Audiology Testing & Principles Flashcards
Describe Interaural attenuation. What levels of attenuation can be achieved by bone conduction, headphones and insert ear phones?
Interaural attenuation: The reduction in sound intensity as it travels from one ear to the other. The degree of interaural attenuation varies depending on how sound is presented, and is used to determine when masking is needed.
Bone conduction: 0dB (all sound needs to be masked)
Over the head earphones: 35-50dB attenuated
Insert ehadphones: ~60-65dB attenuated
Greater interaural attenuation occurs at higher frequencies
Define crossover
Crossover occurs when a sound volume exceeds the interaural attenuation with a given test device and then crosses over from the test ear to the non-test ear
√What are five characteristics of the decibel scale?
- Non-linear
- Logarithmic scale
- Relative measure
- Incorporates a ratio
- Expressed with different reference levels
√What is masking?
Making is required when you would expect to experience crossover.
In order to ensure thresholds are from the test ear, a sound stimulus is presented to the non-test ear in order to overcome crossover. Narrow band noise used for pure tongues, and speech noise for speech signals.
This is ALWAYS REQUIRED FOR ANY BC TESTING because interaural attenutation with BC is 0.
Masking with air conduction varies depending on the type of headphone (supraaural or insert), the model, and the volume presented).
Masking signal to the non-test ear is via AC, and if crossover occurs, the sound is perceived on the non-test ear as BC.
Describe the general principles of when masking is required3.
What is the initial masking level?
When testing air conduction:
- AC masking is required if the test ear AC exceeds non-test ear BC by 40 (supra-aural) or 50 (inserts) dB. (AC TE - BC NTE = 40-50)
- Initial masking level = AC threshold of NTE + 5dB (minimal effective masking correction) + 10dB (safety factor)
When testing bone conduction:
- BC masking required if air-bone gap of test is ear >0 (some say 10dB) (AC TE - BC TE = 0-10)
- OR when BC of test ear exceeds non-test ear by 10dB (BC TE - BC NTE = 10)
What is the masking dilemma? How can this be over come?
Seen in patients with large bilateral conductive hearing loss, when enough masking it too much - when both AC thresholds approach the level of interaural attenuation (~40dB - bilateral air bone gaps 40-50). In these cases, the amount of masking needed to mask the test ear (which is high because of the conductive hearing loss) will exceed the interaural attenuation and then cross back over to the test ear. This will inadvertently mask the test signal, and the non-test ear can not be masked because any masking sound that will be loud enough to exceed the interaural attenuation will still cross over.
Can be mitigated with insert earphones (have a larger interaural attenuation). If CHL still exceeds this, then it will be marked as “could not mask”
Go through scenarios of masking and non-masking
Kevan’s notes page 14
√What is a decibel?
Bel = Unit of sound intensity relative to a reference intensity. Intensity is related to the perception of loudness
- Unit to express intensity of sound; Specifically, the logarithm of the ratio of two sound intensities. Decibel is One-tenth of a Bel
- Ratio may be power, sound pressure, voltage, or intensity
- For audiometry, the decibel refers to sound pressure
Bel = log10 (Is/Ir) - Sound intensity / Reference intensity (reference intensity dependent on the dB scale being used)
Decibel dB = 10Log10 (Is/Ir)
Intensity level - Magnitude of sound. Sound pressure (pascals) is proportional to the square root of intensity and therefore when substituting pressure into the formula it needs to be squared - dB = 10log10(Ps/Pr)^2 = 20log10(Ps/Pr)
Sound pressure dB = 20log (Ps/Pr)
Pr = sound pressure level at 20µPa
√How many times louder is 60dB vs. 0dB? What about 60dB vs. 40dB?
60 vs 0:
dB = 10 log10 (Is/Ir)
60=10log10(Is/Ir)
Is/Ir = 10^6 = 1 000 000 times louder
60 vs 40:
dB = 10 log10 (Is/Ir)
60-40=10log10(Is/Ir)
20=10log10(Is/Ir)
Is/Ir = 10^2 = 100 times louder
See Vancouver notes 224
√Define the following terms:
dB SPL
dB HL
dB nHL
dB SL
dB = 10log10 (Is/Ir) (sound intensity/reference intensity)
dB SPL = dB Sound Pressure Level
- Most common measure of sound
- Amount of sound pressure that is produced at a given frequency (pressure to move the TM), also a logarithmic ratio
- Values are all normalized against a reference sound pressure level (20microPascal, or 0.01mPa = 0dB)
- Used for tympanometry and stapedial reflexes
dB HL = dB Hearing Level
- Not all sound pressures are equally loud
- Human ear does not respond equally to all frequencies - much more sensitive to sounds in the frequency range about 1kHz to 7kHz than to very low or high frequency sounds
- Audiometric test tones are therefore specified as hearing level (HL) rather than SPL, because normal ear is not sensitive to the SPL ranges
- In dB HL, the baseline reference is calibrated to the threshold sound pressure that can be heard in normal patients with normal hearing at each frequency
- 0dB HL is least intensity for the average normal ear to perceive a specific frequency 50% of the time
- Image: Notice that low and high frequencies need higher sound pressure to be audible, while 1kHz to 7kHz is the most sensitive and have the least amount of pressure to create audible sound. These sound pressures can then be normalized and converted at each level to a hearing level.
dB nHL = dB Normal Hearing Level
- A decibel scale used in ABR measurement referenced to average behavioural threshold for the click stimulus of a small group of normal-hearing subjects
dB SL = dB Sensation Level
- Another way to refer to stimulus intensity. It’s reference (denominator) is the threshold (hearing level) of the individual being tested
- E.g. 30dBSL means 30dB above that individual’s threshold for the test stimulus. If the PTA is 30dB HL, then a stimulus presented at 70db HL = 40dB SL.
- dBSL will often be used to specify the level at which speech discrimination tests (SDT) are administered. For example, if an individual’s speech reception threshold (SRT) is 40dBHL, a SDT administered at 30dBSL is given at a hearing level of 70dBHL. If SRT was 10dBHL, the SDT would have to be given at 40dBHL to meet the condition of a 30dBSL presentation
- Each human has different pressure levels for the same frequencies. Therefore each frequency is mathematically normalized to a similar baseline of “0dB SPL”.
https://entokey.com/wp-content/uploads/2016/06/9781604063585_c001_f001.jpg
Audiology half day notes
What frequency do humans hear best at?
Between 500Hz - 4000Hz
√What is the reference level for SPL, HL, and SL?
SPL: Reference sound pressure level of 20 microPa
HL: Reference is the threshold sound pressure that can be heard in normal patients with normal hearing at each frequency
SL: Referenced against patient’s specific hearing thresholds (HL)
√How many decibels is required to double sound energy?
3dB IL or 6dB SPL
Describe the degrees of hearing loss with respect to dB level
Normal: 0-25dB
Mild: 25-40dB
Moderate: 40-55dB
Moderate-Severe: 55-70dB
Severe: 70-90dB
Profound: >90dB
Pediatrics - “slight hearing loss” - 15-25dB, as there are quieter cues that are important for speech and language development at this age
What are the symbols used on an audiogram?
Red
O
Triangle
<
[
Blue
X
Square
>
]
S
Down left arrow
Down right arrow
Right ear:
- RIGHT = RED = ROUND
- O = Unmasked air conduction
- Triangle = Masked air conduction
- < = Unmasked bone conduction
- [ = masked bone conduction
- Down left arrow = no response
Left ear:
- BLUE
- X = Unmasked air conduction
- Square = Masked air conduction
- > = unmasked bone conduction
- ] = masked bone conduction
- Down right arrow = no response
S = sound-field
Interpretation of tuning fork exam
Weber:
- Ipsilateral - CHL
- Contralateral - SNHL
Rinne:
- AC > BC = Normal
- BC > AC = SNHL
- BC (opposite ear) = SNHL ipsilateral
Why does Weber lateralize to the ipsilateral ear in CHL?
Mechanism not well understood, but generally 2 proposed mechanisms:
- Release from masking in the ear with the conductive loss (conductive loss masks the sound) - wounds from the surrounding world cannot mask the tuning fork tone, therefore still goes to the good ear
- Sound is not allowed to filter out through the ossicular chain/TM/EAC, therefore BC when doing Weber is perceived as louder in this ear
Discuss the Pure Tone test Procedure
Threshold of hearing is defined as 2 out of 3 (or 3 out of 5) correct responses during the ascending portion of the tone presentation.
If patient responds when tone is ascending, test will decrease level by 10dB.
Intensity increase will be in steps of 5dB, and decrease will be in steps of 10dB
What are the frequencies tested on Pure Tone Audiometry?
125Hz lowest
Octaves - 250, 500, 1000, 2000, 4000, 8000
1000 is the most important single frequency
Conventional speech ~65 dB SPL
Autophony ~85 dB SPL
Define Pure Tone Average (PTA)
Average of the pure tone thresholds at 500, 1000, and 2000 Hz
Note: Per Baileys, can also use 3000Hz but some centres that don’t use 3000 can include 2K and 4K into average
At what dB HL level are vibrotactile responses experienced at for air conduction and bone conduction?
Air Conduction
- 90dBHL @ 250Hz
- 110 dBHL @ 500 & 1000 Hz
Bone Conduction:
- 30-35dBHL @ 250Hz
- 55dBHL @ 500Hz
- 65-70dBHL @ 1000 Hz
What is 6 differential diagnosis of a flat hearing loss?
- Late Meniere’s
- Ototoxicity (macrolides)
- Otosyphillis
- Presbycusis (strial/metabolic & neural types)
- Sudden SNHL
- Vascular Loop (vascular compression of CNs)
“LOOPS” - Vascular Loop, then LOOPS mnemonic
What is 8 differential diagnosis for a sloping (high frequency) hearing loss?
- Sudden SNHL
- Ototoxicity (cisplatin, aminoglycosides)
- Vestibular Schwannoma
- Presbycusis (sensory & cochlear conductive types)
- Diabetes
- Herpes Zoster Oticus
- MS
- Vascular loop
What is 4 differential for reverse-sloping (rising, or low frequency) hearing loss?
- Early Meniere’s
- Otosclerosis
- SCDS
- Sudden SNHL
What id 3 differential of a cookie-bite hearing loss (mid-range hearing loss, U-shaped)?
- Hereditary
- Cochlear Otosclerosis
- Congenital Rubella
What is 2 differential for reverse-cookie bite (tenting) hearing loss?
- Meneire’s
- Cogan Syndrome (bilateral)
Define Speech Detection Threshold (SDT) vs. Speech Recognition Threshold (SRT)
SDT: The minimum sound threshold needed at which speech is discernable 50% of the time (can recognize presence of speech signal with spondee words). Patients not required to repeat the word back; used when patients don’t speech English or mentally handicapped and cannot repeat words back (not a routine test).
SRT: The minimum sound threshold at which at least 50% of words are understandable (have to repeat them back). Words are taken from a library of spondees (2 syllable words with equal stress on each syllable). Correlates to the PTA - agreement between PTA & SRT should be within 5-10dB HL
Define Spondee
Two syllable words with equal emphasis on both syllables, that are used to determine the speech recognition threshold.
E.g. Sunset, bookmark, baseball, earthquake
Define Speech/Word Discrimination Score (SDS/WDS) or Word Recognition Score (WRS)
Percentage of correct words identified from a phonetically balanced word list (a collection of words matching the phoneme distribution in the english language). Can be an open set (open response) or closed set (closed response - given possible options for each word like multiple choice)
Words are presented at 30-50dB above a patient’s SRT which should be easily audible.
Useful to determine functional ability to hear and understand speech. SDS + PTA should be > 100. If < 100, concern for retrocochlear pathology
E.g. 25 or 50 word library
Define Phonetically balanced word list
50 single syllable words which contains the same proportion of phonemes as that which occurs in connected american english discourse
Phoneme = phonetically distinct unit of sound in a language to distinguish words apart.
E.g. Boat, pool, mode, fat
What is involved in an entire audiologic test battery?
Hearing acuity - air conduction and bone conduction thresholds
Speech testing - SDT, SRT, Speech recognition, subjective report scales.
What is the minimum speech test battery (MSTB)?
Used for adult speech testing for CI Candidacy. Involves 3 tests:
- CNC Word Test (10 lists of 50 words)
- Administration of consonant-nucleus-consonant monosyllabic words (e.g. cat, dog, rat). - AzBio Sentences (8 lists of 20 sentences)
- Setences developed by the Arizona Biomedical Institute - BKB-SIN test
- Bamford-Kowal-Bench Speech-in-noise
- Test of hearing in noise function
What are immitance tests? What are two common types of immitance tests?
Immittance Tests: Measure of how readily the middle ear system can be set into vibration by a driving force
Immittance = admittance + impedance
Admittance - total energy flow through the system
Impedance - total opposition to energy flow or resistance to the absorption of energy
- Tympanometry: Measures acoustic immittance of the TM and middle ear ossicular chain as a function of air pressure variations in the ear canal. Estimates intratympanic pressure, ET function, TM integrity and mobility, and continuity of the ossicular chain.
- Stapedial Reflexes: Determines the softest level of sound that will elicit stapedial muscle contraction. Typically occurs at 70-100dB HL for normal hearing ear (ie. 70-100dB SL)
- Acoustic reflex Decay: Measures the ability of the stapedius muscle to maintain sustained contraction. A response is abnormal if its amplitude decreases to half or less of its original measurement over 5-10 seconds (time varies depending what you read)
What are the normal ear volumes for the EAC, middle ear, mastoid, bony labyrinth, membranous labyrinth?
EAC:
Children - 0.5-1mL
Adults - 0.6-2mL (N~1.4 cm^3)
Middle ear - 0.5-1cm^3
Mastoid - 2-20cm^3
Bony Labyrinth - 0.2cm^3
Membranous Labyrinth - 0.04cm^3
Describe the Stapedial Reflex Pathway
Reflex pathway that is triggered in response to a loud noise, causes tensing of the stapedius muscle (inserts onto stapes) which dampens sound transmission across the oval window. Thought to be protective mechanism against noise induced injury.
Pathway:
Sound –> Cochlea (afferent pathway) –> Vestibulocochlear nerve CNVIII –> Ventral Cochlear Nucleus –> Trapezoid body within the medial superior olivary complex (1st region to receive bilateral info - travels to bilateral bodies) –> Facial motor nucleus (efferent pathway) –> Facial nerve –> Nerve to stapedius –> Stapedius muscle
Measured by looking at changes in TM compliance (with similar probe) caused by contraction of the stapedius muscle
Define Acoustic Reflex Threshold (ART) vs. Acoustic Reflex Decay
Acoustic Reflex Threshold: Softest sound level that elicits stapedial contraction (normal = 70-100dB)
Acoustic Reflex Decay: Inability of stapedial muscle to maintain contraction for 10 seconds with sound presented at 10dB above ART
What are possible test results for the acoustic reflex?
Normal: Present reflexes at normal sound levels, and sustained x 10 seconds at ART
Elevated: Requires more sound to elicit response
Decay: A response is abnormal if its amplitude decreases to half or less of its original measurement over 5 seconds
Absent: No response. Either due to afferent issue (sound isn’t transmitted to inner ear) or efferent issue (can’t trigger stapedial response or measure it due to middle ear pathology)
Diphasic: Increased compliance at the onset, and cessation of the sound stimulus (?)
https://www.interacoustics.com/images/guides/tympanometry/reflex-measurement/reflex9.png
Describe what the stapedial reflex findings would be for right ipsi, right contra, left ipsi, and left contra for the following clinical scenarios:
Right cochlear problem
Right CNVII problem
Right ME problem
Small central brainstem lesion affecting crossing fibers
Large central brainstem lesion
Right cochlear problem:
- Right ipsi: elevated/absent
- Right contra: elevated/absent
- Left ipsi: normal
- Left contra: normal
Right CNVII problem:
- Right Ipsi: elevated/absent
- Right contra: normal
- Left ipsi: normal
- Left contra: elevated/absent
Right ME problem:
- Right ipsi: elevated/absent
- Right contra: elevated/absent
- Left ipsi: normal
- Left contra: elevated/absent
Small central brainstem lesion affecting crossing fibers:
- Right ipsi: normal
- Right contra: absent
- Left ipsi: normal
- Left contra: absent
Large central brainstem lesion:
Absent everywhere bilateral ipsi/contra
Name 6 conditions that may demonstrate absent stapedial reflexes bilaterally
- CHL > 40dB in test ear
- SNHL > 70-80dB in test ear
- Bilateral VII lesions
- Bilateral VIII lesions (e.g. NF2)
- Brainstem lesion
- Multiple Sclerosis
1 and 2
Sound not loud enough to stimulate the reflex
Reason SNHL is higher threshold is because lots of patients with SNHL have hyperacusis so they have lower threshold for louder sounds, so don’t need as much loudness to trigger the reflex
Describe how to draw a tympanogram
X-axis: Air pressure (in daPa or mmH2O) from -400 to +200 (in increments 100)
Y-axis: Immitance (compliance) in mmho (volume) from 0 to 1.5 (up in increments of 0.3)
See Vancouver notes page 227
Describe the differential for each Jerger Tympanogram 2 each
Type A: Normal
Type As (shallow/stiff):
- Otosclerosis
- Tympanosclerosis with fixation
Type Ad (deep or discontinuity):
- Ossicular chain discontinuity
- Large monomeric drum
Type B (flat):
- Middle ear effusion
- TM perforation
- Seal hitting against EAC
- Foreign body/Cerumen
Type C (negative):
- Eustachian tube dysfunction
Type D (notched)
- Scarred TM (two pressures produced)
Describe how you would draw each tympanogram
Type A:
- Peak between ± 100daPa
- Compliance 0.3-1.5mL
Type As:
- Peak between ± 100daPa
- Compliance < 0.3mL
Type Ad:
- Peak between ± 100daPa
- Compliance >1.5mL
Type B:
- No peak, flat
Type C:
- Peak at < -100daPa
- Compliance 0.3-1.5mL
Type D:
- Notch at the peak
