From January 1992 to January 2017, 7893 cochlear implant surgeries were carried out in the Unified Health System accredited services in Brazil.1 In this time frame, the device manufacturers invested in new technologies in order to provide maximum effectiveness and accessibility to users, such as new signal processing strategies and directional microphone technologies, in an attempt to improve speech perception in noise.2–5 The frequency modulation (FM) system is a device that enables speech perception in noise by reducing the harmful effects of reverberation and the distance between the speaker and the listener.6,7 The FM system is currently considered the most effective approach to improve speech recognition in noise in cochlear implant users.8

The FM system was introduced in the Unified Health System in Brazil on June 25, 2013, through Ordinance no. 12749 and is intended for individuals between 5 and 18 years of age. Subsequently, the hearing health services accredited by the Unified Health System throughout the country have been prepared to carry out FM fitting.

Guidelines to assist audiologists in the selection, fitting, and verification of the FM system for children requiring hearing aids have been made available.10 According to these guidelines, performing a careful check is required before fitting the FM system to hearing-impaired children. The electroacoustic test recommended for hearing aids adopts the concept of transparency between the FM system and the hearing aid.

Although there are recommendations regarding the behavioral tests that should be performed at the fitting the FM system to cochlear implant users,10 there are no published recommendations regarding the electroacoustic test. Indeed, there is only one report suggesting the performance of an electroacoustic verification protocol of FM system coupled to the cochlear implant for the assessment of the transparency between the devices.11

Considering that each child with a cochlear implant has its own pace of oral language development, which is related to intrinsic and extrinsic factors, a significant number of children may not be able to report the benefit of coupling the FM system to the cochlear implant only through behavioral measures. Thus, it is necessary to implement a thorough protocol that includes objective tests for electroacoustic verification, in order to achieve the best use and to fit the device accurately regardless of the child's response.

By providing this real benefit to the patient, it is expected that the adherence to the use of the FM system will increase. Thus, in addition to the individual benefits, the implementation of a thorough protocol will also have a positive impact on the public policies of hearing health care in Brazil. Indeed, the FM system is an expensive device, and it is thus essential that the hearing health services are enabled to perform accurate fitting in order to avoid negative impacts on the users and the public money.

The study was carried out in the Craniofacial Anomalies Rehabilitation Hospital, University of São Paulo, Bauru, São Paulo, Brazil and began once the approval of the Research Ethics Committee was obtained, under opinion no. 1,992,217.

Table 4 summarizes the results of the electroacoustic verification procedure (transparency evaluation). We detected transparency between the FM system and the cochlear implant in 34 (85%) of the 40 participants. The results in which no transparency was observed are highlighted in bold in Table 4.

Based on ANOVA, there was no statistically significant difference between the values of transparency (mean) in the different brands (p=0.545) and models (p=0.327).

Table 5 summarizes the results of the cases in which there was no transparency between the devices, and the results after modifying the FM gain adjustment using the “FM SuccessWare” software.

After adjusting the gain of the FM receiver, the devices of participants 4, 15, 16, and 18 exhibited transparency when the electroacoustic verification test was repeated. Furthermore, participants 4, 16, and 18 exhibited a better performance in speech perception in noise after a new adjustment; thus, in these cases, the electroacoustic transparency caused behavioral transparency.

In the case of participant 15, the FM gain was modified and a new electroacoustic verification was performed. However, the speech perception in noise could not be performed owing to the level of language development. Indeed, participant 15 could not perform the Brazilian version of the Hearing in Noise Test (HINT),14 which had been suggested in the initial methodology. It should be noted that the evaluation of this participant was performed at the beginning of data collection and, therefore, before sending the amendment to the Research Ethics Committee requesting the inclusion of the PINT test.13 in the methodology. Participant 15 did not return to the service until the end of this data acquisition.

In the case of participant 33, for whom there was no electroacoustic transparency of the FM system coupled to the cochlear implant, the modification in the receiver gain adjustment reduced the FM system gain. Participant 33 used the Freedom speech processor, for which the manufacturer of the FM system Phonak recommends that the FM receiver gain be set to 0dB (Table 4). Therefore, adjusting the FM gain could negatively affect the FM system benefit for this participant.

Participant 9, for whom there was no electroacoustic transparency of the FM system coupled to the cochlear implant, did not remain long enough in the outpatient routine to perform the procedures of FM gain adjustment and speech perception test.

The results shown in Table 4 reflect the importance of performing electroacoustic verification of the FM system coupled to the cochlear implant, considering that transparency was achieved in 85% of the cases. This result can be explained by the fact that the strict adjustment of the speech processors and FM gain was performed thoroughly. Although the FM systems are conceptually simple in their technologies and handling, one major challenge in fitting them is the need to strike a proper balance between the gains of this system and those of the hearing aid.10

FM system technology has stimulated the initial questions, for example, whether a monaural fitting is better than a binaural one, and suggested questions related to adjustments performed in the speech processor of the cochlear implant and in the receiver of the FM system during fitting.15 A study in adults using unilateral cochlear implants concluded that FM receiver gain has the potential to directly influence speech recognition in noise.16 Another study compared speech recognition in noise in adolescent and adult users of FM systems electrically and electromagnetically coupled to cochlear implants. The findings indicated that different FM gain adjustments may be required to achieve optimal performance.17 Clinical studies have shown that gain adjustments in wireless communication systems can have a considerable effect on the performance of the users of these devices when coupled to the cochlear implant.18

The speech recognition in noise test “Phrases in Noise Test” (PINT)13 was performed in three out of the 6 (15%) cases in which transparency was not achieved (Table 4). Table 5 indicates a better performance of the three participants in the PINT13 test after the new adjustment of the receiver gain when the devices were set up in order to achieve transparency. Based on this, we can suggest that electroacoustic transparency caused behavioral transparency. These participants needed a new gain setting to obtain greater benefit from the FM system, thus proving that the effective benefit is directly related to an adequate adjustment of the receiver gain, which is in line with previous studies.11,18 Considering that these three participants were the youngest in the present study and were developing their language skills, the need for this new adjustment was only realized after the electroacoustic verification test. Thus, it is perceived that the use of a thorough protocol during the fitting of the FM system to the cochlear implant in children, including objective tests in addition to behavioral tests, is essential to ensure effective measurement and fitting.

A previous study evaluated the frequency of use of the FM system in 70 users of cochlear implants in the classroom. A total of 52.8% said they did not use or partially used the device. Thus, although the literature reports the advantages of using the FM system, there are still patients who own the device and do not use it. The authors found that 10% out of the 52.8% of the patients who did not use of the FM system effectively stated that they did not perceive any benefit in the FM system. It can be affirmed that the proper adjustment of the FM system is directly related to the greater benefit of the technology and, therefore, to the greater adherence to its use. Thus, in addition to providing a proper fitting, the electroacoustic verification test, when related to increasing adherence to the use of FM systems, can positively affect the public policies related to granting this device to cochlear implant users, thus potentially avoiding the waste of public funds.19

As discussed previously, there is only one previous report on the development of an electroacoustic evaluation protocol for FM systems coupled to cochlear implants.11 The authors evaluated transparency in three models of speech processors: Harmony, Opus 2, and Nucleus 5, and made different combinations using Phonak and Oticon FM transmitters. Thus, the discussion of the data shown in Tables 1 and 2 is comparatively based on the results reported in this previous study regarding the use of the Inspiro transmitter and MLxi receptors, both Phonak-branded, which are the same used in our study.

Table 4 indicates that only 1 (16.6%) of the six tests performed on the Harmony speech processor model did not show transparency. It was necessary to adjust the FM gain in the case of participant 4, in which the gain of +10dB was reduced to +8dB in order to achieve transparency (Table 5). The above-mentioned study11 established combinations among three different receivers and four different transmitters for the test with the same speech processor. The authors reported that, when using the Inspiro transmitter with the MLxi receiver coupled to the Harmony speech processor, transparency was achieved with gain of +4dB. This variability of the FM gain adjustment to achieve transparency may occur, but the speech perception test must be performed to verify if the benefit is maintained.

For the tests performed with the 24 users of Opus 2 speech processors, there was no transparency in 4 (16.6%) cases. From these, it was possible to perform a new adjustment in the FM gain in three cases. As shown in Table 5, it was necessary to increase the FM gain from +10dB to +12dB for participant 15 in order to achieve transparency. For participants 16 and 18, it was necessary to decrease the FM gain from +10dB to +8dB. These results are in line with previous data.11 The evaluation with the Opus 2 speech processor indicated that variable gain settings were necessary in order to achieve transparency. In particular, in the combination of the MLxi receiver and the Inspiro transmitter, the authors found that the FM gain required to achieve transparency was 0dB. In 83.4% of the cases that presented transparency without the need of a new adjustment, it was observed that there was a difference of 10dB between the results found in the present study and the results found in the previous study.11

The interest of this study lies in the fact that the results indicated a variability in the FM gain adjustment when the same speech processor model was coupled to the same FM system technology, but with different users (n=33), except for the Nucleus 5 speech processor model. This is in contrast to the findings reported in the United States,11 which pointed to variability in the FM gain adjustment when a single speech processor was coupled to different FM system technologies.

Regarding the electroacoustic evaluation of the FM system coupled to the Nucleus 5 speech processor, Table 4 shows that transparency was achieved in the seven (100%) cases with FM gain at +2dB, with no need for a new adjustment. The gain settings that are needed to achieve transparency have been previously reported to be highly variable in a study combining four transmitters and four receivers for the evaluation of transparency with the Nucleus 5 speech processor.11 Regarding the use of the Inspiro transmitter combined with the use of the Phonak receivers, the authors reported that it was not possible to achieve transparency when using the MLxS receiver, a previous generation receiver. For the use of the MLxi receiver, it was necessary to adjust the FM gain to +8dB for transparency. Comparing the results obtained in the present study with those obtained in the aforementioned study, a 6dB difference was observed in the gain needed to achieve transparency. However, it is noteworthy that this study used the ML14i receiver, a specific device for connection to the Nucleus 5 speech processor. Thus, the difference between the gain settings can be explained by the fact that those authors used a universal receiver, which requires an adapter to be connected to the cochlear implant. Thus, the receivers used differed in the connection mode. In this study, all FM receivers coupled to the Nucleus 5 speech processor belonged to specific models.

In summary, owing to the variability found in the FM gain settings to achieve transparency, it is highly recommended to perform the electroacoustic verification test of the FM system when coupled to the cochlear implant, particularly in children. It is believed that the transparency between the FM system and the cochlear implant can positively affect the adherence to the use of the FM system, and will consequently affect the best use of public money in relation to the granting of this device by the Brazilian Unified Health System. Indeed, between 2013 and 2017, 16,141 FM system Kits were granted under Ordinance 1274.9 The longitudinal monitoring of these participants in future studies may provide more specific information about their adherence to the use of the FM system.

Based on the present findings, we conclude the following: (1) The electroacoustic evaluation protocol suggested was effective in evaluating transparency between the FM system and the different models of speech processors of cochlear implants; (2) There was a greater benefit in the speech recognition in noise when there was a transparency between the FM system and the cochlear implant; (3) Adjusting the FM system gain can be very helpful for many cases when fitting this device.

The research reported in this publication was supported by the Coordination of Superior Level Staff Improvement (CAPES) and by São Paulo Research Foundation (FAPESP) grant no. 2014/20398-1.

The authors declare no conflicts of interest.