A COMPARATIVE STUDY OF THE AUDIOLOGICAL OUTCOMES WITH RETRO-X (SEMI-IMPLANTABLE HEARING AID SYSTEM) AND CONVENTIONAL OPEN FITTING HEARING AIDS.

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1 A COMPARATIVE STUDY OF THE AUDIOLOGICAL OUTCOMES WITH RETRO-X (SEMI-IMPLANTABLE HEARING AID SYSTEM) AND CONVENTIONAL OPEN FITTING HEARING AIDS. Minoo Lenarz 1, Thomas Lenarz 1, Mark Winter 2 Department of Otolaryngology of Medical University of Hannover, Hannover, Germany 1 Hannover Hearing Center, Hannover, Germany 2 Address correspondence and reprint requests to: Thomas Lenarz, M.D., Ph.D. Professor and Chairman Department of Otorhinolaryngology Medical University of Hannover Carl-Neuberg-Str. 1 D Hannover Phone: Fax: lenarz@hno.mh-hannover.de 1

2 Abstract Objective: The objective of this study was to compare the results of hearing augmentation with the Retro-X semi-implantable hearing aid with a conventional non-implantable open canal hearing aid with the same software technology (Titan-X, auric Hearing Systems, HiKaNo.: ). Subjects: Nineteen subjects (20 ears) with mild to moderate high-frequency sensory-neural hearing loss were included in this clinical study. Methods: All the subjects were first fitted with a conventional BTE open canal hearing aid (Titan-X). After a period of 4 to 6 weeks audiological evaluations were performed using standardized speech tests in quiet and noise. Subjective evaluation was performed with the help of standardized questionnaires. After this phase the patients received the semiimplantable Retro-X device under local anaesthesia and 4 weeks later were fitted with a hearing module with the same software technology as the conventional Titan-X hearing aid. 4 weeks after the first fitting the same audiological evaluations were performed under similar conditions and the patients were evaluated again using the same questionnaires in order to compare the results of the Retro-X semi-implantable system with the conventional open canal hearing aid. Results: Audiological evaluations revealed better results with the semi-implantable Retro-X in the adaptive speech in noise test but the results of the monosyllabic word test in quiet were similar for the Retro-X and conventional open canal hearing aid. The patients subjectively preferred the improved wearing comfort of the semi-implantable device. 2

3 Conclusions: The Retro-X semi-implantable hearing device provides better speech perception in noise and higher wearing comfort in comparison to the conventional open canal hearing aids. Considering these improvements and the simple implantation procedure under local anaesthesia with low complication rate, Retro-X is an alternative to the conventional open canal hearing aids in patients with mild to moderate high frequency sensory-neural hearing loss. Key words: Semi-implantable hearing aid; open fitting; Retro-X; sensorineural hearing loss. 3

4 Introduction The most common complaint of individuals with high-frequency sensorineural hearing loss is impaired speech understanding in noise. Conventional hearing aids usually cause an uncomfortable occlusion effect due to obstruction of low frequency conduction in the ear canal [19]. This can be solved with open canal hearing aids (with skeleton or perforated earmolds) which alleviate the acoustic occlusion effect and provide a more natural quality of sound. However, systems with skeleton or perforated earmolds still cause a partial occlusion and change the physical characteristics of travelling sound wave in the ear canal. In addition open fitting in general constitutes a major challenge for audiologists, as feedback problems limit the obtainable gain. RetroX, is a semi-implantable transcutaneous air conduction hearing aid (TACHAS) which will be implanted at the posterior wall of the cartilaginous ear canal and provides an alternative to the conventional open fitting hearing aids. The goal is hearing augmentation with no obstruction and minimal change in the physical properties of the ear canal. The preliminary audiological results with this system have already been published elsewhere [1, 7, 26-28]. The aim of the present study is two folds: a) to evaluate the incidence of complications due to device implantation and b) to compare the patient satisfaction and audiological outcomes with Retro-X and a conventional BTE open canal hearing aid with the same digital signal processing algorithm in the same group of patients. Subjects and methods The present study was performed on 19 subjects (20 ears) with mild to moderate high frequency sensory-neural hearing loss who matched the audiological criteria for hearing augmentation with Retro-X semi-implantable hearing aid [26]. They were six females and 13 males with an average age of 57 years (± 9 years). Only one subject was implanted 4

5 sequentially on both sides and was evaluated on each side separately according to the study protocol. Figure 4 shows the non-aided air conduction thresholds of the 20 ears which were selected for this study and the selection criteria for the Retro-X. All subjects had previous experience with conventional hearing aids prior to participation in this study but were not satisfied with their conventional hearing aids due to wearing discomfort, chronic otitis externa or lack of improved speech understanding in noise. The patients were initially fitted with a behind-the-ear (BTE) hearing aid (Titan-X, Auric Hearing Systems, HiKa No.: ) with open skeleton earmolds (Fig. 2). The fitting was performed using Navig-X software (version 1.82). After a trial period lasting approximately four to six weeks (including fine-tuning sessions), the subjects were evaluated in free-field condition, using standard audiological tests in quiet and noise. The subjective evaluation was performed by means of 3 questionnaires. After this phase the patients were subsequently implanted with Retro-X and 4 weeks later implantation were fitted with the same software (Navig-X version 1.82). After 4 to 6 weeks of device use the patients were evaluated again in free-field condition, using the same audiological tests under similar conditions and received the same questionnaires for subjective evaluation. Surgical Procedure Implantation was performed in an outpatient basis under local anaesthesia. In order to choose the right length of the implant, the thickness of the posterior wall of the cartilaginous ear canal was measured with the injection needle and a measuring template. The implant should be 1-2 mm longer than the thickness of the posterior canal wall in order to prevent any pressure on the retro-auricular skin. A skin incision around 4 mm in length was made in the retroauricular fold at the level of the upper edge of the tragus (Fig. 3a). A trocar-like instrument was then mounted using a handpiece, a guide, the implant and a cutting tip (Fig. 3b). The trocar was inserted and pushed towards the ear canal near the junction between cartilaginous 5

6 and bony ear canal (Fig. 3c). After entering the ear canal the cutting tip was removed and the sound outlet head was mounted on the implant (Fig. 3d). At the end the trocar was removed and a plug was attached to the implant in order to prevent occlusion of its canal with blood crusts (Fig. 3e). A sterile strip dressing was rapped around the implant, which was removed after one week (Fig. 4f). The first fitting with the hearing module was performed four weeks after implantation to allow adequate wound healing. The patients were evaluated 4 to 6 weeks after the first fitting. Device Fitting The fitting of the Titan-X and Retro-X was both performed using Navig-X software (version 1.82). The two-channel fully digital processor was adjusted to compensate for each subject s individual hearing loss. For purposes of feedback suppression, the processor incorporates both notch filter and peak shifter techniques. Audiological Evaluations All the tests were performed using free field measures, with a unilaterally fitted device and the contralateral ear left unplugged 4-6 weeks after experience with each of the devices. The Freiburg monosyllabic word test in quiet was performed at a sound pressure level (SPL) of 50 and 65 db. The Oldenburg sentence test was used as an adaptive assessment procedure [23-25] in which the speech reception threshold (SRT) was obtained in both quiet (S 0 ) and noise (S 0 /N 0 ). The presented speech level in quiet was varied in order to find the level at which 50% word comprehension is achieved and, in order to measure the signal-to-noise (S/N) ratio, the noise level was held constant at 65 db SPL while the level of the speech signal was varied according to the number of correct responses using a computerized audiometer (Audio-Data, AD 2017). 6

7 Statistical analysis was performed using the Student s t-test and the Wilcoxon signed-rank test. Subjective evaluation Subjects were asked to respond to the International Outcome Inventory for Hearing Aids (IOI- HA) [6], the Oldenburg Inventory [8, 9]. The IOI-HA gives a general idea of the level of satisfaction with the hearing device in which users answer the seven questions on a five-point scale. The higher the score, the more satisfied is the respondent. In order to evaluate the specific characteristics of open fitting, a non-standardized questionnaire, the Retro-X Evaluation Inventory (REI) [28] was used, in which patients were confronted with a separate set of questions dealing with occlusion effect, handling, cosmetics and sound quality. The score represents the level of satisfaction (1 = very dissatisfied; 2 = dissatisfied; 3 = sometimes satisfied, sometimes dissatisfied; 4 = satisfied; 5 = very satisfied). Results In our patients the only complication due to Retro-X implantation was granulation tissue formation around the implant which was observed in 4 subjects (Table 1). Local treatment resulted in complete recovery in 3 cases but in one patient the implant had to be removed 6 months after implantation due to multiple recurrences of granulation tissue. After explantation the skin tunnel closed spontaneously within one week. This patient was re-implanted after a period of 3 months and this time did not have any wound healing problems. It was possible to reach the subjective satisfaction of the patients within two or three fitting sessions (including the fine-tuning). As the test subjects had mild to moderate high-frequency hearing loss with a large dynamic range and amplification occurred with the ear canal open, it was possible to set the compression ratio to low values, resulting in both clear and natural sound output. 7

8 The Freiburg monosyllabic word test revealed significantly improved results using both the conventional BTE device (Titan-X) and the Retro-X compared to the unaided situation in the free-field audiometry (p<0,001; Fig. 5). Mean unaided speech understanding at 50 db SPL was 40.8% (±27.9%) and 72.5% (±21.4%) at 65 db SPL. With the Titan-X the level of speech understanding was 65.8% (±27.0%) at 50 db SPL, and 91.5% (±11.7%) at 65 db SPL. Results obtained with Retro-X were 69.8% (±27.8%) and 94.5% (±10.1%) respectively. The difference between the Titan-X and the Retro-X was not statistically significant (p=0.24 at 50 db SPL; p=0.08 at 65 db SPL). Using the Oldenburg sentence test in quiet, speech reception threshold (SRT) dropped significantly from 37.9 db (±6.6) in the unaided condition to 34.7 db (±5.3) with the Titan-X and 33.9 db (±6.8) with the Retro-X (Table 2). Speech understanding in noise was significantly enhanced from -2.8 db (±1.3) in the unaided condition to -3.8 db (±1.4 db) with the Titan-X and -4.4 db (±1.1) with the Retro-X. The improvement for the Retro-X over the Titan-X was statistically significant in this test (p<0.05) (Table 2). The subject who underwent sequential bilateral implantation with a three-month delay achieved an SRT score in quiet of 44.2 db SPL (right ear, R), 44.1 db SPL (left ear, L) and 42.0 db SPL with both ears (B) unaided. The results with the Retro-X were 39.8 db SPL, 40.1 db SPL and 37.5 db SPL respectively. The SRT in noise improved from -3.5 db (R), -3.7 db (L) and -3.9 (B) to -4.9 db (R), -5.2 (L) and -5.7 db (B). The IOI-HA questionnaire shows that patients preferred the Retro-X device over the conventional BTE hearing aid, owing to its wearing comfort and the more natural sound quality. This is also indicated by the longer duration of device use per day (figure 6). The Oldenburg Inventory reveals that the level of satisfaction under aided conditions (Titan- X, Retro-X) is significantly better than in the non-aided condition (p<0.001). The degree of satisfaction in noisy conditions is significantly higher with the Retro-X than with the conventional hearing aid (p<0.05) (Fig. 7). 8

9 Using the Retro-X Evaluation Inventory (REI), in all categories apart from the question regarding feedback, the Retro-X achieves significantly better scores than the Titan-X (Fig. 8). The most satisfactory aspects were better wearing comfort, less occlusion effect and improved cosmetic appearance. Patients reported that both devices behaved similarly in terms of feedback. Discussion High-frequency hearing loss above 1 khz is related to speech reception in noise, a pure-tone average at 2 and 4 khz (PTA 2.4 ) of 30 db HL constitutes a noticeable impediment to speech understanding in noise [17]. These are the main group of the candidates who can benefit from the hearing magnification by the Retro-X. Garin found an improvement in speech understanding (disyllabic words) of 26% for a signalto-noise (S/N) ratio of -5 db. This is comparable with our findings, namely an improved S/N ratio of 1.6 db (the discrimination function for the Oldenburg sentence test being 17% / db for normal-hearing persons [1, 7]. The high degree of acceptance of the Retro-X device is probably due to two factors: the open ear canal and the low compression setting of the Retro-X hearing processor when fitting patients suffering from mild to moderate high-frequency hearing loss. In this way Retro-X allows a kind of dual sound perception: the natural pathway and the amplified sound delivered through the implant. The use of conventional open canal hearing aids significantly improves both quality and intelligibility of speech especially in background noise even when it has essentially no effect on the low-frequency output [3, 4, 7, 10, 11, 14, 16, 17]. However open fitting without an earmold or perforated plug of any kind would be even better and preserves the physical characteristics of the outer ear canal, most notably the resonance effect of the ear canal that facilitates natural sound perception and localization. A study by MacKenzie et al. [15] 9

10 involving 106 subjects and three different earmolds (unvented, 0.8 mm vent, 2 mm vent) showed that all three molds were equally uncomfortable (causing a moist, itchy sensation, among other problems). Although the 2 mm vent reduced the occlusion effect from 35% to 13% (although patients still reported discomfort). The improvement yielded by Retro-X over the conventional open canal hearing aids seems to be due to the preservation of the outer ear canal physical characteristics: there is no obstructive material in the concha or ear canal that might influence sound quality and characteristics. Additionally, the very long flexible silicone tube used with BTE hearing aids (typically 75 mm in length) causes resonances in the frequency response (typically around 1, 3 and 5 khz) and has a low-pass filter characteristic. The longer or narrower the tubing is, the more the resonance peaks move to lower frequencies and the more markedly the frequency response above 3 khz is reduced [22]. Different damping and filter elements are necessary in order to straighten the frequency response. The frequency response obtained with the RetroX when working with a sound tube length of around 20 mm is far smoother, which might result in more natural sound perception [29]. Still also with the Retro-X the possible gain at the high frequencies is limited to about 30 db because of the propensity for acoustic feedback to occur. As feedback constitutes the major problem in open fitting of hearing aids, the level of subjective satisfaction as indicated by responses to the relevant question in the RetroX Evaluation Inventory (REI) - is still limited and revealed no difference between the RetroX and the TitanX. Conclusions The improved speech understanding in noise and subjectively better wearing comfort resulting from lack of ear canal occlusion is the major advantage of Retro-X in comparison to other conventional open canal hearing aids. Considering the simplicity of the surgical 10

11 approach and the low rate of minor complications for device implantation Retro-X offers an alternative for hearing augmentation in patients suffering from mild to moderate highfrequency hearing loss. 11

12 References 1. Barbara M, Bandiera G, Serra B, Marrone V, Tarentini S, Pinna JC, Ronchetti F, Graziadio M, Monini S (2005) Digital hearing aids for high-frequency sensorineural hearing loss: preliminary experience with the RetroX device. Acta Oto-Larygologica 125(7): Beamer SL, Grant KW, Walden BE (2000) Hearing aid benefit in patients with highfrequency hearing loss. J Am Acad Audiol 11(8): Brugel FJ, Schorn K, Fastl H (1991) Effect of venting the ear mould on speech discrimination in masking noise. HNO 39(9): Cox RM, Alexander GC (1983) Acoustic versus electronic modifications of hearing aid low-frequency output. Ear Hear 4(4): Cox RM, Alexander GC (2002) The International Outcome Inventory for Hearing Aids (IOI-HA): psychometric properties of the English version. Int J Audiol 41(1): Cox RM, Stephens D, Kramer SE (2002) Translations of the International Outcome Inventory for Hearing Aids (IOI-HA). Int J Audiol 41(1): Garin P, Genard F, Galle C, Jamart J (2004) The RetroX Auditory Implant for High- Frequency Hearing Loss. Otol Neurotol 25: Holube I, Kollmeier B (1991) Ein Fragebogen zur Erfassung des subjektiven Hörvermögens: Erstellung der Fragen und Beziehung zum Tonschwellenaudiogramm. Audiologische Akustik 30: Holube I, Kollmeier B (1994) Modifikation eines Fragebogens zur Erfassung des subjektiven Hörvermögens und dessen Beziehung zur Sprachverständlichkeit in Ruhe und in Störgeräuschen. Audiologische Akustik 33(4):

13 10. Horwitz AR, Dubno JR, Ahlstrom JB (2002) Recognition of low-pass-filtered consonants in noise with normal and impaired high-frequency hearing. J Acoust 111(1): Kuk FK (1991) Perceptual consequence of vents in hearing aids. Br J Audiol 25(3): Lenarz T, Weber BP, Mack KF, Battmer RD, Gnadeberg D (1998) The Vibrant Soundbridge System: a new kind of hearing aid for sensorineural hearing loss. 1: Function and initial clinical experiences. Laryngorhinootologie 77(5): Lenarz T, Weber BP, Issing PR, Gnadeberg D, Ambjornsen K, Mack KF, Winter M (2001) Vibrant Sound Bridge System. A new kind hearing prosthesis for patients with sensorineural hearing loss. 2: Audiological results. Laryngorhinootologie 80(7): Lundberg G, Ovegard A, Hagerman B, Gabrielsson A, Brandstrom U (1992) Perceived sound quality in a hearing aid with vented and closed earmould equalized in frequency response. Scand Audiol 21(2): MacKenzie K, Browning GG, McClymoont LG (1989) Relationship between earmould venting, comfort and feedback. Br J Audiol 23(4): Noble W, Sinclair S, Byrne D (1998) Improvement in aided sound localization with open earmoulds: observations in people with high-frequency hearing loss. J Am Acad Audiol 9(1): Smoorenburg GF (1992) Speech reception in quiet and in noisy conditions by individuals with noise-induced hearing loss in relation to their tone audiogram. J Acoust Soc Am 91(1): Souza PE, Bishop RD (2000) Improving audibility with nonlinear amplification for listeners with high-frequency loss. J Am Acad Audiol 11(4):

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16 Figure 1: Titanium tubing system (two-part) positioned in the soft tissue of the external ear and the postauricular hearing processor. Figure 2: TitanX conventional BTE hearing aid with skeleton earmold. Figure 3: Surgical procedure for implanting the two-part titanium tubing system. Figure 4: Air conduction hearing loss (mean ± standard deviation, n=20). The fitting range is shown in grey. Figure 5: Results of the Freiburg monosyllabic word test at 50 and 65 db SPL for the three test conditions (n=20; S: Significant with p<0,001; NS: Not significant). Figure 6: Results of the International Outcome Inventory for Hearing Aids (IOI-HA) (n=20; *p<0.01; **p<0.05). Figure 7: Score of the Oldenburg Inventory (n=20;). The improvement with RetroX over TitanX is significant for effort involved in understanding speech in noise (p<0.05). Figure 8: Results of the RetroX Evaluation Inventory (n=20; *p<0.01; **p<0.05). 16

17 Table 2:Speech reception threshold (SRT) in quiet and in noise using the Oldenburg sentence test (n=20). Unaided TitanX RetroX In Quiet [db SPL] 37.9 ± ± ± 6.8 In Noise (S 0 /N 0, 65dB SPL ) -2.8 ±1.3 db -3.8 ± 1.4 db -4.4 ± 1.1 db 17