Hearing acuity of diabetics and non-diabetics was measured using a standard pure tone audiometer and high frequency audiometer, which can generate high-pitched tones up to 18kHz. All of the subjects in this study had normal ear drum and no complaints including tinnitus and vertigo. The standard pure tone audiometry revealed a gradual threshold elevation up to the sixties and faster elevation in the older generations. The hearing thresholds at the frequencies above 8kHz were found to start to evidently elevate even in the thirties. The constant threshold elevation seemed to continue until the seventies, in which the ears can hardly hear the sounds of 100dB SPL at these frequencies. On the other hand, comparison between the diabetics and non-diabetics suggested that hearing levels at the frequencies between 1kHz and 8kHz of the standard pure tone audiometry could be better parameters than the high frequency audiometry to detect hearing impairment in diabetics.
The detection of distortion-product otoacoustic emissions (DPOAEs) is highly affected by the detection probe, but studies on its' properties are quite limited. Therefore, the present study was designed to investigate the input-output function of earphones and microphones using ILO92's and our custom-made probes. For analysis of the earphones, the sound pressure level of output sound was measured under the conditions of varied voltages at a fixed frequency and of the varied frequencies at the fixed voltage. The output voltage of microphones was measured at the various sound pressure levels and at the various frequencies, while the frequency was fixed in the former and the sound pressure was kept at a constant level in the latter. The microphones in both probes exhibited a good-correlation in the input-output function and their capacities were sufficient for DPOAEs measurement. The output levels of the sounds from the earphones were inconsistent at the frequencies ranging from 1kHz to 10kHz and were too low to evoke DPOAEs above 10kHz in both probes. The results obtained indicated that the improvement of an earphone is necessary for the further development of DPOAEs' examination.
We studied indications of hearing aids for 67 patients with mild (the average hearing level less than 40dB) hearing loss. 32 patients were indicated to use hearing aids. Those who have occupational needs and strong will were indicated to use hearing aids, regardless of age and hearing level. In analysis of electroacoustic characteristics of hearing aid, the most frequently used gains (averaged in 500, 1000, 2000Hz) were correlated to the average hearing level. When these gains were compared with gains calculated by half gain method, they were smaller than half gains in most cases. As the average hearing level increased, the suitable maximum power output level (averaged in 500, 1000, 2000Hz) was accordingly increased. However, no relation was found between the maximum power output levels and uncomfatable loudness levels.
Results of audiological analysis of Meniere's disease based on audiograms of patients with longterm follo-up, on the average 10 years, were reported. The most characteristic feature was fluctuant hearing impairment with an average hearing changes of 25-30dB in lower frequencies. Hearing impairment progressed in about 40% of the patients during observation period. The impairment progressed in high frequencies in cases with initially well-preserved hearing levels in high frequencies. In cases with high frequency loss, the impairment progressed in middle frequencies. The audiogram of Meniere's disease, in general, show low tone deafness in the beginning, then low and high tone deafness, and lastly flat deafness. The progression is very slow and fluctuation persists for longer periods.
Transient evoked otoacoustic emissions (TEOAEs) reflect the cochlear micromechanics related to the active motile property of outer hair cells. Thus, it may be hypothesized that if hearing impairments is neural origin, normal TEOAEs can be obtained from the cochlea. In the present study, we recorded TEOAEs in 95 acoustic neuroma patients and 50 Meniere's disease patients in order to clarify the relationship between the hearing level and TEOAEs in cochlear and retrocochlear hearing impairments. Mean hearing level of the acoustic neuroma patients in whom TEOAEs were obtained was 28.4±14.6dB and that of the Meniere's disease patients was 28.3±12.5dB. Although there were 3 acoustic neuroma patients with TEOAE in spite of hearing impaiment over 60dB, deterioration in TEP, one of the TEOAE parameters was found comparing with healthy side ear. From these results, we concluded that there must be an affection to the cochlea in almost all acoustic neuroma patients. Thus, the normal TEOAEs could uncommonly be found in acoustic neuroma patients with moderate or severe hearing impairment.
We investigated 62 patients receiving interferon for type B or C chronic hepatitis to determine the incidence of auditory disturbance, such as hearing loss, tinnitus, ear fullness or dizziness during interferon therapy. Examination was made for retinopathy and levels of total cholesterol and triglyceride in serum throughout treatment to determine the relationship between auditory disturbance and vascular disorders. Auditory disturbance was occurred in 10 patients (16%): hearing loss 4 patients, tinnitus in 5, ear-fullness in 2 and dizziness in 1. These signs and symptoms were improved within 1-2 weeks after Interferon therapy was ceased. We found no relationship between auditory disturbance and retinopathy, or levels of total cholesterol and triglyceride in serum.
Digital compression of speech sounds in hearing aids emphasizes consonants more prominantly than vowels. Effects of digital compression were tested by analyzing the results of speech discrimination tests, using 50 monosyllables (57s list), in 20 patients with sensorineural hearing loss. When the digital compression was applied, discrimination scores of the monosyllables were improved. The improvement was observed mainly in consonants rather than in bowels. Consonant confusion was improved in almost of all consonants, especially in voiceless consonant /s/, voiced consonant /g/ and /z/.