News / Ideas / High Technology / Acoustics Children with hearing impairment also benefit from digital hearing instrument technology. 29 Focus Jochen W. Heinz Kinderzentrum, Hörgeräte Iffland GmbH & Co. KG, Esslingen Introduction Digital hearing systems have been routinely recommended for adults for some time. In recent years there has been much discussion regarding the fitting of these digital hearing instruments to children. When we consider the history of amplification technology, new developments have been initially fit to adults, and then subsequently, recommended for children. From the view of a hearingcare professional this is important, since the possibilities and potential benefits of new systems need to be initially verified in the adult population. Only when the results in adults are encouraging, should any attempt be made to fit children. These fittings should then be carefully planned and documented.
Case studies are a particularly useful tool to document possible advantages or disadvantages. It is important to select a fitting procedure, which is accepted worldwide and is valid and reproducible in pediatric fittings. One such fitting method is the DSL [i/o] procedure (Seewald et al.,1996). The advantages of this procedure, especially with children, and the related development of daily experience have been documented by Heinz (1999). This article outlines five case studies designed to understand the benefits that modern digital hearing instrument technology can offer to children. Subjects All the children in the study had at least three years hearing aid experience. We chose five children with ages ranging from 5 to 12 years. All had moderate to severe sensorineural or mixed hearing loss. We purposely chose subjects with a variety of currently available technology (digitally programmable or digital). All participants took part in the study with the consent of their parents. Hearing system The new technology instrument we chose to evaluate was the Claro (211 and 311 daz) hearing system by Phonak, a system which has already shown substantial benefits in the adult population. Claro instruments offer a feature called AutoSelect. This is an automatic program selection mechanism which switches between QuietAdapt (program for quiet) and NoiseAdapt (program for noise). During the trial this feature was purposely not activated. The children were encouraged to use the manual TacTronic switch to select the appropriate program for a given situation. Not only was the use of the TacTronic switch of interest to us, but more importantly: When and in which listening environments did the children switch between hearing programs. The start-up program was Program 1 (QuietAdapt). In order to help the children correctly identify the programs we activated the confirmation beep tones. For the trial we gave access to two programs QuietAdapt and NoiseAdapt. In order to achieve comparable results, we decided not to use the FM option. Method and fitting procedure Before starting the evaluation all children had their hearing tests updated. Unfortunately the start of the study coincided with the beginning of winter and therefore the cold/flu season. For this reason we often had to deal with changing middle ear conditions, which hindered our progress. The audiometric data were obtained using insert earphones, individual earmolds or headphones. Depending on age and knowledge of the speech test materials, the Göttinger Pediatric test II or the Freiburger speech discrimination test for adults (monosyllables) were used. The presentation levels through the headphones (without hearing aids) varied, depending on the hearing loss. In order to allow for individual transmission conditions the Real Ear to Coupler Difference (RECD) was measured for each child (see figure 1). This value and its interpretation is a substantial part of the DSL [i/o] procedure. Its reproducibility based on age has also been described by Sinclair et al. (1996a). RECD measurement and its application is explained in Appendix 1. 3
News / Ideas / High Technology / Acoustics The measurement of the individual RECD and the verification of instrument settings were verified using the Maicoscan MH 20 (outside of Europe: Audioscan RM 500). The programs chosen for evaluation were: Program 1 (QuietAdapt) with Fine-scale Noise Canceller off and fast-adaptive DPP. Program 2 (NoiseAdapt) with Fine-scale Noise Canceller light, fast-adaptive DPP and Adaptive digital AudioZoom. Test procedure To test the benefits of the devices, we chose a test battery, which is used in many pediatric departments in Germany. The speech test material used was the Göttinger pediatric speech test II and in one case, the monosyllabic Freiburger speech discrimination test for adults. The noise levels were altered to reflect the different audiogram configurations and / or the willingness of the children to cooperate at each test session. However, the Signalto-Noise Ratio (SNR) remained constant at 10 db. The Bruckhoff, GS 90 noise simulator presented multi-talker babble. Although clinical tests are necessary to verify pediatric fittings it is clear that clinical tests only provide a snapshot view of a child s benefit from a hearing instrument. Some outdated test procedures, such as functional gain are still routinely used for the verification of hearing instruments. This test has limited reliability to judge the overall success of the Figure 1 To determine the RECD, the sound pressure level in the coupler and the individual ear (with earmold in place) are measured. The difference between these values is the RECD which can then be implemented in the calculation of gain and MPO targets (for more information see appendix 1). db 90 80 70 60 50 40 30 20 10 0 10 20 30 250 500 1k 2k 4k 8k Frequency (Hz) Real ear measurement 2cc coupler measurement RECD (difference between real ear and 2cc coupler measurements) 4
fitting, and does not measure a child's hearing ability in competing noise. In addition, this procedure was developed for verification of linear amplification and does not provide a range of stimulus levels required for verification of non-linear instruments. The main disadvantages of functional gain in the verification of hearing instruments are: The test only provides information about low input levels. There is no information about everyday situations. There is no dynamic range information. The ambient noise level is at least 30 db which can introduce inaccuracies. Particularly for those with mild hearing loss. For this reason we decided not to measure functional gain although this measurement is standard in the evaluation of pediatric hearing aid fittings in Germany (if speech testing is not possible). The disadvantages of functional gain measurements have been described by Sinclair et al. (1996b) and Seewald et al. (1996). Table 2 Test protocol for monaural testing with hearing instruments for each ear Table 3 Test protocol for binaural measurements in noise for each ear Test material Level Angle to Program 1 (db) stimulus Göttinger II 50, 60 45 QuietAdapt or Freiburger + 80 Fine-Scale Noise Canceler not activated fast-adaptive DPP Test material Signal from 0 Noise from Program 2 db(i) 180 Göttinger II 60 or 65 55 or 65 NoiseAdapt or Freiburger Fine-scale Noise Canceler «light» fast-adaptive DPP Case Studies Four of the five children had already been fitted using the DSL [i/o] procedure. One child came to us with hearing instruments, which had been fitted and adjusted according to functional gain results. Case 1, F.K., 5 years F.K. attends pre-school. After being fitted with Claro instruments he spent substantially more time in group activities compared to when using his own aids. He was more concentrated and showed more staying power. His interest in the meaning of words increased rapidly. Although in direct conversation he was always spoken to in German, he started to recite numbers in Italian (his mother runs her own translation business). He was also suddenly able to understand television programs, such as cartoons, which have no visual cues for lip reading. This had not been possible with his previous aids. 5
Case 2, F.J., 12 years Initially F.J. felt uncomfortable with the new fitting. His current hearing aids were more than 5 years old and it was not possible to further improve their performance. It was therefore necessary that his amplification was re-assessed. When he was first fitted with his Claros he described his new experiences with the new instruments. He found soft sounds much more audible and this added to his initial description that everything was loud. He regularly used the option to manually switch programs with the Tac- Tronic switch and chose NoiseAdapt for noisy environments such as the school playground. In this type of difficult listening environment he reported that although he was hearing more softly he was still able to understand well. He was another keen user of the program switch and soon became accustomed to the new clearer sound. Case 3, C.R., 11 years C.R. had very little experience of low frequency amplification before her participation in this evaluation. She had been fitted with an open mould although her hearing level at 125 Hz was 40/45 db and 0/10 db at 6 khz. Therefore she initially used the NoiseAdapt program to imitate the sound quality of her own instruments as closely as possible. There is a low frequency reduction in the Noise- Adapt program. Her own voice also caused problems initially but she soon acclimatized. Her mother noticed that the television volume was set significantly lower and that she reacted more often and sooner when called, even over greater distances. She now only uses NoiseAdapt for difficult noisy situations and is comfortable at other times in Quiet- Adapt. Case 4, M.L., 8 years M.L. was the only participant who did not tolerate the initial setting of the instruments using the described fitting protocol. A possible reason for this may have been his excessive recruitment. His dynamic range in both ears was only 20-30 db. We therefore used the option to establish loudness growth curves for each ear using Loudness Perception Profile which is available in the fitting software. Although M.L. was familiar with a large range of audiometric tests, he was very excited by these measurements. He chose the pediatric design of the categorical scale on the Active Response Unit (see figure 4), which is available with the scaling device and was keen to "try out a procedure which was new to him. Both he and his mother commented that the settings after this procedure were more comfortable. This shows that it is possible to overcome tolerance problems by obtaining an individual Loudness Perception Profile and making additional adjustments where appropriate. The use of the Tactronic switch was also pronounced useful and fun in this case. NoiseAdapt was frequently activated in difficult communication environments. Case 5, S.J., 10 years S.J. initially had similar problems to his brother, F.J. His own hearing aids were getting old, although they were still able to provide adequate amplification for his hearing loss. He also described being able to hear much more than before with the new hearing instruments. Everything seemed much louder. This was compounded by the fact that his classroom is quite noisy. He used the switching option on the Claro system successfully and frequently. After the adaptation period he accepted both programs. There were no indications that the settings were too loud. 6
Results and Discussion The test results demonstrated an absolute benefit for all participants. This was shown particularly clearly by the monaural measurements with hearing instruments in program 1 (QuietAdapt) at low input levels. Figure 4 The measurement of Loudness Perception Profile (LPP) provides information about the loudness perception of the individual. The test signal is narrow band noise generated by the Claro hearing instrument. Using a scale between inaudible and extemely loud the hearing instrument wearer judges the loudness of the signal over a range of frequencies. For children the written categories on the adult scale are replaced with pictures. The binaural tests with hearing instruments and background noise in program 2 (Noise Adapt) showed excellent speech discrimination. However, the results from these fittings in test conditions only provide a snapshot of hearing ability. Much more important are the benefits and acceptance in everyday situations. All parents reported a clear improvement with regard to communication with their children. This not only applies to distance, but also to difficult listening environments. The conscious switching from Program 1 to Program 2 and the associated changes were also described by the parents. They confirmed that it is useful to give children a program choice, which they can control themselves. This also applies to the youngest participant (Case 1). None of the parents had to intervene in any way to help their child. All children showed a clear reduction in listening effort. In the tests it was easier for them, even at low input levels or in background noise, to achieve better results. The improvements in their homelife reflected this. Especially in this age group (pre-school and school age) the children were much less likely to avoid difficult listening situations. With 4 of the children we were able to obtain these results using the DSL [i/o] procedure (Seewald, 1995). In one case (Case 4, M.L.) we had to use a different method due to excessive recruitment. We were able to utilize the high flexibility of the Claro system and the fitting software (Phonak Fitting Guideline PFG) in order to establish Loudness Perception Profiles for each ear. The final settings of the Claro instruments as a result of this differed to the DSL [i/o] target as follows: the initial switch-on gain of 50 db was reduced by 5 db on the right and 6 db on the left. The compression ratios were increased in all frequency bands. 7
Summary The main aim of all clinicians involved in pediatric hearing aid fittings is to optimize individual procedures, which support the progress and integration of hearing impaired children. As pediatric audiologists we have a responsibility to provide the best fitting solution for the hearing impaired child. Hence, there is also a responsibility to examine new fitting methods and modern technology to discover whether they can offer benefits to children. Before new hearing aid technologies are tested on children, we must gain and discuss experiences with adults. When experience and data are available for adults, trials can be carefully planned and executed in the pediatric population. To ensure the results can be reproduced and to compare trials worldwide an established and recognized pediatric fitting procedure must always be chosen. Selecting the DSL i/o procedure with RECD measurements ensured that this was the case in this study. The laboratory measures and especially the real-life situations, demonstrated that children, or perhaps especially children, can profit significantly from modern hearing aid technologies (in this case Phonak Claro BTE Series). This should encourage clinicians to evaluate hearing instruments and fitting methods which can show benefits in areas such as listening effort, ease of communication, etc., so that the fitting success is not based entirely on a snapshot of the child's hearing abilities in the test booth. One of the aspects which can only be assessed in real-life is the use of different listening programs. None of the children had previously used multi-programs. This novelty had to be explained carefully, and the children taught the use of the TacTronic switch. The question, whether and when the children use the switching option which was of great interest to us, was answered by the children themselves. At first it was amusing to them as their hearing aids not only heard but also beeped. On the first day of the fitting all of them played with the TacTronic switch, simply because it was new. From the second and third day the switching became a conscious decision dependent on the acoustic environment. When it s noisy, I push the switch and it beeps twice, then I hear better at lunch break. Or when everyone is talking together I switch over and then it's easier. These were spontaneous comments from the children and demonstrate that even 5 year olds are able to cope with 2 programs. The situations requiring a switch to another program were easy to explain and for the children to understand. The results in background noise tests using the Adaptive digital AudioZoom (daz) technology showed dramatic improvements in speech intelligibility. For real-life environments like school, the use of additional FM technology can further improve communication and hence further reduce stress on the child. The optimization of pediatric communication skills as a result of different technological solutions is described in detail by Buerkly-Halevy and Checkley (2000). During the test phase no FM was used. The management of hearing instruments for children is a continual process, which does not end with the fitting. It is imperative that the fitting process is flexible enough to cope with changing circumstances (e.g. hearing levels, changing ear anatomy, earmolds etc). The hearing system, the fitting software, the chosen fitting protocol and the possibility of Loudness Perception Profile, allowed an optimized fitting in all cases. This flexibility was particularly important, during the test 8
phase which was during the cold and flu season. In many cases this led to changes in the audiological data (due to glue ear etc.) and as the audiological results changed it was possible to modify the instruments simply and effectively. Modern hearing instrument technology means the clinician has highly efficient tools and methods at his disposal which can offer real benefits to children with hearing impairment. Appendix 1 The measurement of RECD There are a number of advantages associated with RECD measurements and the establishment of threshold by using individual ear moulds or insert earphones: The threshold is measured in close proximity to the tympanic membrane. Earmold characteristics such as tube length, canal length and venting are taken into account. Possible changes to ear canal geometry are taken into account. The 2cc coupler is calibrated before testing by using an insert earphone as a noise source. After this an insertion gain tube is inserted into the ear canal so that it extends just past the meatal tip of the earmold. Then the insert earphone is connected to the input sound tube and the stimulus is presented to the ear, taking into account the aspects listed above. The RECD is then calculated by subtracting the 2cc coupler reference curve from the real-ear unaided response curve. Once this has been measured (or renewed after a new ear mould) the hearing instrument can be set in the coupler without the child s presence. This way individual ear canal characteristics are taken into account. Although age dependent averaged data are available, an individual measurement of the RECD should be made wherever possible. Put simply, a tailor-made jacket always fits better than off the peg! 9
Bibliography Buerkli-Halevy, O. & Checkley, P.C. (2000): Matching technology to the needs of infants In: R.C. Seewald (Editor) A Sound Foundation Through Early Amplification Proceedings of an International Conference. Chicago, Ill. 2000. Heinz, J.W. (1999): Grundsätzliche und neue Aspekte zur Hörgeräteversorgung im Kindesalter unter Berücksichtigung des DSL[i/o]- Verfahrens. Hörakustik Heft 1 und 2, 1999. Phonak Background Story (1999): Claro Digital Perception Processing. Article No. 28146. Seewald, R.C. (1992): The desired sensation level method for fitting children: Version 3.0. Hearing Journal 45 (4): 36-41. Seewald, R.C. (1995): The Desired Sensation Level (DSL) method for hearing aid fitting in infants and children. Phonak Focus No. 20. Seewald, R.C., Moodie, K.S., Sinclair, S.T. & Cornelisse, L.E. (1996): Traditional and theoretical approaches to selecting amplification to infants and young children. In : F.H. Bess, J.S. Gravel and A.M. Tharpe (Eds.) Amplification for children with auditory deficits (pp. 161 191) Nashville, TN: Bill Wilkerson Center Press. Sinclair, S.T., Beauchaine, K.L., Moodie, K.S., Feigin, J.A., Seewald, R.C. & Stelmachowicz, P.G. (1996a): Repeatability of real-ear-tocoupler difference measurement as a function of age. Am J of Audiology, 5(3), 52-56. Sinclair, S.T., Moodie, K.S. & Seewald, R.C. (1996b): Case study: Amplification in children. In: F.H. Bess, J.S. Gravel and A.M. Tharpe (Eds). Amplification for children with auditory deficits (pp. 431-440) Nashville, TN: Bill Wilkerson Center Press. 10
Jochen W. Heinz Hearing aid audiologist specializing in pediatric audiology Kinderzentrum, Hörgeräte Iffland GmbH & Co. KG, Esslingen Jochen W. Heinz is a hearing aid audiologist specializing in pediatric audiology. After studying medicine at Eberhard-Karls University in Tübingen (1982 1986), he trained as a hearing aid audiologist with an emphasis on pediatrics. In 1992 he was awarded his masters degree. He is now head of the pediatric department at Hörgeräte Iffland in Esslingen. It is his aim to explore all the potential benefits which new technology can offer to children with hearing impairment. 11
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