening; its diagnostic
Advantages of ABR
-Can get auditory information on all different hearing levels to diagnose hearing loss
-Often can get enough information to move forward with treatment plan
Tympanograms can reveal
-fluid behind the eardrum
- TM perforation
- Negative pressure behind the eardrum
- The type but not the severity of hearing loss
It is best to do immittance testing before
audiometry
When to defer tympanometry
- with a fearful child wait until after you get other results
- if there is drainage in the ear canal
- if the patient reports pain, dizziness or nausea
The "tip" of the tympanogram is
the pressure at which the tympanic membrane/middle ear system is the most compliant
Type A tympanogram
Normal
Type As
- stiff system
- shallow peak
- may indicate otosclerosis
Type Ad
- hypermobile
- may indicate ossicular discontinuity
Type C
- negative pressure
- indicates Eustachian tube dysfunction (ETD)
Type B
- flat tympanogram
- usually suggests fluid behind the eardrum
- almost always have some conductive hearing loss
The acoustic reflex will be absent if there is a
conductive or mixed hearing loss
The presence of a reflex does not rule out
SNHL
Audiometric thresholds cannot be estimated from
acoustic reflex thresholds
Acoustic reflexes help us assess
- CN VIII (auditory nerve) lesions
- CN VII (facial nerve) lesions
- brainstem lesions
positive reflex decay =
- potential tumor
- positive reflex decay is a red flag for retrocohlear disorder such as an acoustic tumor
ABR is not
a test of hearing
OAEs will be absent with
middle ear conductive hearing loss
differential diagnosis
the goal is to efficiently narrow down to a "short list" the possible etiologies or causes for the patient's signs and symptoms
Why a test battery?
- make efficient use of time and resources
- zero in on relevant tests
- hard to test patients, limited window of cooperation
Intact OAEs rule out
conductive hearing loss and rule out SNHL greater than approximately 40 dB HL
Afferent arc
from CNVIII, the auditory nerve
Efferent arc
from CNVII, the facial nerve
Acoustic reflex
the contraction of the stapedius muscle elicited by the presentation of an acoustically loud sound. When either ear is presented with a loud sound, the stapedius muscles on both sides contract.
Cross hearing
you wear hearing aids on both ears, even though you can't hear in one of them. The sound detected by the aid on the "bad ear" is transmitted directly to the aid on the "good ear" side. This gets rid of the "head shadow" effect
Shadow curve
The audiogram recorded in instances of monaural deafness when the receiver is placed at the deaf ear is called the "shadow curve." Apparent hearing with the deaf ear is called "shadow hearing."
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