What are the different styles of hearing aids?
Completely in the canal - CIC Mini Canal - MC In the Canal - ITC Half Shell - HS In the Ear - ITE Mini Behind the Ear - Mini BTE Behind the Ear - BTE
Which hearing aids are appropriate for a mild loss?
All styles OK
Vent is important, beware of occlusion effect
What types of hearing aids are appropriate for a mild/moderate loss?
All styles OK
Vent is important, except in CIC
What types of hearing aids are appropriate for a moderate loss?
All styles are OK except for the mini canal (high risk)
Fitting flexibility or no pots(?) available
What types of aids are appropriate for a moderate/severe loss?
High Risk - ITC
No mini canal
Feedback, max gain is most important consideration
What type of aid is appropriate for a severe loss?
Half Shell is High Risk CIC is High Risk NO In the Canal NO mini canal - feedback, max gain most important consideration
What types of aids are appropriate for a severe/profound loss?
ITE with High Risk
- feedback, max gain most important consideration
What types of aids are most appropriate with a profound loss?
not enough power in smaller aids
What are the four difficult hearing loss configurations to fit with hearing aids?
- cookie bite
- reserve slope (depending on degree)
- NL - No loss with ski slope
Why is a ‘Cookie Bite’ hearing loss hard to fit with hearing aids?
ITC - high risk
NO mini canal
Venting is very important
Why are precipitous losses hard to fit with hearing aids?
No Half Shell No In the Canal No Mini Canal CIC - High Risk Beware of Occlusion Effect and PBK
Why is a reverse slope loss hard to fit with hearing aids?
Depending on Degree
No Mini Canal
Venting important except in CICs
Why is NL (no loss with ski slope) difficult to fit with hearing aids?
High Risk for Half Shells No ITC No mini canal Occlusion effect and Pbk most important Venting important
What is the difference between a BTE and a mini BTE?
Mini BTE has a lower gain and output than the BTE in the matrix and fitting range
What is the “Matrix”
- The Matrix gives the peak output (in dB SPL), and peak gain (in dB) the aid can produce.
- Aid can be programed to lower values for a particular patient if need be.
- NOTE: bottom of fitting range may be optimistic
Receiver in the Ear (RITE) Hearing Aids
- Receiver enclosed in a soft dome or custom shell
- External receiver requires less space in the aid, smaller HA
- Theoretically less feedback, because the receiver and the mic are separated (“body aid effect”)
- Tubing is wire, so sound can’t leak through the tubing -> less feedback, no tubing resistance
What is MSG?
- Maximum stable gain
- This is the max insertion gain that can be provided without audible feedback oscillation with feedback cancelation on
What are some manual dexterity options?
- Helix lock, ITEs only
- Canal lock, available on CICs
- removal filament line
- stacked or raised volume control
- removal notch
What are some wax prevention options?
- spring wax guard
- wax trap
- canal bell
- extended receiver canal
Why would you use a body aid?
used only in rare cases where BTE gain is not sufficient and/or can not get required gain without feedback
*these days almost never used because of feedback reduction and cochlear implants
Lyric Extended Wear CICs
Deeply inserted into bony portion of the canal (~ 4 mm from TM)
- deep mic insertion allows use of pinna and concha cues (resonance and localization)
- smaller residual volume requires less gain
- uses a transmitter and receiver
- BTE transmitter on the poorer ear, sends signal through FM to a receiver on a BTE in good/better ear.
- Can fit BTEs of a variety of manufacturers with the appropriate audio shoe
- even though the sound isn’t being put into the bad ear, use a custom (open) mold for better retention
- BI-CROS sends sound across but also amplifies
What information do you have access to when deciding on the correct amplification device for the patient?
- Case History (start thinking about this while taking case history)
- Age - most relevant with child
- Ear size/shape, from otoscopy may limit some styles like CIC
- Dexterity or vision limitations (from history)
- Loudness Discomfort Levels (LDLs)
- Speech discrimination in quiet and noise
- Communication needs from history and from pre-fitting questionnaire (to supplement history)
Medical Referral Criteria
- Deformity of the outer ear
- Significant cerumen accumulation
- history of drainage within 90 days
- history of sudden loss within 90 days
- acute or chronic dizziness
- unilateral loss of sudden/rapid onset within 90 days
- ear pain or discomfort
- conductive component/ air-bone gap
What is the APHAB?
- abbreviated profile of hearing aid benefit
- one possible pre-fit questionnaire
- can provide information useful in selection or combined with post-fitting APHAB to measure benefit
- results are measured in % problematic, so higher numbers are WORSE - more trouble understanding in those situations
What are the four sub-scales of the APHAB?
Ease of Communication (EC)
Background Noise (BN)
Aversiveness of Sounds (AV)
Which of the APHAB sub-scales can be predicted by the audiogram?
- Audiogram predicts less than 1/2 of the variance of EC and RV and DOES NOT predict BN and AV.
What is the COSI?
- Client Oriented Scale of Improvement
- allows the patient to identify situations in which they need improvement
- same situations will be evaluated post-fitting to measure benefit
- Audiometric battery should include a speech in noise measure
- helps you decide on level of noise reduction, directional mics, ALDs required to improve communication
- mild or moderate = need noise reducing hearing aids (directional mics)
- severe = need ALD
What should you consider when you are fitting only one ear of an asymmetric loss?
- will fitting the better ear make more sounds audible/clearer?
- will fitting the worse ear make more sounds (bilaterally) more audible (i.e. make the bad ear more useful) & give better sound localization
- (but consider limitations of poor discrimination when counseling)
In a symmetrical loss, do you fit one ear or two?
- fit both ears unless you have a good reason not to
- demonstrated binaural interference
If asymmetrical loss, do you fit one ear or two?
- fit both ears when audio-metrically appropriate
When is discrimination so poor that you don’t bother fitting with an aid?
There is no magic number, however Dillon (2001) suggests <50% is a good cutoff point
When is discrimination too poor to bother fitting with an aid? - (binaural fitting)
- always consider wether the patient will do better aided, even if discrimination isn’t optimal … if yes, then fit anyway but counsel appropriately
When is discrimination too poor to bother fitting with an aid? (Unilateral fit/ Asymmetrical fit)
- localization and sound awareness may be helpful even if speech clarity is poor
- headphone testing may not accurately predict hearing aid benefit
- potential for progressive loss
- potential for binaural interference, may need a trial
What is the FDA and what are their regulations regarding hearing aids?
- The food and drug administration oversees the conditions of sales of medical devices, including hearing aids
- Medical Clearance from physician - within last 6 months, preferably from a doctor who specializes in diseases of the ear. If they are over 18, they can waive this by signing a medical waver
- Under 18 you can’t waive the medical clearance (parent and guardian cannot waive either, have to complete medical clearance)
- Patient must be provided with user manual by manufacturer, and you must go over it with them when you give them the aid initially (verbally)
- Dispenser keeps these records on hand for 3 years (at least - HIPPA requires most documents be retained for min of 6 years after last date of service)
What is the major role of compression?
The major role of compression is to decrease the dynamic range of signals in the environment so that all signals of interest can fit within the restricted dynamic range of hearing-impaired person
What is the difference in sound amplification when using compression?
The more intense sounds have to be amplified less than weak sounds
What are the three ways that dynamic range of signals can be reduced
wide dynamic range
How does low level dynamic range compression work?
- gain starts reducing as soon as the input level rises above weak sounds
- by the time a moderate input level has been reached, the gain has been sufficiently decreased, and linear amplification can then be used for higher input levels.
- lower levels are closer together after amplification than before -> upper levels are not affected by amplification
- this means decreased slope of the I-O function for low level signals whil the linear amplification of higher level signals apears as 45% angle
How does high level dynamic range compression work?
- opposite of low level dynamic range compression
- inputs from moderate to intense sounds are squashed together into narrower range of outputs
- “high level compression”
- high level inputs narrowed to a very small range of outputs
What is compression limiting?
- output is not allowed to exceed a set limit so range of inputs is narrowed to an extremely small range of outputs
How does wide dynamic range compression work?
- compression is applied more gradually over a wide range of input levels
- “Wide dynamic range compression (WDRC)”
- the gradual reduction applies over such a wide range of input levels that there are no input levels for which the corresponding output levels are squashed closely together
- I-O curve is never close to horizontal
What is the purpose of a compressor?
- to change the gain depending on changes in the signal level
What is attack time?
the time taken for the compressor to react to an increase in signal level
When is the attack time complete?
When the compressor fully reacts to the increased signal level and gain has decreased compared to its previous gain
What is the release time?
when the input signal decreases in level, detector progressively reacts to the new input level
- control signal decreases gradually and consequently the gain and the output signal increase gradually
- time taken for the compressor to react to a decrease in input level
What will happen if the attack time is too short and the release time is long?
the distortion will be minimal however, extremely brief sounds like clicks will cause the gain to decrease because of the short attack time and the gain will then stay low for a long time afterwards because of log release time
What will happen if the release time is too short compared to the period of the signal being amplified?
the gain will vary during each period, so the compressor will distort the waveform
What does ANSI stand for?
American National Standards Institute
What is the reference plane
this is a plane, at right angles to the longitudinal axis of the ear canal, located at the point in the ear canal where the earmold or ear shell usually terminates
What is a HA1 coupler and which aids is it used for?
has no ear-mold simulator and is used for ITE and ITC aids, which are connected to the coupler via putty. Itis also used for BTE hearing aids not intended to be used with ear molds - typically thin tube BTEs that terminate in a dome or RITE BTEs
What is a HA2 coupler and what is it used for?
includes an earmold simulator, which is connected to the BTE hearing aid via tubing, or into which a receiver for a body aid snaps. The HA4 coupler is a variation of the HA2 intended for BTE or spectacle aids in which the tubing diameter from the hearing aid to the medial tip of the earmold is a constant 2mm diameter. Although this tubing configuration is commonly used in BTE hearing aids, use of the HA4 coupler is less common
What situations will produce inaccurate results when using a coupler or ear simulator?
- the sound bore of an ITE/ITC/CIC hearing aid is poorly sealed to the coupler or simulator
- the tubing connecting to a BTE hearing aid becomes stiff and does not properly seal at either end
- the o-ring connecting a button receiver wears out
- the pressure equalization hole becomes blocked or excessively open
What is an artificial mastoid?
equivalent of a coupler for bone-conduction hearing aids
- standard way to measure force output of a bone-conductor hearing aid over the frequency range of 125-8000 Hz
- not necessarily the same force that would be exerted on a human mastoid
What is a test box?
generates sounds of a required SPL at the hearing aid microphone
What components are included in a test box?
- tone and or noise generator
- control microphone
What is the most realistic assessment of the effect of hearing aid on speech?
When the input spectrum has a spectrum similar to that of speech
Test signal, all with a long-term spectrum matching that of speech, include:
- spectrally shaped random noise
- repetitive waveform with a crest factor (the ratio of a waveform’s peak value to its rms value) similar to that of speech, one example of which is pseudo-random noise
- a series of very short tone bursts that vary rapidly in frequency and amplitude to match both the spectrum and dynamic range of speech
- speech sounds that have been processed to remove the fine detail that provides most of the intelligibility while retaining the temporal fluctuations in amplitude of real speech, such as ICRA noises
- speech syllables extracted from multiple languages and pasted together to sound like speech, referred to as the International speech test signal
- actual continuous speech
What does a hearing aid with adaptive noise reduction do?
decrease the amplification in each channel as the SNR in each channel decreases
What does a hearing aid with feedback cancelation do to a pure tone sweep?
- hearing aids with feedback cancellation (most now have this) may treat swept pure tones as feedback oscillation and decrease the gain at the measurement frequency.
How would you calculate gain at a specific frequency?
The gain at any frequency can be calculated as the output SPL at that frequency minus the input SPL
What level is used to measure max output and why?
IEC and ANSI both specify using a 90 dB SPL input signal to measure the hearing aids max output - OSPL90
- this level is high enough to cause most hearing aids to reach their highest possible output level at each frequency
What is saturation?
when the hearing aid output has reached its limit for any input signal
What is High-Frequency Average (HFA) Gain
Average of the gains at 1000, 1600 and 2500 Hz
What is Special Purpose Average Gain
Average of the gains at three frequencies each separated by 2/3 octaves. This is used for hearing aids with unusual frequency responses
What is Frequency Range?
This is the range of frequencies between the lowest and highest frequencies whose gain are 20 dB below the HFA gain
What are the two volume settings used to test a hearing aid?
full-on gain and reference-test setting
What is the input-output function?
shows the output level versus input level for one frequency or for one broadband test signal
- very important for understanding how the hearing aid is modifying sound
What is feedback reduction?
- You can stop sound from leaking by occluding, but then they may be more plugged up
- Now we have digital feedback reduction
- can be active and ongoing or passive and done only once during the fitting
What are some wind noise reduction options?
- this is really a section of digital noise reduction
- wind hood
- wind screen
What is expansion?
- works to quiet the very low level sounds (probably noise) by adding less and less amplification below a certain knee-point
What do the attack and release time tell us?
- how fast a compressor is working
If you increase the loud sound gain, what have you done to the compression ratio?
You have lowered the compression ratio.
If you have decreased the loud sound gain, what have you done to the compression ratio?
You have increased the compression ratio.
If you increased the gain in the soft sounds, what have you done to the compression ratio?
increased the compression ratio
If you decrease the gain of the soft sounds, what have you done to the compression ratio?
You have decreased the compression ratio.
What does the input - output graph look like when you decrease the compression ratio?
The line becomes more shallow incline
How do you measure a compression ratio?
Change in Input : Change in Output
- Run/rise, opposite of slope (rise/run)
- 1:1 is linear
What are the four components you use when identifying what change needs to be made and where in the hearing aid?
- high frequency?
- low frequency?
- soft sound?
- loud sound?