By Astrid Haastrup, MA, and Jill Mecklenburger, AuD
One exciting aspect of working as an audiologist in Research & Development for a hearing instrument manufacturer is testing the “latest and greatest” innovations with consumers. It is clear that the consumers who participate in these tests also enjoy this unique opportunity to contribute to the development process.
However, each time we conduct a test with a new behind-the-ear (BTE) or receiver-in-the-ear (RIE) design, there are invariably one or two participants who are disappointed or who withdraw from the trial due to the style. They want something that fits completely in the ear.
With in-the-ear (ITE) styles having dropped from near 80% of units sold in the United States to only 27% according to the latest industry statistics,1 being fit with an ITE style might seem akin to buying a VHS player, a rotary dial telephone, or a set of encyclopedias. But does the fall in popularity of this style of hearing instrument mean that it is doomed for obsolescence? Obviously not, since the most logical place for a hearing instrument is still in the ear, and consumer demand for devices that fit in the ear is unlikely to drop. A major reason for continued consumer demand is that hearing instruments that fit in the ear have the potential to be completely invisible when worn.
Cosmetics Still Matter
It has been shown that hearing instrument adoption rates even for those with moderate-to-severe losses are quite low (below 50%) for consumers not yet 65 years of age.2 This finding points toward a significant and continuing age stigma among non-adopters of hearing aids, even in this era of micro BTE and RIE hearing aids. Comments made by survey respondents such as “Hearing aids are a public admission of hearing loss,” as well as hearing aids are “noticeable” and “embarrassing,” suggest a perceived connotation of disability and aging is associated with hearing aids.
In the MarkeTrak VIII survey,3 a slightly different tack in the questions posed was taken. Whereas non-adopters had been asked in previous surveys what was keeping them from acquiring hearing aids, MarkeTrak VIII asked them to indicate financial, hearing aid related, listening utility, and psychosocial factors that would influence them to adopt hearing aids within the next 2 years. The strongest influencer in terms of psychosocial factors (#15 in a list of 53 factors) was that the hearing aid should be nearly invisible.
Given that finding, it makes sense for hearing instrument manufacturers to continue to focus design efforts on creating products that are unnoticeable to others. While a small BTE with a thin tube or wire to the ear canal may satisfy this demand for some consumers, not all find this style sufficiently inconspicuous.
The most invisible style of hearing aid until recent years has been the completely-in-the-canal (CIC) device. The faceplate of a CIC is at least adjacent to, and sometimes 1 or 2 mm inside, the opening of the ear canal. It should also terminate within 5 mm of the tympanic membrane. Although considered to be cosmetically appealing, CICs typically remain visible to the casual observer if the ear is exposed.
Advances in technology have enabled the design and manufacture of an even smaller style of hearing instrument, the ultra-cosmetic invisible-in-the-canal (IIC). Because the IIC can be built smaller, its faceplate can be recessed even farther into the ear canal than a CIC, as shown in Figures 1a-b. The goal for an IIC is for the faceplate to reside between the opening and the first bend of the ear canal rather than near the opening. Due to the recessed nature of the faceplate, the hearing instrument is essentially invisible. Figures 2a-b compare the visibility of a CIC viewed from the side with a ReSound IIC fit to the same ear.
Other CIC/IIC Advantages
Besides the invisibility that many consumers want, other noteworthy benefits of CIC hearing instruments apply to IIC devices as well:
1) Localization and spatial hearing. A primary function of the pinna is to collect and direct sound into the ear canal. But the pinna does not do this indiscriminately. Depending on the location of the sound source, sounds of different frequencies are attenuated or enhanced by the physical characteristics of the external ear. In addition to enhancing speech frequencies, this helps the listener localize sounds and facilitates spatial hearing. ITE hearing instruments preserve this hearing advantage.4,5 Additionally, a microphone location inside the ear canal itself preserves the acoustic cues afforded by nearly all of the acoustic elements of the external ear.6
2) Ease of use with the phone. BTE hearing instrument wearers often struggle to place and maintain the telephone receiver correctly in reference to the hearing instrument microphone or telecoil in order to carry on a conversation. While ITE hearing instruments allow the user to hold the phone receiver more naturally, it can still be uncomfortable to press the phone receiver against the device. Feedback squeal can occur in either situation and is another annoying frustration. CICs have been rated highly in telephone performance, in terms of speech understanding, comfort, and feedback.7 A robust feedback cancellation algorithm, such as ReSound DFS Ultra II, can improve things even further with the potential to completely eliminate feedback issues during telephone usage.
3) Wind noise protection. Wind noise is problematic for hearing aids when the microphone is located in an area where there is turbulent airflow. The worst case is the microphone placement for BTE/RIE where turbulence is created as wind hits the pinna. Despite advances in wind noise reduction algorithms, the best solution for wind noise is to locate the microphone away from areas where turbulent airflow occurs. Hearing aids that are deeply seated in the ear canal, as is the case with the IIC, are immensely effective at protection against wind noise.8
In designing the IIC, the objectives were to develop a product that would be invisible on the ear, fit in the majority of adult ear canals, and not require special techniques or considerations on the part of the clinician. To meet the first two requirements, it was necessary to design a new, smaller hybrid containing the A/D converter, signal processor, memory, and connections specifically for use in this device. An updated technique in manufacturing also allows the production of thinner shells while still retaining mechanical integrity. Finally, an optimized faceplate design with an angled profile and elimination of the flex strip programming connector, as well as a smaller receiver, were key elements to making the smallest device possible. The result of these design changes is shown in Figure 2b.
For an ear canal to accommodate the IIC device, the ear canal opening must be at least 10 mm in the superior-to-inferior direction and at least 5 mm in the anterior-to-posterior position. While it has become standard practice for manufacturers to provide a tool for clinicians to use in evaluating the impressions, ReSound wanted to avoid having to ask clinicians to use such a tool for this product.
One reason is that a typical office already has many small tools to keep track of, each with its own purpose. Some may be for evaluating impressions, others for changing receivers or other parts on the hearing instrument. Not adding to the number of tools seemed desirable. Another issue with tools is consistency in training to use a new tool, which can result in inconsistent usage and defeat the purpose of it. Inconsistent use of an impression evaluation tool to determine candidacy can result in inadequate impressions being sent in, but is just as likely to rule out viable IIC candidates in our experience.
To validate that an impression evaluation tool was not needed for the IIC device, 250 randomly selected impressions were assessed at the ReSound manufacturing facility. Even though none of these impressions were intended for manufacture of an IIC device, it was found that 96% of them met the IIC criteria anyway. As mentioned, an additional benefit to not using an impression evaluation tool to determine IIC candidacy is that more ears can be fit than a tool may have indicated. Figure 3 shows an ear that was fit successfully with an IIC despite having “failed” candidacy using an impression key to evaluate the impression.
|Figure 3. The impression from this ear did not meet candidacy criteria for a CIC or IIC as determined by an impression key. Since ReSound TruFit impression criteria were met, it was possible to successfully fit an IIC device.|
Clinicians have often been advised to make deep impressions for CIC devices—extending far beyond the second bend of the ear canal. Having deep impressions taken is not particularly comfortable for patients. Understandably, clinicians also may be hesitant to take them, especially if deep impressions are not part of their typical workflow.
In 2006, ReSound carried out a field study to understand what comprised a really good impression. This study resulted in what has been termed the ReSound TRUFIT™ impression.9 It is defined by following the 16/4 rule: an impression with a canal length of 16 millimeters, or about 4 mm past the second bend. Approximately 80% of a survey of 3,500 impressions sent to our manufacturing facility met the ReSound TRUFIT™ impression criteria. This suggests that typical impression-taking practice followed by the majority of professionals is satisfactory for production of IIC devices, and no special techniques or tools are needed. Following this guideline most always provides adequate ear geometry and sufficient information so that it is possible to determine the canal direction and provide the best physical fit and acoustic performance of any custom manufactured hearing instrument, including the ReSound IIC.
When assessing hearing instrument candidacy, clinicians are often advised to consider that patients may have difficulties handling the small batteries that power CIC and IIC hearing instruments. While this is important, it is also worthwhile to consider that this style of device is the simplest in terms of operation. If the user is able to manage the battery and insert the devices correctly, they are “wear and forget” devices. Environmentally dependent signal processing features, such as the ReSound Environmental Optimizer II, automatically change gain and noise reduction settings to match the listening situation, thereby obviating the need for multiple programs or manual volume changes.
In addition to the hearing-related benefits already mentioned, field trial participants mentioned many other benefits to the IIC style. These included no interference with eyeglasses, no worries about losing them when running or biking, comfortable to leave in when napping, able to wear with a hat, as well as compatibility with phone headsets and stethoscopes.
The ReSound IIC device is an extremely small hearing instrument with benefits that include not only the cosmetic appeal of true invisibility, but also protection from wind noise, preservation of pinna cues for localization and spatial hearing, improved ease of phone use, and many other practical benefits. No special tools, processes, techniques, or impression materials are required to fit this device, so it fits easily into the existing clinical workflow of a typical practice.
Not all existing hearing instrument users have embraced the BTE/RIE trend, and the IIC style provides an attractive option for them. Furthermore, continued innovation in hearing instrument development that includes invisibility as a design goal can contribute to improving hearing instrument adoption rates. ?
|Astrid Haastrup, MA, is a Senior Audiologist at GN Global Audiology, Ballerup, Denmark, and Jill Mecklenburger, AuD, is a Principal Audiologist at GN ReSound Global Audiology, Glenview, Ill. CORRESPONDENCE can be addressed to Astrid Haastrup at: [email protected]
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