Determining fitting ranges of various bone conduction hearing aids

Transcription

1 Accepted: 3 May 217 DOI: /coa.1291 ORIGINAL ARTICLE Determining fitting ranges of various bone conduction hearing aids D.C.P.B.M. van Barneveld 1,2 H.J.W. Kok 1 J.F.P. Noten 1 A.J. Bosman 1 A.F.M. Snik 1 1 Department of Otolaryngology and Head and Neck Surgery, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands 2 Department of ENT/Audiology, School for Mental Health and Neuroscience (MHENS), Maastricht University Medical Center, Maastricht, The Netherlands Correspondence A.F.M. Snik, Department of Otolaryngology and Head and Neck Surgery, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands. ad.snik@radboudumc.nl Objectives: To define fitting ranges for nine bone conduction devices (BCDs) over different frequencies based on the device s maximum power output (MPO) and to validate the assessment of MPO of BCDs in the ear canal. Background: Maximum power output (MPO) is an important characteristic when fitting BCDs. It is the highest output level a device can deliver and is one of the major determinants of a device s fitting range. A skull simulator can be used to verify MPO of percutaneous BCDs. No such simulator is available for active and passive transcutaneous devices. Design: The MPO of nine different BCDs was assessed either by real-ear measurements and/or with skull simulator measurements. Main outcome measures: MPO and cross-validation of the methods using the Bland Altman method. Results: Percutaneous BCDs have higher MPO levels compared to active and passive transcutaneous devices. This results in a wide dynamic range of hearing for percutaneous devices. Moreover, the assessment of MPO by real-ear measurements was validated. Conclusion: Based on MPO data, fitting ranges were defined for nine BCDs over seven frequencies. 1 INTRODUCTION Bone conduction devices (BCDs) can be used for conductive and mixed hearing loss when reconstructive surgery or conventional hearing aids are not viable. Various types of implantable BCDs are available, and new devices are regularly introduced. There are directdrive and skin-drive devices. 1 In direct-drive devices, the actuator produces vibrations, which are transmitted directly to the bone either via percutaneous coupling (eg, Cochlear BAHA Connect and Oticon Ponto) or with an implanted transducer (eg, Med-EL Bonebridge). Skin-drive devices can be divided into conventional devices, like BCD on softband, and passive transcutaneous devices, such as Cochlear BAHA Attract and Sophono Alpha that are magnetically coupled to an implant in the skull. But how do we select the most appropriate BCD for an individual patient? The manufacturer usually provides the range of sensorineural hearing loss components that can be fitted with a given device. However, information on how these ranges are determined is unclear. When a new BCD is introduced onto the market, studies usually report on a device s functional gain, which is defined as the difference between aided and unaided hearing thresholds. This might not be the best way to evaluate the performance of a BCD. For example, a functional gain of 3 db for a patient with a conductive hearing loss of 3 db (ie, aided sound-field threshold and unaided air-conduction threshold at dbhl and 3 dbhl, respectively) is a perfect result. If the patient, however, had a conductive hearing loss of 6 dbhl, a functional gain of 3 db still leaves a functional air bone gap of 3 db. As BCDs directly stimulate the cochlea, bypassing the pathology that causes the conductive hearing loss component, it is more informative to consider aided thresholds relative to bone conduction thresholds. 2 This is referred to as effective gain, and in mixed hearing loss, this reflects the available gain to deal with the sensorineural hearing loss John Wiley & Sons Ltd wileyonlinelibrary.com/journal/coa Clinical Otolaryngology. 218;43:68 75.

2 VAN BARNEVELD ET AL. 69 component. A hearing device should compensate approximately half of the sensorineural hearing loss (eg, NAL or DSL fitting rule). An often-overlooked aspect when selecting an appropriate device is maximum power output (MPO). Maximum power output of a BCD is the maximum force level that the device can deliver to the cochlea. In other words, it is the loudest sound that can be perceived using that device. Given sufficient gain, a device with low MPO saturates at lower input levels than a device with high MPO. Maximum power output can be used to determine the fitting range (eg, Ref. 3-5 ). The MPO of percutaneous BCDs expressed in dbhl or dbspl can be calculated from datasheets provided by the manufacturer and can be verified with a skull simulator. For other devices, however, such data are not always available and verification equipment is lacking. An alternative to obtain MPO is to determine the input at output saturation by capturing the sound radiated from the BCD inside an occluded cavity, such as the ear canal or nostril, 6,7 and add this to the effective gain 3,5 (see Methods). In the present article, we aim to validate the assessment of MPO of BCDs in the ear canal by comparing three different measurements. In addition, we propose a model to determine fitting ranges for nine implantable BCDs based on MPO results. Keypoints Determination of MPO of nine BCDs. MPO is used to determine fitting ranges. Validation of in-ear measurements to assess MPO. Percutaneous devices have higher MPO than passive and active devices, resulting in a wide dynamic range. was positioned in front of the subject at 1 m distance. We used warble tone stimuli. In case of asymmetric hearing loss with better hearing in the non-implanted ear, we occluded that ear with a deeply fitted plug (EAR TM Classic TM, 3M, Saint Paul, Minnesota, USA) and earmuff. All equipment and sound-field stimulation were calibrated according to ISO-389, and the experiments were conducted in a soundproof double-walled booth. From these measurements, the effective gain is calculated by subtracting aided sound-field thresholds (T) from bone conduction thresholds (BC) (Figure 1C): G ¼ BC T 1 2 MATERIALS AND METHODS 2.1 Patients and BCDs Nineteen patients with conductive or mixed hearing loss who received BCDs at our department participated in the experiments (methods 2 and 3). In addition, the MPO of these and other devices was assessed using a skull simulator instead of patients (method 1). Table 1 gives an overview of the different devices and number of measurements of the present study. Maximum power output is a device property that in principle is not dependent on patient characteristics. We used test devices of the type similar to the patient s own devices that were not individually programmed. The devices were set to deliver maximum amplification without generating feedback and were unlimited in output and in linear amplification mode with omnidirectional microphone settings. All advanced processing algorithms were turned off. All patients participating in this study provided informed consent, and the study has been performed according to the Declaration of Helsinki. The local medical ethical committee refrained from evaluating the study protocol as most of the measurements were part of standard operating procedures. 2.2 Measurements Audiometry: effective gain Bone conduction thresholds were acquired with standard procedures and equipment using the B71 bone vibrator with a clinical audiometer (Affinity or Equinox, Interacoustics, Middelfart, Denmark). Aided sound-field thresholds were assessed with the same audiometer. The loudspeaker (Control 1x, JBL, Harman, Stamford, Connecticut, USA) 2.3 MPO Method 1 In method 1, we assessed MPO at 5, 1, 15, 2, 3 and 4 Hz by assessing input output behaviour of the percutaneous BCDs to warble tone stimuli using a skull simulator (SKS1, Interacoustics). See Table 1 for an overview of the devices used per method. Increasing the input while measuring the output allowed us to determine the MPO that a device can deliver in dbfl rel 1 ln. This value was converted into dbhl using RETFLdbc, 8 so it could be related to hearing thresholds and loudness discomfort levels. Figure 1A illustrates this schematically; in this example, the MPO at 1 Hz is 118 db FL rel 1 ln, which is equivalent to 72.5 dbhl Method 2 In method 2, we assessed MPO at 5, 75, 1, 15, 2, 3 and 4 Hz by assessing input output behaviour of the BCDs to warble tone stimuli using a skull simulator (SKS1, Interacoustics) combined with the patients effective gain. See Table 1 for an overview of the devices used. Method 2 (and 3) is based on the definition of maximum output: MPO is the sum of the input level at which the device saturates (I saturation ) plus the (linear) effective gain (G): MPO ¼ I saturation þ G 2 The input level at output saturation (I saturation ) was obtained by intersecting the diagonal of the input output curve and horizontal asymptote at maximum output (Figure 1A,B). The effective gain was obtained using equation 1. Maximum power output was subsequently converted from dbspl to dbhl according to reference. 9

3 7 VAN BARNEVELD ET AL. TABLE 1 Number of devices tested per frequency and per measurement method Company Type of device [1] 5 Hz 75 Hz 1 Hz 15 Hz 2 Hz 3 Hz 4 Hz Method 1 BAHA Cordelle II Cochlear, Sydney, Australia Direct-drive with percutaneous coupling Ponto Plus Power Oticon Medical, Askim, Sweden Direct-drive with percutaneous coupling BAHA5 Cochlear, Sydney, Australia Direct-drive with percutaneous coupling Ponto Plus Oticon Medical, Askim, Sweden Direct-drive with percutaneous coupling BAHA BP11 Connect Cochlear, Sydney, Australia Direct-drive with percutaneous coupling BAHA4 Cochlear, Sydney, Australia Direct-drive with percutaneous coupling Method 2 Oticon Ponto Plus Power Oticon Medical, Askim, Sweden Direct-drive with percutaneous coupling BAHA BP11 Connect Cochlear, Sydney, Australia Direct-drive with percutaneous coupling BAHA BP11 Attract Cochlear, Sydney, Australia Skin-drive with passive transcutaneous coupling Method 3 Oticon Ponto Plus Power Oticon Medical, Askim, Sweden Direct-drive with percutaneous coupling BAHA BP11 Connect Cochlear, Sydney, Australia Direct-drive with percutaneous coupling BAHA BP11 Attract Cochlear, Sydney, Australia Skin-drive with passive transcutaneous coupling Bonebridge Med-EL, Innsbruck, Austria Direct-drive with active transcutaneous coupling Sophono Alpha2 Medtronic, Boulder, USA Skin-drive with passive transcutaneous

4 VAN BARNEVELD ET AL. 71 (A) 118 Skull simulator 1: maximum output (B) In ear 3: input at output saturation (C) 2 Frequency (Hz) Output (db rel 1 µn) 2: input at output saturation Output Input (db HL) Input (db SPL) Input (db SPL) 1 12 FIGURE 1 Schematic representation of the methods. (A) Schematic representation of an input output curve measured using the skull simulator. Method 1 determines the maximum power output (MPO) by reading off the maximum value of the input output curve in dbfl rel. 1 ln. Method 2 uses the input at output saturation, which is determined by intersecting the diagonal of the input output curve and horizontal asymptote at maximum output, denoted by the vertical dashed line. (B) Schematic representation of an input output curve measured in the ear canal with device on (black line) and device tuned off (grey line) measuring direct sound. Method 3 uses the input at output saturation measured in the ear canal, which is obtained by intersecting the first diagonal of the input output curve and horizontal asymptote at output saturation. Note that the main outcome is the input at output saturation and that output is in not specified as it depends on variables such as distance of the probe microphone to the bone conduction device. (C) Example audiogram. In method 2 and method 3, MPO is obtained by adding the input at output saturation to the effective gain. The effective gain is defined as the aided sound-field threshold (T) subtracted from the bone conduction threshold (<). Circles denote air-conduction thresholds measured with headphones or insert phones Figure 1A illustrates this method. The input at output saturation is 78 db SPL. The effective gain is determined from the audiogram at panel C using equation 1, which is 15-25= 1 db at 1 Hz in this example. Using equation 2 gives an MPO of 781=68 dbspl, which equals 62 dbhl at 1 Hz Method Loudness discomfort level In method 3, we assessed MPO at 5, 75, 1, 15, 2, 3 and 4 Hz by assessing input output behaviour of the BCDs to warble tone stimuli similar to method 2. Instead of the skull simulator to assess the input level at output saturation, we used a probe tube microphone (Equinox, Interacoustics) to measure the sound radiated inside the plugged ear canal. The probe tube was placed inside the ear canal through the occluding insert-phone earplug (EAR Link 3A, Sanibel, Middelfart, Denmark). To ensure direct sound did not mask the radiated sound in the occluded ear canal, we performed control measurements with the device turned off. See Table 1 for an overview of the devices used per methods. The input level at output saturation was obtained by intersecting the diagonal of the input output curve and horizontal asymptote at maximum output (Figure 1B) and used in equation 2 to obtain MPO. The MPO was converted from dbspl to dbhl according to reference. 9 Figure 1B illustrates this method. The input at output saturation is 79 db SPL. The effective gain is determined from the audiogram at panel C using equation 1, which is 15-25= 1 db at 1 Hz. Using equation 2 to get the MPO gives 791=69 dbspl, which equals 63 dbhl at 1 Hz. The in-the-ear measurements were performed in both ears, and the resulting MPOs were averaged to increase reliability, as these two values should, in principle, be the same. In case of unilateral atresia, the measurements could only be performed in the contralateral ear. Output (db HL) /3 of Audible range 35 db Dynamic range Threshold Sensorineural hearing loss (db HL) FIGURE 2 The suggested maximum power output as a function of sensorineural hearing loss component (black line) when the dynamic range is equal to 2/3 of the audible range and at least 35 db wide (black lines). The theoretical loudness discomfort level (LDL) is suggested by Dillon and Storey 11

5 72 VAN BARNEVELD ET AL. 2.4 Statistics Bland Altman analysis 1 is used to assess the similarity of the three methods. This analysis looks at the difference between two methods as a function of the average between the two methods. If two methods are comparable, there is no relationship between the difference and average. 2.5 Fitting ranges A patient s dynamic range of hearing is, by definition, the difference between hearing thresholds and loudness discomfort levels. The discomfort levels we use in this study are taken from published data, 11 as it is not possible to collect this information in bone conduction stimulation due to the limited output of any bone conductor. We used the published three frequency average of loudness discomfort levels and converted them to dbhl. 9 As MPO limits the dynamic range of hearing, we tried to define the minimum hearing range, or in other words, the lowest acceptable MPO for a given sensorineural hearing loss component. Based on the width of the speech area (3-35 db), Zwartenkot et al. 5 introduced a minimum dynamic hearing range of 35 db. We extended that the hearing range should be at least 35 db while no more than 1/3 of the hearing range is missed owing to the low MPO (see discussion for arguments). This criterion is referred to as the 2/3 rule. Figure 2 displays suggested MPO (bold black line) as a function of the sensorineural hearing loss component. 3 RESULTS 3.1 Overall outcome Figure 3 shows the measured average MPO per frequency for the nine BCDs, and Table 2 lists a summary of the data. The Cochlear BAHA (Cochlear, Sydney, Australia) Cordelle II has the highest MPO, 1 Cordelle 1 Ponto Plus Power 1 BAHA Ponto Plus 1 BP11 Connect 1 BAHA BP11 Attract 1 Bonebridge 1 Sophono MPO (db HL) Frequency (khz) FIGURE 3 Average maximum power output as a function of frequency for the three measurement methods (circle: method 1, square: method 2, triangle: method 3). Error bars denote one standard deviation

6 VAN BARNEVELD ET AL. 73 TABLE 2 Average maximum power output (MPO) values together with standard error of the mean (in brackets) and the suggested fitting ranges of the sensorineural hearing loss component rounded to 5 db based on these MPO values Maximum power output (dbhl) Maximum loss (dbhl) 5 Hz 75 Hz 1 Hz 15 Hz 2 Hz 3 Hz 4 Hz 5 Hz 75 Hz 1 Hz 15 Hz 2 Hz 3 Hz 4 Hz Cochlear BAHA Cordelle II 8 (1.2) 77 (.3) 82 (.3) 87 (.3) 82 (.3) 8 (.4) Oticon Ponto Plus Power 59 (.6) 78 (4.3) 74 (.4) 77 (.4) 81 (.2) 76 (.2) 73 (.2) Cochlear BAHA5 58 (.) 68 (.1) 74 (.1) 79 (.1) 74 (.1) 73 (.1) Oticon Ponto Plus 6 (.1) 72 (.1) 76 (.1) 78 (.1) 74 (.1) 7 (.1) (.9) 72 (4.3) 68 (.9) 72 (.7) 77 (.7) 72 (.7) 71 (.7) Cochlear BAHA BP11 Connect Cochlear BAHA4 49 (.1) 59 (.1) 67 (.1) 74 (.1) 78 (.1) 67 (.1) (2.6) 61 (4.8) 56 (5.) 66 (3.3) 51 (n/a) (n=1) Cochlear BAHA BP11 Attract Med-EL Bonebridge 56 (1.4) 55 (8.7) 55 (8.9) 59 (4.7) 67 (.3) 7 (n/a) (n=1) Sophono Alpha2 35 (n/a) 5 (6.3) 71 (n/a) 44 (1.1) (n=1) (n=1) 1 The results of method 1 are presented for percutaneous devices (except at 75 Hz). For the other devices and at 75 Hz, the results of method 3 are presented. followed by Oticon (Oticon Medical, Askim, Sweden) Ponto Plus Power, Cochlear BAHA5, Oticon Ponto Plus, Cochlear BP11 Connect, Cochlear BAHA4, Cochlear BP11 Attract, Med-EL Bonebridge (Med-EL, Innsbruck, Austria) and Medtronic Sophono (Medtronic, Boulder, USA). The difference in MPO between BP11 Attract and BP11 Connect (i.e. same device with a different configuration) is 5 db in the low frequencies and up to 21 db in the high frequencies, due to the less-effective transcutaneous coupling. 3.2 Comparison of measurement methods The MPO of the BP11 Connect and Ponto Plus Power was assessed in three different ways (see methods). Figure 3 displays the outcomes for each device according to each measurement method and, as shown in the figure, the contours are comparable. The variability of in-the-ear measurements (method 3) seems to be larger than the variability of skull simulator measurements (method 1). Figure 4 presents the outcome of the statistical analysis. The average difference between the methods is within 5 db, and 95% of the differences between methods are smaller than 15 db. Therefore, it is concluded that the three methods give comparable results, which cross-validates the measurements. 3.3 Fitting ranges Next, we determined the maximum sensorineural hearing loss components allowed using the 2/3 rule (see Materials and Methods). If this rule is applied to MPO results as found in this study, we find the maximum sensorineural hearing loss components allowed, presented in Table 2. The Cordelle II is the most powerful BCD and can be used for sensorineural hearing loss components up to 45-5 dbhl. Thus, up to 45-5 dbhl sensorineural hearing loss, a dynamic range of hearing of 2/3 of the unaided dynamic range with a minimum of 35 db is available. The transcutaneous devices have the most limited fitting ranges. 4 DISCUSSION In the present paper, we determined the MPO of nine BCDs using three methods, which resulted in consistent MPO values. Therefore, if a skull simulator is not available or if the device cannot be coupled to such a simulator, one can use in-ear measurements to assess MPO. MPO differs substantially among devices with BAHA Cordelle II being the most powerful device and the passive transcutaneous implants the least powerful device. Maximum power output of these passive transcutaneous devices is 1 to 15 db lower than that of the percutaneous devices. Furthermore, comparing BAHA BP11 Attract and BP11 Connect MPO capabilities, we see a decreased MPO of 5 db in the low frequencies and a decrease of up to 21 db in the high frequencies. This is not surprising given that the skin and subcutaneous layers dampen the vibrations when transcutaneous coupling is used

7 74 VAN BARNEVELD ET AL. 2 2 Difference between method 2 and method Difference between method 3 and method Hz 75 Hz 1 Hz 15 Hz 2 Hz 3 Hz 4 Hz Average between method 1 and method Average between method 1 and method 3 FIGURE 4 Bland Altman analysis of methods 1 and 2 (left panel) and methods 1 and 3 (right panel). Dashed lines represent the mean and 1.96 * SD of the difference between the methods (95% confidence intervals) Obviously, the MPOs of all nine devices are well below the loudness discomfort level (typically between 9 and 11 dbhl) 11. This implies that the dynamic range of hearing cannot be fully exploited by these BCDs. 4.1 Comparison with previous research Our study is an extension of previous work published by Zwartenkot et al.. 5 More recently, introduced devices were measured, and to validate the data, a comparison was made between three methods. The results are largely in agreement with previous data. 3-5 However, for Sophono at 2 khz, our results show a more limited MPO than has been shown before, 14 although the number of measurements is limited. At present, we have no explanation for that finding. It is suggested that intersubject variability might arise from the differences in coupling efficiency, the patient s ability to concentrate during the threshold measurements and the quantisation step (5 db) of the sound-field measurements. 4.2 Fitting ranges Generally, for normal hearing subjects 65 dbhl is a comfortable listening level 15 and 1 dbhl is perceived as too loud. 11 For subjects with a sensorineural hearing loss, the loudness discomfort levels might be slightly higher. 11 Similar to fitting a conventional hearing aid for subjects with a (pure) sensorineural hearing loss, a BCD should preferably have an MPO close to the loudness discomfort level so that the complete dynamic range of hearing is used. As MPO of all BCDs is limited, MPO compromises the aided dynamic range of hearing. What size of aided dynamic range of hearing should be available for a patient? As argued before, normal speech audibility requires a hearing range of 3-35 db, 16 eventually combined with wide dynamic range compression. Patients with limited sensorineural hearing loss components have been shown to use a large dynamic range of at least two-thirds of the unaided dynamic range 17 ; the users of linear BCDs set the volume wheel of their devices so that MPO equals about 2/3 of a user s unaided hearing range. When determining fitting ranges, we used the 2/3 rule (see methods and table 2 for the outcomes). Maximum power output is an important factor that determines fitting range, but it is not the only factor. Feedback-free gain is also important (e.g. Ref. 18 ). Although one can determine and apply the feedback thresholds in most modern BCDs, feedback thresholds might compromise the fitting range. Next, BCDs are nowadays equipped with wide dynamic range compression, to allow input to be processed without peak clipping distortion. However, compression has been designed to account for the different loudness growth that patients with sensorineural hearing loss have. Patients with predominately conductive hearing loss have the same loudness growth as normal hearing subjects and, as such, do not require compression. In the case of a limited effective dynamic range of hearing, the better option is to choose a device with higher MPO instead of using compression. Lastly, the noise floor could be problematic. According to Carlsson and Hakansson 2 and manufacturer s data (Bonebridge and Sophono), the noise floor of standard BCDs is not audible. As such, it does not need to be considered. In conclusion, devices with higher MPOs are preferable over devices with lower MPOs as the increased MPO enables the largest dynamic range without the need of wide dynamic range compression. This allows patients to better enjoy sounds and to have more spare room for the future if hearing deteriorates due to, for example, ageing. ACKNOWLEDGEMENTS We thank our colleagues for providing valuable feedback on this manuscript.

8 VAN BARNEVELD ET AL. 75 CONFLICTS OF INTEREST There is no conflict of interest. REFERENCES 1. Reinfeldt S, Hakansson B, Taghavi B, Eeg-Olofsson M. New developments in bone-conduction hearing implants: a review. Med Devices (Auckl). 215;8: Carlsson PU, Hakansson BE. The bone-anchored hearing aid: reference quantities and functional gain. Ear Hear. 1997;18: Mertens G, Desmet J, Snik A, Van de Heyning P. An experimental objective method to determine maximum output and dynamic range of an active bone conduction implant: the Bonebridge. Otol Neurotol. 214;35: Rahne T, Plontke SK. Apparatieve Therapie bei kombiniertem H orverlust; Ein audiologischer Vergleich aktueller H orsysteme. HNO. 216;64: Zwartenkot JW, Snik AFM, Mylanus EAM, Mulder JJS. Amplification options for patients with mixed hearing loss. Otol Neurotol. 214;35: Fagelson M, Martin FN. Sound pressure in the external auditory canal during bone-conduction testing. J Am Acad Audiol. 1994;5: Snik A, Noten J, Cremers C. Gain and maximum output of two electromagnetic middle ear implants: are real ear measurements helpful? J Am Acad Audiol. 24;15: Carlsson P, Hakansson B, Ringdahl A. Force threshold for hearing by direct bone conduction. J Acoust Soc Am. 1995;97: Bentler RA, Pavlovic CV. Transfer functions and correction factors used in hearing aid evaluation and research. Ear Hear. 1989;1: Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1: Dillon H, Storey L. The National Acoustic Laboratories procedure for selecting the saturation sound pressure level of hearing aids: theoretical derivation. Ear Hear. 1998;19: Hakansson B, Tjellstrom A, Carlsson P. Percutaneous vs. transcutaneous transducers for hearing by direct bone conduction. Otolaryngol Head Neck Surg. 199;12: Hakansson B, Tjellstrom A, Rosenhall U. Hearing thresholds with direct bone conduction versus conventional bone conduction. Scand Audiol. 1984;13: Hol MK, Nelissen RC, Agterberg MJH, Cremers CWRJ, Snik AFM. Comparison between a new implantable transcutaneous bone conductor and percutaneous bone-conduction hearing implant. Otol Neurotol. 213;34: Hochberg I. Most comfortable listening for the loudness and intelligibility of speech. Audiology. 1975;14: Mueller HG, Killion MC. An easy method for calculation the articulation index. Hearing Journal. 199;43: Snik AFM. Are today s implantable devices better than conventional solutions for patients with conductive and mixed hearing loss? ENT and Audiology news. 214;23: Bosman AJ, Snik AFM, Mylanus EAM, Cremers CWRJ. Fitting range of the BAHA Cordelle. Int J Audiol. 26;45: How to cite this article: van Barneveld DCPBM, Kok HJW, Noten JFP, Bosman AJ, Snik AFM. Determining fitting ranges of various bone conduction hearing aids. Clin Otolaryngol. 218;43: