Appendix 1: History of the website and
acknowledgements
In September 2014, Franco Trabalzini organised the EAONO meeting in Siena and asked me, Ad Snik, to organize a panel on Consensus on Auditory Implants. Preparing that panel, I wrote a document what can be considered as the bleu print of the present website. Later that year, I sent an updated version of that document to my colleagues from Auronet (Auronet is a private initiative to develop a ’core-set’ of patient-centred outcome measures which enable the search for the best treatment options for a patient with conductive or mixed hearing loss; Tysome et al., 2015). Comments by my Auronet colleagues, especially Bill Hodgetts and Penny Hill, encouraged me to go on and to publish the document in the form of a website.
As a start, on April 22, 2014, chapters 1 to 3 were published. Chapters 4 and 5 were added on May 6th and June 16th. During the Osseo meeting in Lake Louise, Alberta (May 21-23, 2015), the website was introduced to the audience for the first time.
On July 28th 2015, chapter 5.3 and 6 were uploaded. Martijn Agterberg critically read this part of the website before it was published. Chapter 7 was added in August. Owing to comments by Arjan Bosman, Martijn Toll, Tove Rosenbom and Marc Flynn, the text of chapters 1 to 4 was revised (September 7th and October 8th). During the latter update, the option for the readers to respond online, was skipped. From the start until early October, more then 90 responses were collected and all of them were spam.
On March 29th 2016, chapters 5 and 6 were revised and Appendix 2 was added and on August 12th 2016, chapters 5 to 7 and Appendix 2 were updated. The remarks made by Hannes Maier are acknowledged. Chapter 8, on the use of auditory implants in patients with pure sensorineural hearing loss, was added on August 20th 2016.
January 20th 2017, data regarding relatively new devices was added (Chapter 3). This concerned the Sophono Alpha 2 processor, the Cochlear Baha Attract and the Med-El ‘Bonebridge’. On May 2nd 2017, chapter 1 was revised and chapters 2, 3 and 5 were updated. Amongst others, new data was added concerning new super-power percutaneous ‘BCDs’. Appendix 2 was rewritten. In the month of November 2017, this website was fully re-designed.
August 2018, Chapters 3, 4 were updated and in December 2018, Chapters 6 and 8. Blog 2018-4 added and in April 2019, Blog 2019-1 added. In October 2019, Tables 2.1, 4.1 were updated as well as Figure 4.2. In December 2019, Blog 2019-2 was added.
October 2020: Chapter 7 was updated. Blog 2019-2 was removed (concerned a power-point presentation at the Osseo conference). November 2020: Chapter 8 was updated and revised as two of the discussed auditory implants were taken off the market end 2019. On February 5th, 2021, Chapters 2, 4 and paragraph 5.3 were revised. Chapter 6 was updated and Chapter 8 was extended.
5 May 2024: Chapters 2.3, 4.1, 4.2 and 5.1.2 were updated and Chapter 9 was added. In July 2024, Martijn Agterberg took over the responsibility for the website as Ad Snik retired. An option was added to choose for the original English text or a translated Dutch version. For a proper automatic translation, several parts of the English texts have been reformulated.
About the authors:
Ad Snik studied physics at the Eindhoven University of Technology and got the master’s degree in 1976 and in 1982, he acquired the doctor’s degree from the same university. Afterwards he specialized in medical physics and was registered in 1987 as a medical physicist/ audiologist. In 1988 the author was employed as a clinical audiologist and researcher at the ENT department of the Radboud University Medical Centre Nijmegen and appointed as a professor in 2006 until his retirement in 2017. Since 2010, he worked one day a week as a researcher at the department of Biophysics, Radboud University Nijmegen until mid-2022. Ad Snik participated as an author in more than 250 peer-reviewed papers in the field of Audiology. His last paper concerning auditory implants was a consensus paper that he wrote together with Hannes Maier. The set-up was unique, based on a multi-stakeholder approach. Not only clinicians and audiologists participated in the consensus meetings but also representatives of all the major companies, and they were involved in the final report as (one of the 90) authors (Maier et al., Consensus Statement on Bone Conduction Devices and Active Middle Ear Implants in Conductive and Mixed Hearing Loss. Otol Neurotol. 2022;43(5):513-529).This paper covers most of the subjects addressed on this website.
‘Disclosure’:
The authors have and had no financial interests in any of the devices described in this webside, nor in any alternative device. This webside is partly based on research carried out at the Radboud University, which was supported by Nobelpharma, Entific, Cochlear BAS, Symphonix, Med-El, Otologics, KNO fonds Nijmegen, Heinsius Houbolt fonds, the William Demant Foundation and European Union Grants.
Appendix 2: Quantifying the gain (amplification) of auditory implants
A2.1 Introduction
Outcome measures used to validate the fitting of a hearing device can be divided into subjective measures and objective measures. In general, subjective refers to the assessment of patients’ opinions while objective refers to data that are measured with equipment, like hearing thresholds and speech recognition (Humes, 1999). To evaluate a hearing aid fitting, the most popular ‘objective’ outcome measure is the gain (amplification) provided by the device and the improvement in speech recognition (Gatehouse, 1998; Gurgel et al., 2012). Often, the ‘functional gain’ is reported which is the difference between the hearing thresholds without and with the fitted hearing device. However, although this approach is widely used, it has significant limitations.
Note: references are listed at the end of this Appendix 2
A2.2 Quantifying the amplification of a MEI in patients with sensorineural hearing loss
The use of the ‘functional gain’ implicitly assumes linear amplification. Nowadays, most auditory implants don’t use linear amplification but non-linear amplification or compression amplification. The most frequently used type of compression amplification (wide dynamic range compression; WDRC) implies that for soft sounds the gain provided by the device is relatively high, while for louder sounds, the gain is gradually reduced to prevent uncomfortable loud sound levels (Dillon 2012). A direct consequence is that the hearing thresholds with the device are lower (better) than those when using linear amplification; therefore, the ‘functional gain’ is also higher. It should be noted that here, the ‘functional gain’ assesses just the amplification for soft sounds (e.g. Stelmachowicz et al., 2002).
Snik and Cremers (2001) discussed two options to estimate the amplification of an auditory implant (MEI, VSB) at more realistic listening levels (thus at supra-tone- threshold levels). They suggested determining the ‘gain at the patient’s most-comfortable-listening level (MCL)’. In short, the patient’s MCL is determined (at octave frequencies) twice, once without and once with the auditory implant switched on, and the results are subtracted. In this way, the ‘gain-at-MCL’ is determined, frequency specific. Snik and Cremers compared amplification measures in 14 VSB users with 304 processor using WDRC. Averaged at 0.5, 1, 2 and 4 kHz, the ‘gain-at-MCL’ was indeed approx. 10 dB lower than the ‘functional gain’. From the data published by Rameh et al. (2010) the ‘functional gain’ was calculated. They also provided the speech-recognition-thresholds (SRT) with and without the VSB (an alternative option for the ‘gain-at-MCL’ (Snik and Cremers, 2001), however, not frequency specific). They included 112 VSB users with sensorineural hearing loss. Using their data, a similar difference (10 dB) was found between ‘functional gain’ and the ‘gain-in-SRT’. So, the ‘functional gain’ should not be used or in combination with a supra-threshold measurement of amplification whenever compression amplification is used.
Furthermore, it should be noted that hearing thresholds with a hearing device might be further affected by advanced signal processing: viz. by expansion amplification used to prevent the patient from hearing the microphone noise of the device, or by noise reduction algorithms.
To evaluate MEI fittings in sensorineural hearing loss, the ‘functional gain’ is often used. However, when evaluating devices with non-linear amplification ‘functional gain’ doesn’t have the usual significance. Additionally, the supra-threshold ‘gain-at-MCL’ or ‘gain-at-SRT’ should be reported.
A2.3 Qualifying amplification in patients with conductive or mixed hearing loss using MEIs or ‘BCDs’
To assess benefit of auditory implants for patients with mixed or conductive hearing loss, the ‘functional-gain’ is not an appropriate measure at all, for a second reason. It should be realized that MEIs with their actuator coupled to one of the cochlear windows as well as ‘BCDs’ directly stimulate the cochlea; consequently, the mal-functioning outer/middle ear plays no role. However, the status of the outer/middle ear, as quantified by the width of the AB-gap (the difference between the air- and bone-conduction thresholds) significantly affects the ‘functional gain’. To illustrate this, let us assume a patient with pure conductive hearing loss of 65 dB HL (full bony atresia of the ear canal) using a powerful ‘pBCD’ that stimulates the cochlea rather perfectly (thresholds with the ‘pBCD’ at 15 dB HL). Then, following the definition, the ‘functional-gain’ is 65-15=50 dB. However, if the AB gap is 30 dB instead of 65 dB (partial atresia of the ear canal) while using the same device, then the ‘functional-gain’ is (only) 30-15=15 dB. This example shows that owing to its definition, the ‘functional gain’ depends strongly on the width of the AB-gap, and, therefore, it is an inadequate amplification measure.
How to proceed? If a patient with pure conductive hearing loss is fitted with a powerful ‘pBCD’ and if some every-day sound of 40 dB is indeed perceived as 40 dB by the patient, evidently, the gain is 0. In other words, the ‘pBCD’ has effectively compensated the conductive hearing loss. In the audiogram, this shows up as device-aided thresholds coinciding with the cochlear (thus bone-conduction) thresholds. This gain, the difference between the ‘BCD’-aided thresholds and the bone-conduction thresholds is referred to as the ‘bone-conduction gain’ (Carlsson and Hakansson, 1997) or the ‘effective gain’ (e.g., Bush et al., 2017). Note that by definition, the ‘functional gain’ equals the ‘effective gain’ plus the AB-gap. Once more; the bigger the AB-gap, the higher the ‘functional gain’. Therefore, in contrast to the ‘effective gain’, the ‘functional gain’ is not a measure of the capacity of the particular device used.
The ‘effective-gain’ might be negative, indicating that the device-aided thresholds are worse than the bone-conduction thresholds; see Chapter 3 and 4. That means that every-day sounds are (still) perceived attenuated and, in the audiogram, a persistent, although reduced AB-gap is seen. When the patient has mixed hearing loss with an obvious sensorineural hearing loss component (SNHLc) of e.g., 50 dB HL, obviously an‘effective gain’ of 0 is not enough; part of the SNHLc should be ‘compensated’ as well, to make speech sufficiently audible. The ‘effective gain’ should be positive, e.g., 22 dB (calculated target gain using the adapted NAL-rule; see Chapter 4); then, a 28 dBHL sound is just audible for his patient, using that amplification.
As said before, device-aided thresholds are affected by the kind of amplification that is used; linear versus expansion- and/or compression-amplification. Compression amplification, to deal with a relatively low maximum output of MEIs and ‘BDCs’ (Chapter 3) results in low (thus favourable) device-aided thresholds and expansion (to deal with device noise) results in higher (worse) device-aided thresholds. Consequently, the ‘effective gain’ respectively over- and under-estimates the amplification of sounds at e.g., normal conversational levels.
In the previous section (A2.2) we discussed the use of alternative, supra-threshold amplification measures (viz. ‘gain-in-SRT’ and ‘gain-at-MCL-level’). However, these measures cannot be applied easily in conductive or mixed hearing loss. This is caused by limitations of the bone-conduction transducer (part of the audiometer) used to determine the bone-conduction stimulation. The standard B71 bone-conduction transducer has a relatively low maximum output (might be at or below the patient’s MCL levels) affecting the MCL measurements, especially in high and low frequencies (Alomari, 2014). Additionally, perception of speech produced by the B71 might be affected by distortions, especially of low-frequency sounds and the poor frequency response of the B71 (limited bandwidth).
Evidently, to avoid or minimalize problems with quantifying the gain caused by non-linear amplification, always use auditory implants with a high MPO so that compression amplification is not needed or with reduced compression settings.
If MEI/’BCD’ are used in patients with conductive or mixed hearing loss, the ‘functional gain’ doesn’t provide any useful information on the quality MEI/’BCD’-fitting. Instead, the ‘effective gain’ should be used, as it is a fitting-quality measure. The ‘effective gain’ is by definition the difference between bone-conduction thresholds and device-aided thresholds and, therefore, might be negative (what is acceptable according to the new practise-based device-fitting procedure introduced in Chapter 4).