An Illustrative Case Study of Hearing Aid Orientation and Troubleshooting

Troubleshooting Common Problems

• During the first few weeks of using a hearing aid, it is common for your patients to encounter some problems
  • most can be solved through a phone call, text or email
  • others require a patient visit
  • some require careful thinking and others simply may not be solvable

The Occlusion Effect

• the occlusion effect is best described as an echo, "boomy" (as in an over abundance of low-frequency energy), or hollow sensation occurring when the patient is speaking or chewing
• sensation can be highly annoying and is most likely to be annoying for patients having 30 to 40 dB HL thresholds in the low frequencies
• addressing the possibility of the occlusion effect is part of the verification process and it is relatively easy to measure with your probe microphone equipment at the time of the fitting
• the most common way to fix the occlusion effect problem is through venting
• When a vent of 2mm or more is created, sound energy can readily escape
  • the larger you make the vent, the more likely you are to solve the occlusion problem
• General treatment process for the post fitting complaint of occlusion goes something like the following
  • determine that indeed the patient is reporting the occlusion effect and not a general dissatisfaction related to too much low frequency amplification
    • for fittings not expected to be open, measure the magnitude of the occlusion effect using probe microphone techniques
    • if the occlusion effect is less than 5dB or so, the complaint may be related to low frequency gain, not the occlusion effect. Many patients do not find the occlusion effect to be particularly bothersome until it reaches 8 to 10 dB
  • For fittings using an open eartip, determine whether the fitting is open through the use of REOG measures or by measuring the occlusion effect
  • if the fitting is is not open, use increased venting or a different fitting tip to allow for a more open ear canal
  • if the fitting was made more open, before the patient leaves the clinic ensure that two key conditions hold
    • you have not created a feedback problem
    • the increased venting did not remove necessary low-frequency information needed for speech understanding

To illustrate how we might handle occlusion effect problems in the clinic, we have a case study of a 55 year old woman with a unilateral hearing loss who was fitted with a mini-BTE RIC instrument using a double dome eartip (reasonably tight). She had a relatively flat hearing loss (40 dB in the lows sloping slightly to 65 to 70 dB in the highs). The degree of hearing loss in the lows is what prompted the audiologist to select a relatively tight-fitting dome. The patient returned to the clinic after one week of using her hearing aid, reporting that the hollowness of her own voice was very annoying to the point that she was not using the hearing aid. Here is the step by step procedure an audiologist might use to address this patient's issue:
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STEP 1

• we ask the patient to read a passage that contains vowels that trigger the occlusion effects, with the hearing aid on and also turned off.
  • "Through three cheese threes three free fleas flew."
• If the problem is truly an occlusion effect, it should be present not only with the hearing aid on but also with the hearing aid off

​STEP 2

• for this patient we want to see whether using a dome that is not as tight fitting can solve the problem without creating a new one. Our probe microphone equipment will provide the data to ensure that we are approaching things correctly. We first measure the REOG (Real Ear Occluded Gain) for the dome she is using and for a second dome that does not fit as tightly. We also measure her REUG (Real Ear Unaided Gain) just to have a reference regarding the degree of openness.
• Figure 18-1: Observe that, indeed, the REOG for the replacement dome (dome B) is more similar to the REUG than the original dome (dome a), suggesting that the fit is more open. So we know that we are going in the right direction.

Observe that, indeed, the REOG for the replacement dome (dome B) is more similar to the REUG than the original dome (dome a), suggesting that the fit is more open. So we know that we are going in the right direction.

STEP 3

• The REOG is not a direct measure of the occlusion effect, so our next step is to assess the occlusion effect directly. In the clinic, we may skip step 2 and jump straight to step 3 to save time, if we planned to measure the occlusion effect all along
• Figure 18-1B shows the occlusion effect for the open ear (for reference), the original tighter fitting dome (dome A) and the new dome (dome B) which is more open. Notice that with the original dome, this patient had more than 20dB occlusion effect with a peak around 250Hz. With the new dome, we reduced this occlusion effect by approximately 15dB. The patient also reports a very noticeable improvement

​STEP 4

• Now that we have successfully reduced the occlusion effect, we must determine what effect this looser fitting dome has on the hearing aid output. We expect some reduction in the low frequencies because the increased venting caused the reduction in the occlusion effect.
• Figure 18-2 shows the speech mapping results for the hearing aid fitted to NL2 with the original dome (dome A) and the results we have now with the new dome (dome B). Note that there is an ~ 10dB reduction in output for the new dome from 750 to 1000Hz and we also are no longer at target in those frequency ranges. This needs to be fixed so we adjust gain in the hearing aid to rematch prescriptive target values using our probe microphone equipment.

STEP 5

• After the hearing aid is reprogrammed we ensure that this "more open" fitting does not create . feedback issue.

Using the Acoustic Telephone Program in Background Noise

• As the degree of hearing loss increases, particularly in the low frequencies, it is likely the amount of venting will decrease and consequently more amplified low frequency sound bandwidth will be maintained
• one phone solution for such hearing aid wearers is an acoustic telephone program
• such programs are being used increasingly because modern feedback-suppression algorithms can limit feedback as long as not too much gain is required
• these algorithms often do not provide the SNR benefits associated with a t-coil or more modern wireless streaming technologies
• As shown in the figure, research suggests an acoustic telephone program is not useful at all in noisy environments for listeners with more severe hearing loss.
• therefore, we need to explore other options for patients who are dissatisfied with the performance of an acoustic phone program in noisy environments
  • phone placement; counsel patients to place the phone directly over the ear 
  • phone equipment choices
  • signal choices; switch the patient to t-coil or other wireless streaming technologies for telephone use