Outcome measures of hearing aid performance: verification and validation Flashcards
Why do we need outcome measures?
To assess whether the patient is getting the best possible result from the hearing aid we have fitted
What kind of questions should be asked to the patient immediately after fitting the hearing aid?
- Is the aid comfortable in the ear?
- What do they think about the quality of sound (own voice, audiologist’s voice, other sounds?)
- Loudness of sound- is it what they expected? Too loud? Too quiet?
What kind of questions should be asked to the patient at the hearing aid review appointment?
- How long do they wear the aid every day?
- What do they think of the sound quality?
- Are there any particular problem situations?
- How does their own voice sound?
- Any problems with loud sounds?
- Any problems with acoustic feedback?
- Can they insert/ remove the mould?
- Is the aid comfortable to wear?
What are the two main reasons for measuring outcomes?
- Patient-oriented- assess patient’s needs, assess effectiveness of rehabilitation and need for further help
- Service-oriented- to evaluate service and change to service
What are the three main types of outcome measures in hearing aid assessment? What are some examples of each?
- Audibility: aided thresholds and speech tests
- Technical outcomes: real ear measurements (REMs)
- Self report questionnaires: hearing aid benefit, satisfaction with aids, satisfaction with services
What are aided thresholds?
-Aided vs unaided thresholds
-A measurement of functional gain
-Soundfield presentation e.g. warble tones/ narrow band noise
How do you calculate functional gain?
Functional gain= Unaided threshold- aided threshold
In what situation are aided thresholds particularly useful?
When REMs are impossible e.g. congenital atresia of external meatus
What is the advantage of using aided thresholds to measure hearing aid outcome?
May be useful to demonstrate to others (e.g. parent, significant other) that the HA is making a difference
What are the disadvantages of using aided thresholds to measure hearing aid outcome?
-Time-consuming to perform
-Results can be variable depending on patient concentration
-Does not measure dynamic aspects of HA performance e.g. wide dynamic range compression
How can speech tests be used to measure hearing aid outcome?
-Test the client’s hearing for speech when wearing the hearing aid
-Test prior to fitting for reliable results and repeat once the aids have been fitted
-Can also be used to ensure adequate speech development in hearing impaired children
-Can use live voice or recorded, in quiet or in noise, with or without visual information
Name two speech tests
AB word list and BKB sentences
What are the advantages of speech tests in measuring hearing aid outcomes?
-High “face validity”
-Can readily demonstrate difference between unaided and aided situation to patients/ others
-Some tests e.g. FAAF can identify particular speech sounds which are causing difficulty
- Auditory alone vs audiovisual can demonstrate the importance of visual cues to communication
What are the disadvantages of speech tests in measuring hearing aid outcomes?
-Cannot replicate real-life listening conditions easily in the clinic
-May be time consuming to do
-Results dependent on measurement conditions e.g. noise/ no noise, signal-to-noise ratio
-Unless many items are used, the % difference between conditions A and B has to be quite large for statistical significance
How can speech in noise testing be used to measure hearing aid outcomes?
-Test speech intelligibility in background noise
-Difficulties in background noise is one of the most common complaints for hearing impaired people even when wearing hearing aids
-These tests can demonstrate functional improvements following hearing aid fittings or changes to hearing aid settings
Name three examples of speech in noise tests
-Hearing in Noise Test (HINT)
-QuickSIN
-Bamford-Kowal-Bench SIN (BKB-SIN)
How can Real Ear Measurements (REMs) be used to measure hearing aid outcomes?
-Measures the hearing aid output in the ear canal of the wearer
-Small “probe tube” microphone is inserted into the ear canal
-A reference microphone is placed next to the pinna
-Sound stimuli are produced and the sound level within the canal is compared to the level at the reference mix
-Can be carried out with or without the hearing aid in place
What are the advantages of REMs?
-Produces an entire objective measure of what the aid is doing
-Little patient co-operation required
-Quick and easy to perform
-Gives information about the whole frequency range
-Can immediately demonstrate the effect of changes to the hearing aid settings
-Good test-retest repeatability
What are the disadvantages of REMs?
-They are only as good as the prescription formula used
-This can be a problem as prescription rule developments usually follow developments in technology- current formulas don’t take the latest technologies into account
-Audiologists can become too REMs driven and forget about the needs of the patient
-Cannot perform if excessive wax or infection are present
-Results can be affected by changes in the placement of the probe mic
-Can be difficult to perform on children as they have narrow ear canals and do not like to keep their heads still
What are the most commonly used questionnaires to assess hearing aid benefit in the NHS?
Glasgow Profules and Client Oriented Scale of Improvement (COSI)
What are the advantages of using questionnaires to measure hearing aid benefit?
-Allow comparisons before and after fitting and to normative data
-Enable services to gather data about the local population in terms of both the hearing loss and hearing AI
What are the disadvantages of using questionnaires to measure hearing aid benefit?
-Measure different things- not comparable
-Can be time consuming
-The patient may not be able to complete the questionnaire if they do not understand the questions
What is the real ear unaided response?
-The sound level recorded in the open ear canal plotted on a graph across the frequencies
-Hearing aid is not inserted in the ear
Where should there be a REUR resonant peak in an adult?
At approximately 2.7 kHz but it differs in all individuals
What is the real ear occluded response (REOR)
-The sound level recorded in the ear canal when the hearing aid is inserted in the ear
-Resonant peak may be ‘lost’ because the earmould or aid stops the ear canal from resonating
What kind of fit is it when the REUR and REOR are similar?
Open fit
What is the real ear aided response (REAR)?
-The sound level in the ear canal across frequencies of sound with the hearing aid in the ear and turned on
-Used to compare hearing aid output to prescription targets
What is the real ear insertion response (REIR)?
The difference (in dB) between the sound levels measured in the ear with hearing aid in and on and without the hearing aid in the ear
How is the REIR calculated?
-REAR-REUR= REIR
-Area between blue line (REUR) and red line (REAR) is the REIR
What is the real ear saturation response (RESR)?
-The maximum sound pressure level the aid is capable of delivering in the client’s ear, across the frequencies, measured with the aid in saturation
-This is an extremely loud stimulus level so is not used routinely in clinical testing
What is the purpose of measuring the REUR?
To establish the baseline sound level in the ear
What is the purpose of measuring the REOR?
To identify whether we have an open or occluded fit so we can select the correct method of calibration for the equipment
What is the purpose of measuring the REAR?
To identify whether the hearing aid meets prescription fitting targets
Why do we need to calibrate the probe tube?
-The probe tube and microphone don’t have a flat frequency response
-The probe tube is changed regularly so different tubes will affect the real ear measurements we make
-We need to correct for this by making the probe tube “invisible”
-Probe calibration resets the internal equipment settings to eliminate the acoustical effects of the probe tube
-The REM equipment measures probe microphone (PM)- reference microphone (RM) during calibration