SISB Lec 21: HA verification - REMs 2

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Revision Session Overview

• The session serves as a revision for exams, focusing on important procedures and topics related to hearing aids and measurements.

• Importance of preparation for both an Objective Structured Clinical Examination (OSCE) and a written exam mentioned.

Discussion Points

Clinical Experience with Equipment

• Discussion about practical experience using insertion gain and unaided gain in a clinical setting.

• Calibration of equipment is emphasized as crucial: "You should be calibrating things."

Foundational Knowledge

• Acknowledgment that foundational knowledge should be solid by this stage of the semester

• Reference to the necessity of feeling comfortable with:

  • Working with hearing aids

  • Using relevant software

  • Performing real ear measures

OSCE Preparation

• Emphasis on the importance of attending classes that simulate OSCE practice, specifically mentioning the lecture planned for the following week.

• The session aims to ensure students are familiar with hearing aid verification procedures.

Hearing Aid Verification Procedures

• Key topics to be reviewed:

  • Unaided Gain

  • Insertion Gain

  • Aided Response

• Discussion about the limitations and inaccuracies in real ear measures (REM) and additional measures like saturation and occluded response.

• Aided thresholds and functional gain will also be addressed as methods for assessing the benefit of hearing aids in the absence of real ear measures.

Importance of Real Ear Measures (REM)

• REM are crucial because they measure the specific amplification a hearing aid provides in a person's ear:

  • "If we don't measure what the hearing aid is doing in the ear, we're guessing."

• Reasons for using REM include:

  1. Real World Variability: Variations in ear shape and coupling affect sound gain.

  2. Manufacturer Software Limitations: Dependence solely on manufacturer defaults can lead to inadequate fit and poor outcomes, such as:

  • Reduced speech audibility

  • Poor speech understanding

  1. Demonstrated Better Outcomes: Studies show that clinical providers who utilize REM achieve better fittings and more satisfied clients.

Graphical Representation of Gain Deviations

• Graph represents the deviation from fitting targets using manufacturer first-fit settings for hearing aids from five different manufacturers, highlighting that there are often 5-10 dB discrepancies in actual ear measurements.

• Acknowledgment of the importance of performing REM based on these deviations to ensure accurate fittings.

Probe Tube Measurements

Overview of Probe Tube Technology

• Probe tube measures sound pressure levels in the ear canal using a microphone system.

• Rationale for measurements includes:

  • Unaided Gain: Measures the natural resonance in the canal; indicates how the ear’s shape contributes to hearing.

  • Aided Gain: Evaluates what the hearing aid provides in terms of additional gain.

• Equipment includes:

  • Probe microphone

  • Reference microphone (to measure sound intensity)

  • Output for real ear coupler difference

Calibration of Equipment

• Importance of calibrating probe tubes to ensure accurate readings:

  • Calibration helps eliminate resonance effects of the tube itself from measurements.

  • Recommendations suggest calibrating in the morning or when any discrepancies arise.

Procedures for Real Ear Measurements

Required Steps

1. Check for Wax: Removal is essential as it affects resonance measurement.

2. Measure Depth: The probe tube must be placed 5mm past the end of the hearing aid or mold, with specific recommendations based on ear canal length variations.

   • Adult ear canal length averages around 24mm.

3. Conducting Measurements: Execute unaided gain followed by insertion gain using calibrated equipment and consistent reference signals.

Measurement Types

• Unaided Gain: Evaluates the resonance and natural amplification of the ear without hearing aids.

• Insertion Gain: Calculates the difference in gain when the hearing aid is in operation. It is crucial to ensure consistent probe tube positioning throughout measurements.

Insertion Gain Procedure

• The insertion gain is derived from:

  • 
    $ext{Insertion Gain} = ext{Aided Gain} - ext{Unaided Gain}$

• The procedure involves:

  • Retaining the probe tube in the same position throughout measurements.

  • Utilizing a speech-weighted signal for insertion gain determination to capture real-world performance.

• Discussion about related response, primarily how it’s used outside Australia.

Measurement Implications

• Understanding that the effectiveness of fitting should rely on accurate measurement data, highlighting the importance of maintaining the probe tube’s position to avoid inaccuracies.

Alternate Measures in Hearing Aid Fitting

Saturated Response

• Definition: This measurement indicates the maximum output level of a hearing aid at high input levels (e.g., 90 dB SPL)

• Use of swept wobble tones ensures accuracy, as 90 dB SPL equals saturation across frequencies.

Occluded Response

• Measures how the hearing aid alters the natural resonance of the ear canal when turned off, which can inform on occlusion effects.

Real Ear to Coupler Difference (RECD)

• This measurement compares sound pressure levels in the ear versus a standardized 2 cc coupler to provide a correction factor for accurate fitting information.

• Valid for ensuring precise fit, relevant when performing fittings for clients unable to return to clinics frequently.

Aided Thresholds and Functional Gain

• Aided thresholds refer to testing hearing thresholds with the aid of devices during a hearing assessment in a controlled environment.

• Calculation is based on differences between unaided and aided thresholds, emphasizing an improvement quantifiable in real-world terms.

• Functional gain highlighted as an indicator of the benefits provided by hearing aids.

Conclusion

• The session concludes with an emphasis on thorough understanding of the real ear measurements and effectiveness in aiding clients successfully through accurate fittings.

1⃣ Lecture Overview & Purpose

• Session type: End-of-semester revision lecture (pre-OSCE + written exam).

• Main aim: Refresh knowledge of real-ear measurement (REM) procedures for hearing-aid verification.

• Topics covered:

  1. Importance of REMs.

  2. Unaided & insertion gain procedures.

  3. Aided response vs insertion gain.

  4. Common errors & abnormal tracings.

  5. Limitations / inaccuracies.

  6. Additional measures: saturation response & occluded response.

  7. Aided thresholds & functional gain.

  8. Real-ear-to-coupler difference (RECD).

• Key goal: By the end, students should recall and describe the verification steps used in clinic, recognise abnormal results, and understand optional diagnostic tools.

2⃣ Why Perform Real-Ear Measures?

• Core principle: Without measuring the sound in the client’s ear canal, fitting relies on guesswork.

• Reasons:

  1. Individual ear variability: Shape, venting, and insertion depth all alter acoustic gain.

  2. Manufacturer first-fit ≠ accurate:

     • Based on average ear data.

     • Under-amplifies high frequencies → poorer speech audibility.

     • Studies show reduced satisfaction and understanding when relying only on first-fit.

  3. Measured fittings improve outcomes:

     • Higher satisfaction & speech performance.

     • Even a basic device, if verified well, can outperform a premium one fitted poorly.

• Conclusion: Always verify; first-fit alone is inadequate.

3⃣ REM Equipment & Components

• System: Probe-microphone headset + loudspeaker + software (e.g., Affinity).

• Key parts:

  • Probe microphone: Measures SPL inside the ear canal (via probe tube).

  • Reference microphone: Monitors the sound level near the ear to adjust output automatically (pressure method).

  • Output for RECD: Port used for test-box or coupler calibration.

Tip: Always check colour markings (left = blue, right = red). Mis-swapping clips or hooks → incorrect side placement.

4⃣ Calibration of Probe Tubes

• Purpose: Remove tube resonance from the measurement.

• Process:

  • Calibrate at the start of the day (standard) or for each new probe tube.

  • Resonance values stored in software.

• If tracing looks odd: Re-run calibration to rule out tube defects.

5⃣ Preparation Before Measurement

1. Otoscopy:

   • Check & remove wax → prevents resonance distortion or blockage.

2. Measure probe-tube depth:

   • Use ruler or hearing aid as guide.

   • Typical: 5 mm beyond mould tip.

   • Adult ear canal length: ~24 mm → target ≈ 20 mm insertion (5 mm from TM).

   • Shorter for deep-fit CIC/IIC; slightly longer for shallow moulds.

   • Keep tube at top of canal for accuracy.

3. Consistency:

   • Do not move probe between unaided & aided runs.

6⃣ Real-Ear Unaided Gain (REUG) / Response

• Purpose: Measure the ear’s natural canal resonance.

• Displays:

  • Gain (dB difference) = REUG.

  • Response (dB SPL) = REUR.

• Clinical use: Detect abnormal ear-canal or TM pathology.

  • Tiny perforations → resonance shift to lower frequencies.

  • Different ear shapes show natural variability.

• Reason for use: Each ear’s resonance differs → must account for it before adding amplification.

7⃣ Real-Ear Insertion Gain (REIG) / Aided Gain

• Procedure:

  1. Keep probe in place.

  2. Insert hearing aid (programmed to first-fit).

  3. Present same speech-weighted signal.

  4. Software calculates:
     Insertion Gain = Aided Gain − Unaided Gain.

• Interpretation:

  • Shows how much louder the hearing aid makes sounds inside the ear canal.

• Signal choice: Speech-weighted or speech-like stimulus.

  • Pure tones risk being detected as feedback.

  • Reflects realistic dynamic compression & noise-reduction behaviour.

• Measurement family:

  • Standard = 65 dB SPL (conversational).

  • Optional = 55 / 75 dB SPL for soft / loud inputs → “family of curves”.

8⃣ Real-Ear Aided Response (REAR)

• Definition: SPL at eardrum with hearing aid on.

• Difference from REIG:

  • REIG = relative gain (dB difference).

  • REAR = absolute output (dB SPL).

• Advantages:

  • Directly shows loudness at the TM → strong clinical relevance.

  • Simpler (no unaided run).

• Limitations:

  • May miss perforations/abnormalities detectable in unaided tracing.

• Why Australia still uses REIG:

  • Historical legacy—older prescription targets (e.g., POGO, NAL-R) defined in gain, not SPL.

  • Modern systems (NAL-NL2, DSLv5) now allow SPL-based verification, but tradition persists.

9⃣ Common Inaccuracies & Troubleshooting

General approach:

1. Check tube position.

2. Check for wax / split / blockage.

3. Verify calibration.

4. Consider pathology.

🔟 Client & Loudspeaker Setup

• Distance: 0.5 – 1 m from speaker.

• Orientation:

  • Binaural fitting → 0° azimuth.

  • Monaural → 45° toward test ear (reduces head-shadow).

• Speaker height: Ear level.

• Method: Pressure method (automatic level adjustment).

  • Reference mic monitors SPL continuously.

  • Compensates for small movements.

• Alternative: Substitution method (reference mic off → no auto-adjust).

11⃣ When to Perform REMs

• Initial fitting (mandatory).

• Follow-ups after major programming or acoustic changes.

• After receiver or vent modifications.

• After hearing-threshold changes.

• Trial fittings: optional but explain limitations if skipped.

12⃣ Interpreting Abnormal Examples (from class practice)

1. Flat line (0 gain): Probe tube not inserted.

2. Negative gain: Hearing aid off / muted or blocked probe.

3. Noisy, jagged trace: Talking or environmental noise.

4. Unusual large dips: TM perforation / mastoid cavity.

5. High-freq dip only: Standing wave → advance tube.

6. Weird shape post-wax: Wax obstruction or compression.

Systematic troubleshooting → inspect, recalibrate, re-measure.

13⃣ Additional / Advanced Measures

A. Real-Ear Saturation Response (RESR)

• Definition: Maximum output (MPO) of hearing aid in client’s ear.

• Stimulus: Swept warble tone at ≈ 90 dB SPL.

• Purpose:

  • Check that loud sounds stay comfortable & below LDL.

  • Verify output limiting / compression.

• Not routine: uncomfortable; replaced by subjective loudness check (“hand-clap / cup-and-spoon”).

• Graph: Unaided ≈ 60 dB SPL → Aided curve → Saturation ≈ 90 dB SPL.

B. Real-Ear Occluded Response (REOR)

• Definition: SPL in canal with aid inserted but turned off.

• Compares to: Unaided response.

• Uses:

  • Assess degree of occlusion / tightness of fitting.

  • Evaluate vent effect & low-freq attenuation.

  • Guide dome or vent selection.

  • Confirm vent-related resonances.

• Typical patterns:

  • Open dome → little change.

  • Closed dome → ≈ 10 dB attenuation.

  • Power dome → substantial attenuation (low-freq loss).

C. Real-Ear-to-Coupler Difference (RECD)

• Concept: Difference (dB SPL) between a person’s ear canal SPL and a 2 cc coupler SPL.

• Coupler: Standardised cavity simulating an average adult ear canal.

• Applications:

  • Fitting children or remote fittings when direct REM impossible.

  • Calibrating test-box fittings.

• Procedure:

  1. Measure ear-specific RECD if client present.

  2. Later fit aid in test box → apply RECD correction to approximate ear response.

• Accuracy:

  • Average RECD = less precise (population mean).

  • Individual RECD = more accurate (requires prior measurement).

• Advanced ear simulators (e.g., Zwislky coupler) better mimic ear acoustics but costly.

14⃣ Aided Thresholds & Functional Gain

Aided Thresholds

• Definition: Behavioral hearing thresholds measured in free field with aids on.

• Procedure:

  1. Calibrated sound-treated room.

  2. Client 0.5–1 m from loudspeaker (warble tones).

  3. Test unaided → then aided (same setup).

  4. Compare results.

• Use cases:

  • When REM impossible (e.g., gag reflex).

  • Bone-conduction device verification.

  • Demonstrate benefit (e.g., occupational medical proof).

• Masking: Optional to isolate ears.

• Check: Use client’s usual volume / fit-to-target program.

Functional Gain (FG)

• Formula:
  FG = Unaided Threshold − Aided Threshold (at each frequency).

• Interpretation: Improvement in dB SPL from amplification.

• Advantages:

  • Easy to explain to clients.

  • Demonstrates clear improvement visually.

• Disadvantages:

  • Time-consuming (two audiograms).

  • Does not reflect hearing-aid processing of speech.

  • Less precise than REM.