The increasing degree of sophistication in hearing aid technology calls for appropriate fitting strategies, as otherwise hearing aid users cannot receive the full benefit from the most modern technological achievements. This paper describes the state of the art in hearing aid fitting procedures and offers a look into possible future developments. Currently, threshold-based fitting formula compete with loudness- and sound-based fitting procedures. Whereas threshold-based approaches are straightforward and timesaving, they do not consider loudness growth and the sound preferences of the listener. On the other hand, loudness- and sound-based procedures do take these aspects into account, but they are time consuming and it is not yet proven that they provide higher benefit for the end user. This may be due to the fact that either there is actually no extra benefit or more likely that the evaluation tools or study designs have to be improved. Concerns about how to fit more advanced future hearing instruments seem to be inappropriate, as an analysis of possible future signal processing algorithms shows that they probably do not need extra fitting to the individual hearing impairment but rather need optimization according to the acoustical environment.
Calculations of the needs of healthcare, hearing healthcare included, are usually based on clinical data rather than on valid prevalence figures. According to our recent population study, the number of citizens needing hearing aids in Finland will be twice the figure usually presented, 280 000 for the country as a whole (population 5.1 million). The penetration of hearing aids was only 41%. Taking this and the ageing of the population into account, the economic challenges of hearing healthcare will be alarming in the new millennium.
The majority of hearing impaired children live in the developing countries. Limited resources are available for screening, prevention, diagnosis and intervention. These problems were the topic for discussion in a special session in the Congress.
Brainstem auditory-evoked potential (BAEP) examinations were performed in 15 patients with long-standing type-1 diabetes mellitus (DM). Cardiovascular reflex tests were applied for assessment of autonomic neuropathy. The aim of our investigation was to compare the BAEP results of this patient group with controls and to look for a possible correlation between the alteration of the auditory brainstem function and the cardiovascular autonomic neuropathy. Analysis of the latencies (waves I, II, III and V) and the inter-peak latencies (waves I-III and I-V) of BAEPs revealed a significant difference between diabetics and healthy controls. The amplitudes of waves I, III and V were definitely lower in comparison with those of healthy controls. A positive correlation was observed between the overall autonomic score and the latencies (waves III and V) and inter-peak latencies (waves I-III and I-V). These data support the hypothesis that long-standing DM and diabetic neuropathy might be related as a cause of certain dysfunctions of the central auditory pathways.
The role of medial efferent system in regulating outer hair cell function has been studied by many investigators. Usually narrow band noise or white noise as contralateral stimulation (CS) suppressors have been used and changes in OAE amplitudes estimated. Thirty children aged 6-15 years (mean 12.5 ± 4.7), without any changes in tonal and impedance audiometry and with negative history regarding otiatric diseases were examined. Transient evoked otoacoustic emissions (TEOAE) were recorded using ILO 92 Otodynamics Analyser. CS was performed using 1.0 kHz and 2.0 kHz continuous pure tones of 30 dB SL or 50 dB SL. Effects of CS on TEOAE evoked by click of 80, 70 and 60 dB SPL were investigated. TEOAE analysis included assessment of TEOAE amplitude of half octave frequency bandwidth (HOFBW-1.0; HOFBW-1.5; HOFBW-2.0; HOFBW-3.0 and HOFBW-4.0 kHz) and 0.8 kHz frequency bandwidth (0.8-FBW) amplitudes centred at 1.0; 2.0; 3.0; 4.0 and 5.0 kHz. TEOAE amplitude recorded for stimuli 80, 70 and 60 dB SPL without CS decreased: mean values respectively 6.1 ± 4.2; 5.4 ± 4.5 and 3.3 dB SPL ± 4.3. CS effect on TEOAE was observed for all CS options, however, larger suppressive effect was recorded on TEOAE elicited by 70 dB SPL stimulus using 1 kHz/50 dB SL tone as a suppressor and on TEOAE elicited by 60 dB SPL stimulus using 2 kHz/50 dB SL tone as a suppressor. HOFBW and 0.8-FBW analyses showed the association between the frequency/intensity of the suppressors and decreasing of amplitudes of adequate frequency bands. It is concluded that the described method of investigating of the medial olivocochlear efferent system seems to be sensitive and confirms frequency-dependent suppressive effect on OAE.
