New technology can benefit established middle ear implant users: Samba 2 vs previous models of audio processors for Vibrant Soundbridge

The Vibrant Soundbridge (VSB) is a partially implanted middle ear device (Med-El, Innsbruck, Austria) which was introduced in 1996 [1, 2]. It is intended for patients with acquired and congenital moderate to severe sensorineural, conductive, or mixed hearing loss who have contraindications to, or limitations with, the use of conventional hearing aids [3‐5]. The approach of having the FMT attached to the long process of the incus was introduced to treat patients with SNHL. The newer coupling techniques using various types of couplers have been developed for treating conductive and mixed hearing loss. Currently, the FMT can also be placed on the round window, using direct or indirect coupling [6‐8]. The 25-year history of this solution has led to multiple reports of its safety, effectiveness, and improvement in the quality of life of patients [9‐12]. During this time there have also been new developments in medical technology. In terms of middle ear implants, there have been several generations of audio processors (APs) with new functions. The first VSB was the D404 (transferred to Med-El in 2003), the Amadé processor introduced in 2009, and the Samba processor in 2015. The latest VSB processor is the Samba 2, launched in 2020. New functions include advanced signal processing, noise reduction, multi-microphone technology, speech tracking, and remote control. Signal processing and functionality have improved over the generations [13]. The multi-microphone technique (on which we focus here) has been used for several years in both hearing aids and various types of implants [14‐17]. It was presumed the technique would bring measurable benefits to our study group, although the improvements are difficult to measure objectively because of the built-in adaptive circuitry: measurements would need to simulate a rapidly changing acoustic scene to reproduce the conditions under which adaptive microphones operate. An easier alternative is to assess the benefits of using this technology by using Patient-Reported Outcome Measures (PROMs). The combination of both objective and subjective measures allows a reliable assessment to be made of the device’s benefits—understood as the reduction in the user’s limitations caused by hearing loss.

Thanks to the compatibility of newer APs with older implants, access to modern technology is even possible for long-term users. Patients can gain in two areas: they receive a new device that is more reliable than the old one, and they gain access to modern technology that was unavailable in their legacy processor. To the authors' knowledge, there has been only one previous study on upgrading the VSB technology—from Samba to Samba 2 [18].

The aim of this study was to assess the benefits to users from upgrading their previous generation processor to Samba 2 in terms of hearing sensitivity and speech discrimination outcomes as well as in terms of PROMs.

To the authors' knowledge, there are few studies on upgrading the VSB audio processor. Older works compare the benefits of the 3-channel processor to the 8-channel, showing an auditory benefit [21, 22]. In the study of Todt et al. in 2005, the D-type audio processor was replaced by a Signia-type processor in three patients [22]. Due to the small number and markedly older technology of processors, the results are not comparable with those obtained here.

Table 4 gives an overview of recent studies. These studies cover speech discrimination in quiet and in noise, free-field thresholds, and PROMs. In all three studies there were no statistically significant differences between the old and the newer APs in terms of hearing thresholds in free-field. By way of contrast, in the study here there were statistically significant differences in mean hearing thresholds: in the old processor the mean PTA4 value was 42 dB HL, whereas in the new it was 38 dB HL.

In terms of speech discrimination in quiet, only Rahne et al. showed a statistically significant difference in WRS in favor of the new processor, with an improvement from 66 to 74% when the Samba processor was changed to the Samba 2. These WRS scores are in line with the results of our study, where the WRS in the old processor (D404 or Amadé) was 61% compared to 75% with the new Samba 2.

The results of speech-in-noise discrimination from previous studies are more difficult to compare with our results. The reasons are methodological. Although all authors used adaptive tests, differences in loudspeaker configuration, sound direction, word material, processor settings, and other details were employed. In the work of Mühlmeier et al., the measurement conditions largely corresponded to those used in our study, although a constant noise of 70 dB SPL was used instead of the 65 dB SPL used in our work [23]. The SRT obtained for the S0-N180 condition was 5.9 dB SNR for the Amadé and 2.3 dB SNR for the Samba processor, a difference which was statistically significant [14]). For similar measurement conditions in our work, the SRT was 7.0 and 3.5 dB SNR for the old and new processors, respectively. In the case of replacing the processors with the latest Samba 2, Rahne et al. observed a statistically significant improvement in speech-in-noise discrimination after the use of a newer processor for multiple configurations of speech and noise sources. However, the types of stimuli and noise, as well as the spatial configurations of the loudspeakers, were different from what we used here. Nevertheless, the conditions used (S0-N120, N180, N240) are roughly similar to the one (S0-N180) used in our paper (since in both studies speech was presented from the front and noise from the back). Thus, we can broadly compare the improvement of 2.3 dB identified by Rahne et al. for S0-N120, N180, and N240 to the 3.5 dB improvement for the S0-N180 condition in our study. The slightly larger improvement reported by us could stem from the extra noise sources used by Rahne et al. (N120, N240) which could reduce the benefit from the directional microphone in the new processors.

Because speech and noise signals were spatially separated in our work, the differences in speech reception threshold in noise between the old and new processors may be due to a markedly difference in the way the microphones in the older and newer processors operate. The previous generation processors used an omnidirectional mode microphone, whereas the Samba 2 processor uses an advanced directional microphone system that is automatically adaptive.

In our study, a statistically significant difference was observed for the S0-N0 condition. A better result was obtained for the newer processor (Samba 2), with an SRT of 5.0 dB SNR compared to the 7.0 dB SNR for the older ones. The difference in SRT between APs was smaller when signal and noise were spatially separated.

There are certain difficulties in determining the most appropriate measurement setup for assessing modern technologies—for example, directional microphones, speech tracking, acoustic scene analysis, and others. The results of tests for hearing sensitivity and speech discrimination obtained in a clinical setup may not correspond with patients' needs and expectations in everyday life. This is the reason questionnaire tools (PROMs) were also used.

There are two other reasons for using PROMs. First, it is not easy to test new front-end processing features. During a single test session, simulating multiple environments is difficult, and so the user’s self-report (the PROM) becomes an important measure of how well this new technology works under different common situations. Second, there are many real-life situations—such as activity limitations and participation restrictions—which cannot be gauged by a speech discrimination test. These problems are unique and depend on personal circumstances, family situation, life-style, and so on, making PROMs necessary to quantify performance [24‐26].

In the current study, the PROM results pointed to an appreciable subjective improvement when the speech processor was upgraded to the new technology. According to SSQ, patients reported less hearing disability and more satisfaction with the new AP, particularly in terms of its usability (APSQ).

Patients indicated that, compared to the legacy processor, the Samba 2 gave better spatial hearing, speech hearing, and better other qualities of hearing. Spatial hearing involves judgements of direction, distance, and movement. Speech hearing relates to diverse situations: noisy background conditions, reverberation, multiple voices, and the ability to ignore one voice while attending to another, following a conversation that switches quickly from one person to another, or following two speakers simultaneously. Other qualities of hearing refer to signal segregation, identification/recognition, clarity, naturalness, and ease of listening [27]. Improvements in spatial hearing and in speech hearing due to the upgrade is especially encouraging, as it indicates clear advantages of the new technologies, particularly automatic scene analysis when listening in difficult acoustic conditions.

In two previous studies in which the processor was replaced with a newer one, the SSQ questionnaire was used, after which a statistically significant improvement was noticed on all three dimensions: speech hearing, spatial hearing, and qualities of hearing [18, 28].

In the work of Zimmermann et al., the improvements with the new processor in the speech hearing dimension were on average 1.1 points, in the work of Rahne et al. they were 2.0 points, and in our study 1.5. In the spatial hearing dimension, the improvements were 0.8 points in Zimmermann's work, 1.7 in Rahne's, and 1.2 in ours. In the qualities of hearing dimension, the improvement reported by Zimmermann was 1.7 points, by Rahne et al. 1.5, and in our study 1.7. The average SSQ total score calculated in Rahne et al.'s work was 5.2 in the old processor and 7.0 in the new, while in our work it was 4.8 in the old and 6.3 in the new. In general, the differences between SSQ scores obtained with the old and new processors were statistically significant, both for the total score and for the individual dimensions, and consistent with the ones reported in the literature.

In the APSQ, the results obtained for both the new and old AP for each of the three dimensions exceeded 8 points. A statistically significant difference between the results for the new and old processors was obtained only for the usability dimension (9.4 for the new vs. 8.8 for the old). This dimension consists of questions about the ease of placing the AP properly on the head, ease of changing the battery, ease of switching on and off, proper functioning of the AP, and ease of care. For the APSQ total score, the difference was not statistically significant. In the work of Rahne et al., the mean total score was 8.2 for the older and 9.0 points for newer processors. They observed statistically significant improvements in total score, social life, and usability. In the usability dimension, the difference between the older and newer processor was 0.8 points, compared to 0.6 in our study.

As already stated, in the patient-centered care model, it is important not only for clinicians to obtain objective, measurable benefits under experimental conditions, but also that patients themselves report benefits in everyday functioning. The rationale is that numerous publications have shown that audiological measures generally correlate poorly with PROMs [29‐32]. Dornhofer et al., in a group of 95 hearing aid users, correlated aided audiological measures (PTA, Nu-6, SPIN) with aided APHAB subscales and global score; they saw no significant relationship. Absent or low correlations between patient self-reported scores and speech recognition have also been reported among cochlear implant users [33‐35]. Mertens et al. reported that self-assessment tools, like SSQ, offer insights into dynamic hearing capacities that cannot be easily measured in the laboratory and provide useful information about the hearing status of CI users [33]. The results obtained in this study are consistent with the conclusions from other work, confirming the lack of correlation (or weak correlation) between the results of speech discrimination in quiet and noise and the results of PROMs. When testing the relationship between speech hearing dimension in the SSQ and the result of speech tests with the new AP, a significant negative correlation was obtained for S0-N0; a smaller (also negative) but not significant correlation for S0-N180, and no correlation for WRS obtained in quiet. A similar relationship was noted by Remakers et al., who found, using SSQ, a significant (but weak to moderate) negative correlation between the subjective test results of the speech hearing dimension and the related objective speech perception in noise test [35]. In the recently published ‘Consensus Statement on Bone Conduction Devices and Active Middle Ear Implants in Conductive and Mixed Hearing Loss’, the authors address an important issue, noting that companies introducing new processors should enable patients with older implants to reap the benefits of new features and signal processing developments [36]. We see the opportunity here for long-term users of implantable devices: they do not need surgical intervention to gain access to modern technologies (ignoring, of course, issues relating to cost and insurance). Upgrades offer a way of reducing the impact of hearing impairment in everyday life and offering better functional performance.

By replacing the processor, modern technology can bring measurable benefits, particularly in terms of speech discrimination. PROMs confirm the obtained benefits: a reduced impact of hearing impairment on everyday functioning. Patients also notice the practical, functional benefits of the newer solutions. This study has shown that the use of the latest solutions—adaptive microphone directionality, speech tracking, and environmental sound classification—can provide significant benefits to patients.