NEW ASPECTS IN HEARING-AID FITTING

Improved methods to diagnose a hearing loss and the enormous progress in the development of digital and programmable hearing aids have been helpful in promoting the social integration of patients, even of those affected by a profound deafness. Besides the hearing loss, recruitmen t effects and alteration of sound can also be compensated by the new h earing aids. However, one precondition is that the hearing aid fitting is carried out professionally, with plenty of time, and including the new hearing aid fitting methods. The new techniques developed in our hospital to optimize hearing aid fitting are pointed out. Fitting shou ld start by considering what kind of ear mould and what kind of differ ent modifications are to be taken. In a great number of patients we we re able to verify that venting combined with the insertion of a Bakke- or Libby-horn increases not only the subjective acceptance of the hea ring aid, but also significantly improves speech discrimination, parti cularly under background noise. The preselection of the hearing device and precise adjustment are based on the hearing loss in different fre quencies, involving the principle that the frequency response of the h earing aid and the audiogram mirror each other accordingly, whereas th e gain of the hearing aid can not be recognised exactly from the audio gram. In contrast to the POGO- and the NAL-method, we recommend a grea ter amplification, especially in the higher range of frequency. Today, the in-situ-measurement with a probe microphone is considered to be t he method of choice for accurate frequency adjustment. This in-situ-me asurement allows an exact determination of the frequency response of a hearing aid and enables to perceive unpredictable resonance effects i n the external ear canal. This is of particular importance when checki ng the hearing devices of children who have a significantly altered ex ternal ear resonance. When evaluating the speech discrimination in the presence of background noise, it is necessary to use different noises . We could determine that the masking effects were very different, whe n speech-noise, Doring noise and Fastl noise were used. For the accura te adjustment of hearing devices, we also have to take into account th e dynamic range. Comparative measurements show that the determination of the uncomfortable loudness level with monosyllables is absolutely i nsufficient, particularly when new multichannel hearing aids are fitte d. The uncomfortable loudness level for narrow band noise and sinus to nes is frequency-dependent and differ from the UCL of monosyllables. L ikewise, for adjusting the PC and AGC, the in-situ-measurement has tur ned out to be reliable, because the hearing aid characteristics in the protocols of the hearing aid companies show big differences, because they are measured with a 2 cm(3)-coupler. As before, the reliability o f the otometry to verify the range of comfortable hearing has been est ablished. In case the adjustment of a hearing aid is especially diffic ult, the temporal resolution should be taken into account. We were abl e to verify in a great number of patients that the temporal resolution of the hearing can improve or deteriorate by fitting a hearing aid. I f a suitable hearing aid is used, an improvement in the temporal resol ution capacity proceeds with an increased subjective acceptance of the hearing aid and usually, with an improved speech discrimination under background noise.